Surface damage in brittle materials
It has long been recognized that structural modifications of the surface layers of materials induced by mechanical processing may affect adversely the performance of engineering components in service. Traditionally, the most deleterious changes have manifested themselves as residual stresses that lower the fatigue life or distort the shape of metallic components. In recent years, however, increasing attention has been paid to the consequences of subsurface damage in brittle materials such as engineering ceramics, optical glasses and crystals, semiconductors, and polymers. Defects in such solids may limit severely the service life of components by failure of critical optical or electronic properties, as well as by catastrophic fracture. In this chapter, therefore, attention will be concentrated on the nature of permanent changes in the near-surface region of nominally brittle solids associated with mechanical contact, especially during abrasion, machining and polishing. We begin by examining the simplest type of static contact.
KeywordsResidual Stress Plastic Zone Silicon Nitride Brittle Material Surface Damage
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- 35.Such structural damage may be severe enough to cause a change in phase of the material, as described in section 10.4.2 for silicon.Google Scholar
- 36.The variability of data from fracture tests is often quantified by the “Weibull modulus”, a parameter derived from extreme value theory for normal distributions. In the present case some doubt attaches to the use of Weibull statistics since the parent distribution of strengths in silicon nitride may be severely skewed or bimodal (Quinn, 1992; Puttick et al., 1993), leading to large sampling errors.Google Scholar