Observing 3-D deformation of silica sand under in-situ quasi-static compression

Synchrotron micro tomography was used to identify the failure process and damage mechanisms during in-situ compressive loading on confined silica sand. In these tomography experiments, sand grains were confined inside a polycarbonate tube. These confined sand grains were loaded under strain control using a custom built X-ray imaging compatible load frame. The behavior of sand under increasing strain was observed in-situ with 23.8 keV X-rays and spatial resolution 1.45 μm/pixel. A software procedure was developed for processing the reconstructed data and for visualizing and understanding crack propagation in the sand grains. Deformation modes were observed macroscopically across many grains and microscopically within the grains. On the scale of a few sand grains, observations showed deformation effects such as preferred orientation of grains along which stresses were transferred. On a microscopic scale, micro-cracking within individual grains was followed by fragmentation of individual sand grains. Over a maximum applied strain of 34% on the column, the observed deformations were localized within a near-field comprising the top 60% of the sand volume.

► Cross sectional views of sand grains undergoing deformation under compressive loads were represented in high resolution.
► A visual method of observing these transformations in sand grains has been devised.
► A method of relating the particle sizes to crack initiation stress has been developed.