Development of a Thermal Autofrettage Setup to Generate Compressive Residual Stresses on the Surfaces of a Cylinder

Recently, a heat treatment technique has been proposed to induce compressive residual stresses at the vicinity of the outer wall of a thermally autofrettaged cylinder. In the proposed technique, the outer wall of a thermally autofrettaged vessel is heated above the lower critical temperature while temperature of the inner wall is kept below it. The cylinder is then quenched, which induces compressive residual stresses both at the inner and outer walls. This article presents the construction and working of an experimental setup to carry out the proposed heat treatment coupled thermal autofrettage process. Experiments are carried out on AH36 mild steel cylinders to assess the presence of the compressive residual stresses. Measurement of microhardness and opening angle of cut in a thermally autofrettaged AH36 steel cylinder provided the evidence for compressive residual stresses at the outer wall of the cylinder. A finite element method (FEM) technique was used to predict the opening angle of cut. Predicted opening angle was fairly close to experimental observation.