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1 INTRODUCTIONAdamageevolutionmodelofhightemperatureplasticdeformationisderivedinthispaperbyusingsomebasicconcepts ,principlesand 相似文献
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本文介绍了镁合金材料的超塑性研究现状和发展方向 ,以及连续损伤力学基于含内变量热力学势函数建立的金属超塑性变形损伤演变方程 ,并从微损伤演化物理规律及统计细观损伤力学出发 ,建立超塑性材料空洞损伤的演化方程 ,预测材料超塑性变形失稳和成形极限 相似文献
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Y. Kan Z. G. Liu S. H. Zhang L. W. Zhang M. Cheng H. W. Song 《Journal of Materials Engineering and Performance》2014,23(3):1069-1076
Modeling and prediction of the damage evolution in particle reinforced composites is a complex problem. Microstructure characters such as the particle morphologies, sizes, and distribution significantly affect the damage evolution in composites. A numerical simulation has been performed to investigate the damage evolution of SiCp/AA2009 composites. Tensile deformation in SiCp/AA2009 composites was simulated using the microstructure-based model constructed from the metallograph. Matrix damage, particle cracking, and interface debonding were simulated combining the ductile damage model, the normal stress criterion, and the maximum stress ratio criterion. The simulation results show that under tensile loading, damage initiates at the interface, and then propagates along the weakest direction. The simulation microstructures agree well with experimental results in which interface debonding, particle cracking, and matrix damage co-exist. In addition, the effects of component properties on the damage evolution are examined for various situations. 相似文献
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采用半自动光学显微镜、激光共焦显微镜、MTS-Landmark电液伺服力学性能试验机等设备,研究了GH4169合金经不同直径弹丸喷丸处理后的微观组织和力学性能。利用数字图像相关方法(DIC),对材料单轴拉伸过程的表观损伤演化行为进行分析。结果表明,随着弹丸直径由ϕ0.6 mm增大到ϕ4.3 mm,GH4169合金的表面细晶层厚度由420 μm 增大到530 μm,其表面粗糙度最大较原始试样增大了80.8%。喷丸处理后,材料的屈服强度和抗拉强度均有所提高,其伸长率下降。随着塑性变形增加,喷丸前后GH4169合金的损伤演化规律相似,变形初期材料发生均匀变形且变形缓慢,损伤因子达到临界值后材料开始快速损伤。喷丸直径越大,临界塑性应变越小,材料越早发生快速损伤。建立了不同喷丸直径GH4169合金的损伤演化方程,对喷丸强化材料的寿命评估具有重要意义。 相似文献
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A. GhahremaninezhadK. Ravi-Chandar 《Acta Materialia》2012,60(5):2359-2368
Ductile failure in nodular cast iron is explored through uniaxial tension and notched tension experiments. Specimens obtained through tests interrupted at various stages of deformation and failure evolution were examined through quantitative microscopy to discern the mechanisms of failure and to quantitatively evaluate the local strain evolution. Fractographic observations were used to identify the onset and evolution of damage processes during the deformation and failure of nodular cast iron. These tests and observations reveal that void growth and coalescence occurred only within a narrow localized band, whose size is comparable with the size of the graphite nodules; no statistically significant changes in the porosity were observed outside this zone. 相似文献
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Evolution of deformation and friction during multimode scratch test on TiN coated D9 steel 总被引:1,自引:0,他引:1
Three different scratch modes were used to induce deformation in TiN coating deposited on D9 substrate. The consequent surface damage was analyzed using optical and scanning electron microscopy. Main deformation mechanisms found during Progressive Load Scratch Test and Constant Load Scratch Test were cohesive cracking, coating spallation and adhesive failure. However, ductile fracture was induced during Multi Pass Scratch Tests (MPSTs) performed at three different loads. The trend of evolving coefficient of friction was found to be different for three kinds of scratch modes and the evolution of coefficient of friction has been correlated with coating deformation. 相似文献
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H.C.Yu S.S.Xie H.C.Yang 《金属学报(英文版)》2004,17(4):606-611
The tensile creep deformation and damage evolution in a Ni-base superalloy at 900℃/170MPa were investigated. At the first creep stage, abnormal creep occured due to the resolution of fine particles, and the deformation initiated from grain boundary areas. It is evident that nearly all of the dislocations were in γ matrix channels in form of dislocation pairs and the dislocations were impeded at γ /γ‘ interfaces, thus the dislocation networks developed deformation. At the steady creep stage, impeded dislocations at γ/γ‘ interfaces climbed over γ‘ phases by diffusion-dominant mechanism. At the last creep stage, voids were formed around carbides at grain boundary which leaded to accumulated damage and caused creep rate accelerated. With the dislocation networks being broken, the voids connected and grew into micro-cracks gradually. Finally the cracks propagated along grain boundary area and resulted in failure. 相似文献
