抗转动对散粒介质三轴剪切力学行为的影响机制

Mechanism of the rolling resistance effect on triaxial shear behavior of granular medium

颗粒间的抗转动对散粒介质的力学特性有重要影响,但目前对其内在机制的认识还不够充分。采用三维离散单元法模拟了散粒介质三轴固结排水剪切试验,分别给出了宏观、微观和细观3个尺度的模拟结果并进行了关联分析,揭示了密实散粒介质荷载传递和变形发展的过程,并探究了抗转动对散粒介质力学行为影响的内在机制。结果表明:在应变硬化阶段,力学配位数降低,组构各向异性增大,成链颗粒数增加,力链变长,力链数减少,平均法向接触力增大,小颗粒簇的数量和体积占比均减小而大颗粒簇的数量和体积占比均增加,故试样在初始弹性压密后即发生剪胀;当三轴剪切荷载增加到一定程度时,力链中颗粒间接触力很大,而力链周围的大颗粒簇体积占比已较高,此时部分力链将发生屈曲或坍塌,组构各向异性降低,成链颗粒数开始减少,力链长度变短,宏观上对应了应变软化;在应变硬化阶段,颗粒间较大的抗转力矩能有效抑制力链中颗粒之间的相对转动且减弱了力链周边大颗粒簇的可变形性,这使得力链的稳定性大大提高,故能有效提高散粒介质的抗剪强度;在应变软化阶段,由于抗转动使得颗粒位置不易及时调整,试样变形将主要集中于力链屈曲或坍塌的局部区域,这些区域内颗粒转动越来越大,且易形成更大的颗粒簇,故此时试样的软化和剪胀更显著,并产生了明显的剪切带。该研究加深了对散粒介质复杂力学行为的认识和理解,且可为散粒介质多尺度本构理论研究提供一定的启发。

Rolling resistance between particles significantly influences the mechanical properties of granular media,yet the underlying mechanisms remain incompletely understood.We conducted several drained triaxial shear tests on granular media using the three-dimensional discrete element method.The simulation results were quantitatively analyzed at macroscopic,microscopic,and mesoscopic scales,followed by a detailed correlation analysis.The study revealed the load transfer and deformation processes in dense granular media,and explored the internal mechanism of the influence of rolling resistance on the mechanical behavior of granular medium.The results show that in the strain hardening stage,the mechanical coordination number decreases,the fabric anisotropy increases,the number of chained particles increases,the force chains become longer,the number of force chains decreases,the average normal contact force increases,the number and volume proportion of small clusters decrease while the number and volume proportion of large clusters increase,and so dilatancy occurs immediately in the specimen after its initial elastic compaction.As the triaxial shear load increases,the contact force between particles in force chains becomes substantial,and the proportion of large clusters surrounding them rises significantly.Consequently,some force chains buckle or collapse,leading to decreased fabric anisotropy,a reduction in the number of chained particles,shortened force chains,and macroscopic strain softening.During the strain hardening stage,large rolling resistance effectively inhibits relative rolling between particles in force chains and reduces the deformability of surrounding large clusters,thereby enhancing force chain stability and increasing the shear strength of the granular medium.During the strain softening stage,rolling resistance prevents timely rearrangement of particles,causing deformation to concentrate in local areas where force chains have bent or collapsed.In these areas,particle rotation increases,leading to the formation of larger clusters.Consequently,the softening and dilatancy of the sample become more pronounced,resulting in the formation of a clear shear band.This study provides deep insights into the complex mechanical behavior of granular media and offers inspiration for the development of multi-scale constitutive theories.