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Keywords = notched tensile specimen

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29 pages, 8597 KiB  
Article
Study on the Damage Mechanisms in the Forming Process of High-Strength Steel Laser Tailor Welded Blanks Based on the Johnson–Cook Damage Model
by Xianping Sun, Huaqiang Li, Song Gao and Qihan Li
Materials 2025, 18(15), 3497; https://doi.org/10.3390/ma18153497 - 25 Jul 2025
Viewed by 613
Abstract
This paper, based on the Johnson–Cook damage model, investigates the damage mechanism of high-strength steel tailor welded blanks (TWBs) (Usibor1500P and Ductibor500) during the forming process. Initially, specimens with varying notch sizes were designed and fabricated to perform uniaxial tensile tests to determine [...] Read more.
This paper, based on the Johnson–Cook damage model, investigates the damage mechanism of high-strength steel tailor welded blanks (TWBs) (Usibor1500P and Ductibor500) during the forming process. Initially, specimens with varying notch sizes were designed and fabricated to perform uniaxial tensile tests to determine their mechanical properties. Then, the deformation process of the notched specimens was simulated using finite element software, revealing the distribution and variation of stress triaxiality at the fracture surface. By combining both experimental and simulation data, the parameters of the Johnson–Cook (J–C) damage model were calibrated, and the effects of temperature, strain rate, and stress triaxiality on material fracture behavior were further analyzed. Based on finite element analysis, the relevant coefficients for stress triaxiality, strain rate, and temperature were systematically calibrated, successfully establishing a J–C fracture criterion for TWB welds, Usibor1500P, and Ductibor500 high-strength steels. Finally, the calibrated damage model was further validated through the Nakajima-type bulge test, and the simulated Forming Limit Diagram (FLD) closely matched the experimental data. The results show that the analysis based on the J–C damage model can effectively predict the fracture behavior of tailor welded blanks (TWB) during the forming process. This study provides reliable numerical predictions for the damage behavior of high-strength steel laser-customized welded sheets and offers a theoretical basis for engineering design and material performance optimization. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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17 pages, 3279 KiB  
Article
Rapid Assessment of Ti-6Al-4V Fatigue Limit via Infrared Thermography
by Chiara Colombo, Antonio Salerno, Arthur Teyssiéras and Carlo Alberto Biffi
Metals 2025, 15(8), 825; https://doi.org/10.3390/met15080825 - 23 Jul 2025
Viewed by 261
Abstract
The experimental tests needed for the estimation of the fatigue limit generally require extensive time and many specimens. A valid but not standardized alternative is the thermographic analysis of the self-heating phenomenon. The present work is aimed at using Infrared thermography to determine [...] Read more.
The experimental tests needed for the estimation of the fatigue limit generally require extensive time and many specimens. A valid but not standardized alternative is the thermographic analysis of the self-heating phenomenon. The present work is aimed at using Infrared thermography to determine the fatigue limit in two kinds of Ti-6Al-4V samples obtained by hot rolling: (1) with the standard dog-bone shape (unnotched specimen) and (2) with two opposed semicircular notches at the sides (notched specimen). Uniaxial tensile experiments are performed on unnotched samples, and the surface temperature variation during loading is monitored. The stress corresponding to the end of the thermoelastic stage gives a rough indication of the fatigue limit. Then, fatigue tests at different sinusoidal loads are performed, and the thermographic signal is monitored and processed. The results obtained using lock-in thermography in dissipative mode, e.g., analyzing the second harmonic, showed a sudden change in slope when the applied stress exceeded a certain limit. This slope change is related to the fatigue limit. In addition, the ratio between the fatigue limits obtained for notched and unnotched specimens, e.g., the fatigue strength reduction factor, is consistent with literature values based on the selected geometry. Full article
(This article belongs to the Special Issue Fracture Mechanics of Metals (2nd Edition))
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22 pages, 16747 KiB  
Article
Development of a Technique for Toughness Estimation in Dual-Phase Steels Using Representative Volume Elements
by Amin Latifi Vanjani, Hari M. Simha and Alexander Bardelcik
Metals 2025, 15(7), 788; https://doi.org/10.3390/met15070788 - 11 Jul 2025
Viewed by 217
Abstract
A novel approach to estimating the absorbed energy (toughness) in a uniaxial tensile test with only knowledge of the microstructure is presented. The flow behavior of each Dual-Phase (DP) steel grade is predicted using idealized Representative Volume Elements (RVEs) up to uniform elongation. [...] Read more.
