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THE EFFECT OF STRAINING MODE ON void growth

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Acta Mechanica Sinica 1999年第2期15卷 126-133页

作者：凌贤伍李国琛 LNM Institute of Mechanics The Chinese Academy of Sciences Beijing China 100080

Large strain finite element method is employed to investigate the effect of straining mode on void growth. Axisymmetric cell model embedded with spherical void is controlled by constant triaxiality loading, while plane-stress model containing a circular void is loaded by constant ratio of straining. Elastic-plastic material is used for the matrix in both cases. It is concluded that, besides the known effect of triaxiality, the straining mode which intensifies the plastic concentration around the void is also a void growth stimulator. Experimental results are cited to justify the computation results.

关键词： void growth elastic-plastic material damage

void growth AND CAVITATION IN NONLINEAR VISCOELASTIC SOLIDS

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Acta Mechanica Sinica 2003年第4期19卷 380-384页

作者：张赟黄筑平 DepartmentofMechanicsandEngineeringScience PekingUniversityBeijing100871China

This paper discusses the growth of a pre-existing void in a nonlinear viscoelastic material subjected to remote hydrostatic tensions with different loading rates. The constitutive relation of this viscoelastic material is the one recently proposed by the present authors, which may be considered as a generalization of the non-Gaussian statistical theory in rubber elasticity. As the first order approximation, the above constitutive relation can be reduced to the "neo-Hookean" type viscoelastic *** of the influences of the material viscosity and the loading rate on the void growth, or on the cavitation are carried out. It is found that: (1) for generalized "inverse Langevin approximation"nonlinear viscoelastic materials, the cavitation limit does not exist, but there is a certain (remote)stress level at which the void will grow rapidly; (2) for generalized "Gaussian statistics" (neo-Hookean type) viscoelastic materials, the cavitation limit exists, and is an increasing function of the loading *** present discussions may be of importance in understanding the material failure process under high triaxial stress.

关键词： void growth cavitation viscoelastic non-Gaussian statistical theory inverse Langevin approximation

SURFACE EFFECT ON NANOSIZED void growth IN A RIGID-PERFECTLY PLASTIC MATERIAL

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Acta Mechanica Solida Sinica 2008年第1期21卷 9-14页

作者： Tong Hui Yiheng Chen School of Aerospace MOE Xi＇an Jiaotong University Xi＇an 710049 China

The influence of the surface effect on the nanosized spherical void growth in a rigidperfectly plastic material is analyzed and the mechanism of the nanosized void growth with high triaxiality is given. Based on the Rice and Tracey model for a macro void growth, the present model is proposed to account for the nanosized void growth under a uniform remote strain rate field with consideration on the surface effect. It is concluded that the surface effect yields an evident resistant influence on the nanosized void growth. That is, this influence decays as the void radius increases. With high triaxiality, the nanosized void growth is divided into two stages： the initial stage and the mature stage. At the first stage, the void grows slowly and the influence of surface effect is relatively weak, whereas at the second stage, the influence is significant and the void grows drastically.

关键词： nanosized void extended variational principle void growth surface effect high triaxiality

Molecular dynamics study on the nano-void growth and coalescence at grain boundary

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Science China(Physics,Mechanics & Astronomy) 2012年第1期55卷 86-93页

作者： LIN EnQiang NIU LiSha SHI HuiJi DUAN Zheng Applied Mechanics Laboratory School of Aerospace Tsinghua University Beijing 100084 China

Molecular dynamics simulations using embedded atom method (EAM) potential were performed to study nano-void growth and coalescence at grain boundary in face-centered cubic bicrystal copper. Thin-plate specimens subjected to uniaxial tension strain with one-void and two-void at the centered grain boundary were employed to analyze the effect of specimen size, temperature and applied strain rate on the stress-strain response, incipient yield strength and macroscopic effective Young's modulus. The evolutions of dislocations, twin bands and void shapes under different specimen sizes were also presented. The obtained results show that, regardless of the void numbers, the specimen sizes, temperature, the applied strain rate had significant influence on the void shape evolution, stress-strain curve and incipient yield strength, while negligible effects on the macroscopic effective Young's modulus except for the temperature. Moreover, the voids growth rate along the grain boundary was also found to be associated with the specimen sizes.

