摘要
The internal length scale(ILS)is a dominant parameter in strain gradient plasticity(SGP)theories,which helps to successfully explain the size effect of metals at the microscale.However,the ILS is usually introduced into strain gradient frameworks for dimensional consistency and is model-dependent.Even now,its physical meaning,connection with the microstructure of the material,and dependence on the strain level have not been thoroughly elucidated.In the current work,Aifantis'SGP model is reformulated by incorporating a recently proposed power-law relation for strain-dependent ILS.A further extension of Aifantis'SGP model by including the grain size effect is conducted according to the Hall-Petch formulation,and then the predictions are compared with torsion experiments of thin wires.It is revealed that the ILS depends on the sample size and grain size simultaneously;these dependencies are dominated by the dislocation spacing and can be well described through the strain hardenmg exponent.Furthermore,both the original and generalized Aifantis models provide larger estimated values for the ILS than Fleck-Hutchinson's theory.
内禀材料长度是应变梯度塑性理论中最重要的参数,被用于成功地解释了微尺度下金属材料的尺寸效应.内禀材料长度在应变梯度框架中通常扮演着平衡量纲的角色,并且其取值依赖于模型.目前,内禀材料长度物理意义、与材料微观结构的关联以及随变形的演化尚未完全明确.本研究对Aifantis应变梯度塑性模型进行了修正,在其中引入了一个最新提出的幂律形式的内禀材料长度演化关系.在此基础上进一步考虑晶粒尺寸效应,基于Hall-Petch关系对Aifantis应变梯度塑性模型进行了扩展,使用上述修正的模型对细丝扭转的实验结果进行了模拟,研究结果表明,内禀材料长度同时取决于试样尺寸和晶粒尺寸,这些相关性主要由位错间距决定,并可以通过应变硬化指数很好地描述.此外,原始Aifantis模型和修正的Aifantis模型中的内禀材料长度的取值均比Fleck-Hutchinson模型的取值更大.
