Topic Editors

Prof. Dr. Alberto Campagnolo
Department of Industrial Engineering, University of Padova, 35131 Padova, Italy
Prof. Dr. Alberto Sapora
Department of Structural, Geotechnical and Building Engineering, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy

Fatigue and Fracture Assessment of Structural Components and Materials

Abstract submission deadline
31 December 2022
Manuscript submission deadline
30 April 2023
Viewed by
18337

Topic Information

Dear Colleagues,

Dealing with fracture and fatigue assessments of structural components made of metallic, polymeric, ceramic or composite materials, different approaches have been proposed in the literature. They are usually divided into three subgroups: stress-based, strain-based and energy-based criteria; however, coupled approaches are also widely employed, e.g., stress–energy-based ones. Such approaches are based on analytical/numerical calculations or on experimental derivations. Typical applications include both linear elastic and elasto–plastic materials, plain and notched or cracked components ranging from nano to macro scales and subjected to static or cyclic loadings. Aim of this Topic is to provide an update to the state-of-the-art on these approaches, including coupled criteria. The topics which deserve particular interest are: applications to new advanced materials, such as additive materials; applications to complex and real structures; recent advanced criteria for fracture and fatigue predictions under complex loading conditions, such as mixed mode static loading or multiaxial constant amplitude and variable amplitude/random fatigue loadings.

Prof. Dr. Alberto Campagnolo
Prof. Dr. Alberto Sapora
Topic Editors

Keywords

  • local approach
  • energy-based approach
  • stress-based approach
  • strain-based approach
  • stress–energy coupled approach
  • finite fracture mechanics
  • fracture assessment
  • fatigue assessment
  • crack
  • notch
  • size effects

Participating Journals

Journal Name Impact Factor CiteScore Launched Year First Decision (median) APC
Applied Sciences
applsci
2.838 3.7 2011 17.4 Days 2300 CHF Submit
Materials
materials
3.748 4.7 2008 15.3 Days 2300 CHF Submit
Metals
metals
2.695 3.8 2011 16 Days 2000 CHF Submit
Polymers
polymers
4.967 5.7 2009 13 Days 2400 CHF Submit
Applied Mechanics
applmech
- - 2020 15.7 Days 1000 CHF Submit

Published Papers (41 papers)

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Article
Fatigue Crack Arrest Induced by Localized Compressive Deformation
Materials 2022, 15(13), 4553; https://doi.org/10.3390/ma15134553 - 28 Jun 2022
Abstract
The localized compressive deformation (LCD) effect generated by an indentation process at the crack tip on the fatigue crack growth of the 7075-T651 aluminum alloy is reported. Eccentrically loaded single-edge crack tension specimens (ESE(T)) were pre-cracked at a crack length of about 20 [...] Read more.
The localized compressive deformation (LCD) effect generated by an indentation process at the crack tip on the fatigue crack growth of the 7075-T651 aluminum alloy is reported. Eccentrically loaded single-edge crack tension specimens (ESE(T)) were pre-cracked at a crack length of about 20 mm by applying a constant amplitude fatigue loading. Subsequently, the LCD process was performed by using a semi-spherical indenter with a radius of 16 mm to compress the crack tip zone at different forces (5.0, 7.0, 12.5, 13.5, 15.5 kN), applied on the opposite surfaces of the specimens. The fatigue cracking process was continued on the compressed samples until an overall crack length of about 30 mm was obtained. The compressive load and the number of delayed cycles is discussed in terms of crack length and crack tip opening displacement (CTOD). A direct relationship between the compressive force induced by the LCD process and the delay of the crack propagation due to the crack arrest was observed. This effect became evident at a compressive force of 5.0 kN, where the crack propagation was arrested for about 9000 cycles in comparison with the non-LCD sample. However, when the force increased, the crack arrest also increased. The crack was considered to be completely arrested at a compressive load of 15.5 kN, since the crack did not grow after the application of more than 3 × 106 cycles. Full article
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Article
Fatigue Factor Assessment and Life Prediction of Concrete Based on Bayesian Regularized BP Neural Network
Materials 2022, 15(13), 4491; https://doi.org/10.3390/ma15134491 - 25 Jun 2022
Abstract
Concrete tensile properties usually govern the fatigue cracking of structural components such as bridge decks under repetitive loading. A fatigue life reliability analysis of commonly used ordinary cement concrete is desirable. As fatigue is affected by many interlinked factors whose effect is nonlinear, [...] Read more.
Concrete tensile properties usually govern the fatigue cracking of structural components such as bridge decks under repetitive loading. A fatigue life reliability analysis of commonly used ordinary cement concrete is desirable. As fatigue is affected by many interlinked factors whose effect is nonlinear, a unanimous consensus on the quantitative measurement of these factors has not yet been achieved. Benefiting from its unique self-learning ability and strong generalization capability, the Bayesian regularized backpropagation neural network (BR-BPNN) was proposed to predict concrete behavior in tensile fatigue. A total of 432 effective data points were collected from the literature, and an optimal model was determined with various combinations of network parameters. The average relative impact value (ARIV) was constructed to evaluate the correlation between fatigue life and its influencing parameters (maximum stress level Smax, stress ratio R, static strength f, failure probability P). ARIV results were compared with other factor assessment methods (weight equation and multiple linear regression analyses). Using BR-BPNN, S-N curves were obtained for the combinations of R = 0.1, 0.2, 0.5; f = 5, 6, 7 MPa; P = 5%, 50%, 95%. The tensile fatigue results under different testing conditions were finally compared for compatibility. It was concluded that Smax had the most significant negative effect on fatigue life; and the degree of influence of R, P, and f, which positively correlated with fatigue life, decreased successively. ARIV was confirmed as a feasible way to analyze the importance of parameters and could be recommended for future applications. It was found that the predicted logarithmic fatigue life agreed well with the test results and conventional data fitting curves, indicating the reliability of the BR-BPNN model in predicting concrete tensile fatigue behavior. These probabilistic fatigue curves could provide insights into fatigue test program design and fatigue evaluation. Since the overall correlation coefficient between the prediction and experimental results reached 0.99, the experimental results of plain concrete under flexural tension, axial tension, and splitting tension could be combined in future analyses. Besides utilizing the valuable fatigue test data available in the literature, this work provided evidence of the successful application of BR-BPNN on concrete fatigue prediction. Although a more accurate and comprehensive method was derived in the current study, caution should still be exercised when utilizing this method. Full article
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Article
On the Influence of the Initial Shear Damage to the Cyclic Deformation and Damage Mechanism
Metals 2022, 12(7), 1072; https://doi.org/10.3390/met12071072 - 23 Jun 2022
Abstract
The accuracy and precision of lifetime predictions for cyclically loaded technical components are still lacking. One of the main reasons for the discrepancy between the calculated life time and experimental results is that it is not yet possible to create a model capable [...] Read more.
The accuracy and precision of lifetime predictions for cyclically loaded technical components are still lacking. One of the main reasons for the discrepancy between the calculated life time and experimental results is that it is not yet possible to create a model capable of describing the microstructural damage process that occurs in the tested material and to subsequently incorporate this model into the calculation. All of the presently available research results recognize that the growth of microcracks is significantly influenced by the microstructure of the material. In order to take into account the influence of the microstructure on the damage process, research on the very early fatigue damage is carried out. The results are obtained from tension and torsion fatigue testing. For this purpose, the surfaces of the tested specimens are carefully observed to discover and analyze microcracks, which are classified according to their orientation. Moreover, the mechanisms of crack initiation and propagation are major points of interest. Through a mix of mechanical and metallurgical points of view, calculations and multi-level FEA modeling are carried out to gain a better understanding of the properties of the phases. The simulation is based on continuum mechanics, which considers the positions and mechanical metallurgy, which account for each constituent character’s failure laws. It is concluded that both the experimental and computational approaches conform, showing that such an approach is indeed a necessity and should become a trend in the near future. Statistically, microcracks under tension modes are highest at 45° (approximately 30%), while under torsion they are highest at 0° (approximately 20%) with respect to the sample orientation. The influence of the microstructure is explained via the finite element analysis. Full article
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Article
Detecting Broken Strands in Transmission Lines Based on Pulsed Eddy Current
Metals 2022, 12(6), 1014; https://doi.org/10.3390/met12061014 - 15 Jun 2022
Abstract
High-voltage transmission lines are the main facilities for power transmission, and they are mainly composed of aluminum conductor steel-reinforced (ACSR). Over long-term outdoor use, overhead transmission lines will encounter lightning strikes, chemical pollutant corrosion, deicing, wind vibration, and other external forces. This often [...] Read more.
