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Torsional fatigue Cracking and fracture Behaviors of Cold-Drawn Copper:Effects of Microstructure and Axial Stress

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Acta Metallurgica Sinica(English Letters) 2019年第12期32卷 1521-1529页

作者： Rong-Hua Li Peng Zhang Zhe-Feng Zhang School of Mechanical Engineering Liaoning Shihua UniversityFushun 113001China laboratory of fatigue and fracture for materials Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China

The fatigue cracking and fracture behavior of cold-drawn copper subjected to cyclic torsional loading were investigated in this study.It was found that with increasing stress amplitude,the fracture mode of cold-drawn copper gradually changes from a shear fracture on transverse maximum shear stress plane to a mixed shear mode on both transverse and longitudinal shear planes and finally turns to the shear fracture on multiple longitudinal shear planes.Combining the cracking morphology and the relationship between torsional fatigue cracking and the grain boundaries,the fracture mechanism of cold-drawn copper under cyclic torsional loading was analyzed and proposed by considering the effects of the microstructure and axial stress caused by torsion.Because of the promotion of the grain boundary distribution on longitudinal crack propagation and the inhibition of axial stress on transverse crack grown,the tendency of crack propagation along the longitudinal direction increases with increasing stress levels.

关键词： Torsion fatigue behavior Crack propagation fracture mechanisms Axial stress Copper

fatigue Crack Initiation and Propagation Dominated by Crystallographic Factors in TiB/near a-Ti

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Acta Metallurgica Sinica(English Letters) 2024年第5期37卷 763-776页

作者： Fanchao Meng Rui Zhang Shuai Wang Fengbo Sun Run Chen Lujun Huang Lin Geng School of materials Science and Engineering Harbin Institute of TechnologyHarbin 150001China Waikato Centre for Advanced materials and Manufacturing School of EngineeringUniversity of WaikatoHamilton 3240New Zealand State Key laboratory of Advanced Welding and Joining Harbin Institute of TechnologyHarbin 150001China

Discontinuously reinforced titanium matrix composites(DRTMCs)with a network structure have been extensively researched due to their superior combination of strength and ductility.However,their fatigue performance has remained unknown.In order to elucidate the fatigue behavior of DRTMCs,a tension-tension fatigue test was performed on a TiB/nearα-Ti composite with network structure.The results showed that the variability of fatigue lifetime increased as the stress level decreased.Fractography analysis indicated that fatigue crack initiation was associated with facet formation,while the subsequent propagation was hindered by the network structure comprising TiB whiskers and silicides.Crystallographic characterization further revealed that facets formed due to a combination of shear and normal stress.The reduction in fatigue lifetime was attributed to an increase in the effective slip length,which was influenced by the orientation of grains near the crack-initiation sites toward basal slip in the life-limiting specimen.Quasi in situ observation suggested that the crack initiation was facilitated by both basal and prismatic slip ofα-Ti as well as fracture of TiBw.Crack propagation was found to be associated with basal and prismatic slip systems with high Schmid factors,regardless of whether the crack was intergranular or intragranular.

关键词： Titanium matrix composite TiBw fatigue lifetime variability Crack initiation Crack propagation

Predictive fatigue crack growth law of high-strength steels

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Journal of materials Science & Technology 2022年第5期100卷 46-50页

作者： H.F.Li P.Zhang B.Wang Z.F.Zhang laboratory of fatigue and fracture for materials Shi-changxu Innovation Center for Advanced MaterialsChinese Academy of SciencesInstitute of Metal ResearchShenyang 110016China State Key laboratory of Mechanical Behavior and System Safety of Traffic Engineering Structures Shijiazhuang Tiedao UniversityShijiazhuang 050043China

The fatigue resistance of metallic materials is generally attributed to both strength and toughness.Unfortunately,these properties are mutually exclusive in most materials.Classical theories like Paris’law only provide some data correlation schemes rather than a predictive capability,which cannot satisfactorily guide the anti-fatigue design.In this study,for the first time,the predictive fatigue crack growth rate law is proposed by considering the effects of both strength and toughness.Accordingly,a quantitative criterion is established for judging the fatigue crack resistance of high-strength steels.The predictive law would provide a unique view to the quantitative anti-fatigue design of metallic materials.

