共查询到20条相似文献,搜索用时 0 毫秒
1.
2.
In this paper, fully coupled constitutive equations accounting for combined isotropic and kinematic hardening as well as the isotropic ductile damage are implemented into the general purpose finite element code for metal forming simulation. The associated numerical aspects concerning both the local integration of the coupled constitutive equations as well as the global (equilibrium) integration schemes are presented. Various 2D and 3D examples are given in order to show the capability of the proposed numerical methodology to predict the ductile fracture initiation and growth during metal forming processes. 相似文献
3.
X. Teng 《Engineering Fracture Mechanics》2008,75(8):2020-2041
Ductile specimens always exhibit an inclined fracture surface with an angle relative to the loading axis. This paper reports a numerical study on the cup-cone fracture mode in round bar tensile tests and the slant fracture in plane-strain specimens based on continuum damage mechanics. A combined implicit-explicit numerical scheme is first developed within ABAQUS through user defined material subroutines, in which the implicit solver: Standard, and the explicit solver: Explicit, are sequentially used to predict one single damage/fracture process. It is demonstrated that this numerical approach is able to significantly reduce computational cost for the simulation of fracture tests under quasi-static or low-rate loading. Comparison with various tensile tests on 2024-T351 aluminum alloy is made showing good correlations in terms of the load-displacement response and the fracture patterns. However, some differences exist in the prediction of the critical displacement to fracture. 相似文献
4.
5.
针对板料成形中的韧性断裂准则预测成形极限的方法,进行了综述和分析,提出了利用韧性断裂准则能够较好地预测塑性差的板料成形极限,而且还能考虑应变路径的变化.将Cockroft和Latham准则应用到高强度钢板DP590的成形预测中.对高强钢DP590进行了单向拉伸试验,获得了相应的物性参数.同时对该高强钢进行了方盒件成形试验,并进行了相应的有限元模拟.通过对高强钢的极限试验,利用有限元模拟获得了该材料的Cockroft和Latham准则常数.最后利用该常数对方盒件的拉深过程进行了缺陷的预测,模拟结果和试验结果完全吻合.表明韧性断裂准则是可以应用到高强度钢板的成形中的. 相似文献
6.
金属韧性断裂准则的数值模拟和试验研究 总被引:1,自引:1,他引:0
对不同外形的45钢试件进行了拉伸、压缩和扭转等材料试验,对工程中常用的5个韧性断裂准则的适用范围进行了对比研究,并采用Gurson-Tvergaard(GT)多孔材料本构模型对试验过程进行了数值模拟.指出目前使用的断裂准则都不可能对材料在多种变形条件下给出一个固定临界值.根据金属成形工艺特点,综合考虑拉伸型和剪切型2种不同韧性断裂机制,提出一个统一的韧性断裂准则形式.试验和数值计算结果证明了该准则的有效性和普适性,进而利用单向拉伸和扭转试验确定的材料常数合理地预测压缩过程中的韧性断裂现象. 相似文献
7.
8.
The ductile fracture in the simulation of sheet-metal-forming processes is evaluated by the ellipsoidal void model previously proposed by the author. In the present study, the simulation and experiment of the hole expansion test are performed using six types of metals. For an alloy, the relationship between prestrain and hole expansion ratio calculated using the ellipsoidal void configuration and ellipsoidal void shape and that calculated using the ellipsoidal void configuration and circular void shape agree with the relationship obtained experimentally. For a pure metal, the relationship between prestrain and hole expansion ratio calculated using the average void configuration and average void shape agrees with that obtained experimentally. Furthermore, the method of introducing prestrain to an as-rolled sheet is proposed, and the prestrain in this sheet is estimated. 相似文献
9.
