单轴压缩下沙柳颗粒致密成型力链特性

Characterization of dense forming force chain of salix granules under uniaxial compression

为研究对沙柳颗粒致密成型过程中的力链特性,在采用PFC2D离散单元法的基础上,分析了强力链长度和数量等随轴向应变的变化。研究结果表明:模型加载使得更多的高应力颗粒相互粘接形成强力链;强力链长度和数量成反比,统计发现最长的力链是由9个颗粒构成的;初始孔隙率对强力链数量和短程力链影响较大。对不同应变时期的强弱力链进行量化处理发现:强力链聚集在轴线附近,对体系稳定发挥了巨大作用;弱力链聚集在模型边壁和底部,对体系的稳定性影响不大。沙柳颗粒单轴压缩过程经历应力强化、应力波动2个时期,选取时间顺序为轴向应变0.91%,1.88%,2.82%,3.75%时对力链的平面分布进行细致分析,力链整体强度依次递增。模型加载过程中随着应变的增大,强弱力链数量均发生变化,最终在模型顶部生成的力链最强、中心层次之、底部最弱。力链网络显示出很强的各向异性,较为集中的竖直方向力链为体系稳定性发挥了巨大作用,力链各个方向的接触个数和法向接触力分布变化证明了此论断。

With the rapid development of the economy, China’s energy demand grows rapidly, and the vigorous deve-lopment of biomass can ease China’s consumption of fossil energy and ensure energy security. In order to investigate the characteristics of force chains during the dense forming of salix particles, this study analyzed the variation of the length and number of strong force chains with axial strain based on the PFC2D discrete unit method. The results showed that the proportion of high-stress particles decreased from 38.9% to 30.9%. On the contrary, the proportion of strong force chain particles increased with the increase of strain from 20.3% to 25.8%, and model loading made more high-stress particles bond with each other to form strong force chains. The length and number of strong force chains were inversely proportional, and the longest force chain was found to be composed of nine particles. Initial porosity had a great influence on the number of strong force chains and short-range force chains. The strong and weak force chains were quantified for different strain periods. The strong force chains gathered near the axis to provide a great effect on the stability of the system, while the weak force chains gathered at the side walls and bottom of the model, which had little effect on the stability of the system. Uniaxial compression process of salix granules underwent two periods of stress intensification and stress fluctuation, and the plane distribution of the force chains was carefully analyzed by selecting the time sequence of axial strain 0.91%, 1.88%, 2.82% and 3.75%, and the strength of the force chains increased in sequence. The number of strong and weak force chains changed as the strain increased during the loading process. The final model generated the strongest force chain at the top, the second strongest at the center and the weakest at the bottom. The number of contacts and the contact force in each interval were counted, and from the statistical diagram of the normal contact force direction, it could be seen that the force chain network showed strong anisotropy, and gradually converge to the maximum main stress y direction. The more concentrated vertical force chains provided a significant contribution to system stability, the number of contacts and the distribution of contact forces in each direction of the force chain proved this assertion, and the results of this study provide the theoretical reference for the quantification of force chains in the forming process of salix granules.