Prediction of ductile fracture induced by contraction twinning in AZ31 sheet subjected to uniaxial and biaxial stretching modes
Prediction of ductile fracture induced by contraction twinning in AZ31 sheet subjected to uniaxial and biaxial stretching modes
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DOI：
10.1016/j.ijplas.2016.05.004
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发表时间：
2016-09
影响因子：
9.8
通讯作者：
Kengo Yoshida
中科院分区：
文献类型：
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作者：
Kengo Yoshida
对AZ31镁合金板材进行了单轴拉伸、平面应变拉伸和等双轴拉伸的成形性能试验研究。单轴拉伸时，试样的极限应变是合理的，但在双轴拉伸模式下，试样的极限应变急剧降低。全场应变分析和断口观察表明，试样断裂时没有形成明显的局部颈缩。为了使用基于晶体塑性的有限元方法预测断裂行为，开发了平均场模型来解决母晶和孪晶之间的机械相互作用。通过引入断裂准则作为收缩孪晶区内累积滑移的函数，模拟了试样的失稳。模拟结果表明，在双向拉伸模式下，材料的应变不均匀性很强，而在单向拉伸模式下，由于棱柱滑移的激活，材料的应变不均匀性明显降低，从而使材料的应变分布趋于均匀。收缩孪晶成核在较小的应变水平在双轴拉伸模式，和过早失效的预测在双轴拉伸模式作为结果的积累在孪晶区域的滑移。参数研究表明，即使当孪晶的体积分数很小，他们有一个显着的影响AZ31板材的塑性。
The formability of AZ31 sheets was experimentally measured for uniaxial tension, plane strain stretching, and equi-biaxial stretching modes. The limit strain of the specimen was reasonable under uniaxial tension but was drastically reduced in the biaxial stretching modes. Full-field strain analysis and the observation of the fracture surface revealed that the specimen fractured without the formation of a visible local necking. To predict the fracture behavior using a crystal plasticity-based finite element method, a mean field model was developed to solve the mechanical interplay between the parent and twins. The destabilization of the specimen was simulated by introducing fracture criteria as functions of the accumulated slip inside the contraction twin region. Simulations revealed that strong strain heterogeneity forms in the case of the biaxial stretching modes, and this heterogeneity is apparently reduced under uniaxial tension as a result of the activation of prismatic slip, which produces a uniform strain distribution. Contraction twins nucleate at smaller strain levels in the biaxial stretching modes, and premature failure is predicted in the biaxial stretching modes as a result of the accumulation of slip in the twinned regions. Parametric studies show that even when the volume fraction of twins is small, they have a significant impact on the ductility of AZ31 sheets.