PSI - Issue 60

Behrooz Tafazzolimoghaddam et al. / Procedia Structural Integrity 60 (2024) 575–581 Author name / StructuralIntegrity Procedia 00 (2019) 000–000

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and damping stress concentration during the cut. After the first cut, the two ligaments left beyond the two pilot holes are severed. The plate was secured by a custom-made jig on an Agie-Charmille wire EDM machine (FI 440 ccS) using “ skimsettings ” with 250 µ m diameter brass wire. These setting have been chosen to minimse the influence of cutting by removing minimal material and by minimizing any stress induced by the cutting process. The plate was stress free before hardfacing as it was received from the milled annealed condition and was not heat treated after it. During the deposition process the plate was not constrained and the plate was contracted by the overlay material during solidification and cooldown. It should be noted that the contour cut did not cause noticeable long range deformation in the sample so only the cut surface displacements were used in the residual stress assessment. 2.3. Surface Measurement The out of plane displacement fields of the two cut surfaces were measured using Zeiss Eclipse Co-ordinate Measuring Machine (CMM) in a temperature-controlled room at the metrology laboratory of The Open University. A Micro-Epsilon laser probe was used to measure the surface displacements and a 2 mm diameter ruby-tipped Renishaw PH10M touch-trigger probe mapped the perimeter of the cut surfaces. The touch probe pitch for the perimeter measurement was 0.25 mm and the cut surface displacement was measured at 0.1 × 0.1 mm grid points. The measured displacement of the two cut surfaces was averaged to remove the effect of shear stress and any symmetric cutting artefact according to the approach described in [11] and [13]. After removing the outliers and the noise, a smooth surface is fitted to the data points using the Robust Polynomial Approach (Proprietary local polynomial fitting, developed by StressMap, UK, Sep. 2019). The smoothed data is used to calculate the displacement boundary condition at nodes on the cut surface in the FE model. In addition to this displacement, two nodes at two corners of the cut surface were constrained as shown in Figure 2 to restrict the rigid body movement. 2.4. FE Model The FE model was created in Abaqus 6.12 [14] using the measured perimeter of the cut surface and extruding it 7.5 cm (half-length). The smoothed out of plane displacement of the cut surface was applied to the cut surface of the FE model as the boundary condition. Two corner nodes of the part were also constrained in the XY plane to stop rigid body motion. The part was meshed using 8 node quad elements with 0.5 × 0.5 × 1 mm dimensions on the cut surface and gradually larger elements away from it (Figure 2). Linear elastic analysis was used to calculate the stress in the out-of-plane direction and parallel to the weld beads to capture the transverse stresses using E= 195GPa and u = 0.265 for the base plate and E= 220 and u = 0.280 for the clad.

Figure 2 A 3D model of the cut sample half was created in ABAQUS by extruding the measured perimeter of the cut surface. The part was meshed using 8-node linear brick elements (C3D8R) with reduced integration, hourglass control, and mesh density bias towards the cut surface.