High-voltage transmission lines are the main facilities for power transmission, and they are mainly composed of aluminum conductor steel-reinforced (ACSR). Over long-term outdoor use, overhead transmission lines will encounter lightning strikes, chemical pollutant corrosion, deicing, wind vibration, and other external forces. This often results in a series of potential failures, such as breakage, for the strands. In order to ensure the safe operation of the power grid and avoid fatal accidents, such as line breaks, it is necessary to identify and repair line faults. Among them, the main basis for the regular detection and replacement of high-voltage transmission lines is whether a broken strand defect appears. In this paper, a type of pulsed eddy current (PEC) sensor is developed to detect the broken strand defect in transmission lines. The simulation and experimental results showed that the designed PEC sensor could effectively and accurately identify the fault. Full article
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Article
Experimental Investigation of Shale Tensile Failure under Thermally Conditioned Linear Fracturing Fluid (LFF) System and Reservoir Temperature Controlled Conditions
Polymers 2022, 14(12), 2417; https://doi.org/10.3390/polym14122417 - 14 Jun 2022
Abstract
Linear fracturing fluid (LFF) provides viscosity driven benefits of proppant suspensibility and fluid loss control, and with the use of a breaker agent, flowback recovery can be greatly enhanced. Shale tensile strength is critical in the prediction of fracture initiation and propagation, but [...] Read more.
Linear fracturing fluid (LFF) provides viscosity driven benefits of proppant suspensibility and fluid loss control, and with the use of a breaker agent, flowback recovery can be greatly enhanced. Shale tensile strength is critical in the prediction of fracture initiation and propagation, but its behavior under the interaction with LFF at reservoir temperature conditions remains poorly understood. This necessitated an in-depth investigation into the tensile strengths of Eagle Ford and Wolfcamp shales under thermally conditioned LFF and reservoir temperature controlled conditions. Brazilian Indirect Tensile Strength (BITS) testing was carried out for the quantitative evaluation of shale tensile strength, followed by extensive failure pattern classifications and surface crack length analysis. The thermally conditioned LFF saturation of shale samples led to average tensile strength (ATS) increases ranging from 26.33–51.33% for Wolfcamp. Then, for the Eagle Ford samples, ATS increases of 3.94 and 6.79% and decreases of 3.13 and 15.35% were recorded. The exposure of the samples to the temperature condition of 90 °C resulted in ATS increases of 24.46 and 33.78% for Eagle Ford and Wolfcamp shales, respectively. Then, for samples exposed to 220 °C, ATS decreases of 6.11 and 5.32% were respectively recorded for Eagle Ford and Wolfcamp shales. The experimental results of this research will facilitate models’ development towards tensile strength predictions and failure pattern analysis and quantifications in the LFF driven hydraulic fracturing of shale gas reservoirs. Full article
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Article
Environmental Stress Cracking of High-Density Polyethylene Applying Linear Elastic Fracture Mechanics
Polymers 2022, 14(12), 2415; https://doi.org/10.3390/polym14122415 - 14 Jun 2022
Abstract
The crack propagation rate of environmental stress cracking was studied on high-density polyethylene compact tension specimens under static loading. Selected environmental liquids are distilled water, 2 wt% aqueous Arkopal N100 solution, and two model liquid mixtures, one based on solvents and one on [...] Read more.
The crack propagation rate of environmental stress cracking was studied on high-density polyethylene compact tension specimens under static loading. Selected environmental liquids are distilled water, 2 wt% aqueous Arkopal N100 solution, and two model liquid mixtures, one based on solvents and one on detergents, representing stress cracking test liquids for commercial crop protection products. The different surface tensions and solubilities, which affect the energetic facilitation of void nucleation and craze development, are studied. Crack growth in surface-active media is strongly accelerated as the solvents induce plasticization, followed by strong blunting significantly retarding both crack initiation and crack propagation. The crack propagation rate for static load as a function of the stress intensity factor within all environments is found to follow the Paris–Erdogan law. Scanning electron micrographs of the fracture surface highlight more pronounced structures with both extensive degrees of plasticization and reduced crack propagation rate, addressing the distinct creep behavior of fibrils. Additionally, the limitations of linear elastic fracture mechanisms for visco-elastic polymers exposed to environmental liquids are discussed. Full article
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Article
Oxidation Damage Evolution in Low-Cycle Fatigue Life of Niobium-Stabilized Austenitic Stainless Steel
Materials 2022, 15(12), 4073; https://doi.org/10.3390/ma15124073 - 08 Jun 2022
Abstract
Austenitic stainless steel is a vital material in various industries, with excellent heat and corrosion resistance, and is widely used in high-temperature environments as a component for internal combustion engines of transportation vehicles or power plant piping. These components or structures are required [...] Read more.
Austenitic stainless steel is a vital material in various industries, with excellent heat and corrosion resistance, and is widely used in high-temperature environments as a component for internal combustion engines of transportation vehicles or power plant piping. These components or structures are required to be durable against severe load conditions and oxidation damage in high-temperature environments during their service life. In this regard, in particular, oxidation damage and fatigue life are very important influencing factors, while existing studies have focused on materials and fracture behavior. In order to ensure the fatigue life of austenitic stainless steel, therefore, it is necessary to understand the characteristics of the fracture process with microstructural change including oxidation damage according to the temperature condition. In this work, low-cycle fatigue tests were performed at various temperatures to determine the oxidation damage together with the fatigue life of austenitic stainless steel containing niobium. The characteristics of oxidation damage were analyzed through microstructure observations including scanning electron microscope, energy-dispersive X-ray spectroscopy, and the X-ray diffraction patterns. In addition, a unified low-cycle fatigue life model coupled with the fracture mechanism-based lifetime and the Neu-Sehitoglu model for considering the influence of damage by oxidation was proposed. After the low-cycle fatigue tests at temperatures of 200–800 °C and strain amplitudes of 0.4% and 0.5%, the accuracy of the proposed model was verified by comparing the test results with the predicted fatigue life, and the validity by using the oxidation damage parameters for Mar-M247 was confirmed through sensitivity analysis of the parameters applied in the oxidation damage model. As a result, the average thickness of the oxide layer and the penetration length of the oxide intrusion were predicted with a mean error range of 14.7% and 13%, respectively, and the low-cycle fatigue life was predicted with a ±2 factor accuracy at the measurement temperatures under all experimental conditions. Full article
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Article
The Influence of Heat Input on the Formation of Fatigue Cracks for High-Strength Steels Resistant to Low Temperatures
Metals 2022, 12(6), 929; https://doi.org/10.3390/met12060929 - 28 May 2022
Abstract
Welding is one of the most widely used metal joining techniques. However, improper technique and handling may lead to weld defects. Cracks that occur during the exploitation of the welded joints in places of increased stress concentration are called fatigue cracks. In our [...] Read more.
Welding is one of the most widely used metal joining techniques. However, improper technique and handling may lead to weld defects. Cracks that occur during the exploitation of the welded joints in places of increased stress concentration are called fatigue cracks. In our previous study, we suggested that lowering the stress concentration in the zone of the weld face may prevent surface cracks in butt-welded joints. Here, we further examined how welding heat input and external factors can be controlled to minimize the occurrence of fatigue cracks on welded joints. The fatigue cracks analyzed in this study occurred during the exploitation and are a consequence of the increased stress concentration at the toe of the weld. We performed twenty-four welding experiments comprising the following four welding conditions: torch angle, number of cover passes, length of electrode stick-out, and shielding gas (two environments were used). Stress concentration factors and heat input were determined via experimental data. The results suggested that higher heat input is associated with a lower risk of developing fatigue cracks. Thus, we concluded that fatigue cracks could be minimized by increasing the arc voltage and current while also reducing the welding speed. Full article
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Article
Study on the Influence of Selected Fabrics and Stitching on the Strength of Upholstery Covers
Materials 2022, 15(11), 3854; https://doi.org/10.3390/ma15113854 - 28 May 2022
Abstract
So far, no coherent and comprehensive method has been elaborated allowing investigation of tensile strength of upholstery seams dedicated to upholstered furniture. Producers of this type of furniture are interested in the assessment of the quality of upholstery material joints, which seems to [...] Read more.
