玻璃-橡胶混合颗粒体系的弹性行为研究

废旧橡胶制品颗粒与砂土颗粒混合物作为建筑填充材料具有环保、轻质、减震效果好等特点.软硬组分的混合比例可以调制体系力学性能从而实现兼顾材料柔韧性与强度的需求,但细观层面上材料性能改变的原因尚不明确.本文主要研究玻璃-橡胶混合颗粒体系的弹性行为及其微观机制.利用飞行时间法测量混合材料等效动弹性模量,发现随着橡胶颗粒增加,体系逐渐从类玻璃刚性行为转变为类橡胶柔性行为.离散元模拟结果与实验结果类似.此外,模拟显示低橡胶颗粒占比样品内主要由玻璃颗粒构成主力链结构,而橡胶颗粒基本不参与强力链的构成.当橡胶颗粒占比较大时,玻璃颗粒和橡胶颗粒共同构成主力链网络结构,但颗粒间法向接触力分布相对更为均匀,可视为玻璃颗粒悬浮于橡胶颗粒中.基于上述结果,提出了改进的等效介质理论,用于描述混合颗粒体系的弹性行为.研究认为:橡胶颗粒占比较小时内部颗粒的变形相对均匀,材料近似满足等应变假设,视为并联弹簧模型;橡胶颗粒占比较大时混合材料近似满足等应力假设,视为串联弹簧模型.两种模型得到的结果与模拟结果一致.上述结果有利于从微观角度揭示混合颗粒材料弹性行为的变化机制.

Elastic behavior of glass-rubber mixed particles system

The mixture of scrap rubber particles and sands has been extensively used as geotechnical engineering recycled materials due to its environmental protection performance, light quality and excellent energy dissipation capability. The mechanical properties of the system can be modulated by the mixing ratio between soft and hard components. But the reasons for such a change on a particle scale are not yet clear. In this paper the elastic behaviors of glass-rubber mixed particles are studied by the sound velocity measurement and discrete element simulation. The velocity of compressional wave and the dynamic effective elastic modulus of mixed sample under hydrostatic stress are measured by time-of-flight method. It is found that the wave velocity is almost constant and the modulus decreases slightly with the proportion of rubber particles increasing to 20%. After that the wave velocity and modulus decrease rapidly and the system transforms from rigid-like behavior to soft-like behavior until the proportion of rubber particles reaches to 80%. When the proportion of rubber particles are more than 80%, the compressional wave velocity and the dynamic effective elastic modulus remain stable again. Such experimental results are consistent with discrete element method analyses which provide more in-depth insights into the micromechanics of the mixture. The simulation reveals that at low rubber fraction the main force chain structure is basically composed of glass particles without rubber particles, which accounts for the phenomenon that the velocity of the compressional wave is basically constant. When the glass particles and rubber particles co-construct the main force chain structure, the distribution of the normal contact force is relatively uniform at high rubber fraction. This can be regarded as the glass particles suspending in the rubber particles. An improved effective medium theory is proposed to describe the elastic behavior of the mixed particles system. It is considered that the deformation of the internal particles is relatively uniform for glass dominated mixture which satisfies the isostress hypothesis. A parallel spring model can be used to describe the nonlinear contact model of particles in such materials. On the other hand, rubber dominated mixture approximately satisfies the isostrain hypothesis, which can be described by a series spring model. The outcomes of such models are in agreement with the simulation results for rigid glass dominated mixture and soft rubber dominated mixture. This study is helpful in exploring the mechanisms that are responsible for the macroscale elastic behavior of mixed granular material from the microscopic point of view.