位错热激活滑移的数值模拟

SIMULATION OF THERMALLY ACTIVATED DISLOCATION SLIP

在三维离散位错动力学模型中,用Langevin力描述温度对位错的影响作用,模拟了位错克服晶格Peierls应力与阻尼应力的滑移过程.模拟结果表明,位错克服Peierls应力的热激活效应随温度的升高而增大,随应变率的增高而减小.利用热激活本构模型描述了位错热激活滑移过程,拟合了Peierls应力的激活能,结果表明含温度的离散位错动力学模型能较正确地模拟位错的热激活滑移过程.但Peierls阻碍的非离散化处理使激活能与指前因子均随温度升高而增大,这表明离散位错动力学模型模拟Peierls阻碍存在不足之处,其本质原因是介观级的位错动力学模型目前还无法正确模拟微观级的位错芯性质.

Using the Langevin force to describe the effect of temperature on the dislocation behavior, the slip of dislocation overcoming the Peierls stress and drag stress is simulated by the three-dimensional discrete dislocation dynamics model. Numerical results indicate that the thermally activated effect of dislocation overcoming the Peierls stress increases with temperature increasing, and decreases with strain rate increasing. Finally, using the thermally activated constitutive model to describe the thermally activated slip of dislocation, the activation energy of Peierls stress is obtained by fitting simulation data. The results show that the discrete dislocation dynamics model,which contains the temperature effect, can correctly simulate the thermally activated slip of dislocation. But the non-discrete slip of dislocation makes the activation energy and the pre-exponential factor increase with temperature increasing, which indicates a shortcoming exists in the present discrete dislocation dynamics model for simulating the slip of dislocation overcoming the Peierls stress. The essential reason is that the microscopic property of the dislocation core can not be simulated precisely in the present mesoscale dislocation dynamics model.