So far, no coherent and comprehensive method has been elaborated allowing investigation of tensile strength of upholstery seams dedicated to upholstered furniture. Producers of this type of furniture are interested in the assessment of the quality of upholstery material joints, which seems to be particularly important for ensuring the appropriate quality of products. Therefore, the objective of this research was to investigate the influence of the type of material used and the direction of the fabric cut on the strength of upholstery covers. Static tensile testing of selected upholstery fabric samples was performed, and an attempt was made to identify the most optimal fabric–seam joints. It was stated as a conclusion that the fabric tensile strength was the highest for Secret 10 fabric. In addition, the strength of upholstery covers is not influenced by the direction of the fabric die cut. For each fabric, a different configuration is preferable, as shown by results (Power 13: A-B, Secret 10: B-B, Soft 10: A-A). The method, implemented for upholstered furniture, allows for an objective assessment of the strength of upholstery covers and the selection of the most advantageous fabric–seam combination for future furniture designs. Full article
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Article
Experiment and Numerical Simulation of Damage Progression in Transparent Sandwich Structure under Impact Load
Materials 2022, 15(11), 3809; https://doi.org/10.3390/ma15113809 - 27 May 2022
Abstract
Crack initiation and propagation is a long-standing difficulty in solid mechanics, especially for elastic brittle materials. A new type of transparent sandwich structure, with a magnesium–aluminum spinel ceramic glass as the outer structure, was proposed in this paper. Its dynamic response was studied [...] Read more.
Crack initiation and propagation is a long-standing difficulty in solid mechanics, especially for elastic brittle materials. A new type of transparent sandwich structure, with a magnesium–aluminum spinel ceramic glass as the outer structure, was proposed in this paper. Its dynamic response was studied by high-speed impact experiments and numerical simulations of peridynamics under impact loads, simultaneously. In the experiments, a light gas cannon was used to load the projectile to 180 m/s, and the front impacted the transparent sandwich structure. In the numerical simulations, the discontinuous Galerkin peridynamics method was adopted to investigate the dynamic response of the transparent sandwich structure. We found that both the impact experiments and the numerical simulations could reproduce the crack propagation process of the transparent sandwich structure. The radial cracks and circumferential cracks of the ceramic glass layer and the inorganic glass layer were easy to capture. Compared with the experiments, the numerical simulations could easily observe the damage failure of every layer and the splashing of specific fragments of the transparent sandwich structure. The ceramic glass layer and the inorganic glass layer absorbed the most energy in the impact process, which is an important manifestation of the impact resistance of the transparent sandwich structure. Full article
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Article
Reinforcement Design of the Support Frame of a Petrochemical Heater
Appl. Sci. 2022, 12(10), 5107; https://doi.org/10.3390/app12105107 - 19 May 2022
Abstract
In this paper, we investigated the operating security of the support frame of a petrochemical heater under the action of a strong wind. When the fatigue limit was exceeded, the support frame was damaged. We monitored the heater before reinforcement and then applied [...] Read more.
In this paper, we investigated the operating security of the support frame of a petrochemical heater under the action of a strong wind. When the fatigue limit was exceeded, the support frame was damaged. We monitored the heater before reinforcement and then applied the finite element method to analyze and compare nine different kinds of reinforcement methods for the support frame. From the results of the finite element analysis, fatigue failure of the support frame before reinforcement occurred at locations where the computed stresses from the finite element analysis were large, thus partially justifying the adequacies of the present analysis methods and results. Among the nine reinforcement methods, we suggest case 9 to reinforce a support frame so that its operating security under the action of a strong wind can be improved. At the end of this paper, several future studies are suggested, including verification of the reinforcement for the support frame and the establishment of the system for automatic stress monitoring and analysis. Full article
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Article
The Mechanical Behavior of a Screwless Morse Taper Implant–Abutment Connection: An In Vitro Study
Materials 2022, 15(9), 3381; https://doi.org/10.3390/ma15093381 - 08 May 2022
Abstract
The use of screwless Morse taper implant–abutment connections (IAC) might facilitate the clinician’s work by eliminating the mechanical complications associated with the retention screw. The aim of this study is to evaluate the effect of artificial chewing on the long-term stability of screwless [...] Read more.
The use of screwless Morse taper implant–abutment connections (IAC) might facilitate the clinician’s work by eliminating the mechanical complications associated with the retention screw. The aim of this study is to evaluate the effect of artificial chewing on the long-term stability of screwless Morse taper IACs. Thirty-two implant abutments restored with an upper central incisor zirconia crown were used and divided into four groups according to the implant–abutment assembling manner (C1,H: screw retained (20 Ncm); C2: tapped; or C3: torqued (20 Ncm; the screws were removed before the dynamic loading)). All specimens were subjected to a cyclic loading (98 N) for 10 million chewing cycles. The survived samples were exposed to a pull-off force until failure/disassembling of the connection. All the samples revealed a 100% survival. Regarding the pull-off test, the screw-retained internal hexagonal IAC revealed significantly higher resistance to failure/disassembling (769.6 N) than screwless conical IACs (171.6 N–246 N) (p < 0.0001). The retention forces in the Morse taper groups were not significantly different (p > 0.05). The screw-retained hexagonal IAC showed the highest retention stability. The screw preload/retention in the conical IAC was lost over time in the group where the screws were kept in place during loading. Nevertheless, the screwless Morse taper IACs were stable for an extended service time and might represent a valid form of treatment for single-tooth replacement. Full article
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Article
Contact Characteristics and Tribological Properties of the Weaving Surface of Mn-Cu and Fe-Zn Damping Alloys
Materials 2022, 15(9), 3303; https://doi.org/10.3390/ma15093303 - 05 May 2022
Abstract
In this paper, laser texturing is performed on the surface of Mn-Cu and Fe-Zn damping alloys and the tribological properties of the samples with various surface weaves under dry-sliding conditions are investigated. The results show that the surface weave parameters affect the size [...] Read more.
In this paper, laser texturing is performed on the surface of Mn-Cu and Fe-Zn damping alloys and the tribological properties of the samples with various surface weaves under dry-sliding conditions are investigated. The results show that the surface weave parameters affect the size of the contact surface and change the number of micro-convex bodies at the contact interface. This leads to changes in the tangential damping of the contact and further affects the magnitude of the friction coefficient. Additionally, the damping properties significantly affect the wear mechanism and make it more prone to adhesive wear. Full article
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Article
Multi-Scale Approach of HCF Taking into Account Plasticity and Damage: Application to LPBF Materials
Appl. Mech. 2022, 3(2), 544-559; https://doi.org/10.3390/applmech3020032 - 29 Apr 2022
Abstract
Laser additive manufacturing enables economical production of complex lightweight structures. To realize the potential benefits of additive manufacturing technology in industrial applications, the fatigue performance of parts additively manufactured materials must be modelized. The aim of this paper is to present a new [...] Read more.
Laser additive manufacturing enables economical production of complex lightweight structures. To realize the potential benefits of additive manufacturing technology in industrial applications, the fatigue performance of parts additively manufactured materials must be modelized. The aim of this paper is to present a new modeling approach combining plasticity and damage, and appropriate for as-built Laser-Powder Bed Fusion (LPBF) structures. The model presented is an extension of the Dang Van criterion, including damage, defined as porosity in the case of LPBF. Attention is focused on the integration of damage in a fatigue criterion using the concept of elastic shakedown. Finally, the case of 316L will illustrate the results of the model by fatigue tests with deterministic defects. Full article
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Article
Prediction of Fracture Behavior of 6061 Aluminum Alloy Based on GTN Model
Materials 2022, 15(9), 3212; https://doi.org/10.3390/ma15093212 - 29 Apr 2022
Abstract
To determine the Gurson-Tvergaard-Needleman (GTN)damage model parameters of 6061 aluminum alloy after secondary heat treatment, the uniaxial tensile test was carried out on the aluminum alloy circular arc specimen, and the mechanical properties parameters and the load-displacement curve of aluminum alloy tube were [...] Read more.
