P-20 Fatigue crack propagation life of the autofrettaged compound cylinder

Abstract

The autofrettage process is commonly used to produce compressive tangential residual stresses near the bore of high-pressure compound cylinder. The multi-layered cylinders can be manufactured with combining autofrettage and shrink fit process to extend fatigue lifetimes. And compressive stresses improve the fatigue life of the vessel during the loading-unloading high-pressure cycles. This paper presents the fatigue design of an autofrettaged compound cylinder for gun barrel which working at high internal pressure(707 MPa). To ensure the structural integrity of the autofrettaged compound cylinder subjected to cyclic internal pressure loading, the fatigue crack propagation life of the cylinder was evaluated. Stress intensity factors of the external cracked compound cylinder due to internal pressure and autofrettage loadings were calculated using the finite element method. The fatigue crack propagation life of the compound cylinder based on the fracture mechanics concepts were predicted and compared to the fatigue crack propagation life of the single cylinder. For FE simulations, the material has been modeled considering an elasto-plastic behaviour for the loading phase. As a result, predicted fatigue crack propagation life of the compound cylinder was about 1.3〜3.3 times more than those of the single cylinder depending on the level of autofrettage.