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Particle Impact Breakage
Published in Ko Higashitani, Hisao Makino, Shuji Matsusaka, Powder Technology Handbook, 2019
Highly localized loading in this mode of failure may lead to the formation of Hertzian cone cracks. Oblique impacts cause tilting of the cone angle, as the tensile stress trajectories are modified by the frictional traction, and this can produce small chips from the particles, which is responsible for the erosive wear of the particles.12
Dynamic behaviors and protection mechanisms of sulcata tortoise carapace
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2021
P. Jearanaisilawong, N. Jongpairojcosit, C. Glunrawd
Table 3 summarizes the projectile and rebound velocities from the impact tests. Each sample was shot at firing pressure of 1, 2 and 3 bars with a single test on each firing pressure. Only the projectile of Shot 6 could penetrate the carapace. Figure 10 presents a series of images of sample B under impact loading from the high speed camera. As projectile velocity increased, the keratin scutes layer was damaged and the carapace was penetrated in Shot 6. The images also show that the curvature of the carapace influences its protection performance. The convex structure of the carapace leads to a rebound of the projectile and the wavy surface of the keratin scutes cause an oblique ricochet providing the lower impact velocity compared to a normal impact. Figures 11 and 12 demonstrate the impact face and cross-section of Samples A and B after the tests, respectively. On Sample A, small dents could be observed on the keratin scutes layer without cracks. However, some cracks occurred on the keratin scutes for Shot 4 and 5. Shot 6. The behaviors of bone-like layer differ from those of keratin scutes. Cracks on bone-like layer can be observed within the dorsal cortex and along the boundary of dorsal cortex and cancellous interior in Shot 2 and detachment of layers are presented in Shot 3 to 6. The crack of bone-like layer has a conical shape that corresponds to the fracture of a brittle material from projectile impact (Zaera and Sanchez-Galvez 1998). The conical crack is produced by contact load that propagates through a brittle material from the impact point which is referred to as the Hertzian cone crack. The failure of the carapace bone-like layer is caused by the stress wave in the material. As the projectile hits the target, the compressive wave occurs and transfers to the back surface. At the free surface, the wave reflects back into the material as a tensile wave. As a brittle layer, the dorsal cortex starts to crack by the tensile wave. The variation of the results of Sample A and B at the same firing pressure are caused by the inconsistency of the biological materials, thickness differences and target curvature. The carapace thickness of Shot 1 to 6 are listed in Table 3.