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Fracture and Fatigue Assessments of Structural Components Ⅱ

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A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Mechanical Engineering".

Deadline for manuscript submissions: closed (20 September 2021) | Viewed by 34242

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Dr. Alberto Campagnolo

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Department of Industrial Engineering, University of Padova, Via Venezia 1, 35131 Padova, Italy
Interests: fracture mechanics; fatigue experimental testing; welding strength; fatigue and fracture analysis; fatigue crack growth; crack paths; fatigue crack growth rate
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Dear Colleagues,

Different approaches have been proposed in the literature to deal with fracture and fatigue assessments of structural components. These are usually divided into three subgroups: stress-based, strain-based, and energy-based criteria. The latter, coupling stresses and strains in a single parameter, have been proven to efficiently assess both static and fatigue strength of structural components. Typical applications of energy-based approaches include both linear elastic and elastoplastic materials, and plain and notched or cracked components under both static and fatigue loadings.

The aim of this Special Issue is to provide an update to the state-of-the-art on these approaches. The topics which deserve particular attention in this Special Issue 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 multiaxial constant amplitude and random fatigue loadings.

Dr. Alberto Campagnolo
Guest Editor

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Keywords

Fracture assessment
Fatigue assessment
FEM analysis
Advanced materials
Complex loading
Crack
Etc.

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Published Papers (11 papers)

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Research

41 pages, 148577 KiB

Open AccessArticle

Study of Local Fatigue Methods (TCD, N-SIF, and ESED) on Notches and Defects Related to Numerical Efficiency

by Michael Stoschka, Michael Horvath, Stefan Fladischer and Matthias Oberreiter

Appl. Sci. 2023, 13(4), 2247; https://doi.org/10.3390/app13042247 - 9 Feb 2023

Cited by 3 | Viewed by 1823

Abstract

The fatigue strength of structural components is strongly affected by notches and imperfections. Both can be treated similarly, as local notch fatigue strength methods can also be applied to interior defects. Even though Murakami’s √area approach is commonly used in the threshold-based fatigue design of single imperfections, advanced concepts such as the Theory of Critical Distances (TCD), Notch Stress Intensity Factors (N-SIF), or Elastic Strain Energy Density (ESED) methods provide additional insight into the local fatigue strength distribution of irregularly shaped defects under varying uniaxial load vectors. The latter methods are based on the evaluation of the elastic stress field in the vicinity of the notch for each single load vector. Thus, this work provides numerically efficient methods to assess the local fatigue strength by means of TCD, N-SIF, and ESED, targeting the minimization of the required load case count, optimization of stress field evaluation data points, and utilization of multi-processing. Furthermore, the Peak Stress Method (PSM) is adapted for large opening angles, as in the case of globular defects. In detail, two numerical strategies are devised and comprehensively evaluated, either using a sub-case-based stress evaluation of the defect vicinity with an unchanged mesh pattern and varying load vector on the exterior model region with optimized load angle stepping or by the invocation of stress and strain tensor transformation equations to derive load angle-dependent result superposition while leaving the initial mesh unaltered. Both methods provide numerically efficient fatigue post-processing, as the mesh in the evaluated defect region is retained for varying load vectors. The key functions of the fatigue strength assessment, such as the evaluation of appropriate planar notch radius and determination of notch opening angle for the discretized imperfections, are presented. Although the presented numerical methods apply to planar simulation studies, the basic methodology can be easily expanded toward spatial fatigue assessment. Full article

(This article belongs to the Special Issue Fracture and Fatigue Assessments of Structural Components Ⅱ)

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14 pages, 5081 KiB

Open AccessArticle

Numerical Evaluation of Fatigue Crack Growth of Structural Steels Using Energy Release Rate with VCCT

by Yusuf O. Busari, Yupiter H. P. Manurung, Martin Leitner, Yusuf L. Shuaib-Babata, Muhd F. Mat, Hassan K. Ibrahim, David Simunek and Mohd Shahar Sulaiman