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Hiroyuki Toda Zul Azri Bin Shamsudin Kazuyuki Shimizu Kentaro Uesugi Akihisa Takeuchi Yoshio Suzuki Mitsuru Nakazawa Yoshimitsu Aoki Masakazu Kobayashi 《Acta Materialia》2013,61(7):2403-2413
It has recently been revealed that high-density pre-existing hydrogen micropores, formed during production processes, exhibit premature growth and coalescence under external loading at room temperature, thereby inducing ductile fracture. This process is incidentally supplemented by the well-established ductile fracture mechanism based on particle damage. It is reasonable to assume that the pre-existing hydrogen micropores may also contribute to damage evolution at high temperatures. In the present study, synchrotron X-ray microtomography was applied to the in situ observation of deformation and fracture in Al–Mg alloys at a high temperature. High-density hydrogen micropores were observed in the alloys. Flow localization controlled deformation through the mechanism of solute drag creep. A combined effect of grain boundary sliding and heterogeneous nucleation on particles was also confirmed to accelerate the growth of pre-existing hydrogen micropores and cavities. Although continuous nucleation occurred together with the growth of pre-existing hydrogen micropores, the effects of the pre-existing hydrogen micropores, especially those located on grain boundaries, were predominant in the overall damage evolution. It seemed likely that supersaturated hydrogen in the aluminum alloys might also make an appreciable contribution to cavitation during high-temperature loading. 相似文献
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The tensile creep deformation and damage evolution in a Ni-base superalloy at 900℃/170MPa were investigated. At the first creep stage, abnormal creep occured due to the resolution of fine particles, and the deformation initiated from grain boundary areas. It is evident that nearly all of the dislocations were in γ matrix channels in form of dislocation pairs and the dislocations were impeded at γ/γ′ interfaces, thus the dislocation networks developed deformation. At the steady creep stage, impeded dislocations at γ /γ′ interfaces climbed over γ′ phases by diffusion-dominant mechanism.At the last creep stage, voids were formed around carbides at grain boundary which leaded to accumulated damage and caused creep rate accelerated. With the dislocation networks being broken, the voids connected and grew into micro-cracks gradually.Finally the cracks propagated along grain boundary area and resulted in failure. 相似文献
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《Acta Materialia》2008,56(16):4402-4416
A simplified model is proposed to quantify the effect of damage in the form of particle cracking on the elastic and plastic behaviour of particle-reinforced metal matrix composites under uniaxial tensile loading: cracked particles are simply replaced, in a mean-field model, with as much matrix. Pure aluminium reinforced with 44 vol.% alumina particles, tested in tension and unloaded at periodic plastic deformations, is analysed by neutron diffraction during each reloading elastic step, at 30%, 50%, 70% and 90% of the tensile flow stress. The data give the evolution of the elastic matrix strains in the composite and also measure the progress of internal damage by particle cracking. The test gives (i) the evolution of the in situ matrix flow stress, and (ii) the evolution of load partitioning during elastic deformation with increasing composite damage. Predictions of the present model compare favourably with relevant results in the literature, and with results from the present neutron diffraction experiments. 相似文献
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王学滨 《中国有色金属学会会刊》2009,19(5):1280-1285
A method for calculating the evolution of the local damage variable at the adiabatic shear band (ASB) center was proposed. In the present method, the JOHNSON-COOK model and the nonlocal theory were adopted, and the damage variable formula applicable for the bilinear (linearly elastic and strain-softening) constitutive relation was further generalized to consider the plastic deformation occurring in the strain-hardening stage. Aiming at Ti-6Al-4V, the effect of strain rate on the evolution of the local damage variable at the ASB center was investigated. In addition, a parametric study was carried out, including the effects of strain-hardening exponent, strain rate sensitive coefficient, thermal-softening exponent, static shear strength, strain-hardening modulus, shear elastic modulus, work to heat conversion factor, melting temperature and initial temperature. The damage extent at the ASB center in the radial collapse experiment was assessed. It is found that at higher strain rates the damage in the ASB becomes more serious at the same average plastic shear strain of the ASB. 相似文献
