Damage-coupled FLD of Sheet Metals for Warm Forming and Nonproportional Loading
Damage-coupled FLD of Sheet Metals for Warm Forming and Nonproportional Loading
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DOI：
10.1177/1056789510396331
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发表时间：
2011-01
影响因子：
4.2
通讯作者：
M. Jie;C. Chow;Xin Wu
中科院分区：
文献类型：
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作者：
M. Jie;C. Chow;Xin Wu
提出了一种高温非比例载荷下板料成形极限预测方法。该方法考虑了材料在高温下的应变软化行为。提出了一种基于各向同性损伤耦合声张量的局部颈缩准则，并将其用于确定应变软化材料的成形极限。在热-力学框架下建立了损伤演化方程。将损伤演化方程与局部颈缩准则耦合，导出了成形极限应变的封闭表达式。结合塑性增量理论、损伤演化方程和局部颈缩准则，编制了计算几种非比例加载路径下成形极限应变的计算机程序。通过一系列单轴拉伸试验，测量了450℃高温下AA6061的相关力学性能。材料损伤变量由一系列加载和卸载路径的测量弹性模量确定。根据试验数据，建立了450℃下AA6061的损伤演化方程。将计算的极限应变与不同加载路径下的试验结果进行了比较，结果吻合较好。研究发现，临界损伤值与应力状态和加载路径无关。可以得出结论，应用材料损伤作为局部颈缩的可靠判据，包括非比例加载情况。
A method of forming limit prediction for sheet metals at high temperatures and under nonproportional loading is presented. The method takes into account the strain-softening behaviors of the material at elevated temperatures. A localized necking criterion based on an isotropic damage-coupled acoustic tensor is developed and employed to determine the forming limits of strain-softening materials. The damage evolution equation is developed within the thermo-mechanical framework. A closed-form expression of the forming limit strains is derived by coupling the damage evolution equation into the localized necking criterion. A computer program, incorporating the incremental theory of plasticity, the damage evolution equation and the localized necking criterion, is developed to compute the forming limit strains under several nonproportional loading paths. A series of the uniaxial tensile tests is performed to measure the relevant mechanical properties of AA6061 at the elevated temperature of 450°C. The material damage variables are determined from the measured elastic modulii from a series of loading and unloading paths. The damage evolution equation of AA6061 at 450°C is formulated based on the test data. The computed limit strains are compared with the test results under various loading paths and a good agreement is observed. It is found that the critical damage value is independent on the stress states and loading paths. It may be concluded that the application of the material damage as a reliable criterion of localized necking including the nonproportional loading cases.