Brittle materials fail rapidly after yield because they cannot deform plastically. Ductile materials have a period of decreasing stress after the ultimate stress because they can deform plastically.
What is brittle materials?
Brittle materials includes glass, ceramic, graphite, and some alloys with exceptionally low plasticity, in which cracks can form without plastic deformation and quickly evolve into brittle breakage. The microcutting model does not appear to be appropriate for such materials. It has been demonstrated experimentally that when a single particle meets brittle material, cracks often form at the faulty impact places when the particle impact velocity reaches a particular value, the threshold velocity.
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