Investigation of the Relaxation of Residual Stresses in Autofrettaged Cylinders

Autofrettaged cylinders have been restricted in their use to relatively low temperatures because of the stress relieving effect of high temperatures. Thus, it was felt that high-temperature operation would alter the stress pattern to such an extent that the auto-frettage process would be of little benefit. This study was conducted to determine what the effects of time and temperature would be on the residual stresses. Small-size autofrettaged cylinders were subjected to temperatures varying from 400 to 850 F for times varying from 1 hr to 72 hr. The residual stresses were determined using a modification of the Sachs’ boring-out technique. The results indicated a stress relief in all the cylinders subjected to high temperatures. However, it was found that for a given temperature and time the bore tangential stress relaxes in a manner that can be predicted by means of creep data. This relation appears to have a limiting value related to the creep-resistant characteristics of the material.