Abstract The metals with gradient nanostructures possess exceptionally superior mechanical properties. Here, the gradient-nanotwinned 304 stainless steel wires are fabricated by surface mechanical attrition treatment (SMAT) with a range of process time. The quasi-static tensile tests and dynamic compressive tests are conducted to examine the constitutive response of gradient-nanotwinned 304 stainless steels under different loadings. The experimental measurements show that under static and dynamic loadings, their mechanical properties are closely related to the SMAT process time. With an increase in the process time, their yield strength is improved, while their ductility is weakened. Furthermore, a theoretical model is proposed to describe the static and dynamic constitutive relation of gradient nanotwinned 304 stainless steels. The micromechanical model of nanotwinned composite is developed to characterize the constitutive relation of the material with nanograins embedded in nanotwinned matrix in depth. For the constitutive relations of each phase in nanotwinned composite structure, the athermal behaviors of dislocations are only considered in describing the flow stress under the static loadings. The size-dependent athermal flow stress and rate-dependent thermal flow stress are both involved under the dynamic loadings. The theoretical simulations demonstrated that the mechanical response of gradient-nanotwinned 304 stainless steels under different loadings can be successfully characterized by the presented model. A good agreement is obtained between the numerical results and experimental measurements. Furthermore, the mechanical properties of gradient-nanotwinned 304 stainless steels are forecasted for the various distribution of twin spacing along the depth. The results in this work are helpful for optimizing the static and dynamic mechanical performance of the gradient-nanostructured metallic materials through controlling microstructural size and distribution.

中文翻译：

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具有复合结构的梯度纳米孪晶不锈钢的静态和动态力学行为：实验和建模

摘要 具有梯度纳米结构的金属具有异常优异的机械性能。在这里，梯度纳米孪晶 304 不锈钢线是通过表面机械磨损处理 (SMAT) 和一系列工艺时间制造的。进行了准静态拉伸试验和动态压缩试验，以检验梯度纳米孪晶 304 不锈钢在不同载荷下的本构响应。实验测量表明，在静态和动态载荷下，它们的机械性能与 SMAT 工艺时间密切相关。随着加工时间的增加，它们的屈服强度提高，而它们的延展性减弱。此外，提出了一个理论模型来描述梯度纳米孪晶304不锈钢的静态和动态本构关系。开发了纳米孪晶复合材料的微观力学模型，以表征材料与纳米颗粒深度嵌入纳米孪晶基体的本构关系。对于纳米孪晶复合结构中各相的本构关系，在描述静载荷下的流动应力时只考虑了位错的非热行为。动态载荷下涉及尺寸相关的非热流应力和速率相关的热流应力。理论模拟表明，梯度纳米孪晶 304 不锈钢在不同载荷下的机械响应可以通过所提出的模型成功表征。在数值结果和实验测量之间获得了很好的一致性。此外，梯度纳米孪晶 304 不锈钢的力学性能预测为孪晶间距沿深度的不同分布。这项工作的结果有助于通过控制微观结构尺寸和分布来优化梯度纳米结构金属材料的静态和动态机械性能。