Computational methods for designing components under cyclic loading

Abstract

When a component is under the action of a cyclic load the component can fail either by fatigue or by ratchetting. This thesis examines finite element computational methods that can assist designers to investigate component failure when subject to a cyclic load. In fatigue analysis an important factor is the cyclic stress range. Traditionally the stress range is based on the nominal stress. However, the use of the structural stress is increasing, particularly in fatigue analysis of welded components. Methods that can be used to calculate the structural stress are investigated. These methods are linearization through thickness, surface stress extrapolation and the nodal force method. A comparative study is carried out on these methods. In the comparative study a number of examples are analysed and the structural stress results obtained from the methods are discussed. When designing to prevent ratchetting a finite element method that can be used to determine the elastic shakedown load is called the Non-linear Superposition method. This method can be applied for cases of proportional and non-proportional loading. In this dissertation the suitability of this method to various examples involving mechanical and thermal loads, and different load histories is demonstrated.