Appl. Sci. 2022, 12(5), 2641; https://doi.org/10.3390/app12052641 - 3 Mar 2022

Cited by 5 | Viewed by 2774

Abstract

This research presents the numerical evaluation of fatigue crack growth of structural steels S355 and S960 based on Paris’ law parameters (C and m) that are experimentally determined with a single edge notched tension (SENT) specimen using optical and crack gauge measurements on an electromotive resonance machine at constant amplitude load. The sustainable technique is replacing destructive, time-consuming and expensive approaches in structural integrity. The crack propagation is modelled using the 3D finite element method (FEM) with adaptive remeshing of tetrahedral elements along with the crack initiator elements provided in simulation software for crack propagation based on linear elastic fracture mechanics (LEFM). The stress intensity is computed based on the evaluation of energy release rates according to Irwin’s crack closure integral with applied cyclic load of 62.5 MPa, 100 MPa and 150 MPa and stress ratios of R = 0 and 0.1. In order to achieve optimized mesh size towards load cycle and computational time, mesh and re-mesh sensitivity analysis is conducted. The results indicate that the virtual crack closure technique VCCT-based 3D FEM shows acceptable agreement compared to the experimental investigation with the percentage error up to 7.9% for S355 and 12.8% for S960 structural steel. Full article

(This article belongs to the Special Issue Fracture and Fatigue Assessments of Structural Components Ⅱ)

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13 pages, 3370 KiB

Open AccessArticle

Compilation of Load Spectrum for 5MN Metal Extruder Based on Long Short-Term Memory Network

by Xiaole Cheng, Te Han, Peilin Yang and Xugang Zhang

Appl. Sci. 2021, 11(20), 9708; https://doi.org/10.3390/app11209708 - 18 Oct 2021

Viewed by 1878

Abstract

As an important condition for fatigue analysis and life prediction, load spectrum is widely used in various engineering fields. The extrapolation of load samples is an important step in compiling load spectrum. It is of great significance to select an appropriate load extrapolation method. This paper proposes a load extrapolation method based on long short-term memory (LSTM) network, introduces the basic principle of the extrapolation method, and applies the method to the data set collected under the working state of 5MN metal extruder. The comparison between the extrapolated load data and the actual load shows that the trend of the extrapolated load data is basically consistent with the original tendency. In addition, this method is compared with the rain flow extrapolation method based on statistical distribution. Through the comparison of the short-term load spectrum compiled by the two extrapolation methods, it is found that the load spectrum extrapolation method based on LSTM network can better realize load prediction and optimize the compilation of load spectrum. Full article

(This article belongs to the Special Issue Fracture and Fatigue Assessments of Structural Components Ⅱ)

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14 pages, 5793 KiB

Open AccessArticle

Mechanical and Metallurgical Properties of CO₂ Laser Beam INCONEL 625 Welded Joints

by Harinadh Vemanaboina, Edison Gundabattini, Suresh Akella, A. C. Uma Maheshwer Rao, Ramesh Kumar Buddu, Paolo Ferro and Filippo Berto

Appl. Sci. 2021, 11(15), 7002; https://doi.org/10.3390/app11157002 - 29 Jul 2021

Cited by 23 | Viewed by 3609

Abstract

In the frame of the circular economy, welding of Ni-based superalloys has gained increasing importance when applied, for instance, to repairing highly expensive components widely used in strategical sectors, such as the defense and aerospace industries. However, correct process parameters avoiding metallurgical defects and premature failures need to be known. To reach this goal, Inconel 625 butt-welded joints were produced by CO₂ laser beam welding and different combinations of process parameters. The experimental investigation was carried out with three parameters in two levels with an L₄ orthogonal array. Laser power, welding speed, and shielding gas flow rate were varied, and the results were reported in terms of mechanical properties, such as microhardness, tensile strength, distortion, residual stress, and weld bead geometry, and metallurgy. At a lower welding speed of 1 m/min, the full penetration was observed for 3.0 kW and 3.3 kW laser powers. However, sound welds (porosity-free) were produced with a laser power of 3.3 kW. Overall, the obtained full-penetration specimens showed a tensile strength comparable with that of the parent material with residual stresses and distortions increasing with the increase in heat input. Full article

(This article belongs to the Special Issue Fracture and Fatigue Assessments of Structural Components Ⅱ)

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21 pages, 19252 KiB

Open AccessArticle

Mechanical and Acoustic Emission (AE) Characteristics of Rocks under Biaxial Confinements

