Pub Date : 2026-01-03DOI: 10.1016/j.ijfatigue.2025.109479
Tao Shi , Yadong Zhou , Ruiyang Li , Feng Zhang , Jingyu Sun , Guian Qian
GH4169 superalloy was manufactured by laser powder bed fusion process, and the effects of two types of heat treatment strategies (solution + aging (SA), and hot isostatic pressing + solution + aging (HSA)) on superalloy microstructure evolution and fatigue performance were studied. A detailed microstructural characterization of the initial material and fatigue failure specimen was carried out, and it was found that HSA treatment eliminated the cellular and lamellar substructures of the material, increased the grain size, reduced dislocation density and the size of precipitates, thereby reducing the fatigue resistance compared to SA-treated material. In addition, different types of strengthening mechanisms were superimposed to estimate the yield strength of these two types of heat-treated materials. Finally, a crystal plasticity finite element model combined with thermodynamic entropy generation was established to predict fatigue life.
{"title":"Fatigue behavior of laser powder bed fusion GH4169 superalloy using different heat treatment methods","authors":"Tao Shi , Yadong Zhou , Ruiyang Li , Feng Zhang , Jingyu Sun , Guian Qian","doi":"10.1016/j.ijfatigue.2025.109479","DOIUrl":"10.1016/j.ijfatigue.2025.109479","url":null,"abstract":"<div><div>GH4169 superalloy was manufactured by laser powder bed fusion process, and the effects of two types of heat treatment strategies (solution + aging (SA), and hot isostatic pressing + solution + aging (HSA)) on superalloy microstructure evolution and fatigue performance were studied. A detailed microstructural characterization of the initial material and fatigue failure specimen was carried out, and it was found that HSA treatment eliminated the cellular and lamellar substructures of the material, increased the grain size, reduced dislocation density and the size of precipitates, thereby reducing the fatigue resistance compared to SA-treated material. In addition, different types of strengthening mechanisms were superimposed to estimate the yield strength of these two types of heat-treated materials. Finally, a crystal plasticity finite element model combined with thermodynamic entropy generation was established to predict fatigue life.</div></div>","PeriodicalId":14112,"journal":{"name":"International Journal of Fatigue","volume":"206 ","pages":"Article 109479"},"PeriodicalIF":6.8,"publicationDate":"2026-01-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145895489","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-03DOI: 10.1016/j.ijfatigue.2025.109478
Tian Xu , Huwei Qiu , Wentao Huang , Delong He , Yao Chen , Chong Wang , Qingyuan Wang , Jinbo Bai , Fulin Liu , Yongjie Liu
To meet the application requirements for aero-engine Blisks, very high cycle fatigue (VHCF) behavior of Ti60/TC17 linear friction welded (LFW) joints was investigated at room temperature (RT) and high temperatures (HT). The results indicate that fatigue strength decreases with increasing temperature. Fatigue fractures predominantly occur in the weaker Ti60 base material at all test temperatures. Nearly all fatigue crack initiation sites are characterized by facet morphologies formed through the cleavage of α grains. Specifically, subsurface failures originate from an oversized facet, whereas internal failures arise from facet clusters. Microstructural analysis reveals that cracks primarily nucleate at the α/β phase interface and along slip bands within equiaxed α grains. Notably, high temperature significantly influences the crack initiation mechanism, causing a transition in facet formation from basal slip dominance at RT to synergistic basal and prismatic slip at HT. Furthermore, for subsurface crack initiation at HT, the synergistic effect of prolonged high-temperature exposure and dislocation-assisted oxygen diffusion facilitates brittle oxide formation at the crack tips, thereby accelerating fatigue failure.