A novel approach to estimating the absorbed energy (toughness) in a uniaxial tensile test with only knowledge of the microstructure is presented. The flow behavior of each Dual-Phase (DP) steel grade is predicted using idealized Representative Volume Elements (RVEs) up to uniform elongation. To estimate the flow behavior beyond uniform elongation, the stress-modified fracture strain in a non-local damage model was implemented in Abaqus. Damage parameters were calibrated using Finite Element (FE) simulations of purely ferritic tensile specimens. The damage parameters remained unchanged, except for the coefficient of triaxiality. This coefficient was adjusted based on the average triaxiality of ferrite elements at the instability point of the uniaxially loaded RVEs for each DP steel grade. The proposed approach comprises two steps: micron-sized RVEs to predict the flow behavior up to the point of uniform elongation and the average triaxiality and full-scale tensile-test simulations to predict the rest of the curves. The results show that the damage parameters calibrated for high-strain ferrite effectively estimate the absorbed energy during failure in tension tests. This approach is also geometry-independent; varying the geometry of the tensile specimen, including miniature or notched specimens, still yields predicted absorbed energies that are in good agreement with the experimental results. Full article
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16 pages, 4552 KiB  
Article
Life Prediction of Crack Growth for P92 Steel Under Strain-Controlled Creep–Fatigue Conditions Using a Sharp Notched Round Bar Specimen
by A. Toshimitsu Yokobori, Go Ozeki, Kazutaka Jinno, Hiroaki Seino, Ryuji Sugiura and Isamu Nonaka
Metals 2025, 15(7), 737; https://doi.org/10.3390/met15070737 - 30 Jun 2025
Viewed by 206
Abstract
Testing and the estimation methods for predicting the life of crack initiation and crack growth for P92 steel using a circular sharp notched round bar specimen (CNS) under strain-controlled creep and fatigue conditions have been reported previously. A unique estimation method for the [...] Read more.
Testing and the estimation methods for predicting the life of crack initiation and crack growth for P92 steel using a circular sharp notched round bar specimen (CNS) under strain-controlled creep and fatigue conditions have been reported previously. A unique estimation method for the cycle-sequential characteristics of tensile and compressive peak stresses is proposed; specifically, the nominal stress range σnet=(σmaxσmin)net and the measurement of crack length using the direct current electric potential drop (DCPD) method were adopted. This method was effective in specifying the failure life and crack initiation life by verifying the crack growth length. However, to show the universality of these results, it is important to compare the experimental results obtained under strain-controlled creep and fatigue conditions with those obtained under stress-controlled creep and fatigue conditions and with those for smooth specimens estimated based on the linear and nonlinear damage summation rule. Furthermore, it may also be important to compare these results with those of smooth specimens estimated based on the Manson–Coffin law when the failure life is fatigue-dominant. Considering these aspects, detailed experiments and analyses were systematically conducted for P92 steel in this study, and the above comparisons were conducted. The results aid in achieving a unified understanding of the law of fracture life, including those under stress- and strain-controlled creep and fatigue conditions. Full article
(This article belongs to the Special Issue Creep and Fatigue Behavior of Alloys)
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21 pages, 6854 KiB  
Article
Ductile Fracture Prediction in Mg-ZM51M Alloy Using Inverse-Calibrated Damage Models
by Thamer Sami Alhalaybeh, Ashiq Iqbal Chowdhury, Hammad Akhtar and Yanshan Lou
Metals 2025, 15(7), 722; https://doi.org/10.3390/met15070722 - 28 Jun 2025
Viewed by 325
Abstract
Magnesium (Mg) alloys are gaining widespread use in the automotive and construction industries for their potential to enhance performance and lower manufacturing costs, making them ideal for lightweight structural applications. However, despite these advantages, extruding Mg alloys remains technically challenging due to their [...] Read more.