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采用光滑和缺口拉伸试样进行不同温度(950、1050和1150 ℃)和不同应变速率(0.5、1.0和5.0 s-1)的高温拉伸试验,研究了40CrNiMo钢在高温拉伸时的力学性能变化、微观组织演变以及塑性损伤形成机理,分析了不同应力三轴度对高温塑性损伤的影响。结果表明,提高变形温度或降低应变速率会降低峰值应力;应变速率从0.5 s-1增大至5 s-1,晶粒大小不均匀程度增加,材料更容易产生塑性损伤;变形温度从950 ℃提高到1150 ℃,晶粒尺寸增大近3倍;损伤经历形核、长大并形成微裂纹3个步骤,应力三轴度与缺口半径成负相关关系,应力三轴度的增大会加剧塑性损伤的发生,使得拉伸试件的断裂应变值降低。在车轴实际轧制过程中,在保证一定生产效率的前提下,可以通过尽可能减小楔横轧模具的成形角,并适当增大展宽角的方法,来降低材料塑性变形时内部各处的动态应力三轴度值,降低损伤发生的概率。 相似文献
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Kerim Isik Gregory Gerstein Thomas Schneider Robert Schulte Daniel Rosenbusch Till Clausmeyer Florian Nürnberger Milan Vucetic Sergej Koch Sven Hübner Bernd-Arno Behrens A. Erman Tekkaya Marion Merklein 《Production Engineering》2016,10(1):5-15
Sheet-bulk metal forming processes combine conventional sheet forming processes with bulk forming of sheet semi-finished parts. In these processes the sheets undergo complex forming histories. Due to in- and out-of-plane material flow and large accumulated plastic strains, the conventional failure prediction methods for sheet metal forming such as forming limit curve fall short. As a remedy, damage models can be applied to model damage evolution during those processes. In this study, damage evolution during the production of two different toothed components from DC04 steel is investigated. In both setups, a deep drawn cup is upset to form a circumferential gearing. However, the two final products have different dimensions and forming histories. Due to combined deep drawing and upsetting processes, the material flow on the cup walls is three-dimensional and non-proportional. In this study, the numerical and experimental investigations for those parts are presented and compared. Damage evolution in the process chains is simulated with a Lemaitre damage criterion. Microstructural analysis by scanning electron microscopy is performed in the regions with high mechanical loading. It is observed that the evolution of voids in terms of void volume fraction is strongly dependent on the deformation path. The comparison of simulation results with microstructural data shows that the void volume fraction decreases in the upsetting stage after an initial increase in the drawing stage. Moreover, the concurrent numerical and microstructural analysis provides evidence that the void volume fraction decreases during compression in sheet-bulk metal forming. 相似文献
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In this paper, a blanking process of sheet metal is studied by the methods of numerical simulation and experimental observation. The effects of varying technological parameters related to the quality of products are investigated. An elastoplastic constitutive equation accounting for isotropic ductile damage is implemented into the finite element code ABAQUS with a user-defined material subroutine UMAT. The simulations of the damage evolution and ductile fracture in a sheet metal blanking process have been carried out by the FEM. In order to guarantee computation accuracy and avoid numerical divergence during large plastic deformation, a specified remeshing technique is successively applied when severe element distortion occurs. In the simulation, the evolutions of damage at different stage of the blanking process have been evaluated and the distributions of damage obtained from simulation are in proper agreement with the experimental results. 相似文献
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This paper examines the efficiency and capability of Dynet, a recurrent neural network model for the prediction of the damage evolution during hot non-uniform, non-isothermal forging on the basis of a limited number of damage snapshots during the process. A Bayesian algorithm is introduced to optimise the hyperparameters related to the noise level and weight decay. In order to examine the capability of the model to capture the underlying trends when presented with sparse and noisy evidence, a synthetic relation between damage accumulation in a metal matrix composite and strain, strain rate and deformation temperature has been used to generate training data (evidence) of varying accuracy and sparseness. The results show that the Bayesian algorithm performs very well, and that no significant overfitting is observed. In addition, this algorithm not only gives the expectation value of damage level, but also an estimate of its uncertainty. 相似文献