Accession Number : AD0285254

Title :   THE ANISOTROPIC EXTENSION OF MICROCRACKS BY PLASTIC FLOW IN SEMI-BRITTLE SOLIDS

Corporate Author : HONEYWELL RESEARCH CENTER HOPKINS MINN

Personal Author(s) : STOKES,R.J. ; LI,C.H.

Report Date : AUG 1962

Pagination or Media Count : 1

Abstract : A mechanism for the growth of microcracks from subcritical to critical Griffith dimensions by plastic flow is described. The mechanism is based on experimental observations on sodium chloride over a range of temperature. It is proposed that the main factor responsible for extending a surface microcrack is the local plastic constraint that it exerts. The magnitude of the constraint in a single crystal depends upon the orientation of the surface with respect to the Burgers vector. Microcracks extend anisotropically to form slits along channels between slip bands. This is because slip bands resist crack propagation across them but enhance propagation parallel to them. Raising the temperature from liquid nitrogen to 150 C promotes a change from straight to wavy glide. Wavy glide relaxes the plastic constraint at the surface whereas straight glide cannot. It is shown that the change in slip mode accounts for the brittle to ductile transition in sodium chloride. (Author)

Descriptors :   *BRITTLENESS, *CREEP, *FRACTURE (MECHANICS), ANISOTROPY, CRYSTAL DEFECTS, CRYSTALS, DEFORMATION, LOW TEMPERATURE RESEARCH, MECHANICAL PROPERTIES, SINGLE CRYSTALS, TEMPERATURE

Distribution Statement : APPROVED FOR PUBLIC RELEASE