Abstract:

The key to autofrettage technology of thick-walled cylinders lies in pre-stresses. In traditional autofrettage technology, pre-stresses in cylinders are produced by mechanical actions, that is, the cylinders are subjected to pressures higher than operation pressures for pre-stresses to be produced before they are put into use. In consideration of that there are thermal stresses in the wall of a cylinder when there is temperature difference between the inside and outside surfaces, for autofrettage of thick-walled cylinder, the technology of autofrettage with thermal pre-stresses is thus proposed. The effects of thickness and temperature difference on thermal stresses and total stresses (thermal stresses plus operation stresses) are studied. The varying trends of thermal stresses and total stresses are analyzed. The conditions of constraints on a variety parameters are investigated. On the basis of analyzing the characteristics of thermal stresses and the total stresses, the optimum design conditions are obtained, and a methodology for design of autofrettaged thick-walled cylinders with thermal pre-stresses based on the fourth strength theory is presented. It is shown that the thermal pre-stresses can effectively reduce and even the operation stresses of a thick-walled cylinder, and according to the presented methodology for design, the maximum load-bearing capacities and the minimum thicknesses of cylinders can be obtained under the prerequisite for ensuring safety of cylinders.

Key words: autofrettage, strength, thermal pre-stresses, total stress, thick-walled cylinder