Application and comparison of deterministic and stochastic methods for the evaluation of welded components’ fatigue lifetime based on real notch stresses

This paper presents two advanced methods for modelling the fatigue lifetime of welded components with an irregular distributed geometry and compares the results achieved. The first approach, applies a deterministic method in, order to analyse implicit gradient models, whereas the second one examines a Weibull-based model using a stochastic method. Both models can be combined in order to encompass the stress gradient and the statistical size effect. In order to determine the parameters for both models, an examination of specimens from five different test series with different macro-geometries and from different test laboratories is performed. After measuring the geometry of the welded components using a laser scanning system with high accuracy and resolution, the linear-elastic notch stresses on the real geometries of each specimen are calculated using FEM. Effective stresses are calculated with different parameters using the implicit gradient model. These notch stresses and effective stresses are used as input parameters for a Weibull-based method to model the crack initiation phase. This initiation phase includes cracks with a length of 3-5 mm. Both methods can be applied on a standalone basis or in combination. However, it has been observed that either combining the two mdthods or using exclusively the implicit gradient model other than the Weibull model leads to no better results. (C) 2016 Elsevier Ltd. All rights reserved.