Influence of Welding Residual Stresses on the Closure and Propagation Behavior of Fatigue Cracks Growing at a Fillet Weld Toe

Abstract

Fatigue tests were performed at three R-ratios (-I, -2 and O) and different stress amplitudes on cruciform welded joints both in the as-welded and stress relieved conditions.A sensitive system using micro-strain gages installed close to the weld toe allowed monitoring of the crack length and opening level from 10 -20 pm. The effect of residual stresses on crack propagation and closure behavior is described for different loading conditions.The experimental data confirm the predictions that can be derived from an elastic analysis based on the crack closure concept, such as a more pronounced effect under partially compressive loading but reaching a saturation below a certain value of R. Further, they give a direct evaluation of the relative residual stress intensity KrlKmax and of its progressive decrease as the crack grows, as well as a better understanding of plasticity effects. G. Beck et al. (eds.), International Conference on Residual Stresses

Early Development of Fatigue Cracking at Manual Fillet Welds

“…7. They are similar to those obtained in our previous studies on automatic welds [5,6]. In particular, under R = -1 loading, initial transient variations within the notch cyclic plastic zone are observed in the stress relieved specimens, as well as strongly negative values of Sop (at least until 0.5 mm) in the as-welded specimens ( Fig.…”

“…Data in Fig. 3 obtained at L 118 MPa present much scatter but a pronounced effect has been reported under R = -1 loading [6]. This effect can be again interpreted by crack closure arguments.…”

“…This term could be replaced by "short crack propagation life" since the actual initiation life has been shown to represent a very small portion of the total life. The work is based on the experience and the equipment from previous studies on the short crack behavior and the influence of tensile residual stresses at automatic fillet welds (MIG process) [ 5,6]. These welds present a severe V-notched geometry that is very regular along the toe, with the result that one straight-fronted crack develops at the very beginning of fatigue life.…”

Short Crack Growth and Coalescence Along the Toe of a Manual Fillet Weld

“…In the ~(~1 0~) as-welded condition, short crack growth is faster by nearly one order of magnitude. This difference is associated to a difference in crack opening levels [4]. The tensile residual stresses at the toe of the weld result in a residual stress intensity factor that is superimposed on the loading and that makes the crack open during the compressive portion of the cycle.…”

“…This technique was developed a few years ago to investigate short crack behavior and the influence of tensile residual stresses at automatic fillet welds (MIG process) [3,4]. These welds present a severe V-notched geometry that is very uniform along the toe, with the result that one straight-fronted crack develops from the early stages of fracture.…”