医疗植入器械等微型产品的广泛应用和微成形技术的快速发展对金属板料在不同尺度下塑性变形行为更为精确的描述提出了新的要求。由于尺度效应的存在，不同尺度下材料屈服行为和强化规律存在差异，宏观尺度下的塑性变形知识无法完全适用于微塑性成形过程。同时，由于缺乏对多尺度下材料屈服强化特性的全面认知以及现有屈服准则和强化模型在微尺度下有效性的研究，使得微成形技术离批量化和精确化生产还有一定的差距。本项目将通过十字形试件双向加载实验和有限元方法系统研究不锈钢薄板在不同尺度下的屈服行为和强化规律，探讨几何尺寸、晶粒大小和材料微观组织对薄板屈服轨迹和强化特性的影响，并验证和评估现有屈服准则和强化模型在微塑性变形过程中的适用性及有效性。基于尺度效应和材料微观组织演变对屈服强化特性的影响规律，提出适合描述金属薄板微塑性变形的屈服准则和强化模型，并通过微充液拉深工艺实验验证所建立的微尺度屈服准则和强化模型的有效性。

With the ubiquitous trend of product miniaturization and rapid development of microforming technology, a demand for the precision description of multi-scale deformation behavior of sheet metal increases urgently. Due to the size effect with miniaturization, the material yielding behavior and hardening law may be different under multi-scale, meanwhile, the knowledge of macroscopic plastic deformation can not be completely applicable to micro-scaled plastic forming process. In addition, the multi-scale yielding and hardening behaviors and the validity of existing yield criteria and hardening models have not yet been systematically explored and studied, which would cripple the wide applications of microforming technology in production of microparts. In this project, the yielding behavior and hardening law of sheet metal in multi-scale plastic deformation process will be systematically explored and how different geometry and grain size effects, material microstructure evolution affect them will be also extensively explored via multiaxial loading experiment and finite element method. The validity of yield criteria and hardening models, which are widely used in macro-scale forming, will be evaluated under different workpiece geometry and grain size scenarios. By employing the outcome of size affected yielding and hardening characteristics, the yield criterion and hardening model, which are suitable for describing micro-scaled plastic deformation of sheet metal will be established, Through the micro hydrodynamic deep drawing (MHDD) of a semicircle micropart, the developed knowledge of yielding and hardening behaviors and the determined criteria will be verified and validated. The project will thus focus on (a) Geometry and grain size effects on yielding behavior and hardening law of sheet metal; (b) Validity of existing yield criteria and hardening models under micro-scale plastic deformation; (c) Case study and verification of the developed knowledge.