关键词： bicrystal void growth void coalescence grain boundary molecular dynamics simulations embedded atom method

CONSTITUTIVE POTENTIAL FOR DUCTILE DAMAGED MATERIAL AND void growth RATE

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Acta Mechanica Sinica 1989年第2期5卷 125-135页

作者： Wang Tzuchiang (Institute of Mechanics,Academia Sinica,Beijing,China) 1. Institute of Mechanics Academia Sinica Beijing China

In this paper a general formula for plastic potential including isotropic ductile damage has been present ed on the basis of the thermodynamics for irreversible process and internal variable the- *** this formula the mass conservation law is satisfied and it also contains a series of unknow coefficients which are the function of macro equivalent stress and the average micro equivalent stress and an unknown function which is the function of two generalized forces. The approximate yield surface equation for isotropically damaged materials is *** this equation the void growth rate is calculated for nonlinear material containing *** present re- sults are in good agreement with the numerical results given by the cell model.

关键词： constitutive potential damaged materials void growth thermodynamics irreversible process

void growth and Interaction in a Structural Aluminum Alloy: Experiments and Theory

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Journal of Minerals and Materials Characterization and Engineering 2021年第1期9卷 14-37页

作者： Scott Gampert Abu Bakar Siddique Tariq A. Khraishi Mechanical Engineering Department University of New Mexico Albuquerque USA

The problem of void growth and interaction is of importance to understanding the mechanics of failure in metals exhibiting ductility. In this work, the growth and interaction of voids in 6061-T6 aluminum were studied experimentally. Specifically, holes of varying numbers and relative placement were investigated for their normalized area growth with applied displacement. Flat dog-bone specimens were carefully drilled in their gauge area with no (zero) holes, one hole, and two holes (arranged vertically or horizontally) for experimentation after polishing. The growth of holes, captured by video recordings, exhibited exponential behavior and was influenced greatly by the number and arrangement of holes with the horizontal voids growing the fastest and the vertical ones growing the slowest. Also, the ensuring deformation of the sample was studied using load-displacement curves, pictography and videography, SEM imaging and Atomic Force Microscopy (AFM). The methods revealed that although the major part failure is due to large crack formation, it was preceded by intense dislocation slip activity and the formation of micro cavities. Also, the AFM quantified the three-dimensional nature of crystal or grain deformation and how it is greatly influenced by distance and location from the hole. Lastly, theoretical understanding of hole growth was offered.

关键词： voids Holes Stress Concentration void growth void Interaction

4D imaging of void nucleation,growth,and coalescence from large and small inclusions in steel under tensile deformation

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Journal of Materials Science & Technology 2022年第28期123卷 168-176页

作者： Yi Guo Timothy L.Burnett Samuel A.McDonald Michael Daly Andrew H.Sherry Philip J.Withers Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China Henry Royce Institute Department of MaterialsUniversity of ManchesterM139PLUK European Synchrotron Radiation Facility(ESRF) 6 rue J Horowitz38000 GrenobleFrance National Nuclear Laboratory Chadwick HouseBirchwood ParkWarringtonWA36AEUK

Samples of SA508 grade 3 nuclear pressure vessel ferritic steel were subjected to tensile straining whilst being simultaneously imaged in 3D in real time using high resolution,high frame rate time-lapse synchrotron computed tomography(CT).This enabled direct observation of void development from nucleation,through growth to coalescence and final failure validating many inferences made post-mortem or by theoretical models,as well as raising new *** sparse,large inclusions were found to nucleate voids at essentially zero plastic strain(consistent with zero interfacial strength);these became increasingly elongated with *** contrast,a high density of small spherical voids were found to nucleate from the sub-micron cementite particles at larger strains(>200%)only in the centre of the necked(high triaxiality)*** interfacial strength approaching 2100 MPa was inferred and soon after their nucleation,these small voids coalesce to form internal microcracks that lead to the final failure of the *** surprisingly,under these conditions of generally low triaxial constraint the large voids are simply cut across and appear to play no significant role in determining the final *** implications of these results are discussed in terms of ductile fracture behaviour and the Gurson model for ductile fracture.