{"title":"Crack initiation mechanisms of linear friction welded dissimilar Ti60/TC17 joint in very high cycle fatigue regime at different temperatures","authors":"Tian Xu , Huwei Qiu , Wentao Huang , Delong He , Yao Chen , Chong Wang , Qingyuan Wang , Jinbo Bai , Fulin Liu , Yongjie Liu","doi":"10.1016/j.ijfatigue.2025.109478","DOIUrl":"10.1016/j.ijfatigue.2025.109478","url":null,"abstract":"<div><div>To meet the application requirements for aero-engine Blisks, very high cycle fatigue (VHCF) behavior of Ti60/TC17 linear friction welded (LFW) joints was investigated at room temperature (RT) and high temperatures (HT). The results indicate that fatigue strength decreases with increasing temperature. Fatigue fractures predominantly occur in the weaker Ti60 base material at all test temperatures. Nearly all fatigue crack initiation sites are characterized by facet morphologies formed through the cleavage of α grains. Specifically, subsurface failures originate from an oversized facet, whereas internal failures arise from facet clusters. Microstructural analysis reveals that cracks primarily nucleate at the α/β phase interface and along slip bands within equiaxed α grains. Notably, high temperature significantly influences the crack initiation mechanism, causing a transition in facet formation from basal slip dominance at RT to synergistic basal and prismatic slip at HT. Furthermore, for subsurface crack initiation at HT, the synergistic effect of prolonged high-temperature exposure and dislocation-assisted oxygen diffusion facilitates brittle oxide formation at the crack tips, thereby accelerating fatigue failure.</div></div>","PeriodicalId":14112,"journal":{"name":"International Journal of Fatigue","volume":"206 ","pages":"Article 109478"},"PeriodicalIF":6.8,"publicationDate":"2026-01-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145894531","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-01DOI: 10.1016/j.ijfatigue.2025.109461
Yang Meng, Chungen Zhou, Kezhi huang, Leyu Li, Zihua Zhao
The interaction between oxidation and fatigue under lower stress in Ni-based single crystal superalloys remains insufficiently explored. In this study, a newly designed notched plate specimen was developed for VHCF testing at 1000 °C to investigate these phenomena. Quasi-in-situ observations were employed to monitor crack initiation and crack propagation processes. The results shown that all fatigue cracks initiated at the notch root and propagated in a Mode I manner. The fracture surface consists of two distinct regions, an oxidation-dominate zone (ODZ) characterized by extensive oxide coverage, and the fatigue-dominated zone (FDZ) marked by clear fatigue striations. Over 90 % of the total fatigue life was spent in the ODZ. As cracks propagated, thermally grown stress in the oxide near the crack tip altered the local stress field, promo6ting γ′ rafting and aluminum diffusion. These effects transformed the crack-tip oxide from a multilayered structure to a continuous Al2O3-rich scale. Within the ODZ, oxidation-induced crack closure suppressed crack growth, rendering the oxidation rate the dominant factor controlling the crack propagation rate. When the effective stress intensity factor exceeded a critical threshold, oxidation penetrated to the γ/γ′ interface within the substrate, triggering a transition from ODZ to FDZ and accelerating crack growth. Overall, these findings confirm that enhancing oxidation resistance is still critical for improving VHCF performance in Ni-based single crystal superalloys.
{"title":"Oxidation-induced crack initiation and propagation behaviors of Ni-based single crystal superalloy in VHCF regime","authors":"Yang Meng, Chungen Zhou, Kezhi huang, Leyu Li, Zihua Zhao","doi":"10.1016/j.ijfatigue.2025.109461","DOIUrl":"10.1016/j.ijfatigue.2025.109461","url":null,"abstract":"<div><div>The interaction between oxidation and fatigue under lower stress in Ni-based single crystal superalloys remains insufficiently explored. In this study, a newly designed notched plate specimen was developed for VHCF testing at 1000 °C to investigate these phenomena. Quasi-in-situ observations were employed to monitor crack initiation and crack propagation processes. The results shown that all fatigue cracks initiated at the notch root and propagated in a Mode I manner. The fracture surface consists of two distinct regions, an oxidation-dominate zone (ODZ) characterized by extensive oxide coverage, and the fatigue-dominated zone (FDZ) marked by clear fatigue striations. Over 90 % of the total fatigue life was spent in the ODZ. As cracks propagated, thermally grown stress in the oxide near the crack tip altered the local stress field, promo6ting γ′ rafting and aluminum diffusion. These effects transformed the crack-tip oxide from a multilayered structure to a continuous Al<sub>2</sub>O<sub>3</sub>-rich scale. Within the ODZ, oxidation-induced crack closure suppressed crack growth, rendering the oxidation rate the dominant factor controlling the crack propagation rate. When the effective stress intensity factor exceeded a critical threshold, oxidation penetrated to the γ/γ′ interface within the substrate, triggering a transition from ODZ to FDZ and accelerating crack growth. Overall, these findings confirm that enhancing oxidation resistance is still critical for improving VHCF performance in Ni-based single crystal superalloys.</div></div>","PeriodicalId":14112,"journal":{"name":"International Journal of Fatigue","volume":"206 ","pages":"Article 109461"},"PeriodicalIF":6.8,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145894533","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-31DOI: 10.1016/j.ijfatigue.2025.109474
