SSPX: A Program to Visualize Strain in Discrete Element Models

SSPX is a Macintosh, Cocoa/Universal application to compute strain from displacement/velocity data in two dimensions (2D) and three dimensions (3D). SSPX can be used to interpret the strain from the particle displacements of discrete element models (DEM). The program computes a best-fit displacement gradient tensor (and strain tensor) that gives the smallest deviation from the displacements of the particle system within smaller subregions of the DEM. Heterogeneous particle displacements can thus be homogenized. The strain computed in SSPX is equivalent to the best-fit strain proposed by Peter Cundall. Strain is based on the displacements of the particle centers. Particle rotations are not taken into consideration. SSPX solves small and large deformation problems, in either the undeformed (Lagrangian) or deformed (Eulerian) configuration. The program offers several options to compute strain: Best fit for all or selected data, strain at a point, strain at stations, Delaunay, grid-nearest neighbor, and grid-distance weighted. SSPX computes strain on a 2D slice. In 3D, the location and orientation of the slice can be varied to visualize the strain along horizontal or vertical sections. Numerous options are available to visualize the magnitude and orientation of strain. We show the application of the program to 2D and 3D DEM simulations of faulting.