To determine the Gurson-Tvergaard-Needleman (GTN)damage model parameters of 6061 aluminum alloy after secondary heat treatment, the uniaxial tensile test was carried out on the aluminum alloy circular arc specimen, and the mechanical properties parameters and the load-displacement curve of aluminum alloy tube were obtained. With the help of the finite element reverse method, scanning electron microscope and a orthogonal test method, the GTN damage model parameters (f0, fN, fC, and fF) were calibrated, and their values were 0.004535, 0.04, 0.1, and 0.2135, respectively. Then the shear specimen and notch specimen were designed to verify the damage model, the results show that the obtained GTN damage model parameters can effectively predict the fracture failure of 6061 aluminum alloy after secondary heat treatment during the tensile process. Full article
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Article
Random Vibration Fatigue Analysis Using a Nonlinear Cumulative Damage Model
Appl. Sci. 2022, 12(9), 4310; https://doi.org/10.3390/app12094310 - 24 Apr 2022
Abstract
The paper’s content allowed us to determine the fatigue life of a component that is being subjected to a random vibration environment. Its estimation is performed in the frequency domain with loading frequencies being closer to the system’s natural frequency. From loads’ amplitude [...] Read more.
The paper’s content allowed us to determine the fatigue life of a component that is being subjected to a random vibration environment. Its estimation is performed in the frequency domain with loading frequencies being closer to the system’s natural frequency. From loads’ amplitude and their interaction effect, we derive a nonlinear damage model to cumulate the generated fatigue damage. The exponent value of 0.4 from the Manson–Halford curve damage model was replaced by a vibration bending stress relation that considers the effect and interaction of loads. The analysis is performed from a progressive accelerated vibration spectrum to predict the fatigue life estimation. From this accelerated scenario, the accelerated coefficients and cumulated damage are both determined. The proposed nonlinear model is based on the following facts: (1) vibration and bending stress σvb values are obtained from the response acceleration of power spectral density (PSD) applied and (2) the model can be applied to any mechanical component analysis where the corresponding acceleration responses Ares and the dynamic load factor σdynamic  values are known. The steps to determine the expected fatigue damage accumulation D by using the curve damage are given. Full article
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Article
Performance Evaluation of Sandwich Structures Printed by Vat Photopolymerization
Polymers 2022, 14(8), 1513; https://doi.org/10.3390/polym14081513 - 08 Apr 2022
Abstract
Additive manufacturing such as vat photopolymerization allows to fabricate intricate geometric structures than conventional manufacturing techniques. However, the manufacturing of lightweight sandwich structures with integrated core and facesheet is rarely fabricated using this process. In this study, photoactivatable liquid resin was used to [...] Read more.
Additive manufacturing such as vat photopolymerization allows to fabricate intricate geometric structures than conventional manufacturing techniques. However, the manufacturing of lightweight sandwich structures with integrated core and facesheet is rarely fabricated using this process. In this study, photoactivatable liquid resin was used to fabricate sandwich structures with various intricate core topologies including the honeycomb, re-entrant honeycomb, diamond, and square by a vat photopolymerization technique. Uniaxial compression tests were performed to investigate the compressive modulus and strength of these lightweight structures. Sandwich cores with the diamond structure exhibited superior compressive and weight-saving properties whereas the re-entrant structures showed high energy absorption capacity. The fractured regions of the cellular cores were visualized by scanning electron microscopy. Elastoplastic finite element analyses showed the stress distribution of the sandwich structures under compressive loading, which are found to be in good agreement with the experimental results. Dynamic mechanical analysis was performed to compare the behavior of these structures under varying temperatures. All the sandwich structures exhibited more stable thermomechanical properties than the solid materials at elevated temperatures. The findings of this study offer insights into the superior structural and thermal properties of sandwich structures printed by a vat photopolymerization technique, which can benefit a wide range of engineering applications. Full article
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Article
Load-Carrying Capacity of Double-Shear Bolted Connections with Slotted-In Steel Plates in Squared and Round Timber Based on the Experimental Testing, European Yield Model, and Linear Elastic Fracture Mechanics
Materials 2022, 15(8), 2720; https://doi.org/10.3390/ma15082720 - 07 Apr 2022
Cited by 1
Abstract
Nowadays, the use of timber as a building material is gaining more prominence. When designing timber structures, it is necessary to pay increased attention to the design of their connections. The commonly used connections are dowel-type connections, which are often used in combination [...] Read more.
Nowadays, the use of timber as a building material is gaining more prominence. When designing timber structures, it is necessary to pay increased attention to the design of their connections. The commonly used connections are dowel-type connections, which are often used in combination with steel plates slotted into cut-outs in timber members. The presented paper deals with the behavior of double-shear bolted connections of squared timber and round timber with slotted-in steel plates. Several variants of connections with different distances between the fastener and the loaded end were selected for the experimental testing. A total of six types of test specimens were made from spruce timber, for which their selected physical properties were determined and evaluated before the experimental testing. Test specimens of bolted connections were first tested in tension parallel to the grain until failure under quasi-static loading. The connections were broken by splitting. Ductile failure preceded brittle failure. The actual load-carrying capacities were lowest for the lowest end distance. The load-carrying capacities for the middle and the longest end distances were comparable. The results of the experiments were then used for comparison with calculation procedures according to the standard for the design of timber structures and with calculations according to the theory of linear elastic fracture mechanics. The experiments and the analytical models were supported by a simple numerical analysis based on the finite element method. Full article
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Article
Evaluating the Residual Stress and Its Effect on the Quasi-Static Stress in Polyethylene Pipes
Polymers 2022, 14(7), 1458; https://doi.org/10.3390/polym14071458 - 03 Apr 2022
Abstract
Residual stress is generated during the production process. It can significantly affect the mechanical performance of pressurized polymer pipes. In this paper, six polyethylene (PE) pipes, including three high-density PEs (HDPE) and three medium-density PEs (MDPE) provided by different suppliers, were tested using [...] Read more.
Residual stress is generated during the production process. It can significantly affect the mechanical performance of pressurized polymer pipes. In this paper, six polyethylene (PE) pipes, including three high-density PEs (HDPE) and three medium-density PEs (MDPE) provided by different suppliers, were tested using a one-slit-ring method to measure the residual stress distribution along the hoop direction. Finite element (FE) simulation and mechanical testing were also employed in an iteration process to obtain the mechanical parameters of the six PE pipes. For the same PE pipe code from different suppliers, the results show that the magnitude of the residual hoop stress can be very different, resulting in different mechanical behaviors. In addition, the results are proposed to explain the scenario that was reported previously, i.e., the different critical quasi-static stress (the time-independent stress) levels of the PE pipes with the same pipe code. Since the quasi-static stress is expected to dominate the long-term behavior of the PE pipes, it is of great importance to carefully consider the effect of the residual stress on the determination of the quasi-static stress. Full article
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Article
Effect of Temperatures and Moisture Content on the Fracture Properties of Engineered Cementitious Composites (ECC)
Materials 2022, 15(7), 2604; https://doi.org/10.3390/ma15072604 - 01 Apr 2022
Abstract
This research will help to improve our understanding of the fracture properties of ECC at low temperatures (long-term low temperatures, freeze–thaw) and evaluate the safety properties of ECC under low-temperature conditions. Three levels of saturation (saturated, semi-saturated, and dry), four target temperatures (20, [...] Read more.
This research will help to improve our understanding of the fracture properties of ECC at low temperatures (long-term low temperatures, freeze–thaw) and evaluate the safety properties of ECC under low-temperature conditions. Three levels of saturation (saturated, semi-saturated, and dry), four target temperatures (20, 0, −20, and −60 °C), and the effect of the coupled of the two on the mode I fracture properties of ECC were investigated. Then, we compared and analyzed the fracture properties of ECC loaded at 20 and −20 °C, after different freeze–thaw cycles (25, 50, 100 cycles), which were compared with saturated specimens without freeze–thaw at the four target temperatures to analyze the differences in low-temperature and freeze–thaw failure mechanisms. Temperatures and saturation have a significant effect on the fracture properties. Low temperatures and freeze–thaw treatments both decreased the nominal fracture energy of ECC. Distinct differences in matrix and fiber-matrix interface damage mechanisms have been discovered. Low temperatures treatment transforms ECC from a ductile to a brittle fracture mode. However, even after 100 freeze–thaw cycles, it remains ductile fractured. This study complements the deficiencies of ECC in low-temperature theoretical and experimental applications, and it sets the stage for a broad range of ECC applications. Full article
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Article
Experimental and Statistical Study of the Fracture Mechanism of Sn96.5Ag3Cu0.5 Solder Joints via Ball Shear Test
Materials 2022, 15(7), 2455; https://doi.org/10.3390/ma15072455 - 26 Mar 2022
Abstract
Ball shear testing is an efficient approach to investigate the mechanical reliability of solder joints at the structural level. In the present study, a series of low-speed ball shear tests were conducted to study the deformation and fracture characteristics of Sn96.5Ag3Cu0.5 solder joints [...] Read more.
