Application of the notch stress concept to the real geometry of weld end points

Abstract

Application of the notch stress concept to the real geometry of weld end points The process used to manufacture modern weld structures often lead to weld start and end points. Under cyclic loading, crack initiation occurs predominantly at the weld start. In particular, for special investigations into thin sheet structures, no approach for the determination of the fatigue life has been established thus far. Therefore, in this research, we have attempted to find a general approach for the assessment of weld ends using the notch stress concept.The primary aim was to obtain the real geometry of weld ends with high precision using a three dimensional scanner. We were able to find an idealised weld end model with the mean toe radius of r = 0,2 mm that provides almost the same notch stresses like the real geometry. The applied load cases were longitudinal and transverse tension as well as bending. The crack always occurs at the weld toe. The notch stress S-N-curve was derived from the fatigue life of the cyclic testing so that the assessment of weld ends is possible for the first time. Moreover, some conversion rules have been developed so that the idealised weld end geometry can be modelled with an arbitrary toe radius. Going one step further, some analyses have been performed regarding to unify the notch stress concept. The existing results of Olivier -who examined long welds with no start and end points -were re-evaluated to unify the results of long regular welds with the local weld end under one scatter band. Using the scanned geometry a good agreement could be achieved. The use of an idealised model will be validated soon.

Modeling and fatigue assessment of weld start‐end locations based on the effective notch stress approach

“…Seto et al [18] report strain measurements and crack growth calculations for cracks initiating at weld toes. Malikoutsakis et al [14,15], and Kaffenberger et al [16,17,19] give experimentally determined Wöhler curves for components providing weld-end failure. In addition, recommendations for modeling and FE meshing of weld ends have been proposed by the authors in [20].…”

“…In addition, recommendations for modeling and FE meshing of weld ends have been proposed by the authors in [20]. To the authors' knowledge, only the recently published works of Kaffenberger et al [16,17,19] contain an integrated and robust modeling methodology based on an experimentally verified effective radius q f = 0.2 mm developed for thinplate (t a 5 mm) welded components. The main features are the detailed directives for the geometrical morphing of the weldstart/end area and the Finite Element (FE) mesh-controlled areas, as well as instructions for assessing the durability of these areas.…”

“…Newly determined master Wöhler curve has been established based on q f = 0.2 mm. Computational results (regardless of q f ) may be transferred to the concept's radius following the formulas given in [16,17,19]. For such a transformation to be valid, the geometrical effect of the radius has been considered along with the statistical size effect, leading to a whole new approach.…”

“…The latter procedure is only feasible if a sufficient number of component prototypes are available in order to average the scanned geometrical data or select a worst case scenario. Such a course has been suggested in [10] and a series of analyses (providing some alterations) have been conducted in [16,17].…”

Schwingfestigkeitsbewertung von Nahtenden unter kombinierter Beanspruchung

“…Heute liegen Konzepte zur Schwingfestigkeitsbewertung von Nahtenden in zug‐ und schubbeanspruchten Nahtenden vor . Hierbei wurden idealisierte FE‐Nahtendmodelle für beide Lastfälle entwickelt.…”