22. Measurement of Stress Network in Granular Materials from Infrared Measurement

Infrared thermography (IR) was used in this work that aims to experimentally evidence the stress network in granular media composed of two materials featuring different stiffness, without cohesion and under confined compression. Cylinders of polyoxymethylene (POM) and high-density polyethylene (HDPE) were used to build 2D composite granular systems. Cylinders were placed parallely and mixed together in a square metallic frame. The experiments were performed using a uniaxial testing machine. The granular media were first compacted in order to reach static equilibrium configurations. A cyclic compressive load was then applied. IR camera was employed to measure the temperature changes due to thermoelastic coupling on the cylinder network cross-sections. Temperature variations were then processed to obtain the maps of the amplitude of the sum of the principal stresses during the cycles. Three configurations were tested by changing the ratio between the POM and HDPE diameters and the ratio between the numbers of POM and HDPE cylinders. The experimental technique enables us to identify the stress network within the granular media. The experimental results are compared with numerical results obtained with a molecular dynamics software.