Hertzian-crack suppression in ceramics with elastic-modulus-graded surfaces
- Univ. of Connecticut, Storrs, CT (United States). Dept. of Metallurgy and Materials Engineering
- Massachusetts Inst. of Tech., Cambridge, MA (United States). Dept. of Materials Science and Engineering
Hertzian (spherical) indentation experiments were carried out in a graded alumina-glass composite whose Young`s modulus increased with depth beneath the indented surface. An in situ processing method involving impregnation of a dense, fine-grained alumina by an aluminosilicate glass was employed to fabricate such a composite. With this technique, a monotonic, unidirectional variation in Young`s modulus of as much as 50% was introduced over a distance of approximately 2 mm, while keeping the coefficient of thermal expansion and the Poisson ratio for the glass and the alumina nearly the same. The macroscopically graded, elastic composite so produced with nearly full density has essentially no macroscopic, long-range residual stresses following processing. The unidirectional variation in Young`s modulus under the indenter is shown to fully suppress the formation of Hertzian cone cracks. Without these elastic-modulus gradients, cone-crack formation was observed in bulk glass and alumina. Finite-element analyses of spherical indentation on elastically graded substrates were also performed to develop a quantitative understanding of the experimental trends. It is reasoned that the present innovations, involving functionally graded surfaces and their in situ processing, provide new possibilities for enhancing certain contact-damage resistance characteristics in various ceramic materials for a broad range of engineering applications. Furthermore, this contact-damage-resistance phenomenon in functionally graded ceramics is elastic in nature, and is, therefore, likely to be immune to mechanical fatigue within the elastic limit.
- Sponsoring Organization:
- Department of the Air Force, Washington, DC (United States); USDOE, Washington, DC (United States)
- DOE Contract Number:
- FG02-93ER45506
- OSTI ID:
- 655384
- Journal Information:
- Journal of the American Ceramic Society, Vol. 81, Issue 9; Other Information: PBD: Sep 1998
- Country of Publication:
- United States
- Language:
- English
Similar Records
ORNL Quasi-Static Mechanical Characterization and Analysis: FY09 Annual Report to TARDEC
Indenter Elastic Modulus and Hertzian Ring Crack Initiation