Abstract
A 3D numerical block of a rock composed of spherical particles embedded into a matrix is simulated by a computer program which allows also to deform the block with novolume change in a coaxial strain regime for different values of the strain ellipsoid: plane strain, constriction and flattening. The influence of several parameters such as size of particles, minimum distance allowed between two particles, particle/matrix viscosity ratio, particle distribution (anticlustering, graded bedding, clustering) are discussed in order to use the centroid method (Fry's method) for strain measurement. Inside the deformed block, calculated and automatically drawn sections are cut parallel to the three principal strain planes (XY, YZ, XZ) . Using the centroid method, the finite strain is calculated by combining the principal strain planes, and compared to the true strain ellipsoid fixed by the initial conditions of simulation. Graphic images are also plotted from the numerical sections. They are investigated by image analysis, centroid are extracted and strain ellipses and ellipsoid calculated. The good correlation between the real strain ellipsoid, the numerical strain ellipsoid and the calculated strain ellipsoid is assessed. Lastly, the centroid method is applied to naturally deformed samples in which data acquisition of centroid is made by image analysis.
