Accession Number : AD0487986

Title :   SEVERITY OF NATURAL FLAWS AS FRACTURE ORIGINS AND A STUDY OF THE SURFACE-CRACKED SPECIMEN.

Descriptive Note : Final rept. 1 Apr 65-31 May 66,

Corporate Author : TRW SYSTEMS REDONDO BEACH CALIF

Personal Author(s) : Randall,Pryor N.

Report Date : AUG 1966

Pagination or Media Count : 112

Abstract : To use fracture mechanics in design requires estimates of the severity of natural flaws. In this program, we have measured the severity of semielliptical surface cracks of various depth-to-length ratios, surface cracks of non-elliptical shape, coplanar surface cracks (both back-to-back and side-by-side), cracks formed by hydrogen embrittlement and by oxygen contamination of weld nuggets. A steel and a titanium alloy were tested, each at two strength levels, which gave also two levels of fracture toughness. For semielliptical cracks of various depth-to-length ratios, the standard expression for fracture toughness accounted for crack shape quite well. For non-elliptical cracks, a crack front curvature measurement was used to compute an equivalent ellipticity, and this procedure gave consistent fracture toughness values. Coplanar cracks, back-to-back, caused somewhat greater magnification of the stress intensity factor than that expected from theory. In the analysis of surface-crack specimen data, there needs to be a correction factor for the back-face free surface and one for the net-section effect. When these were applied to test data for the low-toughness materials fracture toughness was fairly constant with crack size, but for the high-toughness materials tested, fracture toughness increased with crack size.

Descriptors :   (*FRACTURE(MECHANICS), THEORY), BRITTLENESS, OXYGEN, IMPURITIES, HYDROGEN EMBRITTLEMENT, STEEL, TITANIUM ALLOYS, STRESSES

Subject Categories : Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE