PSI - Issue 75

Per-Olof Danielsson et al. / Procedia Structural Integrity 75 (2025) 572–580 Per-Olof Danielsson et al. / Structural Integrity Procedia (2025)

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4. SFM Implementation The SFM approach is implemented at Volvo CE through structured pre-processing and post-processing phases. FE pre-processing utilizes the Ansa software [6], with customized toolbars specifically developed to define weld properties essential for fatigue assessment, see Fig. 7. This process includes: • Creation of FE models for fatigue analysis of welded structures. • Fatigue life prediction executed using the in-house software, SuperFract. • Result visualization and interpretation through the FE post-processing software, Metapost [7].

Fig. 7. Workflow and illustration of the system of software, needed input files and the result files for the implementation of the SFM approach.

SuperFract, developed explicitly for the SFM approach, currently supports common weld types such as single-sided fillet welds and butt welds. For weld toes, SuperFract conservatively calculates fatigue life by assuming pre-existing cracks. Future updates will explicitly also address crack initiation. Mean stress effects, including weld residual stresses, are considered with care, pending full validation and integration of stress-relaxation theories. Key inputs for the SFM method include detailed stress path data derived from FE analyses, defined load signals, and mappings between unit load cases and actual loads. Python scripts handle data processing, invoking specialized Fortran-based routines (SuperFract_pre and SuperFract) for stress transformation, fatigue calculations, and the generation of result files for visualization in Metapost. This structured implementation ensures robust and reliable fatigue analysis, fully integrated into Volvo CE's overall development processes and supporting continuous optimization of welded structural designs 5. SFM use cases To demonstrate the benefits of the SFM approach, fatigue life calculations is shown at four locations, judged critical using the ENS method, on a welded steel frame designed for an articulated hauler. Table 2 compares the calculated fatigue life obtained using the ENS method and SFM, alongside relevant stress levels and stress intensity factors. Table 2: Comparison of fatigue analysis results at four weld root locations on an articulated hauler frame, where  eq is the maximum equivalent principal stress range in the root notch, according to ENS, for 1000 cycles/hour.  K I,eq,init is the equivalent stress intensity factor range for mode I along the crack path when the crack is 0.15 mm, see Fig. 8.a-d.  K I,eq,end is the equivalent stress intensity factor range for mode I along the crack path when the crack front has grown to 70% of the maximum crack length (assumed failure), see Fig. 8.a-d. Fatigue life = (Predicted life / Fatigue life requirement) * 100 considering different levels of weld residual stresses (WRS) for SFM.

K I,eq,init [ MPam 1/2 ]

K I,eq,end [ MPam 1/2 ]

Fatigue life - SFM, WRS=0

Fatigue life - ENS Fatigue life - SFM, WRS>>0

Id  eq [MPa]

1 558 2 449 3 485 4 462

3,8

2,6

37% 74% 51% 65%

2030% 3281%

7789% 4130%

2 5 9

7

21

71% 89%

950% 106%

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