PSI - Issue 8

Paolo Livieri et al. / Procedia Structural Integrity 8 (2018) 309–317 Author name / Structural Integrity Procedia 00 (2017) 000 – 000

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3.2. Effect of weld pattern

In order to consider the increase in fatigue strength of the lap joint, Albright et al. (1990) proposed different types of welded joint configurations. A straight-line lap weld made in a direction perpendicular to the load direction is the simplest laser lap weld for fatigue testing (see table 1). Figure 5 shows four weld patterns very different from the typical lap joint of table 1: longitudinal-line segment group pattern (LLSG), ladder pattern , sawtooth pattern and double circular arc pattern (DCA). The thickness was of 0.61 mm for all specimens with an overlap of 25.4 mm and a width of 38.1 mm. As an example, figure 6 reports a typical mesh used in the analysis of a lap joint for the case of the longitudinal line segment group pattern. For each case a first FE analysis with a raw mesh was used to identify the critical points, then a second FE analysis with a fine mesh was optimized only in the weld zone where the effective stress reaches its maximum value. Furthermore, in order to reduce the number of elements used in the numerical analysis, a plate with a reduced width was considered. On the basis of recent studies about the fatigue strength of arc welds (see Livieri Tovo 2017) the reduction of the width may result in a change in maximum effective stress. The trend of the stress along the weld depends on the ratio between the thickness and the width of the specimen, but this aspect will be considered in our next paper. Table 3 shows the results of the numerical analysis of the joints in figure 5. The numerical results were obtained after careful convergence analysis. Table 3 reports the stress concentration factor K t for the different welded joints defined as:

  max,

eff

t K



(4)

nom

Finally, the fatigue strength of lap joints is reported in figure 7. In terms of maximum effective stress the experimental points fall into the fatigue scatter band of laser joints proposed in figure 5.

LLSG

LADDER PATTERN

SAWTOOTH

DCA

Fig. 5. Different types of lap joints. The thickness of the plates was of 0.61 mm (for geometrical details see Albright et al. 1990)