PSI - Issue 18

Fokion Oikonomidis et al. / Procedia Structural Integrity 18 (2019) 142–162 Dr Fokion Oikonomidis / Structural Integrity Procedia 00 (2019) 000 – 000

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3.2. Estimation of cyclic load for pre-cracking

FEA was used to estimate the range of bending loads required to grow a fatigue crack from the initial EDM notch machined in the leg of the chain link. In the finite element models, the chain was assumed to be stress-free before proof loading. To determine the residual stress at the notch, an elastic-plastic model was analysed, where the proof load was first applied to the link and released (Calas Lopes Pacheco et al., 2002; Bastid et al., 2013). Then elements at the intrados of the leg, in a region whose geometry is identical to that of the notch, were removed, so that the concentration of residual stress at the notch tip could be predicted. Finally, a bending load was applied to the extrados of the leg with a rolling pin to obtain the stress variation in the region of the crack tip and determine which bending load would need to be applied to increase this stress to zero. Linear elastic analyses were performed to calculate the stress intensity factor K at the notch tip or crack tip caused by the bending load. Three different geometries were investigated: the initial notch, with a 200μm tip radius, a planar crack whose depth (15.5mm) was identical to that of the initial notch, and a planar crack with the expected final geometry when the crack has grown to 18mm. The purpose of the analysis of the 15.5mm planar crack was to determine if any difference in the value of K arises when the crack initiates from the notch. The geometry and mesh are shown in Fig. 3 and Fig. 4.

Fig. 3. View of the meshed model for the analyses of proof loading and fatigue pre-cracking.