金属玻璃变形局域化和均匀流动的机理分析

Mechanism of Deformation Localization and Homogeneous Flow in Bulk Metallic Glasses

考虑自由体积、热和静水应力等因素对材料变形和破坏的影响,推导了块体金属玻璃(BMG)的三维热力耦合本构模型;此外,引入了临界自由体积浓度的材料破坏准则。将相应本构模型和破坏准则写入LS-DYNA软件的用户自定义材料子程序(UMAT)中,开展了BMG在不同温度和不同应变率条件下的有限元模拟研究,具体分析相关物理参量的演化特性及其所导致的材料宏观表象。分析结果表明:常温条件下,材料内部基体区域和剪切带弱区的变形和破坏特性差异显著,因此BMG常表现为高度局域化的非均匀变形特性;而在过冷液相区温度范围内,基体区域和剪切带弱区的力学行为相似,因此材料呈现均匀流动特征。

A modified coupled thermo-mechanical constitutive model for bulk metallic glasses( BMGs),which is generalized to the multiaxial stress state and considers all the effects of free volume,heat and hydrostatic stress is proposed. Besides,a failure criterion of critical free volume concentration is introduced. The constitutive model and the failure criterion are implemented into the LS-DYNA commercial software through the user material subroutine( UMAT). Then the finite element method simulations of BMGs at different initial material temperatures and strain rates are conducted,and the evolutions of physical parameters and corresponding macroscopic mechanical behavior of material are analyzed. The analysis result shows that the deformation and failure characters in the shear band zones of BMGs are significantly different from those in the matrix at room temperature,and consequently high deformation localization occurs in the material. In the supercooled liquid region,the mechanical behaviors in the shear band zones are similar to those in the matrix,and thus BMGs usually has homogeneous flow characteristics.