Magnesium (Mg) alloys are gaining widespread use in the automotive and construction industries for their potential to enhance performance and lower manufacturing costs, making them ideal for lightweight structural applications. However, despite these advantages, extruding Mg alloys remains technically challenging due to their inherently limited formability and the strong crystallographic textures that form during deformation. This study aimed to comprehensively characterize the ductile fracture behavior of ZM51M Mg alloy round bars under various stress states and to improve the reliability of ductile failure predictions through the application and calibration of multiple uncoupled damage criteria. Tensile and compressive tests were conducted on specimens of varying geometries (dogbone, notched R5, shear, uniaxial compression, and plane strain compression specimens) and dimensions, meticulously cut along the extrusion direction of the round bar. These tests encompassed a wide spectrum of stress–strain responses and fracture characteristics, including uniaxial tension, uniaxial compression, and shear-dominated states. An inverse analysis approach, involving iterative numerical simulation coupled with experimental data, was employed to precisely determine fracture strains from the test results. The plastic deformation behavior was accurately modeled using the combined Swift–Voce hardening law. Subsequently, three prominent uncoupled ductile fracture criteria—Rice–Tracey, DF2014, and DF2016—were calibrated against the experimental data. The DF2016 criterion demonstrated superior predictive accuracy, consistently yielding the most accurate fracture strain predictions and significantly outperforming the Rice–Tracey and DF2014 criteria across the tested stress states. The findings of this work provide significant insights for improving the assessment of formability and fracture prediction in Mg alloys. This research directly contributes to overcoming the challenges associated with their inherent formability limitations and complex deformation textures, thereby facilitating more reliable design and broader adoption of Mg alloys in advanced lightweight structural solutions. Full article
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28 pages, 17637 KiB  
Article
Investigating Bayesian Parameter Identification Using Non-Standard Laboratory Specimens
by Matej Šodan, Vladimir Divić, Noémi Friedman and Mijo Nikolić
Appl. Sci. 2025, 15(11), 6194; https://doi.org/10.3390/app15116194 - 30 May 2025
Viewed by 589
Abstract
This work investigates the applicability of Bayesian inverse analysis for identifying parameters from non-standard aluminum specimens with notches that induce stress concentrations. Unlike conventional standardized specimens, the notched samples used in this work are typically unsuitable for direct parameter extraction due to geometric [...] Read more.
This work investigates the applicability of Bayesian inverse analysis for identifying parameters from non-standard aluminum specimens with notches that induce stress concentrations. Unlike conventional standardized specimens, the notched samples used in this work are typically unsuitable for direct parameter extraction due to geometric irregularities and size effects. The experimental procedure involved tensile tests conducted using a universal testing machine, with deformation data collected via LVDT sensors and optical measurements with digital image correlation. The numerical simulations were performed using a quadrilateral finite element model with embedded strong discontinuities to capture the complete material response, including elastic, plastic, and fracture behavior. The proposed identification procedure successfully provided reliable posterior parameter estimates on aluminum rectangular and single-notch specimens. Furthermore, the identified parameters were validated on a double-notch specimen made of the same material. The results highlight the importance of parameter interpretation and show that the Bayesian framework can reliably identify key material and model-dependent parameters from non-standard specimens while accounting for uncertainty in both measurements and model formulation. Full article
(This article belongs to the Section Civil Engineering)
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17 pages, 5744 KiB  
Article
Evaluation of Mechanical Characteristics of Tungsten Inert Gas (TIG) Welded Butt Joint of Inconel 600
by Arash Moradi, Fatemeh Marashi Najafi, Yong Chen and Mahmoud Chizari
J. Manuf. Mater. Process. 2025, 9(6), 177; https://doi.org/10.3390/jmmp9060177 - 28 May 2025
Viewed by 546
Abstract
Inconel 600 alloy has gained consideration as a favourable material for heat and power applications, particularly in turbine blades, due to its superior mechanical behaviour encompassing strength, toughness, oxidation resistance, and ductility. Tungsten Inert Gas (TIG) welding is one of the preferred techniques [...] Read more.
