An experimental study of the contact mechanical behaviour of marble spheres under cyclic loading

A series of cyclic compression tests of marble spheres and scanning electron microscopy (SEM) imaging measurements were performed in this work. The cyclic compression tests of marble spheres reveal three different fracture types: Hertzian cracks, oblique fractures and multi-meridian fractures. The displacement of marble spheres with Hertzian cracks or oblique fractures in cyclic compression tests can be significantly larger than the displacement (0.31 mm) corresponding to sample breakage in monotonic compression tests. The SEM observations reveal that mineral fragmentation, plastic shear sliding and crack closure occur in the local contact area, resulting in obvious residual displacement. Hertzian cracks were produced by the combination of densification and shear strength degradation under cyclic loading. Typical two-stage behaviour of cumulative residual displacement and dynamic secant stiffness evolution with the number of cycles was clearly observed. The occurrence of Hertzian cracks or oblique fractures produced significant cumulative residual displacement. The present laboratory results also show that the increase in amplitude can result in a significantly larger cumulative residual displacement and that the number of cycles of marble sphere failure in meridian fracture significantly increases with an increase in the frequency of cyclic loading. The upper contact force ratio and amplitude ratio significantly influence the dynamic secant stiffness evolution. The dynamic secant stiffness of tests under amplitude ratios of 0.7 and 0.8 shows a clear decreasing trend after the initial decelerating stage, which may be related to the loosening and decohesion of mineral particles caused by local significant fragmentation.