摘要
The constitutive behavior of microcrystals remains mysterious since very little,or no information regarding plastic deformation in the measured stress-strain curve is available due to plastic instability.Furthermore,the measured stress-strain curves vary greatly under different control modes,while constitutive behavior should remain unaffected by test methods.Beyond these reasons,probing the real constitutive behavior of microcrystals has long been a challenge because the nonlinear dynamical behaviors of micromechanical testing systems are unclear.Here,we perform and carefully analyze the experiments on singlecrystal aluminum micropillars under displacement control and load control.To interpret these experimental results,a lumpedparameter physical model based on the principle of micromechanical testing is developed,which can directly relate nonlinear dynamics of the micromechanical testing system to the constitutive behavior of microcrystals.This reveals that some stages of the measured stress-strain curve attributed to the control algorithm are not related to constitutive behavior.By solving the nonlinear dynamics of the micromechanical testing system,intense plastic instability(large strain burst)starting from the equilibrium state is attributed to the strain-softening stage of microcrystals.Parametric studies are also performed to reduce the influence of plastic instability on the measured responses.This study provides critical insights for developing various constitutive models and designing a reliable micromechanical testing system.
由于塑性失稳导致的应力-应变测量曲线中塑性变形信息的缺失,使得微晶本构行为仍然很神秘.此外,应力-应变测量曲线在不同控制模式下的测量结果变化很大,而本构行为不应受测量方法的影响.此外,由于微观力学测试系统的非线性动力学行为尚不清楚,微晶真实本构行为的探究一直是一个挑战.本文在位移控制和负载控制下对单晶铝微柱进行了详细的实验和分析.为了解释实验结果,文章基于微观力学测试原理开发了一个聚合参数物理模型,该模型可直接将微观力学测试系统的非线性动力学与微晶的本构行为联系起来.这表明应力-应变测量曲线的某些阶段由控制算法产生,与本构行为无关.通过求解微观力学测试系统的非线性动力学,从平衡态开始的强塑性不稳定性(大应变爆发)归因于微晶的应变软化阶段.文章还进行参数研究以减少塑性失稳对测量响应的影响.本研究为开发各种本构模型和设计可靠的微观力学试验提供了重要的见解.
基金
supported by the National Natural Science Foundation of China(Grant Nos.51731009,12102216,and 11972205)
the Fundamental Research Funds for the Central Universities(Grant No.2020XZZX005-02)
the China Postdoctoral Science Foundation(Grant Nos.2021M691796,and 2021T140379).
