Strain-Based Fatigue Methods Using Modern Finite Element Analysis for the Assessment of Pressure Vessels Equivalent to the ASME III Code

摘要

The use of ASME III Design-By-Analysis assessment methodologies pre-dates the routine use of finite element software which can make the assessment of complex 3D geometries difficult. Recent progress in computing power and software have led to the increased possibility to utilise these developments and undertake ASME III type assessments on 3D components in more efficient and less labour intensive ways. The use of finite element software and post-processing codes is now widespread and full procedures for direct shakedown analysis and whole component fatigue assessment using software applications are becoming more readily available. Utilisation of these procedures can lead to a more robust assessment in a reduced analysis time therefore leading to reduced assessment costs. This paper focuses on the use of strain-based fatigue post-processing software to predict the fatigue life of a component. Strain-based fatigue life prediction provides a direct assessment of plasticity in the component which will lead to less conservative assessment and a less pessimistic fatigue life. Utilising this software also means a fatigue analysis of the whole model can be undertaken potentially reducing the subjectivity of any results obtained. This paper will discuss how strain-based fatigue methods can be applied to results from finite element models and how they compare to fatigue life calculations using traditional methods. Some of the practical implications of undertaking a fatigue assessment using these methods such as cycle counting for multiple transient histories are also discussed. An example based upon a typical reactor plant pressure vessel geometry using these methods is presented in this paper.