Establishing a quantitative relationship between strain gradient and hetero-deformation-induced stress in gradient-structured metals
Establishing a quantitative relationship between strain gradient and hetero-deformation-induced stress in gradient-structured metals
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DOI：
10.1007/s00707-021-03141-y
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发表时间：
2022-02
期刊：
影响因子：
2.7
通讯作者：
Rui-Ning Yuan
中科院分区：
文献类型：
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作者：
Rui-Ning Yuan
最近的实验证据表明，异质变形诱导（HDI）应力并不随应变梯度的增加而线性增加，这与传统的应变梯度塑性理论相矛盾。为了解决这种差异，应变梯度塑性公式修改在这项研究中，考虑到饱和的几何必要的位错（GND）积累由于Frank-Read源的形成和失活之间的动态平衡。将该模型纳入晶体塑性有限元框架，沿着建立了两种分析模型，分别考虑了统计存储位错和几何必需位错，探讨了单辊角轧梯度结构Cu材料变形机制与力学行为之间的内在关系.据透露，样品级GND密度大大有助于总GND密度GS铜，引起显着的HDI强化和加工硬化。此外，晶粒尺寸的减小导致应变梯度强度的增加和样品级GNDs的饱和密度的降低，导致更高的初始增加速率和样品级GND密度随着应变的增加而更早地减慢。它还导致GND密度梯度的增加，从而在样品水平上产生更高的HDI应力。最后，通过修正的应变梯度塑性公式，可以建立应变梯度和HDI应力之间的定量关系，该公式能够捕获具有非均匀微观结构的多晶金属的尺度相关的力学响应。
Recent experimental evidence suggests that hetero-deformation-induced (HDI) stress does not increase linearly with an increasing strain gradient, which contradicts conventional strain gradient plasticity theory. To resolve this discrepancy, a strain gradient plasticity formulation is modified in this study, taking into account the saturation of geometrically necessary dislocation (GND) accumulation due to the dynamic equilibrium between Frank–Read source formation and deactivation. It is incorporated into a crystal plasticity finite element framework, along with two analytical models accounting for the development of statistically stored and geometrically necessary dislocations at grain level, respectively, to explore the underlying relationship between deformation mechanisms and mechanical behaviors of a gradient-structured (GS) Cu material processed via single-roll angular-rolling under deformation. It is revealed that sample-level GND density contributes substantially to the total GND density in GS Cu, giving rise to significant HDI strengthening and work hardening. Furthermore, a decrease in grain size leads to an increase in strain gradient intensity and a decrease in the saturation density of GNDs at sample level, resulting in a higher initial increase rate and an earlier slowdown of sample-level GND density with increasing strain. It also leads to an increase in GND density gradient, giving rise to higher HDI stress at the sample level. Last but not least, a quantitative relationship between strain gradient and HDI stress can be established via the modified strain gradient plasticity formulation, which is capable of capturing scale-dependent mechanical responses of polycrystalline metals with heterogeneous microstructures.