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.
A New Method of Predicting Residual Stresses in Autofrettaged Gun Barrels.
Abstract : The determination of residual stresses in autofrettaged gun barrels has been considered by many investigators using different mathematical methods and material models. Most of the earlier solutions were based on the assumption that the material behaves elastically on the release of the autofrettaged pressure. However, many materials, particularly the quenched and tempered, low alloy steels generally used for high pressure vessels, exhibit a significant Bauschinger effect. In a recent paper, this author presented a closed-form solution of residual stresses in autofrettaged tubes based on a theoretical model considering the Bauschinger and hardening effects during unloading, but neglecting the strain-hardening during loading. A more general theoretical model without this restriction was proposed earlier, but only part of the final results were shown. In the present report, the complete method of stress and deformation analysis based on the general theoretical model is stated. The new model is a better representation of the actual loading/unloading behavior is a high strength steel. The Bauschinger effect factors is treated as a function of overstrain. The strain-hardening effect is taken into account with different parameters used for loading and unloading processes. The formulas for calculating stresses, strains, and displacements are given. The new results indicate that the influence of the Bauschinger and hardening effects on residual stresses is significant. A comparison with two experimental results has been made.
Elastoplastic thick-walled tubes of work-hardening material subject to internal and external pressures and to temperature gradients
Abstract Using Tresca's yield criterion and its associated flow rule, solutions are obtained for the stresses, the elastic and plastic strains and the displacements when a thick-walled tube of work-hardening material is subject to internal and external pressures and its surfaces are maintained at different temperatures. In general a numerical integration is necessary, but the solutions can be expressed explicitly when the work-hardening law is linear. On removal of the pressures and the temperature difference plastic flow may or may not occur. In both cases the residual stresses can be calculated. Specific examples are given.