Ball shear testing is an efficient approach to investigate the mechanical reliability of solder joints at the structural level. In the present study, a series of low-speed ball shear tests were conducted to study the deformation and fracture characteristics of Sn96.5Ag3Cu0.5 solder joints at continuous speeds from 10 μm/s to 200 μm/s. In order to account for randomness, the quantity of tests was repeated for each shear rate. The relationship between mechanical properties and shear speeds was calculated in detail via effective statistical analysis. In addition, by utilizing SEM imaging and ingredient analysis the interfacial effect and fracture mechanism of solder balls were obtained and their fracture mode classified into two types, viz., bulk fracture and interface fracture. Furthermore, by means of statistical analysis and approximate calculation it was proven that bulk fracture balls have greater adhesive powers and reliability compared with interface fracture balls. Full article
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Article
The Influence of Service Temperature and Thickness on the Tensile Properties of Thin T2 Copper Sheets
Materials 2022, 15(7), 2341; https://doi.org/10.3390/ma15072341 - 22 Mar 2022
Abstract
Thin T2 copper sheets with nine different thicknesses were employed in uniaxial tensile tests to investigate the influence of service temperature and thickness on their tensile properties. A total of 33 groups of tensile samples were separately tested at 20 °C, 100 °C, [...] Read more.
Thin T2 copper sheets with nine different thicknesses were employed in uniaxial tensile tests to investigate the influence of service temperature and thickness on their tensile properties. A total of 33 groups of tensile samples were separately tested at 20 °C, 100 °C, 150 °C, 200 °C, and 250 °C to obtain their elongation and their tensile and yield strengths. The change laws of the tensile properties of the investigated T2 copper were analyzed using different fitting functions. The main results show that both sheet thickness and temperature have an important influence on the tensile properties of T2 copper. As the sheet thickness increased, the tensile and yield strengths of the tested materials first increased rapidly, then decreased sharply, and finally stabilized. As the temperature increased, the tensile strength increased linearly while the yield strength decreased linearly. The relationships between the elongation and the sheet thickness and temperature were exponential and polynomial functions, respectively. TtRm, TtRel, and Ttδ empirical formulas were proposed and established to predict the tensile properties of the investigated T2 copper sheet, and the predictive models exhibited solid accuracy. Full article
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Article
Research on Fatigue Life Prediction Method of Key Component of Turning Mechanism Based on Improved TCD
Metals 2022, 12(3), 506; https://doi.org/10.3390/met12030506 - 16 Mar 2022
Abstract
The main objective of this paper is to accurately obtain fatigue life prediction for the key components of a turning mechanism using the improved theory of critical distances (TCD). The irregularly shaped rotating arm is the central stressed part of the turning mechanism, [...] Read more.
The main objective of this paper is to accurately obtain fatigue life prediction for the key components of a turning mechanism using the improved theory of critical distances (TCD). The irregularly shaped rotating arm is the central stressed part of the turning mechanism, which contains notches. It has been found that TCD achieves good results in predicting the fatigue strength or fatigue life of notched components with regular shape but is less commonly used for notched components with irregular shape. Therefore, TCD was improved and applied broadly to predict the fatigue life of an irregularly shaped rotating arm. Firstly, the notch depth and structure net width parameters were introduced into the low-order and low-accuracy classical TCD function to obtain a novel stress function with high computational efficiency and high accuracy, whereas the stress concentration factor was introduced to modify the length of critical distance. Secondly, the improved TCD was used to predict the fatigue strength of notched components with regular shape, and its accuracy was demonstrated by a fatigue experiment. Finally, the improved TCD was applied to predict the fatigue life of an irregularly shaped rotating arm. The deviation between prediction results and experimental results is less than 18%. The results demonstrate that the improved TCD can be applied effectively and accurately to predict the fatigue life of key components of turning mechanisms. Full article
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Article
Simulation Study on Coil of Biomass Carbonization Kettle
Materials 2022, 15(6), 2152; https://doi.org/10.3390/ma15062152 - 15 Mar 2022
Abstract
The damage and failure of coiling tube in biomass carbonization kettle due to the long-term operation was discussed. According to the actual structure of the carbonization kettle, a three-dimensional model was established, and the temperature field was simulated based on the given design [...] Read more.
The damage and failure of coiling tube in biomass carbonization kettle due to the long-term operation was discussed. According to the actual structure of the carbonization kettle, a three-dimensional model was established, and the temperature field was simulated based on the given design parameters. The results show that the temperature distribution is stable during 440~450 °C, and the relative error with the actual temperature 449.2 °C, which is about 0.78%. The tensile specimens made of 20G steel, the common material of the coil, was placed in a tubular furnace, and the real heat treatment conditions were simulated with mixed gas and water vapor. After that, the uniaxial tensile test was carried out on MTS testing machine. The obtained physical parameters such as yield strength and elastic modulus were substituted into the numerical temperature field model to obtain the stress field model. The simulation results indicate that during the initial ventilation of the equipment, the coil compressed with the maximum stress of 8.3 MPa at the bending point of the second and fourth laps and partial failure was prone to occur, which is consistent with the actual coil failure result. Full article
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Article
On Scaled Normal Stresses in Multiaxial Fatigue and Their Exemplary Application to Ductile Cast Iron
Appl. Mech. 2022, 3(1), 259-295; https://doi.org/10.3390/applmech3010018 - 08 Mar 2022
Cited by 1
Abstract
The approaches used to calculate the fatigue life of components must inevitably consider multiaxial stresses. Compared to proportional loading, the calculation of nonproportional loading is particularly challenging, especially since different materials exhibit the effects of nonproportional hardening and shifts in fatigue life. In [...] Read more.
The approaches used to calculate the fatigue life of components must inevitably consider multiaxial stresses. Compared to proportional loading, the calculation of nonproportional loading is particularly challenging, especially since different materials exhibit the effects of nonproportional hardening and shifts in fatigue life. In this paper, the critical plane approach of scaled normal stresses, first proposed by Gaier and Dannbauer and later published in a modified version by Riess et al., is investigated in detail. It is shown that, on the one hand, compatibilities exist or can be established with known proportional strength criteria that can account for the varying ductility of different materials. Furthermore, it is demonstrated that the scaled normal stress approach can be formulated in such a way that different strength criteria can be used therein. As an example, the generally formulated approach for scaled normal stresses is applied to test results from ductile cast iron material EN-GJS-500-14. Different correction factors accounting for nonproportional loading are investigated. Through appropriate parameterization of one of the studied corrections, proportional and nonproportional test results were observed to fall within one common scatter band. Full article
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Article
Investigating the Effect of Low-Temperature Drilling Process on the Mechanical Behavior of CFRP
Polymers 2022, 14(5), 1034; https://doi.org/10.3390/polym14051034 - 04 Mar 2022
Cited by 1
Abstract
Previous research has found that lower temperature drilling is helpful to improve the hole quality of carbon fiber reinforced polymer (CFRP). However, the influence of the lower temperature drilling process on the mechanical behavior of composites is yet not fully understood. To examine [...] Read more.
