The nature of machining damage in brittle materials

TLDR

The study investigates the micromechanics of failure from machining‑induced cracks in brittle materials. In situ monitoring and fractography reveal that residual stresses—especially a crack‑wedging force from the plastic zone beneath the machining groove—dominate crack response, governing stable crack extension and informing acoustic‑wave‑based non‑destructive evaluation.

Abstract

The micromechanics of failure emanating from machining-induced cracks in brittle materials is investigated. In situ monitoring of crack response during breaking tests (with use of acoustic wave scattering), strength measurements and post-failure fractography all indicate that the crack response is dominated by residual stresses. Two components of residual stress have been identified: a crack-wedging force due to the plastic zone beneath the strength-controlling machining groove, and a compressive surface layer due to adjacent grooves. The wedging force dominates and causes stable equilibrium crack extension during a breaking test. The implications of the results for non-destructive evaluation of surface damage by acoustic wave scattering is discussed.