Modelling fatigue assessments for welded components is a challenging task as to achieving accurate results. Several influence factors reduce accuracy and often the difference between the calculated and the effective fatigue life is located in the range of factor 10 and above. This conference paper presents two advanced methods which allow the achievement of better accuracy. The main aspect consists in taking the geometry into account, a procedure that leads, though, to the need of adapting the existing methods for fatigue assessment. One of these advanced methods is used to examine a detail which has been welded with different welding processes and on different positions.

Introduction

In steel and mechanical engineering, there are numerous concepts dealing with the calculation of fatigue strength in the range of high cycle fatigue of mild-steel welded structures. However, in many cases and due to various reasons, the accuracy in the computational determination of the fatigue strength and of the possible number of stress cycles leading to failure is very imprecise. Assessment procedures applied in practical engineering are sometimes built on more or less pure empiric findings rather than on the numerical description of the failure process. Fatigue assessment is often performed by post-processing elastic stress fields, neglecting the local yielding which often occurs in notched areas. From a theoretical point of view, the reason for such a procedure may be the common understanding of the fatigue problem as being of brittle nature, at least on the scale of engineering consideration. In addition, certain aspects of cyclic plasticity, which are not fully understood, do not have to be dealt with. From a practical point of view, elasto-plastic finite element calculations, which are said to be time consuming are avoided [1]. It is well known, that under the assumption of linear-elastic material behavior, stresses are high in notched areas; therefore, a direct comparison to the materials fatigue strength cannot be performed. Besides the nominal stress approach, many of the design concepts apply a form of effective stress or strain definition based on various underlying ideas.