Abstract:

Granular materials usually display strange mechanical behaviours, and their understandings still stay in the infancy so far. It is reported that a large assemblage of individual solids in granular material further form a clear hierarchy, i.e. microscale for single particles, mesoscale for force chains and macroscale for the whole granular material. Especially, the mesoscale force chain is postulated being a determinative factor in higher scale behaviours. In this review, we introduce 5 widely used detecting techniques of contact forces in particle scales. Due to highly sensitive response of force chain to external conditions, we further classify them into noninvasive and invasive 2 types based on the strength of influence on force chain. We propose that the invasive measurement would be promising for granular material study in the future. At this stage, photoelasticity technique is appropriate for 2D systems. Finally, we briefly introduce photoelasticity experiments conducted in Tsinghua University.

Key words: granular material, effective stress, force chains, soil skeleton