Accession Number:

ADA200446

Title:

Micromechanics of an Extrusion in High-Cycle Fatigue

Descriptive Note:

Corporate Author:

CALIFORNIA UNIV LOS ANGELES DEPT OF CIVIL ENGINEERING

Personal Author(s):

Report Date:

1988-08-22

Pagination or Media Count:

29.0

Abstract:

A most favorably oriented crystal located at a free surface of a f.c. c. polycrystal under cyclic tension and compression of high-cycle loading is considered. An extrusion in this crystal is shown to be caused by a positive slip in one thin slice P and a negative slip in a closely located slice Q. An initial tensile strain in the thin slice R sandwiched between P and Q causes an initial compressive stress in R and a positive initial shear stress in P and a negative one in Q. Slices P, Q and R, slip direction alpha and normal to the slip plane beta all make 45 deg with the free surface. The elongation in R induced by this initial strain is called the static extrusion. The difference in resolved shear stresses in P and Q causes the build-up of plastic shear strain in P and Q, hence the extrusion growth. As the extrusion grows, the initial compression in R decreases resulting in a decrease in the extrusion growth rate. This decrease of compression in R tends to activate a second slip system to slide. The plastic strain due to slip in this second slip system has a tensor component which has the same effect as the initial strain in causing the positive and negative resolved shear stresses in P and Q, and hence the additional extrusion growth. In this study with the consideration of the secondary slip in R, the extrusion is shown to grow far beyond the static extrusion. A similar conclusion can be made for the growth of an intrusion.

Subject Categories:

  • Fabrication Metallurgy

Distribution Statement:

APPROVED FOR PUBLIC RELEASE