Inconel 600 alloy has gained consideration as a favourable material for heat and power applications, particularly in turbine blades, due to its superior mechanical behaviour encompassing strength, toughness, oxidation resistance, and ductility. Tungsten Inert Gas (TIG) welding is one of the preferred techniques for joining these alloys. Therefore, the investigation of the mechanical behaviour after the welding process is crucial for selecting the appropriate technique for joining Inconel 600 sheets. This research focuses on investigating the microstructure and mechanical behaviour of TIG-welded Inconel 600 through a series of tests, such as tensile, fatigue, creep, and hardness evaluations. In addition, microstructural analysis is combined with these mechanical evaluations to simulate the operating conditions experienced by turbine blades. Key parameters such as yield strength, tensile strength, and elongation have been evaluated through these analyses. The Ramberg–Osgood relationship has been investigated using the engineering and true stress–strain curves obtained from the welded specimens. The results of the fatigue test illustrate the relationship between strain amplitude and the number of cycles to failure for single and double-edge notched specimens. The test was performed at two different loads including 400 MPa and 250 MPa at a constant temperature of 650 °C, and the corresponding strain-time curves were recorded. The results showed rapid creep failure at 650 °C, suggesting that TIG welding may need to be optimized for high temperature applications. Full article
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16 pages, 5657 KiB  
Article
Tensile Fracture Behaviour of Prismatic Notched Specimens of Cold Drawn Pearlitic Steel: A Macro- and Micro-Approach
by Jesús Toribio, Francisco-Javier Ayaso and Rocío Rodríguez
Materials 2025, 18(8), 1690; https://doi.org/10.3390/ma18081690 - 8 Apr 2025
Viewed by 411
Abstract
This paper focuses on the study of the tensile fracture behaviour of prismatic notched specimens of cold drawn pearlitic steel, providing a macro- and micro-approach. Two types of notched samples with very different notch radius (sharp and blunt notches, PAA [...] Read more.
This paper focuses on the study of the tensile fracture behaviour of prismatic notched specimens of cold drawn pearlitic steel, providing a macro- and micro-approach. Two types of notched samples with very different notch radius (sharp and blunt notches, PAA and PCC) and the same notch depth were studied, thereby allowing a study of the fracture behaviour under different levels of stress triaxiality (constraint) in the experimental specimen. The studied samples are machined from pearlitic steel wires taken from a real cold drawing chain, analysing the entire drawing process, from the initial base material (hot rolled bar; not cold drawn at all) to the final commercial product (prestressing steel wires; heavily cold drawn), including two intermediate stages in the manufacture chain. The aforesaid specimens were subjected to tensile fracture tests and analysed at macroscopic and microscopical level using the scanning electron microscope (SEM), thereby obtaining micrographs of the different areas appearing in the specimens under study and assembling full micro-fracture maps (MFMs) of the fractured area. The aim of the research is to analyse the macro- and microscopic changes produced by the variation in stress triaxiality state (constraint), along with the different fracture processes. The first relevant finding is the increase in fracture path deflection for higher drawing degrees, and for greater triaxiality levels associated with sharp notches. Another finding is the variation in area of the different fracture zones, i.e., outer crown (OC), fracture process zone (FPZ) and intermediate zone (ZINT), which are characterised by their specific micro-mechanisms, micro-void coalescence (MVC), cleavage (C) and special (large) micro-void coalescence (MVC*). The higher the stress triaxiality level, the larger the area occupied by the ZINT in the fracture process. The fracture behaviour tends to unify along with the degree of drawing, with less dependence on the state of triaxiality imposed on heavily drawn wires. Results have been obtained in which the increase in triaxiality, imposed by the smaller radius of curvature of the notch (sharp notch), as well as the greater degree of drawing of the wires, cause the fracture process to place the FPZ at the notch tip. It is demonstrated that the variation in stress triaxiality and the drawing degree can generate different locations of the fracture initiation zone (FPZ). Full article
