The effect of different fracture mechanisms on impact fragmentation of brittle heterogeneous solid
The fragmentation of brittle and heterogeneous spherical solids under impact loading is numerically studied using the combined finite and discrete element method (FDEM) and cohesive crack model. The effect of different fracture mechanisms on the dynamics and statistics of fragmentation is investigated by adjusting the failure criterion of the cohesive interface elements (CIEs). Specifically, three sets of FDEM simulates modeling, the collision of a single spherical specimen against a rigid wall are conducted, each governed by tension-dominated, shear-dominated, and mix-mode fracture mechanisms, respectively.
The influence of fracture mode on the resultant fragment mass distribution and shape characteristics after the impact are analyzed through statistical methods. It is found that the final fragment mass distribution can be characterized by a power law function with a higher power-law coefficient for shear-dominated fracture mode than for the tension-dominated fracture mode. This coefficient increases dramatically with increasing impact velocity in the three considered situations. As the impact velocity increases beyond the critical velocity, such coefficient converges to a relatively constant value around 1.743 ± 0.003, regardless of the controlling of fracture mechanisms.
This value is very close to the mean values reported in other experimental and numerical studies in existing literature. The fracture structure is characterized by the direction distributions of fragment velocity and crack surface norms, and the fracture network is visualized by the spatial distribution of broken CIEs viewed from different perspectives. These statistical inspectors allow quantitative discussion of the effect of fracture mechanisms on the fracture patterns developed during impact. It is also found that shear-dominated fracture mode favors the generation of isotropic, rounded, and convex fragments, while tension-dominated fracture mode encourages elongated, angular, and concave fragments.
Keywords: Impact fragmentation, Fracture mechanism, Fragment mass distribution, Shape characteristics.