Strain-induced damage of metals under large plastic deformation: Theoretical framework and experiments
Strain-induced damage of metals under large plastic deformation: Theoretical framework and experiments
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DOI：
10.1016/j.ijplas.2014.03.011
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发表时间：
2014-08
影响因子：
9.8
通讯作者：
N. Tutyshkin;W. Müller;R. Wille;M. Zapara
中科院分区：
文献类型：
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作者：
N. Tutyshkin;W. Müller;R. Wille;M. Zapara
基于孔洞长大和孔洞形状变化的细观力学概念，给出了金属塑性损伤的耗散势和本构方程。度规变换张量的乘法分解和本构方程的热力学表述导致了对称的二阶损伤张量，这是有物理意义的。它的第一个不变量定义了与由于空洞增长而导致的材料的塑性膨胀有关的损伤。偏差张量的第二个不变量解释了与空洞形状变化相关的损伤。两个物理激励的归一化措施使我们能够表示应变引起的损伤的动力学过程，包括空洞合并和延性断裂开始的极限条件。给出了等效损伤度量与已知准则之间的关系。对DC01钢、铝镁合金AlMg3和纯铜三种延性金属进行了单轴拉伸和镦粗试验，确定了损伤的演化规律。用扫描电子显微镜分析了孔洞的分布、长大和形状变化。揭示了损伤增长和愈合动力学的平衡点。结果表明，如果应变在该平衡点之前没有达到极限值，则材料的进一步压缩伴随着负应力三轴性对缺陷闭合和愈合的影响，从而防止断裂。应变损伤张量框架及其热力学一致性数学模型可用于分析材料承受大塑性变形和非比例加载路径的金属成形过程。
Based on a micromechanical concept of the void growth and a change in the void shape the dissipation potential and constitutive equations for ductile damage of metals are presented. Multiplicative decomposition of the metric transformation tensor and thermodynamic formulation of the constitutive equations lead to a symmetric second order tensor of damage which is physically meaningful. Its first invariant defines the damage related to plastic dilatation of the material due to the void growth. The second invariant of the deviatoric tensor accounts for the damage associated with a change in the void shape. Two physically motivated normalized measures allow us to represent the kinetic process of strain-induced damage including the limit conditions for the onset of void coalescence and ductile fracture. A relation of the equivalent damage measure to the well-known criteria is shown. The evolution of damage is experimentally determined in uniaxial tensile and upsetting tests for three ductile metals: steel DC01, aluminum–magnesium alloy AlMg3and pure copper. Void distribution, growth and changes in shapes are analyzed using scanning electron microscopy. The equilibrium point for the kinetics of damage growth and healing is revealed. It is shown that if the strain does not reach the limit value prior to that equilibrium point then the further compression of the material is accompanied by the growing effect of negative stress triaxiality on closure and healing of defects which prevents the fracture. A tensorial framework for strain-induced damage and its thermodynamically consistent mathematical models can be applied to the analysis of metal forming processes in which materials are subjected to large plastic deformations and non-proportional loading paths.