Effects of material disorder on impact fragmentation of brittle spheres

Abstract

Brittle materials have many excellent properties for structural applications, whereas the brittleness and disorder due to defects and micro-cracks cause failure. Fragmentation may occur and often lead to a catastrophic damage, bring dangers to the users especially when brittle materials suffer dynamic loads like impact and explosion. The impact fragmentation of brittle material belongs to the continuum/discretization domain. The combined finite and discrete element method (FDEM) is used to investigate the impact fragmentation of disordered material in detail. In this work, structural disorder in the brittle material is not considered, and the disorder is only reflected in the strength heterogeneity. Assuming that the mesoscopic fracture parameters of brittle materials obey the Weibull distribution, the degree of disorder can be quantified by the Weibull modulus k. The impact of a brittle sphere against a rigid plate is simulated using the FDEM. The dynamic response can be classified into damage and fragmentation zones. In sphere with low material disorder, cracking pattern is mainly dominated by single or more penetrating cracks. Increasing the disorder degree by smaller k, branch cracks emerge. Finally, it changes into a global branch crack in highly disordered sphere. Besides, mass index analysis indicates that higher disordered sphere has a higher critical velocity in impact events, in which the critical impact velocities equal 10, 15, 40 and 80 m/s when the values of m are 10, 5, 2 and 1, respectively. Furthermore, the principal component analysis is adopted for digging the crack features from fragments morphology description. The statistics of two fragment shape indexes shows that fragments coming from the highly disordered spheres have greater variability with a rougher surface and higher flatness overall, corresponding to the fracture pattern. Finally, we conclude that the effects of disorder on impact fragmentation can be ascribed to the dominant cracking mechanism-specifically, the proportion of shear failure mechanism grows with the disorder degree, implying more non-penetrating branch cracks existing in the fragments. We demonstrate that the effect of disorder on impact fragmentation is probably a consequence of a continuous phase nucleation-avalanche-percolation transition as well.