Accession Number:

ADA285634

Title:

Microstructural Design for Tough Ceramics

Descriptive Note:

Final rept.

Corporate Author:

LEHIGH UNIV BETHLEHEM PA DEPT OF MATERIALS SCIENCE AND ENGINEERING

Personal Author(s):

Report Date:

1994-10-01

Pagination or Media Count:

144.0

Abstract:

Results of a program on the influence of microstructure on the toughness and fatigue properties of ceramics are presented. A theoretical analysis of toughness-curve behavior in two-phase ceramics has been completed. This analysis identifies particle size, volume fraction, and internal thermal expansion anisotropy stress as key microstructural variables in the toughness response. A simple contact fatigue methodology for investigating the accumulation of damage at stress concentrations in tough ceramics, using the Hertzian indentation test in cyclic loading, has been developed. This methodology offers several advantages over traditional long-crack fatigue testing, and relates directly to the stress states that occur in contact bearings. Optical and acoustic emission tests reveal fundamental departures from the classic cone fractures that form in homogeneous brittle materials. Instead, a new kind of damage, shear-initiated microfractures in a distributed zone directly beneath the contact area is observed. The damage thereby occurs in the short-crack region, and is most severe in those ceramics that show the highest long-crack toughness, underlying the need for compromise in materials design. The results bear strongly on such practical properties as bearing fatigue, and strength, wear and erosion of structural ceramics.

Subject Categories:

  • Ceramics, Refractories and Glass
  • Laminates and Composite Materials

Distribution Statement:

APPROVED FOR PUBLIC RELEASE