A Study on Effect of Residual Stress on Crack Growth of Aluminum Plate
One technique used to enhance the fatigue strength of a fastener hole is to introduce a compressive residual stress field around the hole. An applied load must overcome this residual stress before the crack can grow, thus leading to a longer fatigue life. The cold expansion of the holes is largely employed to obtain improvement in fatigue performance of structures with initially uncracked holes. In this research, considered is a fatigue crack growth from a hole under the influence of residual stress. The entire cold working processing- including hole expansion, elastic recovery, and finish reaming of two aluminum alloys 2024-T351 and 7075-T6 is simulated. This method of fatigue life prediction is compared with a superposition technique and experimental data. The crack closure level is computed from a finite element simulation and a fatigue life is predicted. The conclusions obtained here are beneficial to the understanding of the phenomenon of fatigue crack initiation and growth at the perimeter of cold worked holes.
Elastic-plastic analysis of an infinite sheet having a circular hole under pressure
An exact elastic-plastic solution for the stresses in an infinite sheet having a circular hole subject to pressure is obtained on the basis of J2 deformation theory together with a modified Ramberg-Osgood law. The sheet is orthotropic but isotropic in its plane. The results are assessed on the basis of Budiansky's criterion for the acceptability of J2 deformation theory. By using exact elastic-plastic stresses, the function connecting the pressure at the hole with the radial enlargement is obtained. Upon release of the pressure, residual stresses around the hole are produced.
Analysis of Stress Intensity Factors for Plates Containing Random Array of Cracks
This paper presents a general method of stress analysis of cracked wide plates subjected to plane stresses at infinity. Geometric and other parameters may be arbitrarily specified, including the number, locations, directions and lengths of the cracks as well as the stress parameters. The stress function is first assumed as the sum of stress functions having singulariteies within the cracks and at infinity, and the unknown parameters are determined from the boundary conditions using a perturbation technique. Then the stress intensity factors at all the crack tips are given by power series formulae, and they are considered to give practivaly exact values so far as the enclosing circles of all the cracks are not so close to each other. Numerical examples are given for several typical cases of practical importance.