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fracture toughness of a rejuvenated β-Ti reinforced bulk metallic glass matrix composite

Journal of Materials Science & Technology 2022年第11期106卷 225-235页

作者： Devashish Rajpoot R.Lakshmi Narayan Long Zhang Punit Kumar Haifeng Zhang Parag Tandaiya Upadrasta Ramamurty Department of Mechanical Engineering Indian Institute of Technology BombayPowaiMumbai400076India Department of Mechanical and Aerospace Engineering in Nanyang Technological University Singapore 637331Republic of Singapore Department of Materials Science and Engineering Indian Institute of Technology DelhiHauz KhasNew Delhi110016India Shi-changxu Innovation Center for Advanced Materials Institute of Metal ResearchChinese Academy of SciencesShenyang110016China Institute of Materials Research and Engineering Agency for ScienceTechnology and Research(A∗STAR)Singapore 138634Republic of Singapore

A β-Ti dendrite reinforced Zr-based bulk metallic glass composite(BMGC) was found to be brittle when cast in a large size. The reasons for the embrittlement and the effectiveness of the cryothermal cycling(CTC) treatment in restoring the mode I fracture toughness are examined. Plasticity in all the CTC treated BMGC is estimated from the distribution and occurrence of pop-ins in nanoindentation tests and by measuring the magnitude of enthalpy of relaxation(△H_(rel)) via differential scanning calorimetry(DSC). This is further validated by examining the strain-to-failure(ε_(f)) in compression tests. Mode I fracture behaviour of the as-cast embrittled BMGC and the CTC treated BMGC, which exhibits maximum plasticity, is examined. Results show that both BMGCs are equally brittle and exhibit 5 times lower notch toughness(K_(QJ))than their tougher counterpart. Post-facto imaging of the side surfaces reveals the absence of notch-tip plasticity in both BMGCs. The lack of notch tip plasticity of CTC treated BMGC, despite exhibiting signatures of plasticity in nanoindentation and higher △Hrelis rationalized by reassessing the origin of pop-ins in nanoindentation tests and describing the variations in chemical and topological short range ordering during CTC, respectively. Implications of these results in terms of improving the fracture toughness of structurally relaxed BMGCs via CTC are discussed.

关键词： Bulk metallic glass composites fracture Rejuvenation Shear bands Microsegragation

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fracture Toughnesses and Crack Growth Angles of Single-Layer Graphyne Sheets

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Acta Mechanica Solida Sinica 2019年第3期32卷 339-355页

作者： Zonghuiyi Jiang Rong Lin Junhua Zhao Jiangsu Key Laboratory of Advanced Food Manufacturing Equipment and Technology Jiangnan University Wuxi 214122 China Institute of Mechanics and Advanced Materials School of Mechanical Engineering Jiangnan University Wuxi 214122 China

Recently, Shang et al.(Angew Chem Int Ed 57(3):774-778,2018) have developed a method to synthesize ultrathin (around 1.9 nm) graphyne nanosheets. We reported here the mixed-mode I-II fracture toughnesses and crack growth angles of single-layer graphyne sheets using molecular dynamics (MD) simulations and the finite element (FE) method based on the boundary layer model, respectively. The various carbon-carbon bonds of graphyne sheets in the FE method are equated with the nonlinear Timoshenko beams based on the Tersoff-Brenner potential, where all the parameters of the nonlinear beams are completely determined based on the continuum modeling. All the results from the present FE method are reasonable in comparison with those from our MD simulations using the REBO potential. The present results show that both the critical stress intensity factors (SIFs) and the crack growth angle strongly depend on the chirality and loading angle q @= 90° and #= 0° representing pure mode I and pure mode II, respectively). Meanwhile, the fracture properties of single-layer cyclicgraphene and supergraphene sheets are also studied in order to compare with those of the graphyne sheets. The critical equivalent SIFs are derived as 1.55 fracture properties of carbon allotropes and designing the carbon-based nanodevices.

关键词： fracture toughness Graphyne Molecular dynamics Finite element

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fracture MECHANICS CONDITIONS OF WALLROCK ALTERATION

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中国有色金属学会会刊：英文版 1995年第3期5卷 7-12页

作者： Xiaoshuang, Xi Shaoxun, He Central South Univ of Technology Changsha China

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ＦＲＡＣＴＵＲＥＭＥＣＨＡＮＩＣＳＣＯＮＤＩＴＩＯＮＳＯＦＷＡＬＬＲＯＣＫＡＬＴＥＲＡＴＩＯＮ￥Ｘｉ，Ｘｉａｏｓｈｕａｎｇ；Ｈｅ，Ｓｈａｏｘｕｎ（ＤｅｐａｒｔｍｅｎｔｏｆＧｅｏｌｏｇｙ，ＣｅｎｔｒａｌＳｏｕｔｈＵｎｉｖｅｒｓｉｔｙｏｆＴｅｃｈｎｏｌｏ...

