Effect of dislocation density-twin interactions on twin growth in AZ31 as revealed by explicit crystal plasticity finite element modeling
Effect of dislocation density-twin interactions on twin growth in AZ31 as revealed by explicit crystal plasticity finite element modeling
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DOI：
10.1016/j.ijplas.2017.09.002
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发表时间：
2017-12-01
影响因子：
9.8
通讯作者：
Knezevic, Marko
中科院分区：
文献类型：
--
作者：
Ardeljan, Milan;Beyerlein, Irene J.;Knezevic, Marko
在这项工作中，我们采用了最近开发的框架内的三维（3D）晶体塑性有限元（CPFE）模型的离散孪晶层的显式建模研究位错密度在孪晶域孪晶增厚的影响。对AZ 31镁合金中{（1）过棒012}< 10（1）过棒1>拉伸孪晶进行了模拟。该模型的孪晶层占的晶体学孪晶矩阵的取向关系和特征孪晶剪切转变应变。作为孪晶的结果的机械场的计算认为，三种类型的孪晶位错密度相互作用已经发生。有一种情况假定膨胀孪晶在其畴内保持与母体相同的位错密度。第二个认为，孪晶膨胀降低了位错密度的孪晶增厚，和最后一个，Basinski效应，假设当孪晶扫描的区域，位错密度纳入孪晶域放大。在建模方法中，根据在预定义的特征孪晶电阻处保持晶粒附近的应力状态的标准来加厚孪晶。计算结果表明，大多数的平均性能，如在整个孪晶中的位错存储的速率，孪晶生长速率，应力场的孪晶晶粒和钻晶晶粒，并在母体中的滑移活动没有显着改变的位错存储在孪晶。结果表明，然而，在孪晶畴的滑移活动的影响。特别是，在位错密度增加的情况下，当孪晶首先从2%增长到5%体积分数时，孪晶畴中的位错密度的速率在低应变下增加。位错密度存储速率的这种初始提升导致新扩展的位错孪晶包含比所有应变水平的其他情况更多的存储位错。另一个有趣的区别是，对于相同的总孪晶体积分数，倾向于一个或两个孪晶;对于增加的位错孪晶或在生长时保持位错密度的孪晶，倾向于形成两个孪晶。对于去除位错密度的孪晶，优选仅一个孪晶。结果表明，在位错密度降低的情况下，导致较低的存储位错和位错存储率，以及较低的锥体滑移活动。(C)2017爱思唯尔有限公司版权所有
In this work, we employ the recently developed framework for the explicit modeling of discrete twin lamellae within a three-dimensional (3D) crystal plasticity finite element (CPFE) model to examine the effects of dislocation densities in the twin domain on twin thickening. Simulations are carried out for {(1) over bar 012}< 10 (1) over bar1 > extension twins in a magnesium AZ31 alloy. The model for the twin lamellae accounts for the crystallographic twin matrix orientation relationship and characteristic twin shear transformation strain. The calculations for the mechanical fields as a result of twinning consider that one of three types of twin-dislocation density interactions have occurred. One case assumes that the expanding twin retains in its domain the same dislocation density as the parent. The second one considers that twin expansion has lowered the dislocation density as the twin thickens, and the last one, the Basinski effect, assumes that when twin sweeps the region, the dislocation density incorporated in the twin domain is amplified. In the modeling approach, the twin is thickened according to a criterion that maintains the stress state in the vicinity of the grain at a pre-defined characteristic twin resistance. The calculations show that most of the averaged properties, such as the rate of dislocation storage in the entire twin grain, the twin growth rate, the stress field in the twinned grain and neigh-boring grains, and the slip activity in the parent matrix are not significantly altered by dislocation storage in the twin. The results indicate that, however, the slip activity in the twinned domain is affected. In particular, in the increased dislocation density case, the rate of dislocation density in the twin domain increases at low strains when the twin is first growing from 2% to 5% volume fraction. This initial boost in the dislocation density storage rate causes the newly expanded dislocation twin to contain more stored dislocations than the other cases for all strain levels. Another interesting difference concerns the preference for one or two twins for the same total twin volume fraction; for the increased dislocation twin or twin that retains the dislocation density as it grows, formation of two twins is favored. For a twin that removes dislocation density, only one twin is preferred. The results imply that in the case with reduced dislocation density leads to lower stored dislocations and dislocation storage rates, and lower pyramidal slip activity. (C) 2017 Elsevier Ltd. All rights reserved.