Stress Concentration, Stress Intensity, and Fatigue Crack Growth Along Evacuators of Pressurized, Autofrettaged Tubes.
ARMY ARMAMENT RESEARCH DEVELOPMENT AND ENGINEERING CENTER WATERVLIET NY BENET LABS
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A stress analysis has been conducted on a pressurized, fully or partially autofrettaged cylinder with a small diameter evacuator hole penetrating radially through the wall. Pressure was applied on the inside diameter ID of the tube, and all or part of this pressure was applied on the evacuator hole surfaces. Total hoop stress concentrations have been determined for a range of radial locations along the evacuator and stress intensity factors have been determined along a crack emanating from the evacuator hole. Fatigue crack growth rates. and hence crack profiles, were predicted at each of the radial locations. These predictions indicate that the critical location for the crack in a non-autofrettaged tube is at the ID, whereas in a fully autofrettaged tube, it is located approximately halfway through the wall thickness. Stress ratio has a significant influence on crack shape in autofrettaged tubes, however, it has a limited effect upon lifetime. The effect of axial residual stresses upon fatigue lifetime due to the autofrettage process has been described and an insignificant reduction in lifetime was a result of such stresses. Finally, the predicted profiles are compared with experimental observations of fatigue crack evacuators, and a limited comparison of predicted and actual lifetimes is presented. Good agreement has been observed in both comparisons. jg
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