This work presents a new fatigue crack growth prediction model for non-load-carrying fillet welded steel joints. For this joint configuration the fatigue cracks will emanate from the weld toe region. Due to the presence of a V-notch in this region the crack initiation point becomes a point of singularity for the stress field. This may in many cases make it difficult to determine the Stress Intensity Factor Range (SIFR) for small cracks by conventional methods based on Linear Elastic Fracture Mechanics (LEFM). The present approach solves this problem by using the Energy Release Rate (ERR) to determine the SIFR in the small crack growth regime. The model is fitted to crack growth curves from tests with cruciform steel welded joint subjected to constant stress ranges in both axial and bending loading mode. The Paris crack propagation law is adopted and the calculation of SIFR for larger cracks outside the material volume influenced by the V-notch singularity is carried out by the conventional approach. The model gives results in agreement with experimental facts and has also the potential of being extended to variable amplitude loading. The model is also well suited for taking into account the crack initiation phase that is significant for high quality welded joints

Introduction and Development

Modeling the evolution of the fatigue damage in welded steel joints is an important issue for the design of dynamically loaded structures. In fillet welded joints cracks often emanate from the weld toe and subsequently grow through the plate thickness. Common approaches to model the damage process are an application of rules based on S-N curves for life predictions and a facture mechanic model to describe the associated crack growth in more detail. The latter approach has the disadvantage that the modeling of small crack growth in high quality welded joints often is outside the validity range of Liner Elastic Fracture Mechanics (LEFM) theory. The initial crack size is generally unknown. Furthermore, the necessary calculation of the Stress Intensity Factor Range (SIFR) at these small crack depths may be difficult. The limitations are due to the fact that the singular behavior at the point defined by the weld to transition to the plate surface has a great influence on the SIFR calculations. Also the theoretical significance of the SIFR is to be under question. In the present paper, we study the fatigue behavior of fillet welded joint in which the principal significant parameter to calculate the stress intensity factor is the weld toe angle.