Twinning effects in a polycrystalline magnesium alloy under cyclic deformation
Twinning effects in a polycrystalline magnesium alloy under cyclic deformation
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DOI：
10.1016/j.actamat.2013.09.048
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发表时间：
2014
期刊：
影响因子：
9.4
通讯作者：
C. Gu;L. Toth;M. Hoffman
中科院分区：
文献类型：
--
作者：
C. Gu;L. Toth;M. Hoffman
摘要采用Taylor-Lin多晶弹粘塑性本构模型模拟了强基面织构镁合金AZ 31的室温疲劳行为。在压缩-压缩循环模式中，尽管在应力-应变循环曲线中没有发生应变硬化，但显示出广泛的{1 0 1 <$2}拉伸孪晶。使用体积转移方案，模拟孪生，其中孪生变体被预定义为晶粒。通过采用最小弹性能准则选择两个能量最小的孪晶变体，将部分体积的母晶粒转移到孪晶中。通过将孪晶的部分体积转移回母晶，模拟了大量的退孪晶。建模方法导致公平的协议与电子背散射衍射测量的实验双活性。该模型很好地再现了由于孪生而引起的织构变化。此外，在加载和卸载（残余）状态下的多晶中的应力分布进行了检查，分别为母亲和双晶粒人口。结果表明，孪晶中存在较大的残余应力，其分布与母晶中的残余应力有很大的差异。这种偏差是由孪晶的不同取向和晶体塑性自然获得的运动硬化引起的。晶体塑性诱导的随动硬化为多晶镁合金低周疲劳中观察到的大的Bauchinger效应提供了一个很好的解释。
Abstract The Taylor–Lin polycrystal elasto-viscoplastic model was employed to simulate the fatigue behavior of a strong basal textured Mg alloy (AZ31) at room temperature. Extensive {1 0 1¯ 2} tensile twinning in a compression–compression cycling mode was shown though no strain hardening occurred in the stress–strain cyclic curves. Using a volume transfer scheme, twinning was simulated where the twin variants were predefined as grains. Parts of the volumes of the mother grains were transferred to the twins by employing the minimum elastic energy criterion for selecting the two least-energy twin variants. Massive detwinning was shown by simulating through transferring parts of the volumes of the twins back to the mother grains. The modeling approach led to fair agreement with experimental twin activity measured by electron backscatter diffraction. The texture changes due to twinning were well reproduced by the model. Additionally, the stress distribution was examined in the polycrystal in the loaded and unloaded (residual) states, separately for the mother and twin grain populations. It has been found that the twins had large residual stresses which deviated in sign and distribution considerably from the residual stresses in the mother grains. This deviation is caused by the different orientations of the twins and the kinematic hardening obtained naturally with crystal plasticity. The crystal plasticity-induced kinematic hardening offers a good interpretation of the large Bauchinger effect observed in low cyclic fatigue of polycrystalline magnesium alloys.