In order to analyze autofrettage theory of thick-walled cylinders, a bilinear hardening model was established and the analytical solutions of loading stresses, residual stresses and working stresses were derived based on the triple-shear unified strength criterion, which taken the strain hardening, Bauschinger effect, strength difference (SD) effect and the effect of intermediate principal stress into consideration. The optimal autofrettage pressure of thick-walled cylinder was deduced, the influences of ratio among tension stress and compression stress, strength criterion parameters were investigated respectively. In addition, the stress distributions of thick-walled cylinders between autofrettage and non-autofrettage, the bilinear hardening model and elastic-perfectly plastic model were compared. The results show that the optimum autofrettage pressure will increase with the increase of radius ratio and strength criterion parameter; the maximum equivalent working stress will decrease with the increase of radius ratio and strength criterion parameters, but increases with the increase of ratio between tension stress and compression stress; the maximum equivalent stresses in the elastic plastic junctions and the stresses of thick-walled cylinder along the wall thickness are well-distributed; compared with the elastic-perfectly plastic model, the radius of elastic plastic junction and residual stress of bilinear hardening model are lower, meanwhile with the increase of autofrettage pressure, the difference becomes more and more obvious; the curve of equivalent stress along with radius ratio may provide reference for choosing the optimal wall thickness; autofrettage technique may improve the working stress distribution and ultimate bearing capacity of thick-walled cylinders. © 2017, Chinese Mechanical Engineering Society. All right reserved.
