A Study on Cycling Life and Failure Mode of Type3 Cylinder treated with Autofrettage Pressure

Abstract

In this study, series of experiments and finite element method analyses were conducted, and the results were used to demonstrate the effect of the autofrettage pressure on the cycling life and the failure mode, and to determine an optimal condition of autofrettage process for self-contained breathing apparatus. Total 20 vessels went through different autofrettage pressures, i.e., 1.0, 1.1, …, 2.9 times the test pressure. Then, each vessel was subjected to the ambient hydraulic cycling test of the same condition until fluid leaks. Cycling life of a vessel was estimated based on the stress-strain diagram and stress-cycle curve that were obtained by the tensile test and the fatigue test, respectively, of the liner sample. By using ABAQUS code, the compressive residual stress and the maximum strain distribution at each autofrettage pressure were computed. As a result, the failure modes were in good agreements with the computations. And it is concluded that the proportionality factor of 1.7 or above should be applied in the autofrettage process for significant extension of the cycling life, and, with the factor of 2.5, the maximum cycling life and the desired failure mod are achieved simultaneously.