(This article belongs to the Special Issue High-Performance Alloys and Steels)
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16 pages, 3907 KiB  
Article
Application of Pipe Ring Notched Tensile (PRNT) Specimens to Fracture Mechanics Testing of Ductile Metallic Materials
by Isaak Trajković, Jovan Tanasković, Zoran Radosavljević, Miloš Milošević, Bojan Medjo and Jasmina Lozanović
Metals 2025, 15(4), 410; https://doi.org/10.3390/met15040410 - 4 Apr 2025
Viewed by 474
Abstract
This paper presents the results of experimental and numerical analysis of fracture mechanics testing of ductile metallic materials using a non-standard procedure with PRNT (pipe ring notched tensile) ring-shaped specimens, introduced in previous publications through analysis of 3D-printed polymer rings. The main focus [...] Read more.
This paper presents the results of experimental and numerical analysis of fracture mechanics testing of ductile metallic materials using a non-standard procedure with PRNT (pipe ring notched tensile) ring-shaped specimens, introduced in previous publications through analysis of 3D-printed polymer rings. The main focus of this research is the determination of the values of the plastic geometry factor ηpl since the specimen is not a standard one. Toward this aim, the finite element software package Simulia Abaqus was applied to evaluate the J-integral (by using the domain integral method) and the F-CMOD curve so that the plastic geometry factor ηpl can be evaluated for different values of the ratio of crack length to specimen width (a0/W = 0.45 ÷ 0.55). In this way, a procedure and the possibility of practical implementation on the thin-walled pipelines are established. Full article
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21 pages, 42318 KiB  
Article
Effective Ductile Fracture Characterization of 17-4PH and Ti6Al4V by Shear–Tension Tests: Experiments and Damage Models Calibration
by Gabriele Cortis and Luca Cortese
Appl. Sci. 2025, 15(7), 3645; https://doi.org/10.3390/app15073645 - 26 Mar 2025
Viewed by 589
Abstract
An experimental campaign based on multiaxial tests is carried out to characterize the ductile behavior of 17-4PH steel and a Ti6Al4V titanium alloy, and to calibrate numerical ductile damage models, accordingly. This study aimed to identify a minimal set of four specimen types [...] Read more.
An experimental campaign based on multiaxial tests is carried out to characterize the ductile behavior of 17-4PH steel and a Ti6Al4V titanium alloy, and to calibrate numerical ductile damage models, accordingly. This study aimed to identify a minimal set of four specimen types to ensure the robust tuning of the damage models, using only a conventional uniaxial machine for testing. Two different shear–tension candidate geometries are identified, modified, and used together with cylindrical and notched bar specimens to evaluate material plastic strain at fracture under several stress states, characterized by different triaxialities and Lode angles. Finite element analysis and digital image correlation techniques are used to identify local data not directly measured from the tests. Three recent ductile damage models are calibrated using the experimental data. The accuracy of the proposed approach is validated and presented for the two alloys, by comparing the results with calibrations performed on the same materials using more conventional multiaxial tests. It is shown that the new methodology is effective, and how either one of the two shear–tension geometries in addition to tensile tests could replace, with the same level of accuracy, typical more complex calibration procedures involving tests that require dedicated facilities. Full article
(This article belongs to the Section Mechanical Engineering)
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10 pages, 5272 KiB  
Article
Determination of the Fracture Locus of a Cor-Ten Steel at Low and High Triaxiality Ranges
by Axel Baruscotti, Nicholas Miori and Franco Concli
Appl. Sci. 2025, 15(7), 3569; https://doi.org/10.3390/app15073569 - 25 Mar 2025
Cited by 1 | Viewed by 364
Abstract
Cor-Ten steels, also known as weathering steels, are construction materials of growing importance in the field of architecture and crash barriers, not only due to their good mechanical and corrosion resistance properties but also for the appealing color of their oxides. However, a [...] Read more.
