On Theoretical And Experimental Investigations Of Autofrettage Technique

In this thesis, the history and present situation of autofrettage are summarized systematically. The various kinds of mechanical models and its assumptions used in the autofrettage technique are discussed. Using Tresca's yield condition, its associated flow rule and the mixed hardening theory, the analytical solutions have been obtained for elastic-plastic loading and unloading problems in a thick tube autofrettaged by hydraulic pressure. Explicit expressions for the displacements and stresses are given herein under the plane strain, opened-end and closed-end conditions. The results gotten in the thesis are compared with experimental datums. The analysis of stress and displacement, choice of excess, calculation of the push force and shape design for the mandrel are considered in a thick tube autofrettaged by the oversize mandrel by the method combined simplify analysis in the mechanics of plastic forming of metals with elastic-plastic mechanics. A lot of important conclusions are given.Based on the theory of the thesis, the experiments of imitating the autofrettage process, repressurization and measuring the residual stresses in tube are completed. The validity of the theory are proved by the experiments. The method of cutting annular sheet that can be used to get the percent overstrain of the tube is presented The residual stresses in autofrettaged thick tube in the thesis can be expressed by the themal stresses caused by some temperature distributions. The results obtained in the thesis can provide the theoretical and experimental references for development and practice of autofrettage.