M. C. Burstow & I. C. Howard 《Fatigue & Fracture of Engineering Materials & Structures》2000,23(8):691-708
Two-dimensional, plane strain, finite element analyses of strength-mismatched welded joints have been performed using the modified boundary layer formulation. The welds were idealized as two-material joints with the material interface running parallel to the crack, which was embedded in the weld material. The Rousselier ductile damage model was employed within the weld material to simulate crack extension due to the growth and coalescence of microvoids. By analysing models with different levels of material mismatching, weld dimensions and applied T -stress levels, it was possible to analyse the effects of crack tip constraint due to both material mismatching and specimen geometry on the fracture resistance of the weld material.
The results show that material strength overmatching (where the weld material is stronger than the base material) reduces the level of constraint ahead of the crack, which can increase the resistance to fracture of the weld material. Conversely, material strength undermatching increases crack tip constraint, reducing the fracture resistance of the joint. By employing estimates for the crack tip constraint levels, QM , based on the applied load, level of material mismatching and weld region thickness, it has been possible to 'order' the J– resistance curves of overmatched joints by generating a family of J–Q M loci which describe the effects of constraint on the fracture resistance of the weld material. However, it is shown that the Q M -stress parameter is not capable of describing the effect of material strength undermatching on the fracture resistance of a joint, which can be much lower than that obtained from a high-constraint homogeneous specimen of weld material. 相似文献
The results show that material strength overmatching (where the weld material is stronger than the base material) reduces the level of constraint ahead of the crack, which can increase the resistance to fracture of the weld material. Conversely, material strength undermatching increases crack tip constraint, reducing the fracture resistance of the joint. By employing estimates for the crack tip constraint levels, Q
10.
J. ZUO M. A. SUTTON X. DENG 《Fatigue & Fracture of Engineering Materials & Structures》2004,27(3):231-243
Fracture of ductile materials has frequently been observed to result from the nucleation, growth and coalescence of microscopic voids. Experimental and analytical studies have shown that both the stress constraint factor and the effective plastic strain play a significant role in the ductile failure process. Experimental results also suggest that these two parameters are not independent of each other at failure initiation. In this study, a methodology for characterizing the effect of stress constraint Am (which is defined to be the ratio of the mean stress and the effective stress Am=σm/σe ) on ductile failure is proposed. This methodology is based on experimental evidence that shows the effective plastic strain at failure initiation has a one‐to‐one relationship with stress constraint. Numerical analyses based on plane strain and three‐dimensional unit‐cell models have been carried out to investigate failure initiation of the unit cell under different constraint conditions. Results from the numerical studies indicate (a) for each void volume fraction, there exists a local failure locus in terms of mesoscopic quantities, σm and σe, that adequately predict incipient local micro‐void link‐up, (b) the results are fully consistent with a failure criterion that maximizes mesoscopic effective stress for a constant level of stress constraint Am, (c) for high to moderate constraint Am, the link‐up envelope values for σm and σe are consistent with limit load conditions where the critical principal stress σ1c corresponds to the maximum principal stress in the loading history and (d) for low constraint, the link‐up envelope values for σm and σe correspond to link‐up conditions having high levels of plastic strain and a principal stress σ1 that is lower than the maximum value for this loading history. Thus, the results suggest that a two‐parameter ductile fracture criterion is plausible, such as critical crack opening displacement (COD) and stress constraint Am, for predicting the process of stable tearing in materials undergoing ductile void growth during the fracture process. 相似文献
11.
The fracture strain of discontinuously reinforced metal matrix composites (DRMMCs) is studied according to a damage mechanics model proposed by McClintock, with a localized crack propagation hypothesis and particle-related crack initiation mechanism. An estimation equation is proposed. The estimated results are verified with the data available in the literature and those measured on some types of DRMMCs obtained by powder metallurgical techniques. The experimental results show good agreement with the estimation model. 相似文献
12.
13.