Previous research has found that lower temperature drilling is helpful to improve the hole quality of carbon fiber reinforced polymer (CFRP). However, the influence of the lower temperature drilling process on the mechanical behavior of composites is yet not fully understood. To examine the influence of the lower temperature drilling process on the mechanical behavior of CFRP, the open hole CFRP specimens used for mechanical tests were obtained with three cases: drilling with −25 °C/uncoated carbide drills/(1000 rpm, 0.02 mm/r), 23 °C/coated carbide drills/(4000 rpm, 0.03 mm/r), and 23 °C/uncoated carbide drills/(1000 rpm, 0.02 mm/r), respectively; corresponding, three groups of open-hole specimens are obtained: specimens drilling at low-temperature with low damage, specimens drilling at room-temperature with low damage and specimens drilling at room-temperature with low damage; the mechanical behavior of the three groups specimens were obtained by static tensile, tensile–tensile fatigue cyclic tests and residual tensile strength test. The results have shown that the mechanical properties of specimens with a low-temperature drilling process is lower than those of the specimen with a normal drilling process due to the better drilling quality. The damage accumulation in specimens was increased with the damage degree of the original hole, the greater the damage degree, the worse the mechanical properties. Full article
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Article
Stress Field Approach for Prediction of End Concrete Cover Separation in RC Beams Strengthened with FRP Reinforcement
Polymers 2022, 14(5), 988; https://doi.org/10.3390/polym14050988 - 28 Feb 2022
Abstract
End concrete cover separation is one of the most common failure modes for RC beams strengthened with external FRP reinforcement. The premature failure mode significantly restricts the application of FRP materials and could incur serious safety problems. In this paper, an innovative stress [...] Read more.
End concrete cover separation is one of the most common failure modes for RC beams strengthened with external FRP reinforcement. The premature failure mode significantly restricts the application of FRP materials and could incur serious safety problems. In this paper, an innovative stress field-based analytical approach is proposed to assess the failure strength of end concrete cover separation and the conventional plane-section analysis is extended to evaluate the corresponding carrying capacity of FRP-strengthened RC beams. First, the dowel action of reinforcement and the induced concrete splitting, reflecting the interaction between concrete, steel and FRP, are considered in establishing the geometrical relationships of stress field for cracked concrete block. Then, the cracking angle and innovative failure criterion, considering the arrangement of steel and FRP reinforcement and cracking status of concrete and its softening effect, are derived to predict the occurrence of concrete cover separation and related mixed modes of debonding failure. Subsequently, an extended sectional analytical approach, in which the components of effective tensile strain of FRP resulted from flexural and shear actions are both considered, is presented to evaluate the carrying capacity of strengthened beams. Finally, the proposed calculational model is effectively validated by experimental results available in the literature. Full article
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Article
On Wind-Induced Fatigue of Curtain Wall Supporting Structure of a High-Rise Building
Appl. Sci. 2022, 12(5), 2547; https://doi.org/10.3390/app12052547 - 28 Feb 2022
Abstract
Due to the soft stiffness of high-rise buildings in the horizontal direction, strong wind will cause a strenuous structural response. Wind load is one key control load in the design of high-rise buildings. This study analyzes wind-induced fatigue of curtain wall supporting structure [...] Read more.
Due to the soft stiffness of high-rise buildings in the horizontal direction, strong wind will cause a strenuous structural response. Wind load is one key control load in the design of high-rise buildings. This study analyzes wind-induced fatigue of curtain wall supporting structure of a high-rise building in accordance with dynamic pressure measurement data of wind tunnel, acquiring wind pressure in each part of the structure. The finite element model is established for the curtain wall supporting structure, and the fatigue of corresponding nodes is discussed. Moreover, RBF (radial basis function) neural network regression is introduced to predict the fatigue life of unknown working conditions. Based on the joint distribution model of wind velocity and direction, this study explores the distribution law of fatigue life of supporting structure nodes, proposes a hypothesis of life distribution, and conducts a test. Moreover, working conditions with higher probability life are collected to provide a basis for practical engineering applications. The results show that the average deviation is below 10% by using RBF neural network and the probability life of the sample nodes is between 0 and 1016. Wind velocity is 8~15 m/s and azimuth angles of 50°~100°, 120°~200°, and 260°~300° are found in working conditions with low probability life; about 95% of the fatigue damage takes place in the first 30 conditions, and their fatigue damage values are between 3.5 × 10−3~9.36 × 10−2. Full article
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Article
In Vitro Study of Preload Loss in Different Implant Abutment Connection Designs
Materials 2022, 15(4), 1392; https://doi.org/10.3390/ma15041392 - 14 Feb 2022
Abstract
The stability and integrity of the abutment-implant connection, by means of a screw, is fallible from the moment the prosthetic elements are joined and is dependent on the applied preload, wear of the components and function. One of the main causes of screw [...] Read more.
The stability and integrity of the abutment-implant connection, by means of a screw, is fallible from the moment the prosthetic elements are joined and is dependent on the applied preload, wear of the components and function. One of the main causes of screw loosening is the loss of preload. The loosening of the screw-abutment can cause complications such as screw fracture, marginal gap, peri-implantitis, bacterial microleakage, loosening of the crown and discomfort of the patient. It is also reported that loosening of the screw/abutment may lead to a failure of osseointegration. It is necessary to evaluate and quantify, with in vitro studies, the torque loss before and after loading in the different connections. Aim: evaluate the influence of implant- abutment connection design in torque maintenance after single tightening, multiple tightening and multiple tightening followed by mechanical cycling. Materials and Methods: 180 Klockner implants divided in 4 groups: 15 SK2 external connection, 25 Ncm tightening torque; 15 KL external connection, 30 Ncm tightening torque; 15 Vega internal connection, 25 Ncm tightening torque; 15 Essential internal connection, 30 Ncm tightening torque. In each group removal torque values (RTV) were evaluated with a digital torque meter, in 3 distinct phases: after one single tightening, 10 multiple tightenings and 10 multiple tightenings and cyclic loading (500 N × 1000 cycles). Results: After one single tightening, and for all connections, RTV were lower than those of insertion, but only for Essential and Vega internal connections this result was statistically significant. After multiple tightening, RTV were significantly lower in all connections. After repeated tightening followed by cyclic loading, mean RTV were significantly lower, when compared to insertion torque. The multiple tightening technique resulted in higher RTV than the single tightening technique, except for Vega implant. The multiple tightening followed by cyclic load, compared to the other phases, was the one that generated the lowest RTV, for all connections. Conclusions: The connection design, in our study, did not seem to influence the maintenance of preload. Loading influenced the loss of preload, in the sense that significantly decreased the removal torque values. The multiple re-tightening technique resulted in higher removal torque values than the single tightening technique. Clinically, our results recommend to retighten retaining screws, a few minutes after insertion. Full article
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Article
Effects of Blade Numbers on Wind-Induced Fatigue Lives of Straight-Bladed Vertical-Axis Wind-Turbine Tower Bases
Metals 2022, 12(2), 321; https://doi.org/10.3390/met12020321 - 11 Feb 2022
Abstract
Vertical-axis wind turbines (VAWTs) are being reconsidered as a complementary technology to the more commercially used horizontal-axis wind turbines (HAWTs) because of their economical installation and maintenance. The selection of the blade numbers is one of the crucial concerns for VAWTs. This study [...] Read more.
Vertical-axis wind turbines (VAWTs) are being reconsidered as a complementary technology to the more commercially used horizontal-axis wind turbines (HAWTs) because of their economical installation and maintenance. The selection of the blade numbers is one of the crucial concerns for VAWTs. This study focuses on the effects of the blade numbers on the fatigue lives of VAWT tower bases subjected to wind loading. Three straight-bladed VAWTs, with the same solidity ratios but different blade numbers, varying from two to four, were designed. The aerodynamic loading incurred by the VAWTs was computed using the corrected double-disk multistreamtube (DMS) model. The dynamic equations of the turbine systems were solved using the explicit central difference method. Then, a fatigue assessment model, including the crack-initiation and crack-propagation stages, was developed for the turbine tower bases. The results indicate that the three- and four-bladed VAWTs always presented better performances than the two-bladed VAWT in terms of the fatigue life. Moreover, increasing the number of blades from two to three improves the fatigue life of the tower base more than increasing it from three to four at lower wind speeds, while the latter is the more effective way to improve the tower-base fatigue life at higher wind speeds. Full article
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Article
Effect of Prolonged Thermal Exposure on Low-Cycle Bending Fatigue Resistance of Low-Carbon Steel
Metals 2022, 12(2), 281; https://doi.org/10.3390/met12020281 - 04 Feb 2022
Abstract
Using a dynamic mechanical analyzer, the comparative studies of a low-cycle bending fatigue were carried out for AISI 1022 low-carbon steel after extreme thermal exposure, simulating the severe beyond-design-basis accident at nuclear power plants. In the as-delivered state, the steel has a high [...] Read more.
