Accession Number : ADA319999

Title :   Mechanics of Localized Deformation of Solids Under Cyclic and Thermal Loadings.

Descriptive Note : Final technical rept. 15 Feb 92-31 Aug 96,

Corporate Author : CALIFORNIA UNIV LOS ANGELES

Personal Author(s) : Lin, T. H.

PDF Url : ADA319999

Report Date : 23 SEP 1996

Pagination or Media Count : 61

Abstract : Since the 1950's, many metallurgical researches on fatigue crack initiation were undertaken. Now, the difficulty is to see these multitudinous facts as a related and connected whole, largely because of the lack of a sound general theory. This present research is an attempt to develop such a general theory. It is essential in estimating (interpolating and extrapolating) fatigue lives under different design conditions. Fatigue failure has been observed at temperatures as low as 1.7 degrees Kelvin. This indicates that although corrosion and diffusion may have important influence on but not necessary to fatigue failure. This leaves the local stress and strain to provide the basic mechanism of fatigue. Based on the hint of intrusions and extrusions of fatigue specimens, a micromechanic theory of high-cycle fatigue crack initiation has been developed. This theory has been found to have extensive metallurgical verifications. This theory has been applied to study the interaction of multiple fatigue bands and the propagation of fatigue bands across the grain boundary. This propagation of fatigue bands has been found to depend greatly on the misorientation of the neighboring crystal. The effect of the elastic anisotropy of the component crystals of a polycrystal is analyzed.

Descriptors :   *PLASTIC DEFORMATION, *STRESS STRAIN RELATIONS, *CRACK PROPAGATION, LOADS(FORCES), SHEAR MODULUS, CRACKING(FRACTURING), ELASTIC PROPERTIES, EXTRUSION, ANISOTROPY, SHEAR STRESSES, FATIGUE(MECHANICS), FAILURE(MECHANICS), THERMAL CYCLING TESTS, THERMAL STRESSES, GRAIN STRUCTURES(METALLURGY), GRAIN BOUNDARIES, CYCLIC LOADS, POLYCRYSTALLINE, INTERMETALLIC COMPOUNDS, MICROCRACKING.

Subject Categories : Properties of Metals and Alloys

Distribution Statement : APPROVED FOR PUBLIC RELEASE