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Abstract
1-Introduction
2-Modelling Compressive Residual Stress
3- Fatigue Testing
4-Conclusions
Acknowledgements
References
Abstract
This paper presents experimental investigation and numerical modeling of the effect of compressive residual stress on the corrosion fatigue life of a low carbon steel. A fatigue life test methodology based on double notched tensile test specimens is proposed. A new plasticity model is proposed for accurate simulation of compressive residual stress and calibrated to experimental stress-strain curves obtained for low carbon steel. The proposed model is implemented as a user-material in the ANSYS Workbench Finite Element Analysis program and utilized in plastic analysis and fatigue assessment. Corrosion fatigue test results are discussed and compared to numerical predictions.
Introduction
Corrosion fatigue failure is a fundamental design consideration in industries where plant and structures are subject to cyclic loading in a corrosive environment. In many applications, this is addressed through manufacture in corrosion resistant base materials, such as stainless steels, or incorporating barrier linings or coatings to protect the base material from corrosive attack. However, these approaches are not always appropriate for cost or technical reasons. In such cases, an alternative approach may be to enhance resistance to corrosion fatigue failure by inducing compressive residual stress in highly loaded regions of the structure. Residual stress methods such as shot peening, low plasticity burnishing, laser peening, deep rolling and autofrettage are used in a variety of industries to improve fatigue life. The motivation for the work presented here is to develop greater understanding of the autofrettage process in pump applications but it is also relevant to use of other residual stress methods in other applications. Autofrettage is used to improve fatigue performance of pressure retaining structures, such as pressure vessel, gun barrels and pump fluid ends. Compressive residual stress is established by initially subjecting the component to an internal pressure great enough to cause plastic deformation in highly loaded regions. This reduces the local mean stress in these regions under operating conditions [1-5], increasing crack initiation time and fatigue life. The compressive stress field may also arrest growth of the crack after initiation [6, 7].