Using a dynamic mechanical analyzer, the comparative studies of a low-cycle bending fatigue were carried out for AISI 1022 low-carbon steel after extreme thermal exposure, simulating the severe beyond-design-basis accident at nuclear power plants. In the as-delivered state, the steel has a high resistance to low-cycle fatigue (the fatigue strength at N = 3.5 × 104 cycles (σNf) was 360 MPa). Long-term thermal exposure led to a slight decrease in the resistance to low-cycle fatigue of steel: σNf is decreased by 9%. The influence of AISI 1022 steel structure on the characteristics of fatigue strength and fracture mechanisms is analyzed. Full article
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Article
Effects of Long-Term Service on Microstructure and Impact Toughness of the Weld Metal and Heat-Affected Zone in CrMoV Steel Joints
Metals 2022, 12(2), 278; https://doi.org/10.3390/met12020278 - 03 Feb 2022
Abstract
The microstructure and impact toughness of weld metals (WMs) and heat-affected zones (HAZs) of a low-alloy CrMoV steel gas turbine rotor which had served for 14 years were investigated. The ex-service joints in the turbine part (serving at 500–540 °C) and the compressor [...] Read more.
The microstructure and impact toughness of weld metals (WMs) and heat-affected zones (HAZs) of a low-alloy CrMoV steel gas turbine rotor which had served for 14 years were investigated. The ex-service joints in the turbine part (serving at 500–540 °C) and the compressor part (serving below 300 °C) of the rotor were selected for comparative research. The microstructure of the WMs and HAZs between the turbine part and the compressor part was similar, indicating that there was no significant deterioration in microstructure of the turbine part during service. However, compared with the compressor part WM, the impact energy of the turbine part WM decreased significantly, and FATT50 increased greatly. The degraded toughness of turbine part WM was related to more serious intergranular cracking caused by higher segregation level of phosphorus (P) at prior austenite grain (PAG) boundaries. Welding and post-weld heat treatment led to obvious segregation of P at PAG boundaries in WMs, and the segregation of P in turbine part WM was further aggravated during serving at 500–540 °C. Additionally, the inhomogeneous microstructure of the WMs also aggravated the segregation of P. The toughness of the HAZs in both turbine part and compressor part was high, which was because of fine grains. Furthermore, due to there being more grain boundaries and low P content, the segregation of P in HAZs was slight and its adverse effect on the toughness could be ignored. Full article
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Article
Optically Pumped Magnetometer Measuring Fatigue-Induced Damage in Steel
Appl. Sci. 2022, 12(3), 1329; https://doi.org/10.3390/app12031329 - 26 Jan 2022
Abstract
Uniaxial fatigue testing of micro-mechanical metallic specimens can provide valuable insight into damage formation. Magnetic and piezomagnetic testing are commonly used for qualitative characterization of damage in ferromagnetic specimens. Sensitive and accurate measurements with magnetic sensors is a key part of such a [...] Read more.
Uniaxial fatigue testing of micro-mechanical metallic specimens can provide valuable insight into damage formation. Magnetic and piezomagnetic testing are commonly used for qualitative characterization of damage in ferromagnetic specimens. Sensitive and accurate measurements with magnetic sensors is a key part of such a characterization. This work presents an experimental setup to induce structural defects in a micro-mechanical fatigue test. Simultaneously, the resulting piezomagnetic signals are measured during the complete lifetime of the tested specimen. The key component is a highly sensitive optically pumped magnetometer (OPM) used to measure the piezomagnetic hysteresis of a small specimen whose structural defects can be analyzed on a small scale by other metallographic characterization methods as well. This setup aims to quantify the magnetic signatures of damage during the fatigue process, which could enable non-destructive mechanical testing of materials. This paper reports the initial results obtained from this novel micro-magneto-mechanical test setup for a ferritic steel specimen. Full article
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Article
Fracture Resistance of Zirconia Abutments with or without a Titanium Base: An In Vitro Study for Tapered Conical Connection Implants
Materials 2022, 15(1), 364; https://doi.org/10.3390/ma15010364 - 05 Jan 2022
Abstract
Dental implants with tapered conical connections are often combined with zirconia abutments for esthetics; however, the effect of the titanium base on the implant components remains unclear. This study evaluated the effects of a titanium base on the fracture resistance of zirconia abutments [...] Read more.
Dental implants with tapered conical connections are often combined with zirconia abutments for esthetics; however, the effect of the titanium base on the implant components remains unclear. This study evaluated the effects of a titanium base on the fracture resistance of zirconia abutments and damage to the tapered conical connection implants. Zirconia (Z) and titanium base zirconia (ZT) abutments were fastened to Nobel Biocare (NB) implants and Straumann (ST) implants and subjected to static load testing according to ISO 14801:2016. The experiments were performed with 3 mm of the platform exposed (P3) and no platform exposed (P0). The fracture loads were statistically greater in the titanium base abutments than the zirconia abutments for the NB and ST specimens in the P0 condition. In the P3 condition of the ST specimens, the deformation volume of the ZT group was significantly greater than the Z group. The titanium base increased the fracture resistance of the zirconia abutments. Additionally, the titanium base caused more deformation in the P3 condition. The implant joint design may also affect the amount of damage to the implants when under a load. The mechanical properties of the abutment should be considered when selecting a clinical design. Full article
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Article
Effect of Rotational Speed on Static and Fatigue Properties of Rotary Friction Welded Dissimilar AA7075/AA5083 Aluminium Alloy Joints
Metals 2022, 12(1), 99; https://doi.org/10.3390/met12010099 - 04 Jan 2022
Abstract
In this work, rotary friction welding processes of dissimilar AA7075/AA5083 aluminium alloy rods with the diameter of 15 mm were performed at varying rotational speeds, typically 370 to 2500 rpm. The aim of this research is to improve mechanical properties, in particular, strength [...] Read more.
In this work, rotary friction welding processes of dissimilar AA7075/AA5083 aluminium alloy rods with the diameter of 15 mm were performed at varying rotational speeds, typically 370 to 2500 rpm. The aim of this research is to improve mechanical properties, in particular, strength and fatigue performance of the weld joints. Several experiments including macro and microstructural examinations, Vickers microhardness measurements, tensile tests, fatigue tests and residual stress measurements were carried out. Results showed that at higher rotational speeds, typically 540 rpm or above, the dissimilar AA7075/AA5083 rotary friction weld joints revealed a static fracture in the AA5083 base metal side, indicating that the joint efficiency is more than 100%. It seemed that the best weld joint was achieved at the rotational speed of 1200 rpm, in which the friction heat was sufficient to form metallurgical bonding without causing excessive flash and burn-off. In such a condition, the fatigue strength of the weld joint was slightly higher than AA5083 base metal, but it was lower than AA7075 base metal. It was confirmed that the crack origin is observed at the interface followed by fatigue crack growth towards AA5083 side, and the growth of crack seemed to be controlled by microstructure and residual stress. Full article
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Article
Finite Element Simulation of a Crack Growth in the Presence of a Hole in the Vicinity of the Crack Trajectory
Materials 2022, 15(1), 363; https://doi.org/10.3390/ma15010363 - 04 Jan 2022
Cited by 2
Abstract
The aim of this paper was to present a numerical simulation of a crack growth path and associated stress intensity factors (SIFs) for linear elastic material. The influence of the holes’ position and pre-crack locations in the crack growth direction were investigated. For [...] Read more.
The aim of this paper was to present a numerical simulation of a crack growth path and associated stress intensity factors (SIFs) for linear elastic material. The influence of the holes’ position and pre-crack locations in the crack growth direction were investigated. For this purpose, ANSYS Mechanical R19.2 was introduced with the use of a new feature known as Separating Morphing and Adaptive Remeshing Technology (SMART) dependent on the Unstructured Mesh Method (UMM), which can reduce the meshing time from up to several days to a few minutes, eliminating long preprocessing sessions. The presence of a hole near a propagating crack causes a deviation in the crack path. If the hole is close enough to the crack path, the crack may stop at the edge of the hole, resulting in crack arrest. The present study was carried out for two geometries, namely a cracked plate with four holes and a plate with a circular hole, and an edge crack with different pre-crack locations. Under linear elastic fracture mechanics (LEFM), the maximum circumferential stress criterion is applied as a direction criterion. Depending on the position of the hole, the results reveal that the crack propagates in the direction of the hole due to the uneven stresses at the crack tip, which are consequences of the hole’s influence. The results of this modeling are validated in terms of crack growth trajectories and SIFs by several crack growth studies reported in the literature that show trustworthy results. Full article
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Article
Stress Triaxial Constraint and Fracture Toughness Properties of X90 Pipeline Steel
Metals 2022, 12(1), 72; https://doi.org/10.3390/met12010072 - 02 Jan 2022
Cited by 2
Abstract
The X90 pipeline steel with high-strength and high-toughness become the most popular pipeline steel. Due to the stress triaxial constraint and fracture toughness properties are the key factors for the stable work of pipeline steel, the research on the fracture toughness of X90 [...] Read more.
