中文摘要：

颗粒体系是典型的多体相互作用体系,具有多重的能量亚稳态.对于准静态颗粒体系,引入构型颗粒温度T_c描述弹性势能涨落.本文认为平衡的体系具有一定的构型颗粒温度T_a,其量值反映了其结构特征.当外界扰动激发的构型颗粒温度超出T_a时,产生不可逆过程.通过对应力松弛过程的分析,发现（T_c-T_a）激发了弹性弛豫,且（T_c-T_a）越大则松弛过程中应力变化越大,最终构型颗粒温度T_c→T_a时,宏观应力松弛结束,体系达到新的能量亚稳态.

英文摘要：

The granular system has complicated force chain network and multiple relaxation mechanisms.The different relaxation mechanisms have largely effects on others.The force chains divide the whole system into many soft zones which dominate the main dissipation process.The system evolves into lower potential energy state gradually and forms directional arrangement under an external load.During the evolution,the complex relaxation behaviors such as transport and migrant processes,make it difficult to distinguish different dissipated mechanisms.Each single physical mechanism stripping from multiple mechanisms should be studied in depth.While among all the mechanisms,the structure evolution plays a crucial role and needs to be paid more attention to.From the view of potential energy,the detailed energy transformation is illustrated.The granular system is often at a metastable state.When the external disturbance is large enough,the system would step over the energy barrier to a new state.The height of energy barrier is related to the packing structure and grain property.In energy landscape,there exist many energy valleys which correspond to different metastable states.The grain rearrangement and structure reorganization are two main evolution processes at a quasi-static state.The former brings about major potential energy change because of friction and forms certain contact relations.While the latter evolves on the basis of the skeleton formed by grain rearrangement and reaches lower energy state.The conversion among different energy valleys can be used to explain stress relaxation process.In a complex granular system,the choosing of appropriate internal state variables becomes important,which can reflect specific relaxation process and internal characteristics.The energy fluctuation in the system has a huge influence on dissipation process and macroscopic response and is an effective internal variable to have an insight into the structure evolution.Then granular temperature rooted from gas kinetics is introduced to model