关键词： fatigue crack growth Strength and toughness Paris’law High-strength steels

ANOMALOUS STRAIN RATE DEPENDENCE OF FLOW STRESS IN TiAl INTERMETALLIC COMPOUNDS

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Acta Metallurgica Sinica(English Letters) 1992年第5期5卷 390-394页

作者： WANG Liming ZHU Dong YAO Mei CAI Qigong ZOU Dunxu State Key laboratory for fatigue and fracture of materials,Academia Sinica,Shenyang Central Iron and Steel Research Institute,Ministry of Metallurgical Industry,Beijing,China State Key Lab for fatigue and Fracture of Materials Acad Sinica Shenyang China

Plastic deformation of TiAI and TiAI-V intermetallic compounds has been studied by com- pression experiment at various temperatures and strain rates.Results show that the plastic deformation in distinct temperature range is principally controlled by the mechanisms of Peierls-Nabarro,cross slip and creep of dislocations.For TiAI-V alloy deformed at a range of 600—700 K,the negative strain rate dependence of flow stress was observed,i.e.,the more the plastic strain is.the more the negative dependence will be.A possible mechanism of the anomaly could be interpreted by thermal activation of dislocation cross slipping.The effects of temperature and strain rate on work-hardening exponent were also studied and discussed.

关键词： TiAl intermetallic compound strain rate cross-slip

Microstructure,mechanical and fracture properties of friction stir welded 2195 Al-Li alloy joints

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Chinese Journal of Aeronautics 2024年第1期37卷 345-361页

作者： Guangda SUN Weizhao SUN Li ZHOU Sanfeng LUO Zili ZHANG Debo LIU Huiqiang WU State Key laboratory of Advanced Welding and Joining Harbin Institute of TechnologyHarbin 150001China Shandong Provincial Key laboratory of Special Welding Technology Harbin Institute of Technology(Weihai)Weihai 264209China Beijing Institute of Astronautical Systems Engineering Beijing 100076China

The 8 mm-thick 2195 Al-Li alloy joints were achieved by Friction Stir Welding(FSW).The microstructural evolution,temperature-dependent mechanical properties,and fracture properties were studied.The T1,δ’/β’and θ’precipitates were observed in the Base Metal(BM)and the Heat Affected Zone(HAZ).Most of the precipitates,except for re-precipitated δ’/β’phases,were dissolved in the Nugget Zone(NZ).The tensile specimens that failed at cryogenic temperatures(-196℃)had the maximum Ultimate Tensile Strength(UTS),and the fracture surface showed the inter-granular fracture characteristics.Compared to those at room temperature(25℃),the decreasing tensile properties at high temperature(180℃)were related to microstructure and strain hardening effects.The NZ presented the optimal fracture toughness,and the Crack Tip Opening Displacement(CTOD)was mutually dominated by microhardness and grain size.Analysis on fatigue Crack Growth(FCG)rates indicates that the Thermal-Mechanically Affected Zone(TMAZ)exhibited the most superior fatigue resistance performance at stress intensity range below17 MPa.m1/2due to compressive residual stress and the crack closure effect.The fatigue fracture surfaces reveal that the crack propagation zone was characterized by the striations and secondary cracks.Also,inter-granular fracture behavior was responsible for the fastest FCG rates in the NZ.

关键词： Aluminum alloys Friction stir welding Microstructural evolution Mechanical properties fracture mechanism

fatigue behavior of CoCrFeMnNi high-entropy alloy under fully reversed cyclic deformation

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Journal of materials Science & Technology 2019年第3期35卷 334-340页

作者： Y.Z.Tian S.J.Sun H.R.Lin Z.F.Zhang materials fatigue and fracture Division Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences School of materials Science and Engineering University of Science and Technology of China

Bulk ultrafine-grained(UFG) CoCrFeMnNi high-entropy alloy(HEA) with fully recrystallized microstructure was processed by cold rolling and annealing treatment. The high-cycle fatigue behaviors of the UFG HEA and a coarse-grained(CG) counterpart were investigated under fully reversed cyclic deformation.The fatigue strength of the UFG HEA can be significantly enhanced by refining the grain size. However,no grain coarsening was observed in the UFG HEA during fatigue tests. Mechanisms for the superior mechanical properties of the UFG HEA were explored.

