金属材料在人类生活中扮演着不可或缺的角色，然而，它们在强度和韧性之间一直存在着固有的矛盾关系。如何克服这一瓶颈，实现金属材料强度和韧性的协同提升，成为材料领域的一个关键科学问题。因此，本文采用有限元数值模拟和实验两种方法，以深入研究微观结构与力学性能之间的密切关系，并探索能够实现材料力学性能综合提升的微观结构设计。

在有限元数值模拟方面，基于GTN本构模型，采用数学上的平面密铺方案构建了二维Cu/Ni层状结构和砖砌结构复合模型，通过精确控制模型微观几何结构、组分分布和相体积分数特性，并通过数值模拟进行了单轴拉伸和双轴拉伸的分析。研究结果显示，在层状结构中，沿着硬相带方向进行单轴拉伸时，以三角形单密铺模型为代表的结构表现出以拉伸为主导的变形。以三角形密铺模型为代表的砖砌结构发生以弯曲和拉伸（压缩）组合的变形，有助于改善材料的韧性，并同时避免了强度的显著下降。另外，随着硬质相体积分数的增加，材料的整体强度增加，但韧性降低。在双轴拉伸条件下，砖砌结构的四边形密铺方案展现出较好的整体强韧性。本文通过分析复合材料的微观结构和力学性能，为设计和优化复合材料结构提供了重要的指导。

在实验方面，本文提出了一种简单、快速的感应加热淬火方法来制备S38C钢的表面梯度结构，并揭示了其力学行为与失效机理。通过电子背散射衍射技术，对梯度结构从表面到内部的微观结构变化进行了表征，同时进行小尺寸试样的拉伸试验以验证梯度结构在不同深度下的拉伸变形行为。实验结果显示，感应加热产生的表面梯度结构显著提高了表面和亚表面区域的硬度和抗拉强度。此外，通过能量色散光谱、透射菊池衍射和透射电子显微镜对裂纹起始区域进行了详细表征，研究了梯度结构的疲劳裂纹起始机理。这些研究结果显示，梯度结构的强化效果有助于提高S38C钢的抗拉强度和疲劳性能。

Metals play an indispensable role in human life. However, they have long been plagued by an inherent trade-off between strength and toughness. Overcoming this bottleneck to achieve a synergistic enhancement of both strength and toughness in metal materials has become a pivotal scientific challenge in the field of materials science. Therefore, this study employs both finite element numerical simulations and experimental approaches to deeply investigate the intricate relationship between microstructures and mechanical properties. It also explores microstructure design strategies that can comprehensively enhance the mechanical performance of materials.

In the realm of finite element numerical simulations, two-dimensional composite of Cu/Ni laminated and brick-mortar structures were explored utilizing the GTN constitutive model and mathematical plane tessellation schemes. Uniaxial and biaxial stretching behaviors were analyzed by precisely controlling the model microgeometries and phase volume fraction characteristics, using finite element numerical simulations. The results show that the laminated structure represented by the triangular tessellation models exhibits stretching-dominated deformation when uniaxial stretching is carried out along the direction of the hard phase laminae and shows outstanding strength. The brick-mortar structure represented by the triangular tessellation models undergoes deformation in a combination of bending and stretching (compression), which helps to improve the toughness yet avoid a significant decrease in strength. In addition, as the volume fraction of hard phase increases, the overall strength increases, but the toughness decreases. Under biaxial conditions, the quadrangular tessellation scheme for brick-mortar structures shows better overall strength and toughness. By analysing the microstructure-mechanical properties relationship in a two-phase composites, this study provides guidance for material synthesis through structural patterning.

In the realm of experiments, a straightforward and rapid induction heating and quenching method is proposed to create a surface gradient structure on S38C steel, unveiling its mechanical behavior and fatigue mechanisms. Electron Backscatter Diffraction is utilized to characterize the microstructural variations from the surface to the interior of the gradient structure. Additionally, small-scale tensile tests are conducted to verify the tensile deformation behavior at different depths of the gradient structure. Experimental results demonstrate that the surface gradient structure induced by the induction heating and quenching significantly enhances the hardness and tensile strength of the surface and sub-surface regions. Furthermore, detailed characterizations of the crack initiation region are carried out using Energy Dispersive Spectroscopy, Transmission Kikuchi Diffraction, and Transmission Electron Microscope, elucidating the fatigue crack initiation mechanisms of the gradient structure. These research findings underscore that the strengthening effect of the gradient structure contributes to the improved tensile strength and fatigue performance of S38C steel.