关键词： lode structure wallrock alteration rock fracture

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fracture Characteristics of Fully Pearlitic Steel Wire in Tension and Torsion

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Journal of Iron and Steel Research International 2016年第11期23卷 1206-1212页

作者： Tian-zhang ZHAO Guang-liang ZHANG Shi-hong ZHANG Ling-yun ZHANG Key Laboratory of Fundamental Science for National Defence of Aeronautical Digital Manufacturing Process Shenyang Aerospace University School of Mechanical Engineering Taizhou University Institute of Metal Research Chinese Academy of Sciences

The fracture characteristics of fully pearlitic steel wires with fine and randomly oriented lamellae have been investigated after tension and torsion, respectively. It is found that the predominant fracture mode under small pre- deformation is dimple. The analysis of the colony size and the lamellar structure near the fracture surface indicates that each dimple roots from one colony. A simulation of tensile deformation with several pearlitic colonies based on the real scanning electron microscopy （SEM） observation shows that the plastic deformation concentrates and the stress t^hxialit~＂ is larger ~it the boundaries bf colonies. It demonstrates the microe/＇a^ks initialize at colony boundaries. Thus, the colony size is a significant factor for fracture behaviors under small pre-deformation. On the other hand, the fracture surface is investigated after large pre-deformation via torsion. The results show that fracture characteristics vary with radius from dimples, elongated dimples to the fibrous structure. It indicates that the fracture charac-teristics are dependent on the pre-deformation. The fracture mode under large pre-deformation becomes an anisotropic fibrous structure instead of dimples.

关键词： fracture pearlitic steel wire tension torsion

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fracture morphology and crack mechanism in pure polycrystalline magnesium under tension-compression fatigue testing

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Rare Metals 2020年第2期39卷 162-168页

作者： Li Tan Xi-Yan Zhang Ting Xia Guang-Jie Huang Qing Liu College of Materials Science and Engineering Chongqing UniversityChongqing400045China National Engineering Research Centre for Magnesium Alloy Chongqing UniversityChongqing400045China

The fatigue fracture was characterized and the fracture behavior was analyzed,using scanning electron microscope(SEM)and electron back-scattered diffraction(EBSD),the fatigue tests of two strain amplitude at room temperature were 0.5%and 1.0%respectively,and the results showed that the fatigue deformation of different strain amplitude produced two typical fatigue fracture morphology,and when the strain amplitude was 1.0%,fatigue fracture mechanism of AZ31 magnesium alloy induced by{1012}twins,when the strain amplitude is 0.5%,it was induced by{1012}-{1012}double *** the present study,the average thickness of primary twin is^20μm at amplitude of 0.5%and^80μm at amplitude of 1.%.The thickness of{1012}primary twins was large enough to activate{1012}-{1012}secondary twins at a high strain amplitude,while the thickness of{1012}primary twins was too narrow to activate{1012}-{1012}secondary twins at a low strain amplitude.

关键词： Deformation twinning Magnesium fracture Fatigue

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fracture Analysis of Cast Iron Materials with Cracks Based on Elastoplastic Extended Finite Element Method

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Acta Mechanica Solida Sinica 2019年第2期32卷 201-214页

作者： Yanjun Chang Qiao Song Zheng Kuang Keshi Zhang Zhanguang Zheng College of Civil Engineering and Architecture Guangxi University Nanning 530004 China College of Mechanical Engineering Guangxi University Nanning 530004 China Guangxi Key Laboratory of Disaster Prevention and Engineering Safety Guangxi University Nanning 530004 China Key Laboratory of Engineering Disaster Prevention and Structural Safety of Ministry of Education Guangxi University Nanning 530004 China

Based on the ABAQUS platform for finite element analysis, the extended finite element method (XFEM) considering elastoplastic constitutive relationship is developed, by which the displacement discontinuity across the crack surface and the strong nonlinearity near the crack tip can be described more accurately. The strip specimens with unilateral cracks and central cracks under uniaxial tension are simulated using the XFEM and the FEM, respectively. The J-integral across the crack on each incremen t is calcula ted using the equivale nt domain integral met hod (EDIM), the interaction integral met hod and the FEM, respectively. The effec ts of mesh size and mesh shape near the crack tip, element type and different calculation methods on the accuracy of J-integral are analyzed. The simulation results show that the XFEM is more accurate than the FEM with the same element size and type. The fracture tests of cast iron specimens with unilateral cracks under uniaxial tension are performed, and the J-integral criterion is valid to predict the fracture initiation in numerical simulation. The critical value of J-integral is calculated using the EDIM of the XFEM. The comparisons demonstrate that the simulated elastoplastic load-displacement curves with the XFEM are in good agreement with the experimental results.

关键词： J-Integral Extended finite element Elastoplasticity fracture criterion

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fracture Loci in Sheet Metal Forming: A Review

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Acta Metallurgica Sinica(English Letters) 2015年第12期28卷 1415-1425页

作者： M.Beatriz Silva Kerim Isik A.Erman Tekkaya Paulo A.F.Martins IDMEC Instituto Superior Técnico Universidade de Lisboa Institute of Forming Technology and Lightweight Construction Technical University of Dortmund

fracture in sheet metal forming usually occurs as ductile fracture, rarely as brittle fracture, at the operating temperatures and rates of loading that are typical of real processes in two different modes：（1） tensile and（2） in-plane shear（respectively, the same as modes I and II of fracture mechanics）. The circumstances under which each mode will occur are identified in terms of plastic flow and ductile damage by means of an analytical approach to characterize fracture loci under plane stress conditions that takes anisotropy into consideration. fracture loci was characterized by means of the fracture forming limit line and by the shear fracture forming limit line in the fracture forming limit diagram. Experiments were performed with single point incremental forming and double-notched test specimens loaded in tension, torsion and in-plane shear give support to the presentation and allow determining the fracture loci of AA1050-H111 aluminium sheets with1 mm thickness. The relation between fracture toughness and the fracture forming limits was also investigated by comparing experimental values of the strains at fracture obtained from a truncated conical part produced by single point incremental forming and from double-notched test specimens loaded in tension.

关键词： Sheet forming fracture fracture forming limit diagram

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