Biaxial Compression Experimental of Granular Media Based on Photo-Elastic Technique

Abstract:

The strain-controlled biaxial compression experiments in bi-disperse granular system are conducted by using a homemade photo-elastic apparatus， which can provide soft boundary pressure to the granular sample. The Hough transform is used to locate each particle position based on the experimental images. The particle tracking velocimetry （PTV） is applied to track the particle in the time scale. Hence， each particle is marked in both time and space scales. The affine motion of each particle is taken out based on the shear strain and space position of corresponding particle. The non-affine displacement field shows that the main displacements happen close to the compression sides and very small displacement in the center of the sample. Meanwhile， the photo-elastic responds of the granular systems also reveal the cage effect clearly， and some of the particles do not have any force even the sample has been compressed a lot. The anisotropy of the force chain network can be seen at the center of the sample with relatively low packing fraction， which is just the place where the shear band passes through.