Fatigue & Fracture of Engineering Materials & Structures, Jun 22, 2023
This work provides a post‐processing procedure to predict the high‐ and low‐cycle fatigue life of... more This work provides a post‐processing procedure to predict the high‐ and low‐cycle fatigue life of welded structures. The post‐processor calculates the equivalent structural strain range, given the traction stress state at the weld notch, by enforcing the equilibrium condition and Navier's hypothesis. The return mapping algorithm is applied to deal with the low‐cycle fatigue condition in which through‐thickness plastic deformation develops. The proposed method predicts the fatigue life of 793 welded joints of different configurations made from steel, magnesium, titanium, and aluminum alloy. The predicted high‐ and low‐cycle fatigue lives agree equally well with the experimental result.
This paper further investigates into the effectiveness of the structural strain method recently p... more This paper further investigates into the effectiveness of the structural strain method recently proposed by Dong et al. (2014) to model low-cycle fatigue behavior of welded structures. More precisely, an equivalent structural strain range parameter is introduced and implemented here in order to evaluate fatigue behaviors of welded components spanning both low-cycle and high-cycle fatigue regimes. A large number of well-documented fatigue data of weldments with various joint types, loading modes and base materials have been investigated in detail by using the structural strain approach. These components include gusset-to-plate, plate-to-plate and pipe-to-pipe joint. The fatigue loading varys from loadcontrolled to displacement-controlled conditions, and the base metals ranges from structural steel of different grades and aluminum alloys as well as titanium alloys for lightweight applications. The obtained results show that the equivalent structural strain range parameter enables a unified presentation of the fatigue behaviors of all the test data investigated in this paper.
Fillet welded connections are most commonly used for construction of engineering structures that ... more Fillet welded connections are most commonly used for construction of engineering structures that are often subjected to various forms of cyclic loading in service. There exist two potential fatigue failure modes, i.e., weld root cracking through weld throat and weld toe cracking into plate thickness. The former should be prevented at design stage through a proper weld sizing. However, due to difficulties in determining stress concentration at weld throat, existing fatigue design rules, particularly on weld sizing, are largely empirical and often result in excessive conservatisms, leading to oversized welds. As structural lightweighting becomes increasingly important, there is an increasing demand for more quantitative fatigue-based fillet weld sizing criterion. By taking advantage of a comprehensive set of fatigue test results on load-carrying fillet-welded cruciform joints and associated analytical developments reported by Xing et al. (2016), an analytical weld throat stress model taking into account of weld penetration and joint misalignments is presented in this paper for determining critical weld size beyond which weld throat failure become unlikely. Then, it is shown that a weld sizing criterion can be analytically developed and expressed as a function of weld penetration and joint misalignments, which are shown to agree well with the large amount of test data reported by Xing et al. (2016), including a systematic validation by means of a logistic regression method on the same test data. As a result, the present developments provide both analytical and experimental basis for achieving quantitative weld sizing so that weld throat fatigue failure mode can be effectively prevented with a clearly defined confidence level without the need of over-sizing.
International Journal of Pressure Vessels and Piping, Jul 1, 2014
In this paper, a new structural strain method is presented to extend the early structural stress ... more In this paper, a new structural strain method is presented to extend the early structural stress based master SeN curve method to low cycle fatigue regime in which plastic deformation can be significant while an elastic core is still present. The method is formulated by taking advantage of elastically calculated mesh-insensitive structural stresses based on nodal forces available from finite element solutions. The structural strain definition is consistent with classical plate and shell theory in which a linear through-thickness deformation field is assumed a priori in both elastic or elasticeplastic regimes. With considerations of both yield and equilibrium conditions, the resulting structural strains are analytically solved if assuming elastic and perfectly plastic material behavior. The formulation can be readily extended to strain-hardening materials for which structural strains can be numerically calculated with ease. The method is shown effective in correlating low-cycle fatigue test data of various sources documented in the literature into a single narrow scatter band which is remarkable consistent with the scatter band of the existing master SeN curve adopted ASME B&PV Code since 2007. With this new method, some of the inconsistencies of the pseudo-elastic structural stress procedure in 2007 ASME Div 2 Code can now be eliminated, such as its use of Neuber's rule in approximating structural strain beyond yield. More importantly, both low cycle and high cycle fatigue behaviors can now be treated in a unified manner. The earlier mesh-insensitive structural stress based master SeN curve method can now be viewed as an application of the structural strain method in high cycle regime, in which structural strains are linearly related to traction-based structural stresses according to Hooke's law. In low-cycle regime, the structural strain method characterizes fatigue damage directly in terms of structural strains that satisfy linear through-thickness deformation gradient assumption, material nonlinear behavior, and equilibrium conditions. The use of a pseudo-elastic structural stress definition is not fundamental, but merely a means to put low-cycle and high-cycle fatigue test data in a conventional stress-based SeN data representation which is typically preferred in engineering practice, than a strainbased representation.