Cor-Ten steels, also known as weathering steels, are construction materials of growing importance in the field of architecture and crash barriers, not only due to their good mechanical and corrosion resistance properties but also for the appealing color of their oxides. However, a complete description of the fracture locus of Cor-Ten steels in both low and high triaxiality ranges is still lacking. The present study aims at integrating and extending the data available in the literature for this peculiar material by evaluating four different planar specimens with a mixed numerical–experimental methodology. A non-notched specimen was tested in terms of tension to calibrate the true stress–strain curve of the material after necking by means of an iterative process involving the FEM. Once the model had been calibrated, a tensile test of each specimen was simulated, and the corresponding results were validated using the experimental test data. From the FEM results, the quantities of interests, namely, the stress triaxiality, the equivalent plastic strain, and the normalized Lode angle, were extrapolated. Subsequently, the fracture locus of the Cor-Ten steel was determined through the interpolation of the experimental data collected in the present study as well as data available in the literature for low triaxiality ranges. The results confirmed the parabolic trend characterizing the fracture locus at low triaxiality suggested in the literature, and an exponential decreasing trend was found at higher triaxiality values after reaching a local maximum. The results thus confirm that the fracture locus of Cor-Ten steels, as generally found for metallic materials, cannot be completely described by a monotonic function. Moreover, it was found that the highly ductile behavior of the material induces a significant topology change in the specimens before failure, thus making it more complex to forecast the location of crack nucleation and, as a consequence, the stress state. Full article
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15 pages, 10121 KiB  
Article
A Study on Microstructure-Property Relationships and Notch-Sensitive Fracture Behavior of X80 Steel Welds
by Yangfan Zou, Lifeng Li, Shuxin Zhang, Xiangzhen Yan and Shuyi Xie
Processes 2025, 13(3), 763; https://doi.org/10.3390/pr13030763 - 6 Mar 2025
Viewed by 706
Abstract
X80 steel pipelines are widely used in oil and gas transportation, and the quality and fracture behavior of the girth weld have an important influence on the safety and performance of the pipeline. This study presents a comprehensive investigation into the microstructure, mechanical [...] Read more.
X80 steel pipelines are widely used in oil and gas transportation, and the quality and fracture behavior of the girth weld have an important influence on the safety and performance of the pipeline. This study presents a comprehensive investigation into the microstructure, mechanical properties, and fracture characteristics of X80 steel welded joints. Through microstructure analysis and mechanical testing, the hardness, impact, and tensile properties of the base metal, heat-affected zone, and weld zone are evaluated. Digital Image Correlation (DIC) technology is employed to scrutinize the strain behavior under quasi-static tensile tests for both smooth and notched round bar specimens, providing a detailed strain distribution analysis. The findings indicate that, while X80 welded joints are well-formed without significant defects, the hardness and impact properties vary across different zones, with the base metal exhibiting the highest impact toughness and the weld zone the lowest. Notched tensile tests reveal that the presence and geometry of notches significantly alter the stress state and deformation characteristics, influencing the fracture mode. The DIC analysis further elucidates the strain concentration and localization behavior in the weld zone, highlighting the importance of notch size in determining the load-bearing capacity and ductility of the welded joints. This study contributes to a deeper understanding of the fracture mechanics in X80 pipeline girth welds and offers valuable insights for the optimization of welding practices and the assessment of pipeline integrity. Full article
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22 pages, 4812 KiB  
Article
Mechanical Characterization of a Novel Cyclic Olefin-Based Hot-Melt Adhesive
by Vasco C. M. B. Rodrigues, Ana T. F. Venâncio, Eduardo A. S. Marques, Ricardo J. C. Carbas, Armina Klein, Ejiri Kazuhiro, Björn Nelson and Lucas F. M. da Silva
Materials 2025, 18(4), 855; https://doi.org/10.3390/ma18040855 - 15 Feb 2025
Cited by 1 | Viewed by 803
Abstract
A novel hot-melt cyclic olefin-based adhesive was designed as a transparent, non-tacky film of amorphous thermoplastic with a unique polymer micro-structure. The aim of the present paper is to assess the mechanical properties of the 0.1 mm thick COP hot-melt adhesive film through [...] Read more.
