PSI - Issue 57

Cristian Bagni et al. / Procedia Structural Integrity 57 (2024) 859–871 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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materials’ properties as well as fatigue parameters obtained through testing, as described in section 3. An example of a fatigue analysis workflow using nCode DesignLife is illustrated in Fig. 2.

Fig. 2. Example of fatigue analysis workflow using nCode DesignLife.

2.2. Second methodology The second methodolog y is an extension of the previous methodology and considers the life of the hybrid joint as the sum of the life of both the adhesive and the mechanical joints. Therefore, this methodology can be seen as a two-step process:  Step 1 : this step corresponds to the first methodology described above. In this step, the peel stresses from the FE model, recovered at the centroid of the membrane elements along the bond-line, are used together with the load history and materials’ properties as well as fatigue parameters obtained through physical testing, to estimate the life of the adhesive using the DesignLife standard SN Analysis Engine.  Step 2 : in this step the adhesive is considered failed and all the load is carried by the mechanical joints. This step evaluates the fatigue life of the mechanical joints alone and it corresponds to a standard spot welded/riveted joints fatigue analysis as described in the nCode DesignLife Theory Guide (Hottinger Brüel & Kjær (2023)). This second methodology would produce more realistic fatigue life estimations compared to the first methodology. However, it does require higher modelling and computational efforts. Therefore, a cost/benefit analysis must be carried out on a case-by-case basis to identify the most appropriate methodology to adopt. 2.3. Convergence study Two typical specimen geometries, lap shear (LS) and coach peel (CP), were modelled in ANSYS using the FE modelling strategy described above in the first methodology (or first step of the second methodology) and a convergence study was carried out. For this exercise, a unit load was applied, the adherends and mechanical joints were modelled as a generic structural steel, while the adhesive was modelled as a generic epoxy resin using the material properties available in ANSYS material library. The LS specimen was modelled as 370 mm long, 50 mm