关键词： High-entropy alloy(HEA) Ultrafine-grain(UFG) High-cycle fatigue Recrystallization Grain size fatigue strength

A practical model for efficient anti-fatigue design and selection of metallic materials:Ⅰ.Model building and fatigue strength prediction

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Journal of materials Science & Technology 2021年第11期70卷 233-249页

作者： R.Liu P.Zhang Z.J.Zhang B.Wang Z.F.Zhang laboratory of fatigue and fracture for materials Shi-changxu Innovation Center for Advanced MaterialsInstitute of Metal ResearchChinese Academy of Sciences72 Wenhua RoadShenyang 110016China

The high cost and low efficiency of fatigue tests are bottleneck problem for the anti-fatigue design of metallic materials.For this problem,a theoretical fatigue model is proposed in this study,the possible applications have also been discussed.Specific results would be introduced in two serial papers,in which the first paper focuses on the model building and the applications on fatigue strength prediction;the second paper put emphasis on the influencing factors of the model parameters and the applications on fatigue strength improvement.In this first paper,a theoretical model is proposed considering both the strength and plastic restrictions of fatigue strength.As the model builds up a brief relationship among yield strength(Y),tensile strength(T)and fatigue strength(F),it is named as the Y-T-F model.Through the verification with fatigue strength data covering various kinds of metallic materials and loading conditions,this Y-T-F model exhibits both generality and accuracy.With the Y-T-F model,the efficient fatigue strength prediction could be conducted by brief linear fitting and calculation,just through yield strength,tensile strength and several known fatigue strength data.Moreover,through its deduced Y-F model,the analytical formula of fatigue strength continuously changing with materials strengthening can be obtained,as well as the maximum value of fatigue strength and corresponding critical yield strength.In summary,the Y-T-F model would be useful for reducing the fatigue tests,thus providing new possibilities on the efficient anti-fatigue design and selection of metallic materials.

关键词： Yield strength Tensile strength Plasticity fatigue strength Anti-fatigue design

Microstructure and fatigue behavior of laser-powder bed fusion austenitic stainless steel

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Journal of materials Science & Technology 2020年第11期42卷 191-200页

作者： Chenfan Yu Peng Zhang Zhefeng Zhang Wei Liu School of materials Science and Engineering Tsinghua UniversityBeijing 100084China laboratory of fatigue and fracture for materials Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China

The microstructures and stress-controlled fatigue behavior of austenitic stainless steel(AISI 316 L stainless steel)fabricated via laser-powder bed fusion(L-PBF)technique were investigated.For L-PBF process,zigzag laser scanning strategy(scan rotation between successive layer was 0°,ZZ sample)and crosshatching layer scanning strategy(scan rotation between successive layer was 67°,CH sample)were employed.By inducing different thermal history,it is found that the scan strategies of laser beam have a significant impact on grain size and morphology.fatigue cracks generally initiated from persistent slip bands(PSBs)or grain boundaries(GBs).It is observed that PSBs could transfer the melt pool boundaries(MPBs)continuously.The MPBs have better strain compatibility compared with grain boundaries(GBs),thus MPBs would not be the initiation site of fatigue cracks.A higher fatigue limit strength could be achieved by employing a crosshatching scanning strategy.For the CH sample,fatigue cracks also initiated from GBs and PSBs.However,fatigue crack initiated from process-induced defects were observed in ZZ sample in high-cycle regions.Solidification microstructures and defects characteristics are important factors affecting the fatigue performance of L-PBF 316 L stainless.Process-induced defects originated from fluid instability can be effectively reduced by adjusting the laser scan strategy.

关键词： Laser-powder bed fusion Austenitic stainless steel Microstructures fatigue crack

Characteristics of fatigue in a SiC Reinforced Aluminium Alloy

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Journal of materials Science & Technology 1989年第4期5卷 279-283页

作者：于维成袁金才王中光隋全武 laboratory of fatigue and fracture of materials IMRChina

1.IntroductionMetal matrix composite materials exhibitquite a good combination of strength andstiffness of the reinforcing phase withductility and toughness of the matrix.Aluminium alloys reinforced with SiC parti-cles and whiskers are receiving a greatdeal of attention from researchers andengineers,because the engineering properties

关键词： reinforced Al alloy fatigue fracture SiC whisker