Experimental assessment of residual stresses induced by the thermal autofrettage of thick-walled cylinders

In this work, an experimental study of the residual stresses present in the thermally autofrettaged thick-walled cylinders is carried out. The idea of thermal autofrettage has been conceived recently, and due to its simplicity, it has the potential to be competitive with the existing hydraulic and swage autofrettage processes. In thermal autofrettage, the beneficial compressive residual stresses at the inner wall are produced by means of thermal gradient across the wall thickness. In this work, the residual stresses setup in the cylinders are determined experimentally using Sachs boring method. The experimental results are compared with the analytically determined residual stresses and found to be in good agreement. In addition to the Sachs boring method, two other methods, namely, microhardness test and the measurement of opening angle as a result of cutting through the wall of the cylinders, are also carried out in order to infer the generation of residual stresses in the autofrettaged cylinders. All three experimental methods advocate the feasibility of thermal autofrettage for producing beneficial compressive residual stresses at the inner wall.