Abstract: Autofrettage is adopted for improving the elastic load capacity of single-layer extrusion die. Bilinear kinematic hardening autofrettage model is established and the stress formulae of three loading procedures are derived considering the strain-hardening and Bauschinger effect of material. According to the theoretical formulae, autofrettage pressure scope is obtained. The simulations of stress distribution and the inner wall displacement of the autofrettaged extrusion die are performed by using ANSYS finite element software, and the results coincide well with the theoretical derivations. The effect law of strain-hardening and Bauschinger effect on autofrettage is discussed by comparing the results of bilinear kinematic hardening model and ideal elastoplastic model. When the working pressure is constant, the optimum value of the autofrettage pressure is determined to meet high size accuracy and strength requirement of a single-layer extrusion die.

Key words: Autofrettage, Bauschinger effect, Bilinear hardening model, Extrusion die, Strain-hardening