by Kun Du, Minghui Liu, Chengzhi Yang, Ming Tao, Fukang Feng and Shaofeng Wang

Appl. Sci. 2021, 11(2), 769; https://doi.org/10.3390/app11020769 - 14 Jan 2021

Cited by 23 | Viewed by 3119

Abstract

The surrounding rocks of underground engineering are generally subjected to a biaxial compressive stress condition. The failure properties of rocks under such a stress condition are worthy of being studied to ensure the stability of surrounding rock. This study aims to investigate the mechanical characteristics and acoustic emission (AE) properties of granite, marble, and sandstone in biaxial compression tests. Under biaxial confinements, it is evident that the elastic moduli of the three types of rocks decrease, and the plasticity increases monotonously with the increase of the intermediate principal stress σ₂. As σ₂ increases, the biaxial compressive strength σ_bcs of rock increases initially and subsequently decreases. The lateral strain ε₂ of rock under biaxial confinement is controlled by both σ₁ and σ₂, and the restrain degree in the development of microcracks and the constrain extent in the expansion along the direction of σ₂ are both enhanced gradually with increase in σ₂. The sharp increase points of AE hit and AE count indicate that the failure will occur soon. The AF-RA distribution of AE signals shows that the increase of σ₂ causes more tensile cracks in rock. According to the dip failure angle of macro-cracks in rock under biaxial confinement, the failure modes of granite and marble are slabbing, while failure mode of sandstone is shear. In addition, the σ₂ has a positive effect on the mass ratio of large size fragments after rock failure. An exponent relationship between the σ_bcs and σ₂ was found, and the inner apices–inscribed Drucker–Prager criterion can be used to predict the σ_bcs of rock. Full article

(This article belongs to the Special Issue Fracture and Fatigue Assessments of Structural Components Ⅱ)

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11 pages, 6253 KiB

Open AccessArticle

Fatigue Failure of a Pressing Machine

by Martin Garan, Vladimír Chmelko, Miroslav Šulko and Miloš Musil

Appl. Sci. 2021, 11(1), 398; https://doi.org/10.3390/app11010398 - 4 Jan 2021

Cited by 2 | Viewed by 2047

Abstract

This article presents an analysis of the causes of a fatigue crack in the guide bar of a pressing device. The detailed analysis included the analysis of a material’s microstructure and its cyclic properties. Direct measurements of the strains during operation allowed the nominal loading process in the critical cross-section of the press subassembly to be obtained. The notch effect of the inner thread of the guide bar was analyzed using a precision FEM (finite element method) model and was followed by the transformation of the nominal loading into the notch root. A methodological approach was formulated based on the analyses made, which lay in the statistical interpretation of the factors leading to an identification of the cause of an early fracture. Full article

(This article belongs to the Special Issue Fracture and Fatigue Assessments of Structural Components Ⅱ)

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14 pages, 4765 KiB

Open AccessArticle

Crack Detection and Crack Length Measurement with the DC Potential Drop Method–Possibilities, Challenges and New Developments

by Jürgen Bär

Appl. Sci. 2020, 10(23), 8559; https://doi.org/10.3390/app10238559 - 29 Nov 2020

Cited by 18 | Viewed by 5900

Abstract

The direct current potential drop method (DCPDM) is widely used to determine the crack length in fatigue experiments. In practice, some special features of this method must be considered. Aside from general information on the experimental setup and calibration, some special features of the method, such as the influence of the ambient atmosphere and the application of the method to ferromagnetic materials, are presented and discussed. In addition, with the multiple potential drop measurement, a method is presented which improves the resolution of the DCPDM for detection of cracks and allows to determine crack initiation sites. The capabilities provided by this method are demonstrated on the basis of measurements undertaken on notched round bars and single edged notched specimens. Full article

(This article belongs to the Special Issue Fracture and Fatigue Assessments of Structural Components Ⅱ)

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15 pages, 3590 KiB

Open AccessArticle

Fracture Behavior of Two Biopolymers Containing Notches: Effects of Notch Tip Plasticity

by Sahel Shahbaz, Majid Reza Ayatollahi, Ali Reza Torabi and Sergio Cicero

Appl. Sci. 2020, 10(23), 8445; https://doi.org/10.3390/app10238445 - 26 Nov 2020

Cited by 7 | Viewed by 2182

Abstract

This paper analyzes the notch effect on the fracture behavior of two biomaterials (a brittle bone cement and a ductile dental material) under mode I loading. U-notched Brazilian disk (UNBD) specimens of both materials were tested under remote compression, determining the corresponding fracture loads and load-displacement curves. Additionally, cracked rectangular and semicircular bend (SCB) specimens were tested under symmetric three-point bending in order to determine the fracture toughness of the two materials. Then, fracture loads were derived theoretically by applying the maximum tangential stress (MTS) and the mean stress (MS) criteria. Due to the brittle linear elastic behavior of the bone cement material, the MTS and MS criteria were directly applied to this material; however, given the significant nonlinear behavior of the dental material, the two fracture criteria were combined with the Equivalent Material Concept (EMC) for the fracture analyses of the dental material specimens. The results reveal a very good accuracy of both the MTS and the MS criteria for the fracture analysis of bone cement notched specimens. In the case of the dental material, very good results are also obtained when combining the MTS and the MS criteria with the EMC. The proposed approach can be useful for the fracture analysis of a wide range of biopolymers, from brittle to ductile behavior. Full article

