金属粉末压制中多尺度力学特征不均匀性模拟研究

Simulation Study of the Inhomogeneity Characteristics of Multiscale Mechanics during Metal Powder Compaction

针对金属粉末压制过程实际研究的复杂性,基于颗粒物质理论及离散元法进行压制过程的数值模拟,特别是结合宏观应力、细观力链及微观接触力各尺度力学特征量化提取分析方法,通过接触力基尼指数与参与指数、力链强度不均匀度参数、局部应力不均匀度参数对不同颗粒、侧壁摩擦因数工况下的多尺度力学特征不均匀性进行量化分析,同时探讨多尺度力学特征空间不均匀分布演化。多尺度模拟研究表明:随压制进行,各尺度力学特征不均匀性均逐渐降低;而随侧壁及颗粒间摩擦因数增加,各尺度力学特征不均匀性逐渐增加。其中在宏观力学尺度上,侧壁、颗粒间摩擦因数对不均匀性影响均较为显著,而在细观、微观力学尺度上,颗粒间摩擦因数较侧壁摩擦因数对不均匀性影响更显著;各尺度力学特征空间分布亦逐渐向均匀化发展且保持各尺度一致对应性。研究对于粉体成形力学的丰富及致密化行为解释,以及压坯致密化程度与成形质量提升具有理论铺垫及实际指导意义。

In view of the complexity of practical research on the process of metal powder compaction,the simulation of the process of metal powder compaction is realized based on the theory of granular matter and the discrete element method.In particular,combined with the quantitative extraction and analysis methods of mechanical characteristics of stress at macroscopic scale,force chain at microscopic scale and contact force at microscopic scale,the Gini coefficient and participation number of contact force,the force chain strength inhomogeneity parameter,and the local stress inhomogeneity parameter have been used to analyze the inhomogeneity characteristics of multiscale mechanics quantitatively under the conditions of the different side wall friction coefficients and the friction coefficients between particles.The evolution of spatial inhomogeneous distribution of multiscale mechanical characteristics is also discussed.The multiscale simulation results show that the inhomogeneity of multiscale mechanical characteristics all decreases gradually during the process of powder compaction.With the increase of side wall friction coefficient and the friction coefficient between particles,the inhomogeneity of multiscale mechanical characteristics all increases gradually.At macroscopic mechanical scale,the side wall friction coefficient and the friction coefficient between particles both have significant effects on inhomogeneity.But at mesoscopic and microscopic mechanical scales,the friction coefficient between particles has more significant effects on inhomogeneity than the side wall friction coefficient.The spatial distribution of multiscale mechanical characteristics also tends to be homogenized gradually and keeps consistent at different mechanical scales.The works can provide theoretical basis and practical guiding for expanding the powder forming mechanics and the explanation of densification behavior of powder,as well as improving the densification level and the forming quality of green compacts.