Manjiang Yu , Ye Wang , Fangli Duan , Chaofeng Lü
The service failure evaluation of the damaged rail can provide theoretical guidance for the routine maintenance of existing railway lines. In this work, U71MnG rail that failed under traffic loading is selected to investigate the fatigue damage mechanism of pearlitic rail steel. In addition to the conventional surface crack, the branch crack characterized by the ‘Y’ at the subsurface inclusion is also observed. Among them, the leading crack aligned with the rolling direction forms and propagates first, followed by the two trailing cracks propagating in the reverse rolling direction. Driven by the plastic ratcheting at the surface layer and the deeper bending deformation, these two trailing cracks may converge with other adjacent leading cracks, resulting in the formation of the spalling pit hundreds of μm deep. Moreover, the sliding friction in the transverse direction of the rail promotes the formation of wavy pearlite, which reduces the fracture toughness of the outside rail. In the predictive maintenance of rails, it is essential to promptly identify and address potential hazards of surface spalling and transverse fracture.
{"title":"Fatigue damage development and mechanical property degradation of pearlitic rail steel under loaded traffic","authors":"Manjiang Yu , Ye Wang , Fangli Duan , Chaofeng Lü","doi":"10.1016/j.ijfatigue.2025.109474","DOIUrl":"10.1016/j.ijfatigue.2025.109474","url":null,"abstract":"<div><div>The service failure evaluation of the damaged rail can provide theoretical guidance for the routine maintenance of existing railway lines. In this work, U71MnG rail that failed under traffic loading is selected to investigate the fatigue damage mechanism of pearlitic rail steel. In addition to the conventional surface crack, the branch crack characterized by the ‘Y’ at the subsurface inclusion is also observed. Among them, the leading crack aligned with the rolling direction forms and propagates first, followed by the two trailing cracks propagating in the reverse rolling direction. Driven by the plastic ratcheting at the surface layer and the deeper bending deformation, these two trailing cracks may converge with other adjacent leading cracks, resulting in the formation of the spalling pit hundreds of μm deep. Moreover, the sliding friction in the transverse direction of the rail promotes the formation of wavy pearlite, which reduces the fracture toughness of the outside rail. In the predictive maintenance of rails, it is essential to promptly identify and address potential hazards of surface spalling and transverse fracture.</div></div>","PeriodicalId":14112,"journal":{"name":"International Journal of Fatigue","volume":"206 ","pages":"Article 109474"},"PeriodicalIF":6.8,"publicationDate":"2025-12-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145894535","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-30DOI: 10.1016/j.ijfatigue.2025.109476
Jiasen Gu , Deqiao Xie , Xuwen Gu , Shuang Liu , Kai Zhou , Chen Jiao , Rong Jiang , Xinfeng Lv , Juan Hu , Zongjun Tian , Dongsheng Wang , Lida Shen
Fatigue life prediction of laser powder bed fusion (LPBF) components remains challenging because critical defects cannot be reliably identified before service, resulting in large scatter and limited applicability of existing methods. In this study, an integrated framework combining quasi in-situ X-ray computed tomography (XCT), finite element method (FEM), and machine learning (ML) was developed to rapidly screen critical defects and predict fatigue life prior to loading. The results revealed the early-stage evolution of critical defects during crack initiation, and a Murakami-Basquin model was established to quantitatively link defect features with fatigue life. Moreover, the FEM-driven ML approach achieved high-accuracy life prediction within a 1.5× error band, with identified as the dominant factor, followed by defect depth () and , in agreement with classical fatigue criteria. Demonstrated with Ti6Al4V, this work establishes a critical-defect-driven pathway for fatigue life prediction, providing a broadly applicable methodology for defect-sensitive design and life assessment of LPBF components.