A novel hot-melt cyclic olefin-based adhesive was designed as a transparent, non-tacky film of amorphous thermoplastic with a unique polymer micro-structure. The aim of the present paper is to assess the mechanical properties of the 0.1 mm thick COP hot-melt adhesive film through adhesive characterizations tests. The glass transition temperature was determined using dynamic mechanical analysis (DMA). For mechanical characterization, bulk and thick adherend shear specimens were manufactured and tested at a quasi-static rate, where at least three specimens were used to calculate the average and standard deviation values. Tensile tests revealed the effects of molecular chain drawing and reorientation before the onset of strain hardening. Thick adherend shear specimens were used to retrieve shear properties. Fracture behaviour was assessed with the double cantilever beam (DCB) test and end-notched flexure (ENF) test, for characterization under modes I and II, respectively. To study the in-joint behaviour, single lap joints (SLJs) of aluminium and carbon fibre-reinforced polymer (CFRP) were manufactured and tested under different temperatures. Results showed a progressive interfacial failure following adhesive plasticization, allowing deformation prior to failure at 8 MPa. An adhesive failure mode was confirmed through scanning electron microscopy (SEM) analysis of aluminium SLJ. The adhesive exhibits tensile properties comparable to existing adhesives, while demonstrating enhanced lap shear strength and a distinctive failure mechanism. These characteristics suggest potential advantages in applications involving heat and pressure across automotive, electronics and structural bonding sectors. Full article
(This article belongs to the Section Advanced Materials Characterization)
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34 pages, 25406 KiB  
Article
Study on Fatigue Life and Fracture Behaviour of Similar and Dissimilar Resistance Spot-Welded Joints of Titanium Grade 2 Alloy and Austenitic Stainless Steel 304
by Marwan T. Mezher, Alejandro Pereira and Tomasz Trzepieciński
Appl. Sci. 2025, 15(4), 1938; https://doi.org/10.3390/app15041938 - 13 Feb 2025
Viewed by 1295
Abstract
Resistance spot welding (RSW) is now the primary joining process used in the automobile and aerospace sectors. Mechanical parts, when put into service, often undergo cyclic stress. As a result, avoiding fatigue failure should be the top priority when designing these parts. Given [...] Read more.
