Experimental verification of the autofrettage process for thick-walled tubes

Abstract

Abstract

The success of the autofrettage process applied to thick-walled tubes is determined in industry via a control chart representing the measured permanent diametral expansions versus the yield stress of the material. The widely used acceptance limits are due to Hill's analysis of the problem. An experimental investigation showed that the above limits might lead to refusal of a substantial number of autofrettaged tubes. By considering the separate effects of hardening, the Bauschinger factor, reverse yielding, anisotropy and geometrical eccentricity, the need for a more realistic material model is demonstrated. A model incorporating the first three factors, found in the literature, is used to suggest new acceptance limits. Autofrettage experiments on a relatively large number of tubes indicated that the new control limits might render refusals acceptable.