Abstract
The presented article shows an estimation method of optimum autofrettage pressure taking into consideration subsequent cyclic loading. An autofrettage process is used in pressure vessel applications for strength improvement. The process relies on applying massive pressure that causes internal portions of the part to yield plastically, resulting in internal compressive residual stresses when pressure is released. Later applied working pressure (much lower than autofrettage pressure) creates stress reduced by the residual compressive stress improving the structural performance of the pressure vessels. The optimum autofrettage pressure is a load that maximizes the fatigue life of the structure at the working load. The estimation method of that pressure of a hydrogen valve is the subject of the presented work. Finite element and fatigue analyses were employed to investigate the presented problem. An automated model was developed to analyze the design for various autofrettage pressures. As the results of the procedure, the optimum autofrettage pressure is determined. The research has shown that the developed method can profitably investigate the complex parts giving the autofrettage load that maximizes the fatigue life. The findings suggest that the technique can be applied to a large group of products subjected to the autofrettage process.
Highlights
The first set of analyses examined the impact of the autofrettage pressure on the fatigue life of the tube subjected to the cycling load
The fatigue life distributions were plotted for two submodels at the autofrettage pressure of 200 MPa, and all the results are obtained for the defined test pressure cycle
The study has shown the new method of the estimation of the optimum autofrettage pressure for geometrically complex parts
Summary
The autofrettage process depends on applying massive pressure that causes internal portions of the part to yield plastically, resulting in internal compressive residual stresses when pressure is released. When working pressure is applied (much lower than autofrettage pressure), the residual compressive stress helps to resist a newly created stress. The compression mean stress significantly extends the lifetime of those parts. A similar process in its effect is a swage process [3] or shot-peening one [4]; both of them generate residual compressive stress, which significantly helps improve the fatigue life of the parts
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