Resistance spot welding (RSW) is now the primary joining process used in the automobile and aerospace sectors. Mechanical parts, when put into service, often undergo cyclic stress. As a result, avoiding fatigue failure should be the top priority when designing these parts. Given that spot welds are a type of localised joining that results in intrinsic circumferential notches, they increase the likelihood of stress concentrations and subsequent fatigue failures of the structure. Most of the fatigue failures in automotive parts originate around a spot weld. To that end, this study seeks to examine the mechanical properties and fatigue behaviour RSW joints made of titanium (Ti) grade 2 alloy and AISI 304 austenitic stainless steel (ASS) with equal and unequal thicknesses of 0.5 and 1 mm. Based on the mechanical properties and fatigue life results, the maximum tensile shear strength and fatigue life for the RSW titanium joint were 613 MPa and 7.37 × 105 cycles for the 0.5–0.5 mm case, 374.7 MPa and 1.39 × 106 cycles for the 1–1 mm case, and 333.5 MPa and 7.69 × 105 cycles for the 1–0.5 mm case, respectively. The maximum shear strength and fatigue life of ASS welded joints were 526.8 MPa and 4.56 × 106 cycles for the 1–1 mm case, 515.2 MPa and 3.35 × 106 cycles for the 0.5–0.5 mm case, and 369.5 MPa and 7.39 × 105 cycles for the 1–0.5 mm case, respectively. The assessment of the shear strength and fatigue life of the dissimilar joints revealed that the maximum shear strength and fatigue life recorded were 183.9 MPa and 6.47 × 105 cycles for the 1 mm Ti–0.5 mm ASS case, 115 MPa and 3.7 × 105 cycles for the 1 mm Ti–1 mm ASS case, 156 MPa and 4.11 × 105 cycles for the 0.5 mm Ti–0.5 mm ASS case, and 129 MPa and 4.11 × 105 cycles for the 0.5 mm Ti–1 mm ASS case. The fatigue life of titanium and stainless steel welded joints is significantly affected by the thickness, particularly at maximum applied stress (0.9% UTS), meaning that similar thicknesses achieve a greater fatigue life than unequal thicknesses. Conversely, the fatigue life of the dissimilar joint reached the greatest extent when an unequal thickness combination was used. The ductile failure of similar Ti and ASS welded joints was demonstrated by the scanning electron microscopy (SEM) examination of fatigue-fractured surfaces under the high-cycle fatigue (HCF) regime, in contrast to the brittle failure noticed in the low-cycle fatigue (LCF) regime. Brittle failure was confirmed by the SEM fatigue of dissimilar joint fractured surfaces due to interfacial failure. The Ti and ASS fractured surfaces presented river-like cleavage facets. On the Ti side, tiny elongated dimples suggest ductile failure before fracture. The topography results showed that the roughness topography parameters of similar and dissimilar fractured specimens made from Ti grade 2 and AISI 304 for the HCF regime were lower than those of the fractured specimens with LCF. The current study is expected to have practical benefits for the aerospace and automotive industries, particularly the manufacturing of body components with an improved strength-to-weight ratio. Full article
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37 pages, 11657 KiB  
Article
Experimental Evaluation of Temperature and Strain-Rate-Dependent Mechanical Properties of Austenitic Stainless Steel SS316LN and a New Methodology to Evaluate Parameters of Johnson–Cook and Ramberg–Osgood Material Models
by Sanjay Kumar Pandey and Mahendra Kumar Samal
Solids 2025, 6(1), 7; https://doi.org/10.3390/solids6010007 - 11 Feb 2025
Viewed by 1777
Abstract
Austenitic stainless steel SS316LN is used as the material of construction of the vessel and core components of fast breeder reactors, which operate at an elevated temperature of 550 °C. For design and integrity analysis using the finite element method, material models, such [...] Read more.
Austenitic stainless steel SS316LN is used as the material of construction of the vessel and core components of fast breeder reactors, which operate at an elevated temperature of 550 °C. For design and integrity analysis using the finite element method, material models, such as Johnson–Cook and Ramberg–Osgood, are widely used. However, the temperature- and strain-rate-dependent plasticity and damage parameters of these models for this material are not available in the literature. Moreover, the method of evaluation of temperature and strain-rate-dependent plasticity parameters, in literature, has some major shortcomings, which have been addressed in this work. In addition, a new optimization-based procedure has been developed to evaluate all nine plasticity and damage parameters, which uses results of combined finite element analysis and experimental data. The procedure has been validated extensively by testing tensile specimens at different temperatures, by testing notched tensile specimens of different notch radii, and by carrying out high strain-rate tests using a split Hopkinson pressure bar test setup. The parameters of the Johnson–Cook material model, evaluated in this work, have been used in finite element analysis to simulate load-displacement behavior and fracture strains of various types of specimens, and the results have been compared with experimental data in order to check the accuracy of the parameters. The procedure developed in this work shall help the researchers to adopt such a technique for accurate estimation of both plasticity and damage parameters of different types of material models. Full article
(This article belongs to the Topic Multi-scale Modeling and Optimisation of Materials)
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