(This article belongs to the Special Issue Fracture and Fatigue Assessments of Structural Components Ⅱ)

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17 pages, 3266 KiB

Open AccessArticle

An Improved 2D Meshfree Radial Point Interpolation Method for Stress Concentration Evaluation of Welded Component

by Fuming Bao, Bingzhi Chen, Yanguang Zhao and Xinglin Guo

Appl. Sci. 2020, 10(19), 6873; https://doi.org/10.3390/app10196873 - 30 Sep 2020

Cited by 1 | Viewed by 2258

Abstract

The study of characterizing the stress concentration effects at welds is one of the most important research directions for predicting the fatigue life of welded components. Stress solutions at the weld toe obtained from conventional meshfree methods are strongly influenced by parameters used in the methods as a result of stress singularity. In this study, an improved 2D meshfree radial point interpolation method (RPIM) is proposed for stress concentration evaluation of a welded component. The stress solutions are insensitive to parameters used in the improved RPIM. The improved RPIM-based scheme for consistently calculating stress concentration factor (SCF) and stress intensity factor at weld toe are presented. Our studies provide a novel approach to apply global weak-form meshfree methods in consistently computing SCFs and stress intensity factors at welds. Full article

(This article belongs to the Special Issue Fracture and Fatigue Assessments of Structural Components Ⅱ)

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13 pages, 4124 KiB

Open AccessArticle

Analysis of Crack Behaviour in Pipeline System Using FAD Diagram Based on Numerical Simulation under XFEM

by S. Montassir, K. Yakoubi, H. Moustabchir, A. Elkhalfi, Dipen Kumar Rajak and Catalin I. Pruncu

Appl. Sci. 2020, 10(17), 6129; https://doi.org/10.3390/app10176129 - 3 Sep 2020

Cited by 15 | Viewed by 4564

Abstract

For a long time, cracked structures have triggered various researchers to develop a structural integrity approach and design models to address the fracture problems. In the present study, a pipeline with an axial semi-elliptical surface defect was examined in detail. Recent works have highlighted the use of the classical finite element method (CFEM) as numerical tools to solve the fracture mechanics; however, this approach comes with a few difficulties in the modelling aspects. To overcome this issue, we proposed the use of the extended finite element method (XFEM), which was implemented in the commercial version of Abaqus software. Moreover, we have used the results based on this technique in the volumetric method to estimate the stress intensity factors (SIFs). Then, this parameter was employed to build the failure assessment diagram (FAD). The FAD curve was used in the current investigation because it is one of the conventional methods for the evaluation of flaws in steel pipes. The XFEM simulations enable us to draw an FAD curve that can be used as a practical reference for defect evaluation in pipeline systems in the industrial world. Full article

(This article belongs to the Special Issue Fracture and Fatigue Assessments of Structural Components Ⅱ)

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20 pages, 4680 KiB

Open AccessArticle

An Advanced Shear Strength Criterion for Rock Discontinuities Considering Size and Low Shear Rate

by Bowen Zheng, Shengwen Qi, Xiaolin Huang, Songfeng Guo, Chonglang Wang, Zhifa Zhan and Guangming Luo

Appl. Sci. 2020, 10(12), 4095; https://doi.org/10.3390/app10124095 - 14 Jun 2020

Cited by 20 | Viewed by 3244

Abstract

The shear strength of the rock discontinuities under different shear rates is of great importance to evaluate the stability of rock mass engineering, which is remarkably influenced by the size effects induced by both the length and the undulated amplitude of discontinuities. An advanced shear strength criterion taking into account the size and the shear rate simultaneously was proposed. There is an advantage of the dimension unity in terms of the new shear strength criterion in comparison to previous related empirical equations. Additionally, it can be degraded into the International Society for Rock Mechanics (ISRM)-suggested Barton shear strength empirical equation on the peak shear strength of the rock discontinuities. Then, based on a new dynamic direct shear testing device on rock joints, the granite discontinuities with various lengths (200 mm to 1000 mm) and undulated amplitudes (3 mm to 23 mm) were designed to conduct direct shear tests under different low shear rates (0 mm/s to 1 mm/s) to verify the involved empirical equations. It was found that the results predicted by the new shear strength criterion agreed well with the experimental results. It was proved that the new shear strength criterion had a better applicability to characterize the shear strength of the rock discontinuities. Full article

(This article belongs to the Special Issue Fracture and Fatigue Assessments of Structural Components Ⅱ)

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