Mode I stress intensity factors induced by fracture surface roughness under pure mode III loading: Application to the ef
- PDF / 1,144,296 Bytes
- 11 Pages / 597.28 x 785 pts Page_size
- 62 Downloads / 215 Views
I.
INTRODUCTION
W H I L E most fractures of metallic structures occur by propagation of Mode I tensile cracks, there are situations where failure occurs by the growth of Mode II and Mode III cracks. For instance, cracks in a multiaxial stress field will experience Mode II and Mode III displacements. The progressive growth of subsurface Mode II cracks is a central issue in rolling contact fatigue. II-sl Failure of torsionally stressed shafts may occur by linkup of Mode II and Mode III cracks. [6,7,81 Propagation of interfacial cracks in electronic components often occurs in a shear stress field due to thermal strains. 19,1~ Stage I fatigue cracks under uniaxial loading are also shear cracks. There are also many microstructural phenomena in which local failure and damage occur in shear, e.g., in crack initiation at inclusion-matrix interfaces and in fiber-matrix decohesion in composites. It is apparent that there is a need to describe and predict the growth of shear cracks. One of the biggest problems in developing a methodology to describe shear crack growth is to account for the effect of fracture surface roughness. Tschegg was the first to experimentally demonstrate that fracture surface interactions can strongly influence the rate of Mode III fatigue crack growth in steel, m-14~ Tschegg and Suresh 115'16,171 have performed extensive measurements of Mode III and mixed Mode (I and III) fracture toughness of ceramics and steels. Their studies indicate that fracture surface roughness has a profound effect on the apparent value of Kmc and on the mode of fracture. Several groups of investigators have proposed the comparison of Mode III to Mode I stress corrosion cracking resistance as a way to demonstrate that dissolved hydrogen, instead of crack tip dissolution, is reT.S. GROSS, Assistant Professor, is with the Department of Mechanical Engineering, University of New Hampshire, Durham, NH 03824-3591. D.A. MENDELSOHN, Associate Professor, is with the Department of Engineering Mechanics, Ohio State University, 155 W. Woodruff Ave., Columbus, OH 43210-1812. Manuscript submitted December 23, 1987. METALLURGICAL TRANSACTIONS A
sponsible for the stress corrosion cracking, t18-24] The conceptual basis for their argument was that hydrogen concentration is increased at the tip of a tensile crack due to the triaxial tensile stress field only and is unaffected by shear distortion. Since the stress field of an ideal Mode III crack is pure shear and, therefore, has no triaxial tensile stress field according to this hypothesis, there should not be an enhancement of hydrogen concentration for pure Mode III loading. If hydrogen is responsible for the embrittlement of the alloy, then Mode I tensile cracks should show greater stress corrosion cracking sensitivity than Mode III cracks. If a difference was not observed, then the predominant mechanism of stress corrosion crack growth would be by crack tip dissolution. The concept of comparing Mode III and Mode I stress corrosion cracking sensitivity as a way of defining the relative rol
Data Loading...