{"title":"Critical defect-driven fatigue evolution mechanism and life prediction of Ti6Al4V part built by laser powder bed fusion","authors":"Jiasen Gu , Deqiao Xie , Xuwen Gu , Shuang Liu , Kai Zhou , Chen Jiao , Rong Jiang , Xinfeng Lv , Juan Hu , Zongjun Tian , Dongsheng Wang , Lida Shen","doi":"10.1016/j.ijfatigue.2025.109476","DOIUrl":"10.1016/j.ijfatigue.2025.109476","url":null,"abstract":"<div><div>Fatigue life prediction of laser powder bed fusion (LPBF) components remains challenging because critical defects cannot be reliably identified before service, resulting in large scatter and limited applicability of existing methods. In this study, an integrated framework combining quasi <em>in-situ</em> X-ray computed tomography (XCT), finite element method (FEM), and machine learning (ML) was developed to rapidly screen critical defects and predict fatigue life prior to loading. The results revealed the early-stage evolution of critical defects during crack initiation, and a Murakami-Basquin model was established to quantitatively link defect features with fatigue life. Moreover, the FEM-driven ML approach achieved high-accuracy life prediction within a 1.5× error band, with <span><math><msub><mi>σ</mi><mrow><mi>FEM</mi></mrow></msub></math></span> identified as the dominant factor, followed by defect depth (<span><math><mi>h</mi></math></span>) and <span><math><msqrt><mrow><mi>area</mi></mrow></msqrt></math></span>, in agreement with classical fatigue criteria. Demonstrated with Ti6Al4V, this work establishes a critical-defect-driven pathway for fatigue life prediction, providing a broadly applicable methodology for defect-sensitive design and life assessment of LPBF components.</div></div>","PeriodicalId":14112,"journal":{"name":"International Journal of Fatigue","volume":"206 ","pages":"Article 109476"},"PeriodicalIF":6.8,"publicationDate":"2025-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145894536","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-30DOI: 10.1016/j.ijfatigue.2025.109475
Wenyue Zhang , Yong Chen , Xing He , Fang Xue , Peng Xu , Wentao He
This paper proposes a dynamic digital twin framework driven by real-time physical information, which integrates a Radial Basis Function (RBF) neural network and a Dynamic Bayesian Network (DBN). A time-varying fatigue crack growth program is developed to update uncertain crack growth parameters and to enable real-time life prediction under welding residual stress and variable-amplitude loading conditions. A finite element model of welding residual stress is established based on thermo-elastic–plastic theory, and the associated stress intensity factor is calculated using the weight function method. A nonlinear mapping between the stress intensity factor and crack length is constructed using the RBF neural network, accounting for both welding residual stress and variable-amplitude loading. The physics-informed digital twin framework, where the Particle Filter (PF) algorithm drives the DBN, is applied to predict fatigue crack growth and update uncertain parameters in Middle Tension (MT) specimens. Under conditions of periodic multiple overloads, the predicted fatigue life closely matches the experimental results, with an error under 1%. The crack growth process is validated through the co-simulation of ABAQUS and FRANC3D using the updated parameters, with the error between simulated and experimental results remaining below 1%, which demonstrates the high accuracy and robustness of the proposed digital twin framework for fatigue life prediction.