Fatigue & Fracture of Engineering Materials & Structures, Aug 16, 2022
Weld toe and weld root failures dominate the fatigue failures of the load‐carrying cruciform fill... more Weld toe and weld root failures dominate the fatigue failures of the load‐carrying cruciform fillet welded joints. Compared to weld toe failure, the weld root failure is strongly affected by its inherent weld quality and throat size, which is more unpredictable and should be eliminated. This work proposes a weld sizing criterion in terms of two weld leg sizes and weld penetration to avoid root failure. The criterion is obtained by a data‐driven approach with the help of the mechanical‐directed data augmentation technique. The traction‐stress‐based method is applied for the data augmentation to identify the fatigue failure mode, which is statistically tested against 372 experimentally obtained fatigue data.
Fatigue & Fracture of Engineering Materials & Structures
This work provides a post‐processing procedure to predict the high‐ and low‐cycle fatigue life of... more This work provides a post‐processing procedure to predict the high‐ and low‐cycle fatigue life of welded structures. The post‐processor calculates the equivalent structural strain range, given the traction stress state at the weld notch, by enforcing the equilibrium condition and Navier's hypothesis. The return mapping algorithm is applied to deal with the low‐cycle fatigue condition in which through‐thickness plastic deformation develops. The proposed method predicts the fatigue life of 793 welded joints of different configurations made from steel, magnesium, titanium, and aluminum alloy. The predicted high‐ and low‐cycle fatigue lives agree equally well with the experimental result.
Fatigue & Fracture of Engineering Materials & Structures
Weld toe and weld root failures dominate the fatigue failures of the load‐carrying cruciform fill... more Weld toe and weld root failures dominate the fatigue failures of the load‐carrying cruciform fillet welded joints. Compared to weld toe failure, the weld root failure is strongly affected by its inherent weld quality and throat size, which is more unpredictable and should be eliminated. This work proposes a weld sizing criterion in terms of two weld leg sizes and weld penetration to avoid root failure. The criterion is obtained by a data‐driven approach with the help of the mechanical‐directed data augmentation technique. The traction‐stress‐based method is applied for the data augmentation to identify the fatigue failure mode, which is statistically tested against 372 experimentally obtained fatigue data.
Fatigue & Fracture of Engineering Materials & Structures, Jun 22, 2023
This work provides a post‐processing procedure to predict the high‐ and low‐cycle fatigue life of... more This work provides a post‐processing procedure to predict the high‐ and low‐cycle fatigue life of welded structures. The post‐processor calculates the equivalent structural strain range, given the traction stress state at the weld notch, by enforcing the equilibrium condition and Navier's hypothesis. The return mapping algorithm is applied to deal with the low‐cycle fatigue condition in which through‐thickness plastic deformation develops. The proposed method predicts the fatigue life of 793 welded joints of different configurations made from steel, magnesium, titanium, and aluminum alloy. The predicted high‐ and low‐cycle fatigue lives agree equally well with the experimental result.
This paper further investigates into the effectiveness of the structural strain method recently p... more This paper further investigates into the effectiveness of the structural strain method recently proposed by Dong et al. (2014) to model low-cycle fatigue behavior of welded structures. More precisely, an equivalent structural strain range parameter is introduced and implemented here in order to evaluate fatigue behaviors of welded components spanning both low-cycle and high-cycle fatigue regimes. A large number of well-documented fatigue data of weldments with various joint types, loading modes and base materials have been investigated in detail by using the structural strain approach. These components include gusset-to-plate, plate-to-plate and pipe-to-pipe joint. The fatigue loading varys from loadcontrolled to displacement-controlled conditions, and the base metals ranges from structural steel of different grades and aluminum alloys as well as titanium alloys for lightweight applications. The obtained results show that the equivalent structural strain range parameter enables a unified presentation of the fatigue behaviors of all the test data investigated in this paper.
Fillet welded connections are most commonly used for construction of engineering structures that ... more Fillet welded connections are most commonly used for construction of engineering structures that are often subjected to various forms of cyclic loading in service. There exist two potential fatigue failure modes, i.e., weld root cracking through weld throat and weld toe cracking into plate thickness. The former should be prevented at design stage through a proper weld sizing. However, due to difficulties in determining stress concentration at weld throat, existing fatigue design rules, particularly on weld sizing, are largely empirical and often result in excessive conservatisms, leading to oversized welds. As structural lightweighting becomes increasingly important, there is an increasing demand for more quantitative fatigue-based fillet weld sizing criterion. By taking advantage of a comprehensive set of fatigue test results on load-carrying fillet-welded cruciform joints and associated analytical developments reported by Xing et al. (2016), an analytical weld throat stress model taking into account of weld penetration and joint misalignments is presented in this paper for determining critical weld size beyond which weld throat failure become unlikely. Then, it is shown that a weld sizing criterion can be analytically developed and expressed as a function of weld penetration and joint misalignments, which are shown to agree well with the large amount of test data reported by Xing et al. (2016), including a systematic validation by means of a logistic regression method on the same test data. As a result, the present developments provide both analytical and experimental basis for achieving quantitative weld sizing so that weld throat fatigue failure mode can be effectively prevented with a clearly defined confidence level without the need of over-sizing.
International Journal of Pressure Vessels and Piping, Jul 1, 2014
In this paper, a new structural strain method is presented to extend the early structural stress ... more In this paper, a new structural strain method is presented to extend the early structural stress based master SeN curve method to low cycle fatigue regime in which plastic deformation can be significant while an elastic core is still present. The method is formulated by taking advantage of elastically calculated mesh-insensitive structural stresses based on nodal forces available from finite element solutions. The structural strain definition is consistent with classical plate and shell theory in which a linear through-thickness deformation field is assumed a priori in both elastic or elasticeplastic regimes. With considerations of both yield and equilibrium conditions, the resulting structural strains are analytically solved if assuming elastic and perfectly plastic material behavior. The formulation can be readily extended to strain-hardening materials for which structural strains can be numerically calculated with ease. The method is shown effective in correlating low-cycle fatigue test data of various sources documented in the literature into a single narrow scatter band which is remarkable consistent with the scatter band of the existing master SeN curve adopted ASME B&PV Code since 2007. With this new method, some of the inconsistencies of the pseudo-elastic structural stress procedure in 2007 ASME Div 2 Code can now be eliminated, such as its use of Neuber's rule in approximating structural strain beyond yield. More importantly, both low cycle and high cycle fatigue behaviors can now be treated in a unified manner. The earlier mesh-insensitive structural stress based master SeN curve method can now be viewed as an application of the structural strain method in high cycle regime, in which structural strains are linearly related to traction-based structural stresses according to Hooke's law. In low-cycle regime, the structural strain method characterizes fatigue damage directly in terms of structural strains that satisfy linear through-thickness deformation gradient assumption, material nonlinear behavior, and equilibrium conditions. The use of a pseudo-elastic structural stress definition is not fundamental, but merely a means to put low-cycle and high-cycle fatigue test data in a conventional stress-based SeN data representation which is typically preferred in engineering practice, than a strainbased representation.
Fatigue & Fracture of Engineering Materials & Structures, Aug 16, 2022
Weld toe and weld root failures dominate the fatigue failures of the load‐carrying cruciform fill... more Weld toe and weld root failures dominate the fatigue failures of the load‐carrying cruciform fillet welded joints. Compared to weld toe failure, the weld root failure is strongly affected by its inherent weld quality and throat size, which is more unpredictable and should be eliminated. This work proposes a weld sizing criterion in terms of two weld leg sizes and weld penetration to avoid root failure. The criterion is obtained by a data‐driven approach with the help of the mechanical‐directed data augmentation technique. The traction‐stress‐based method is applied for the data augmentation to identify the fatigue failure mode, which is statistically tested against 372 experimentally obtained fatigue data.
Fatigue & Fracture of Engineering Materials & Structures
This work provides a post‐processing procedure to predict the high‐ and low‐cycle fatigue life of... more This work provides a post‐processing procedure to predict the high‐ and low‐cycle fatigue life of welded structures. The post‐processor calculates the equivalent structural strain range, given the traction stress state at the weld notch, by enforcing the equilibrium condition and Navier's hypothesis. The return mapping algorithm is applied to deal with the low‐cycle fatigue condition in which through‐thickness plastic deformation develops. The proposed method predicts the fatigue life of 793 welded joints of different configurations made from steel, magnesium, titanium, and aluminum alloy. The predicted high‐ and low‐cycle fatigue lives agree equally well with the experimental result.
Fatigue & Fracture of Engineering Materials & Structures
Weld toe and weld root failures dominate the fatigue failures of the load‐carrying cruciform fill... more Weld toe and weld root failures dominate the fatigue failures of the load‐carrying cruciform fillet welded joints. Compared to weld toe failure, the weld root failure is strongly affected by its inherent weld quality and throat size, which is more unpredictable and should be eliminated. This work proposes a weld sizing criterion in terms of two weld leg sizes and weld penetration to avoid root failure. The criterion is obtained by a data‐driven approach with the help of the mechanical‐directed data augmentation technique. The traction‐stress‐based method is applied for the data augmentation to identify the fatigue failure mode, which is statistically tested against 372 experimentally obtained fatigue data.
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