Microstructural design for tough ceramics. Final report

Technical Report · Sat Oct 01 04:00:00 EDT 1994

OSTI ID:6722124

Chan, H M; Lawn, B R

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.

• Research Organization: Lehigh Univ., Bethlehem, PA (United States). Dept. of Materials Science and Engineering
• OSTI ID: 6722124
• Report Number(s): AD-A-285634/2/XAB; CNN: F49620-92-J-0039
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360202* -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
360203 -- Ceramics
Cermets
& Refractories-- Mechanical Properties
BRITTLENESS
CERAMICS
DOCUMENT TYPES
EXPANSION
FATIGUE
FRACTURE PROPERTIES
GRAIN SIZE
MECHANICAL PROPERTIES
MICROSTRUCTURE
PARTICLE SIZE
PROGRESS REPORT
SIZE
THERMAL EXPANSION