关键词： void growth Ductile fracture Synchrotron X-ray tomography 4D imaging Bainitic steel

In-situ revealing the degradation mechanisms of Pt film over 1000℃

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Journal of Materials Science & Technology 2021年第36期95卷 10-19页

作者： Dongfeng Ma Shengcheng Mao Jiao Teng Xinliang Wang Xiaochen Li Jin Ning Zhipeng Li Qing Zhang Zhiyong Tian Menglong Wang Ze Zhang Xiaodong Han Beijing Key Lab of Microstructure and Property of Advanced Materials Faculty of Materials and ManufacturingBeijing University of TechnologyBeijing 100124China Department of Material Physics and Chemistry University of Science and Technology BeijingBeijing 100083China YW MEMS(Suzhou)CO. LTDSuzhou 215123China Research Center of Engineering for Semiconductor Integrated Technology Institute of SemiconductorsChinese Academy of SciencesBeijing 100083China State Key Laboratory of Silicon Materials and Department of Materials Science and Engineering Zhejiang UniversityHangzhou 310008China

Degradation of a metallic film under harsh thermal-mechanical-electrical coupling field conditions determines its service temperature and *** this work,the self-heating degradation behaviors of Pt thin films above 1000℃were studied in situ by TEM at the *** Pt films degraded mainly through void nucleation and growth on the Pt-SiN_(x)*** preferentially formed at the grain boundary and triple junction intersections with the *** temperatures above 1040℃,the voids nucleated at both the grain boundaries and inside the Pt grains.A stress simulation of the suspended membrane suggests the existence of local tensile stress in the Pt film,which promotes the nucleation of voids at the Pt-Si *** grain-boundary-dominated mass transportation renders the voids grow preferentially at GBs and triple junctions in a Pt ***,under the influence of an applied current,the voids that nucleated inside Pt grains grew to a large size and accelerated the degradation of the Pt film.

关键词： Platinum In situ transmission electron microscopy (TEM) Thin film void growth Degradation

Assessment of a two-surface plasticity model for hexagonal materials

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Journal of Magnesium and Alloys 2023年第12期11卷 4431-4444页

作者： R.Vigneshwaran A.A.Benzerga Department of Aerospace Engineering Texas A&M UniversityCollege StationTX 77843USA

A computationally efficient two-surface plasticity model is assessed against crystal plasticity. Focus is laid on the mechanical behavior of magnesium alloys in the presence of ductility-limiting defects, such as voids. The two surfaces separately account for slip and twinning such that the constitutive formulation captures the evolving plastic anisotropy and evolving tension-compression asymmetry. For model identification, a procedure is proposed whereby the initial guess is based on a combination of experimental data and computationally intensive polycrystal calculations from the literature. In drawing direct comparisons with crystal plasticity, of which the proposed model constitutes a heuristically derived reduced-order model, the available crystal plasticity simulations are grouped in two datasets. A calibration set contains minimal data for both pristine and porous material subjected to one loading path. Then the two-surface model is assessed against a broader set of crystal plasticity simulations for voided unit cells under various stress states and two loading orientations. The assessment also includes microstructure evolution(rate of growth of porosity and void distortion). The ability of the two-surface model to capture essential features of crystal plasticity is analyzed along with an evaluation of computational cost. The prospects of using the model in guiding the development of physically sound damage models in Mg alloys are put forth in the context of high-throughput simulations.

关键词： HCP metals Plastic anisotropy Reduced order model void growth void coalescence