中文摘要：

以正五棱柱颗粒体系加卸载的光弹试验为基础，通过条纹解析量化了特征颗粒所受接触力，揭示了卸载过程中接触力的演化特征．结果表明：卸载阶段浅层颗粒问基本无残留接触力，而深层颗粒间存在显著接触力残留；最后一级荷载为临界荷载．采用离散元模拟重现了光弹试验，数值模拟所得接触力链、残留接触力及颗粒位移与光弹试验一致，从而验证了数值模拟的有效性．基于数值模型分析了加卸载阶段颗粒体系的应力演化，得出应力与接触力链、残留应力与残留接触力的空间分布均一致．

英文摘要：

Contact forces acted on representative pentagons were achieved through fringe analysis based on the photoelastic experiment of pentagons subject to loading and unloading. The evolution of contact forces reveal that residual contact force lies remarkably in contacts between deep-buried pentagons while barely in contacts between superficial pentagons during unloading. Photo-elastic experiment was reproduced via discrete element simulation, and the comparison of both inter-particle contact force between photo- elastic test and numerical test demonstrates that the numerical model is reasonable. Besides, the stress evolution of pentagon packings during loading and unloading was studied. The results indicate that the spatial distributions of stress and force chain, residual stress and residual contact force are consistent.