Investigation on the static fracture mechanical characteristics of marble subjected to impact damage based on the FDM-DEM coupled simulation

To investigate the mechanical characteristics of static fracture of marble subjected to dynamic damage after cyclic impacts, based on the modeling technology of the finite difference method (FDM) and the discrete element method (DEM) coupling, a three-dimensional numerical model of the split Hopkinson pressure bar (SHPB) was constructed, and the bar system and rock sample were modeled using FLAC3D and PFC3D programs, respectively. The numerical cyclic impact loading tests were carried out on notched semi-circular bend (NSCB) samples at a constant impact velocity, and then the static three-point bending fracture tests were simulated on these damaged samples. The coordinate data of the particles on fracture surfaces of the sample were extracted by compiling the Fish program, and then the fracture surface was reconstructed and the surface roughness was calculated quantitatively. The rationality and reliability of the numerical analysis were verified by comparison with the results of relevant laboratory tests. The results show that in the cyclic impact loading test, the stress-strain curve rebounds, resulting from the release of part of the stored strain energy during the unloading period. With the increase of the impact number n, the numbers of cracks and fragments generated increase. The connected force field becomes more and more chaotic and the number of broken force chains displays an increasing trend. The breakage of the force chains is the root cause of the deterioration of mechanical properties of the sample. The static fracture toughness of the sample after 5 times of impact is 53.35% lower than that of the natural sample, while the failure displacement increases. In the static loading process, more and more cracks and fragments generate as n increases. This is proof that the internal structure of the sample has been damaged in the cyclic impacts. The fracture surface roughness increases as the impact number increases. The research conclusions can provide certain guidance for the engineering practice.