Experimental investigation of failure diffusion in brittle materials subjected to low-speed impact

Abstract

The generalized driving force and local shear resistance are introduced to reveal the intrinsic mechanism of failure diffusion in brittle materials subjected to low-speed impact. Two experiment techniques (i.e. the Split Hopkinson pressure bar (SHPB) test and sphere penetration test), four specimen configurations (i.e. cuboid, trapezoid, sphere, and plate specimens), and three transparent brittle materials (i.e. polymethyl methacrylate (PMMA), glass, and transparent ceramics ALON) are employed in the present study. The generation and propagation of the failure front in the specimens are traced and analyzed based on the high-speed photography and the DIC method. The calculated equivalent strain fields vary greatly with configurations of specimens. The generalized driving force (e.g. calculated based on the strain field) and the shearing diffusion resistance (e.g. calculated based on the strain field and the transmission stress profile) are then proposed to illustrate respectively the deformation-gradient induced driving force and the local shear in the shear-activated process of failure diffusion. The results show that they both increase rapidly in the formation process of the failure front and decrease to almost zero after the specimen is failed; while the velocity of the failure front increases exponentially with the increase of the driving force, and decreases with the increase of local shearing resistance. The relations of the two generalized forces to the geometric structures are obtained, and the local dynamic strength is firstly revealed by the evolution of the shearing resistance. The results are helpful for the profound understanding of the failure mechanism of brittle material subjected to impact loading.