{"title":"Real-Time fatigue crack growth prediction for welded structures based on digital twin framework considering residual stress and variable amplitude loading","authors":"Wenyue Zhang , Yong Chen , Xing He , Fang Xue , Peng Xu , Wentao He","doi":"10.1016/j.ijfatigue.2025.109475","DOIUrl":"10.1016/j.ijfatigue.2025.109475","url":null,"abstract":"<div><div>This paper proposes a dynamic digital twin framework driven by real-time physical information, which integrates a Radial Basis Function (RBF) neural network and a Dynamic Bayesian Network (DBN). A time-varying fatigue crack growth program is developed to update uncertain crack growth parameters and to enable real-time life prediction under welding residual stress and variable-amplitude loading conditions. A finite element model of welding residual stress is established based on thermo-elastic–plastic theory, and the associated stress intensity factor is calculated using the weight function method. A nonlinear mapping between the stress intensity factor and crack length is constructed using the RBF neural network, accounting for both welding residual stress and variable-amplitude loading. The physics-informed digital twin framework, where the Particle Filter (PF) algorithm drives the DBN, is applied to predict fatigue crack growth and update uncertain parameters in Middle Tension (MT) specimens. Under conditions of periodic multiple overloads, the predicted fatigue life closely matches the experimental results, with an error under 1%. The crack growth process is validated through the co-simulation of ABAQUS and FRANC3D using the updated parameters, with the error between simulated and experimental results remaining below 1%, which demonstrates the high accuracy and robustness of the proposed digital twin framework for fatigue life prediction.</div></div>","PeriodicalId":14112,"journal":{"name":"International Journal of Fatigue","volume":"206 ","pages":"Article 109475"},"PeriodicalIF":6.8,"publicationDate":"2025-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145894537","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-30DOI: 10.1016/j.ijfatigue.2025.109477
J.H. Du, P. Chen, Z.P. Jia, X.W. Li
This study systematically investigates the tension–tension fatigue behavior and deformation mechanisms of solution-treated and aging-treated Fe-30.5Mn-8Al-1C (wt%) austenitic low-density steels, focusing on the critical role of κ-carbide precipitation state in controlling fatigue properties. In aged samples, intragranular κ-carbides induce planar dislocation slip through a “glide plane softening” mechanism, enhancing slip reversibility under cyclic loading and thereby improving fatigue life. Strengthening is primarily due to the interaction between dislocations and intragranular κ-carbides. An appropriate increase in the size of intragranular κ-carbides significantly enhances fatigue life and fatigue strength at low stress amplitudes. Conversely, intergranular κ-carbide precipitation impedes slip transmission, intensifies localized stress concentration, and accelerates damage, thus reducing fatigue life at high stress amplitudes. These findings strongly demonstrate that accelerating the precipitation of intragranular κ-carbides while suppressing intergranular precipitation is an effective microstructural pathway to concurrently enhance fatigue performance of Fe-Mn-Al-C austenitic low-density steels across the entire range of stress amplitudes.
{"title":"Fatigue properties of Fe-30.5Mn-8Al-1C austenitic low-density steel: Critical impact of κ-carbide precipitation state","authors":"J.H. Du, P. Chen, Z.P. Jia, X.W. Li","doi":"10.1016/j.ijfatigue.2025.109477","DOIUrl":"10.1016/j.ijfatigue.2025.109477","url":null,"abstract":"<div><div>This study systematically investigates the tension–tension fatigue behavior and deformation mechanisms of solution-treated and aging-treated Fe-30.5Mn-8Al-1C (wt%) austenitic low-density steels, focusing on the critical role of κ-carbide precipitation state in controlling fatigue properties. In aged samples, intragranular κ-carbides induce planar dislocation slip through a “glide plane softening” mechanism, enhancing slip reversibility under cyclic loading and thereby improving fatigue life. Strengthening is primarily due to the interaction between dislocations and intragranular κ-carbides. An appropriate increase in the size of intragranular κ-carbides significantly enhances fatigue life and fatigue strength at low stress amplitudes. Conversely, intergranular κ-carbide precipitation impedes slip transmission, intensifies localized stress concentration, and accelerates damage, thus reducing fatigue life at high stress amplitudes. These findings strongly demonstrate that accelerating the precipitation of intragranular κ-carbides while suppressing intergranular precipitation is an effective microstructural pathway to concurrently enhance fatigue performance of Fe-Mn-Al-C austenitic low-density steels across the entire range of stress amplitudes.</div></div>","PeriodicalId":14112,"journal":{"name":"International Journal of Fatigue","volume":"206 ","pages":"Article 109477"},"PeriodicalIF":6.8,"publicationDate":"2025-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145894539","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-29DOI: 10.1016/j.ijfatigue.2025.109460
Ali Rauf , Indrajit Nandi , Kim Vanmeensel , Reza Talemi
Inconel 718 (IN-718) is a precipitation-strengthened nickel-based superalloy that is widely explored for its applicability in fatigue-critical applications when fabricated using additive manufacturing (AM) at an industrial scale. Among the various factors influencing its performance, the choice of shielding gas during laser powder bed fusion (L-PBF) plays a crucial yet often overlooked role in determining the material’s microstructure and mechanical behaviour. This study investigates the critical influence of shielding gases like argon and nitrogen on the microstructure, defect distribution and the very high cycle fatigue (VHCF) durability of heat-treated L-PBF fabricated IN-718. Defect quantification was undertaken using a combination of optical microscopy, Archimedes density measurements, X-ray computed tomography (XCT), revealing higher defect contents in samples processed under nitrogen shielding. Microstructural analysis through scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and energy-dispersive X-ray spectroscopy (EDS) revealed pronounced variations in grain morphology and inclusion content between the two gas environments. VHCF tests were performed under fully reversed, uniaxial, stress-controlled loading at 20 kHz using dog-bone specimens with larger risk volumes to capture a conservative fatigue life assessment. Fatigue life distributions were analysed using a Weibull accelerated failure time model, revealing similar median lives but narrower scatter for argon-shielded specimens. Fractographic analysis revealed distinct crack-initiation mechanisms, microstructure driven initiation in argon-shielded specimens leaving facets at initiation sites versus defect-assisted initiation often involving inclusions along with pores and lack-of-fusion (LOF) defects in nitrogen-shielded counterparts. Although nitrogen shielding produced a refined microstructure, the elevated porosity and inclusion density-controlled crack initiation and degraded fatigue performance.
