Effect of loading speed on pressure distribution in metal powder pressing based on discrete element method
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摘要: 基于离散元原理，采用三维离散元软件PFC3D模拟冲头加载过程，研究以不同冲头速度撞击金属粉末颗粒所产生的透射波以及对侧壁的压力分布。结果表明，对于离散性介质，冲击加载下的应力波传播不单受到颗粒材质波阻抗的影响，还受到颗粒运动和力链形成的很大影响。通过对比不同冲击加载速度下阴模底部的受力，发现随着冲击速度的提高，透射波的峰值成线性增长；通过均分阴模侧壁的方式得到侧壁不同位置所受的侧压力峰值，发现侧壁所受压力呈波谷式分布，从而分析得到颗粒间力链的传播和分布规律。Abstract: The punch loading process was simulated by three-dimensional discrete element software PFC3D based on discrete element method (DEM), the effects of punch loading speeds on the transmission wave of metal powders generated by the impact and the pressure distribution on the sidewall were investigated. In the results, for the discrete media, the stress wave propagation under impact loading is determined not only by the wave impedance of particle material, but also by the particle motion and force chain formation. By comparing the force on the bottom of female mold in the different loading speeds, it is found that the peak of transmission wave increases linearly with the increase of loading speed. The lateral pressure peak on different positions is obtained by means of the side wall of female mold. It is found that the pressure on the sidewalls is present as the valley-like distribution, and the propagation and distribution of the inter-particle force chains are analyzed.
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Key words:
- discrete element /
- impact loading /
- transmission wave /
- lateral pressure /
- stress wave
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图 3 10 m·s-1冲击速度下模拟颗粒力链生成过程：（a）500步；（b）1500步；（c）2500步；（d）5300步
Figure 3. Simulation process of inter-particle force chains at the impact velocity of 10 m·s-1: (a) 500 steps; (b) 1500 steps; (c) 2500 steps; (d) 3500 steps
图 4 不同冲击加载速度对应的透射波峰值图
Figure 4. Peak value of transmission wave in different impact loading speeds
图 5 透射波峰值与冲击加载速度关系
Figure 5. Relationship of transmission wave and impact loading speed
图 6 不同颗粒填充高度下模壁侧压力随时间变化情况：（a）1#；（b）2#；（c）3#；（d）4#；（e）5#
Figure 6. Relationship of time and lateral pressure on die wall in different particle-filled heights: (a) 1#; (b) 2#; (c) 3#; (d) 4#; (e) 5#
图 7 不同速度下模壁侧压力峰值与颗粒填充高度的关系
Figure 7. Relationship between the peak value of lateral pressure and particle-filled height at different impact loading speeds
表 1 金属粉末冲击加载模拟主要参数
Table 1. Main simulation parameters of metal powder impact loading
密度/(kg·m-3) 颗粒直径/mm 颗粒间摩擦系数 模壁摩擦系数 刚度系数 冲击速度/(m·s-1) 2700 0.15 0.3 0.1 108 10 
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表 2 冲击速度与对应的运行时间
Table 2. Impact speed and corresponding running time
冲模速度/(m·s-1) 5 7 10 14 20 运行总时间/μs 70 50 35 25 17.5
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表 3 不同冲击加载速度和压制时段的透射波振动次数
Table 3. Vibration frequency of transmission wave in different impact loading speeds at different suppression periods
冲击加载速度/(m·s-1) 透射波振动次数 前期 前中期 中期 中后期 后期 5 55 50 34 30 23 7 43 35 17 21 11 10 30 20 14 15 7 14 19 12 12 6 2 20 12 9 2 4 1
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表 4 不同颗粒填充高度下侧压力峰值与冲击加载速度的关系
Table 4. Relationship of impact loading speeds and peak values of lateral pressure on die wall in different particle-filled heights
冲击速度/(m·s-1) 最大压力/(102N) 一层 二层 三层 四层 五层 5 0.52 1.03 1.20 1.52 0.92 7 0.58 1.31 1.20 1.59 1.40 10 0.84 2.12 1.40 2.10 0.70 14 0.86 2.44 2.04 2.44 1.50 20 1.50 3.55 3.60 3.65 2.75
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