PSI - Issue 57

Magnus Andersson et al. / Procedia Structural Integrity 57 (2024) 307–315 M. Andersson et al. / Structural Integrity Procedia 00 (2023) 000–000

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(which have been used in design for over 50 years) but also from customer sites using a digital twin approach. In this paper a new evaluation method for fatigue design of weld roots, the Simplified Fracture Mechanics (SFM) method is outlined. This method addresses several of the shortcomings of other more established methods related to fatigue design of welded structures. The E ff ective notch method uses the maximum principal stress regardless of direction related to the actual crack growth path, it does not consider the stress gradient along the crack path and it is time consuming to use both for designers and for stress analysts. The SFM method is also prepared to use weld residual stresses as input, and to consider the relaxation of these weld residual stresses due to the applied time-based loads.

Fig. 1. Articulated hauler Volvo A60H and autonomous hauler TA15.

1.1. Considered weld geometry

As most of the welding on haulers consists of fillet welds, the method has so far been developed for this kind of welds. In Fig. 2 the geometry is shown for fillet welds. The welds are denoted by the weld penetration, i and weld throat thickness, a (e. g. i2a5, 2mm penetration and a weld throat thickness of 5mm). The fillet welds can be either single or double sided.

Fig. 2. Fillet weld geometry (a) single sided; (b) double sided; (c) fictive e ff ective notch radius on the root side.

2. Fatigue assessment of weld roots at Volvo CE

Today the e ff ective notch method is used Hobbacher (2007). The process is shown in Fig. 3. Loads are determined from multi-body simulations using Adams on customer representative digitized test tracks. The load signals are super imposed with stress results from unit load cases from ANSYS analyses. Fig. 4(a) shows an example of an FE model of a frame. The arrows indicate where forces are applied. For each position in the weld, the stress tensor (as a function of time) is used in a critical plane approach, the Modified Wo¨hler Curve Method (MWCM) Susmel (2010), where the maximum shear stress is calculated. The basis for the e ff ective notch method is that a fictive radius of 1mm shall be added to any real radius in the weld toe or root when modelling the welds in FEM. In order to resolve the stress in the fictive radius an element side length of 0.3 mm approximately is needed. As structures often contains welds that are several meters long, see Fig. 4(b), the FE models may consist of millions of degrees of freedom. Often it is necessary to divide the FE model into submodels where each are solved and evaluated separately, and this is very time consuming.