{"title":"Process gas influence on Very-High-Cycle fatigue response of Inconel 718 fabricated by laser powder bed fusion","authors":"Ali Rauf , Indrajit Nandi , Kim Vanmeensel , Reza Talemi","doi":"10.1016/j.ijfatigue.2025.109460","DOIUrl":"10.1016/j.ijfatigue.2025.109460","url":null,"abstract":"<div><div>Inconel 718 (IN-718) is a precipitation-strengthened nickel-based superalloy that is widely explored for its applicability in fatigue-critical applications when fabricated using additive manufacturing (AM) at an industrial scale. Among the various factors influencing its performance, the choice of shielding gas during laser powder bed fusion (L-PBF) plays a crucial yet often overlooked role in determining the material’s microstructure and mechanical behaviour. This study investigates the critical influence of shielding gases like argon and nitrogen on the microstructure, defect distribution and the very high cycle fatigue (VHCF) durability of heat-treated L-PBF fabricated IN-718. Defect quantification was undertaken using a combination of optical microscopy, Archimedes density measurements, X-ray computed tomography (XCT), revealing higher defect contents in samples processed under nitrogen shielding. Microstructural analysis through scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and energy-dispersive X-ray spectroscopy (EDS) revealed pronounced variations in grain morphology and inclusion content between the two gas environments. VHCF tests were performed under fully reversed, uniaxial, stress-controlled loading at 20 kHz using dog-bone specimens with larger risk volumes to capture a conservative fatigue life assessment. Fatigue life distributions were analysed using a Weibull accelerated failure time model, revealing similar median lives but narrower scatter for argon-shielded specimens. Fractographic analysis revealed distinct crack-initiation mechanisms, microstructure driven initiation in argon-shielded specimens leaving facets at initiation sites versus defect-assisted initiation often involving inclusions along with pores and lack-of-fusion (LOF) defects in nitrogen-shielded counterparts. Although nitrogen shielding produced a refined microstructure, the elevated porosity and inclusion density-controlled crack initiation and degraded fatigue performance.</div></div>","PeriodicalId":14112,"journal":{"name":"International Journal of Fatigue","volume":"206 ","pages":"Article 109460"},"PeriodicalIF":6.8,"publicationDate":"2025-12-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145894569","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-29DOI: 10.1016/j.ijfatigue.2025.109470
Kangnan Zhu, Jiajun Shi, Anji Wang, Guijun Xian, Chenggao Li
Carbon/glass hybrid fiber reinforced polymer (C/GFRP) tubes, which offer both high performance and cost-effectiveness, are often subjected to the synergistic effects of fatigue and creep during their service life as transportation carriers, which reduces the safety of the structure. This study investigates the tension–tension fatigue behavior of C/GFRP tubes under constant stress ratio at different stress levels. The influence of a hygrothermal environment on fatigue failure modes, fatigue life, and stiffness degradation was examined via laboratory accelerated aging (150 days of immersion in distilled water at 60 °C). The creep displacement evolution was investigated by experimental and analytical means. Finally, a modified fatigue stiffness degradation model accounting for creep effects was proposed based on the creep growth curve. During fatigue loading, the primary load-bearing responsibility gradually shifts from the resin to the fibers as the resin deforms. This transition alters the material’s viscoelastic behavior, evolving from resin-dominated viscoelasticity toward fiber-dominated elasticity. Consequently, the total energy dissipated per loading cycle significantly decreases. Hygrothermal aging alters the failure mode, causing irregular serrated matrix fractures due to interface degradation, and significantly reduces fatigue life. After 150 days of accelerated aging, the fatigue life retention rates of the C/GFRP tubes at stress levels of 0.50, 0.45, 0.40, and 0.38 were 16.3 %, 61.6 %, 57.1 %, and 45.8 %, respectively. Creep effects lead to increased stiffness during fatigue in tubes. The modified stiffness degradation model effectively characterizes the actual stiffness evolution of C/GFRP tubes during fatigue process by separating the cyclic creep.
