SEVERITY OF NATURAL FLAWS AS FRACTURE ORIGINS AND A STUDY OF THE SURFACE-CRACKED SPECIMEN.
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.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 01, 1966
- Accession Number
- AD0487986
Entities
People
- Pryor N. Randall