Simulations based on a fracture mechanics approach

The service durability of weld seams is one of the most challenging problems of component fatigue. Hereby, the complexity is due to several peculiarities of welded structures: the detailed weld seam geometry with macroscopic and microscopic notch effects and/or defects, the properties of the welded material, residual stresses and multiaxial proportional or non-proportional loading conditions. Non-experimental approaches to design against fatigue have to account for the difference between weld seams with and without post-weld treatment as well as proportional and non-proportional loading. The application of fracture mechanics parameters allows for a more realistic description of damage progression. This paper is intended to explain possible design approaches based on numerical fracture mechanics and their combination with stress and strain based approaches using clear and classified damage criteria (engineering crack size, fracture). All numerical approaches are presented with special regard to complexity and modeling requirements from the point of view of the practicing design engineer. Non-proportional loading is considered by the identification of a damage critical plane which requires special post-processing routines within the numerical analysis. Again, the question of practicability is raised.