{"title":"Creep-fatigue interaction and hygrothermal aging effect on the fatigue behavior of carbon/glass hybrid fiber filament-wound tubes","authors":"Kangnan Zhu, Jiajun Shi, Anji Wang, Guijun Xian, Chenggao Li","doi":"10.1016/j.ijfatigue.2025.109470","DOIUrl":"10.1016/j.ijfatigue.2025.109470","url":null,"abstract":"<div><div>Carbon/glass hybrid fiber reinforced polymer (C/GFRP) tubes, which offer both high performance and cost-effectiveness, are often subjected to the synergistic effects of fatigue and creep during their service life as transportation carriers, which reduces the safety of the structure. This study investigates the tension–tension fatigue behavior of C/GFRP tubes under constant stress ratio at different stress levels. The influence of a hygrothermal environment on fatigue failure modes, fatigue life, and stiffness degradation was examined via laboratory accelerated aging (150 days of immersion in distilled water at 60 °C). The creep displacement evolution was investigated by experimental and analytical means. Finally, a modified fatigue stiffness degradation model accounting for creep effects was proposed based on the creep growth curve. During fatigue loading, the primary load-bearing responsibility gradually shifts from the resin to the fibers as the resin deforms. This transition alters the material’s viscoelastic behavior, evolving from resin-dominated viscoelasticity toward fiber-dominated elasticity. Consequently, the total energy dissipated per loading cycle significantly decreases. Hygrothermal aging alters the failure mode, causing irregular serrated matrix fractures due to interface degradation, and significantly reduces fatigue life. After 150 days of accelerated aging, the fatigue life retention rates of the C/GFRP tubes at stress levels of 0.50, 0.45, 0.40, and 0.38 were 16.3 %, 61.6 %, 57.1 %, and 45.8 %, respectively. Creep effects lead to increased stiffness during fatigue in tubes. The modified stiffness degradation model effectively characterizes the actual stiffness evolution of C/GFRP tubes during fatigue process by separating the cyclic creep.</div></div>","PeriodicalId":14112,"journal":{"name":"International Journal of Fatigue","volume":"206 ","pages":"Article 109470"},"PeriodicalIF":6.8,"publicationDate":"2025-12-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145881308","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-29DOI: 10.1016/j.ijfatigue.2025.109469
Luohuan Zou , Yu Gong , Dingli Tian , Sizhuo Hao , Jianyu Zhang , Libin Zhao , Ning Hu
Delamination usually occurs and grows in composite laminates under fatigue loading. The stress ratio is an important factor, while its influence law has no consensus yet. In this paper, to fully investigate the influence of fiber bridging and stress ratio on the fatigue delamination behavior, mode I fatigue delamination tests under two stress ratios (0.1 and 0.5) are conducted. Test results reveal that, the initial and steady-state values of the fatigue R-curve are consistent with those of quasi-static ones, while there are significant differences in the growth stage of fiber bridging. Furthermore, it is found that, the slope and intercept of the da/dN-Gmax curves vary under different stress ratios. A novel four-parameter fatigue model considering fiber bridging and stress ratio effects is proposed. The proposed model is compared with other classical models in literatures using the fatigue data of two stress ratios (0.1 and 0.5). It is found that the proposed model can well characterize fatigue delamination behavior. To further verify the model applicability, fatigue tests under stress ratio of 0.3 are supplemented. The predicted da/dN-Gmax curves by the model and experimental results are compared with a 95% confidence interval, which indicates that the proposed model has good applicability and can provide an effective method for fatigue delamination prediction.
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