《Materials at High Temperatures》2013,30(3):137-141
AbstractThe creep life time of a smooth specimen can be predicted using existing laws for creep deformation and steady state creep rate. When crack growth behaviour is involved, it is necessary to construct a law of creep crack growth rate to predict creep fracture life. Creep fracture life can be measured by integrating the law of creep crack growth rate. One example is the creep crack growth rate, represented by the parameter Q*. In this study, we investigated the applicability of this prediction method to creep fracture remnant life for a cracked specimen. The Ω criterion is proposed to predict creep fracture remnant life for a smooth specimen for creep ductile materials. In this study, the correlation between Q*L derived from the paremeters Q* and Ω is investigated. The correlation between QL* and Ω provided a unified theoretical prediction law of creep fracture remnant life for high-temperature creep-ductile materials in the range from smooth to precracked specimens. 相似文献
14.
15.
16.
针对板件初始毛坯形状计算以及正交异性板的快速有限元分析问题,依据拉深件的UG模型,导出了零件的三角网格数据,并采用几何映射方法得到了用于快速有限元分析的拉深件初始展开毛坯.在此基础上,基于理想变形假设以及Hill’48正交异性屈服准则,给出了用于拉深件成形过程快速分析的一步法数学公式和有限元表达,并在Unigraphics系统中进行了有限元分析的后置处理.此外,对TC1钛板筒型拉深件毛坯初始形状进行了优化,并对成形中拉深件厚向应变分布进行了分析,得到了满意结果. 相似文献
17.
18.
J. W. Cho D. Y. Yang W. J. Chung 《International journal for numerical methods in engineering》2002,53(10):2311-2327
A simplified scheme for considering the thickness stress of shell elements induced by contact is presented which improves the accuracy of sheet metal forming analysis. The yield function formulated on the basis of plane stress conditions is modified to incorporate the effect of transverse normal stress induced by contact forces acting on shell elements and return mapping routine is used to update in‐plane stresses at each time step. The transverse normal stress distributions in the thickness direction are determined using the analytic solution of the cylindrical tube under the internal pressure. As numerical examples, uni‐axial compression, bi‐axial tension and bending tests are treated. The problem of cylindrical cup drawing is also calculated. Each result is compared with the results obtained by the analysis using ABAQUS continuum elements. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
19.
G. Bergman M. Oldenburg 《International journal for numerical methods in engineering》2004,59(9):1167-1186
A thermal model based on explicit time integration is developed and implemented into the explicit finite element code DYNA3D to model simultaneous forming and quenching of thin‐walled structures. A staggered approach is used for coupling the thermal and mechanical analysis, wherein each analysis is performed with different time step sizes. The implementation includes a thermal shell element with linear temperature approximation in the plane and quadratic in the thickness direction, and contact heat transfer. The material behaviour is described by a temperature‐dependent elastic–plastic model with a non‐linear isotropic hardening law. Transformation plasticity is included in the model. Examples are presented to validate and evaluate the proposed model. The model is evaluated by comparison with a one‐sided forming and quenching experiment. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
20.
Jae‐Jun Lee Gyung‐Jin Park 《International journal for numerical methods in engineering》2011,85(2):247-268
In the sheet metal forming process, forming the final desired shape is difficult to obtain due to wrinkling, tearing, failure of material, etc. Various conditions of the forming process should be controlled for the desired shape. These conditions are the velocity of the punch, the friction factor, the blank holding force, the initial shape of the blank and others. Many researchers have conducted studies to predetermine the initial blank shape. The structural optimization technique is one of them. Non‐linear response structural optimization is required because non‐linearities are involved in the analysis of the metal forming process. When the conventional method is utilized, the cost is extremely high due to repeated non‐linear analysis for function and sensitivity calculation. In this paper, the equivalent static loads (ESLs) method is used to determine the blank shape which leads to the final desired shape and reduced wrinkling. The ESLs method is a structural optimization method where non‐linear dynamic loads are transformed into ESLs, and these ESLs are utilized as external loads in linear response optimization. The design is updated in linear response optimization. Non‐linear analysis is performed with the updated design and the process proceeds in a cyclic manner. An optimization formulation is defined for the examples, the formulated problems are solved to verify the proposed method and the results are discussed. Non‐linear analysis is performed using the commercial software LS‐DYNA, NASTRAN is used for calculating the ESLs and linear response optimization, and an interface program for LS‐DYNA and NASTRAN is developed. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献