The X90 pipeline steel with high-strength and high-toughness become the most popular pipeline steel. Due to the stress triaxial constraint and fracture toughness properties are the key factors for the stable work of pipeline steel, the research on the fracture toughness of X90 is a great significance to promote the engineering application of high-strength pipeline steel. In order to investigate the stress triaxial constraint and fracture toughness properties of X90 pipeline steel, the experimental rules with different grooves size are proposed using the common toughness experiment and the corresponding numerical models are established in this paper. The resistance curves and fracture toughness of each type of specimens are obtained and compared with that of finite element analysis. Furthermore, the stress distribution, J-integral distribution and stress triaxial constraint of the specimen are analyzed, as well as the influence of side grooves size on the determination of fracture toughness is also discussed. The results obtained from the study will provide a reference to the fracture toughness evaluation research and application of X90 pipeline steel. Full article
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Article
Stress Rupture Life Prediction Method for Notched Specimens Based on Minimum Average Von Mises Equivalent Stress
Metals 2022, 12(1), 68; https://doi.org/10.3390/met12010068 - 30 Dec 2021
Abstract
Creep tests were carried out on notched plate specimens of nickel-based superalloy GH4169 with different stress concentration coefficients. It was found that the duration of the first stage of the creep curve increases with the increase of stress concentration coefficient, while the fracture [...] Read more.
Creep tests were carried out on notched plate specimens of nickel-based superalloy GH4169 with different stress concentration coefficients. It was found that the duration of the first stage of the creep curve increases with the increase of stress concentration coefficient, while the fracture ductility decreases with the increase of stress concentration coefficient. To predict the life of notched plate specimens, four constitutive models were used to analyze the stress and strain of the notches. It was found that the average Von Mises equivalent stress (AVES) on the minimum notch section first decreases and then increases with the creep time, resulting in a minimum value. The minimum average Von Mises equivalent stress (MAVES) is considered as the characteristic stress of notched specimens in this paper. The creep life equation is fitted according to the results of creep tests of smooth specimens, and then the predicted life of notched specimens is obtained by substituting the minimum average Von Mises equivalent stress of notched specimens into the creep equation. The prediction results of the four constitutive models are within 2 times the dispersion band, and the three-stage model is within the 1.5 times dispersion band. Full article
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Article
Low-Velocity Impact Resistance of Al/Gf/PP Laminates with Different Interface Performance
Polymers 2021, 13(24), 4416; https://doi.org/10.3390/polym13244416 - 16 Dec 2021
Cited by 2
Abstract
The weak interface performance between metal and composite (IPMC) makes the composite materials susceptible to impact load. Aluminum/glass fiber/polypropylene (Al/Gf/PP) laminates were manufactured with the aluminum alloy sheets modified by nitrogen plasma surface treatment and the phosphoric acid anodizing method, respectively. FEM models [...] Read more.
The weak interface performance between metal and composite (IPMC) makes the composite materials susceptible to impact load. Aluminum/glass fiber/polypropylene (Al/Gf/PP) laminates were manufactured with the aluminum alloy sheets modified by nitrogen plasma surface treatment and the phosphoric acid anodizing method, respectively. FEM models of Al/Gf/PP laminates under low-velocity impact were established in ABAQUS/Explicit based on the generated data including the model I and II interlaminar fracture toughness. Low-velocity impact tests were performed to investigate the impact resistance of Al/Gf/PP laminates including load traces, failure mechanism, and energy absorption. The results showed that delamination was the main failure mode of two kinds of laminates under the impact energy of 20 J and 30 J. When the impact energy was between 40 J and 50 J, there were metal cracks on the rear surface of the plasma pretreated specimens, which possessed higher energy absorption and impact resistance, although the integrity of the laminates could not be preserved. Since the residual compressive stress was generated during the cooling process, the laminates were more susceptible to stretching rather than delamination. For impact energy (60 J) causing the through-the-thickness crack of two kinds of laminates, plasma pretreated specimens exhibited higher SEA values close to 9 Jm2/kg due to better IPMC. Combined with the FEM simulation results, the interface played a role in stress transmission and specimens with better IPMC enabled the laminates to absorb more energy. Full article
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Article
Ultimate Axial Load Prediction Model for X65 Pipeline with Cracked Welding Joint Based on the Failure Assessment Diagram Method
Appl. Sci. 2021, 11(24), 11780; https://doi.org/10.3390/app112411780 - 11 Dec 2021
Cited by 1
Abstract
Crack defects in the girth welds of pipelines have become an important factor affecting the safe operation of in-service oil pipelines. Therefore, it is necessary to analyze the factors affecting the safe operation of pipelines and determine the ultimate load during pipeline operation. [...] Read more.
Crack defects in the girth welds of pipelines have become an important factor affecting the safe operation of in-service oil pipelines. Therefore, it is necessary to analyze the factors affecting the safe operation of pipelines and determine the ultimate load during pipeline operation. Based on the failure assessment diagram (FAD) method described in the BS 7910 standard, the key factors affecting the evaluation results of the suitability of X65 pipeline girth welds are analyzed, and the effects of crack size, pipe geometry, and material properties on the evaluation results are investigated. The results indicate that the crack depth is more crucial to the safe operation of the pipeline than the crack length. While the effect of wall thickness is not significant, the misalignment can seriously aggravate the stress concentration. In general, the higher the yield ratio and tensile strength of the pipe material, the more dangerous the condition at the weld. The ultimate axial load that a crack-containing girth weld can withstand under different combinations of the above factors was determined. Furthermore, a data driven model via the optimized support vector regression method for the ultimate axial load of the X65 pipe was developed for engineering application, and the comparison results between the FEM results and the predicted results proved its accuracy and reliability. Full article
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Article
Effect of Autoclaving Cycles on the Cyclic Fatigue Resistance of Race and Race Evo Nickel-Titanium Endodontic Rotary Files: An In Vitro Study
Metals 2021, 11(12), 1947; https://doi.org/10.3390/met11121947 - 02 Dec 2021
Cited by 3
Abstract
Objective: The aim of this study was to evaluate the influence of autoclave sterilization on the resistance to cyclic fatigue of two nickel-titanium (NiTi) endodontic files of identical design and taper, but with different NiTi alloy treatments: the newly introduced heat-treated Race Evo [...] Read more.
Objective: The aim of this study was to evaluate the influence of autoclave sterilization on the resistance to cyclic fatigue of two nickel-titanium (NiTi) endodontic files of identical design and taper, but with different NiTi alloy treatments: the newly introduced heat-treated Race Evo and the electropolished Race files. Materials and methods: Fifteen Race (25/0.06) files and fifteen Race Evo (25/0.06) files (n = 30 in total) were randomly assigned to five sub-groups each consisting of three files of the same NiTi alloy treatment. One group served as a control with files unautoclaved. The four remaining groups were sterilized in a steam sterilizer for 1, 3, 5, and 10 autoclave cycles, respectively. Files then underwent cyclic fatigue testing in a simulated metal canal block. A scanning electron microscope was used to inspect the surface of the fractured instruments. Statistical analysis was conducted using independent t-test and multi-factorial analysis of variance with significance set at a p value of ≤0.05. Results: Both Race Evo and Race files showed no significant difference between the different autoclaving cycles in terms of the number of cycles to fracture (p = 0.232 and p = 0.359). Despite rotating at a higher speed, the number of cycles to fracture of heat-treated Race Evo files was significantly higher than that of Race files (p ≤ 0.0001). Conclusion: Autoclave sterilization has no significant effect on the resistance to cyclic fatigue of heat-treated Race Evo or electropolished Race files. However, Race Evo files showed superior resistance to cyclic fatigue irrespective of autoclaving cycles. Full article
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