PSI - Issue 19

Théophane Vanlemmens et al. / Procedia Structural Integrity 19 (2019) 610–616

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Vanlemmens, Elbel, Meneghetti/ Structural Integrity Procedia 00 (2019) 000 – 000

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2. Description of the context

2.1. Description of the current process

The current method used at Liebherr-France to assess the life of the welded components is composed of three steps (Fig. 1 illustrates it): - The first step is a global nominal stress approach where one unique FAT class (dedicated SN curve for weld seams [4]) is applied to all the elements of the structure, and the life is computed using the critical plane approach. - The second step is devoted to the weld seams. It is a nominal stress approach developed for shell elements: only the weld elements are selected and assigned correct FAT classes according to their types and weld parameters. The life is then computed taking into account longitudinal and perpendicular stresses according to the weld line. This method is further described in [1]. - The third step is a local stress approach where the hot spot identified in Step 2 can be (if needed) locally modelled with solid elements according to the R1 concept described in the IIW Guideline [4]. This step is used when the weld parameters have to be optimized, and when a higher precision at the hot spots isneeded. This step is of course the most time and resources consuming.

Fig. 1: Description of the current process

The PSM has been identified as a potential candidate for Step 3. Naturally it allows the same parameter optimization than R1 concept, since the weld is modelled explicitly. The big advantage is that the modelling seems to be easier to realize and that the number of degrees of freedom needed is therefore much smaller. The main goal of this project was to verify if the precision of the method that has been proved to be very good for simple geometries is still comparable to the R1 concept when PSM is used on large structural components from crawler excavators.

2.2. PSM vs R1 concept

In this part, more details will be given to compare the implementation of the PSM compared to the R1 concept on a simple cross joint model. Fig. 2 compares the modelling and shows that the PSM doesn’t require to model any local fictitious radiuses at the notches. The only special feature to add on the model is an opening angle (typically 3° is chosen) at the root. Fig. 3 shows the mesh used for both methods. The order of magnitude of the mesh size is 10 times larger in this example. The only parameter for the mesh generation is the mesh size which can be estimated using Eq. (1) , where L is the length of the non fused root, z the weld leg length and t the sheet thickness: = min( 3 , , ) (1)