PSI - Issue 13

Catrin M. Davies et al. / Procedia Structural Integrity 13 (2018) 1384–1389 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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(b)

Vertical

(a)

Horizontal

Fig. 2: (a) SEN(B) geometry and dimensions (b) schematic illustration of SEN(B) sample orientations relative to the build direction.

Fig. 3: Image of SEN(B) test set-up for fatigue pre-cracking and fracture testing.

3. Finite Element Simulation of SEN(B) Loading

Finite element analysis was performed of the SEN(B) fracture mechanics samples to simulate and verify the load displacement curves measured experimentally. A 2-D plane strain finite element analysis has been performed using the commercial software package ABAQUS (ABAQUS, 2014). A small geometry change analysis was performed employing continuum four noded ‘hybrid’ elements (CPE4H) for the plane strain analysis and reduced integration elements (CPS4R) for the plane stress analyses. Half of the specimen has been modelled and symmetry conditions employed (see Fig. 4). The mesh consists of 1849 elements and 1498 nodes. A focused mesh surrounds a sharp crack tip, modelled using collapsed quadrilateral elements. The model has a crack length to specimen width ratio a/W ≈ 0.5. To simulate the different build orientations and heat treatment conditions, representative tensile data for each orientation and heat treatment condition was taken from Ronneberg. et. al. (2018). This data is illustrated in Fig. 5., where 700H and 700V indicates a sample that has been heat treated to 700 °C and built in the horizontal and vertical directions, respectively. Similarly ABH and ABV indicates a sample tensile tested in the as-built condition and built in the horizontal and vertical directions, respectively. The hardening curve was extrapolated to higher strains, up to 40% in the model. As can be seen in Fig. 5., the samples built in the horizontal direction have higher strengths than samples built in the vertical direction, which is expected to be influenced by the interfacial strength of the build layers which are orientated normal to the principal stress for vertically built samples, in addition to the variation in porosity. After heat treatment at 700 °C, the initial yield strength of the material is reduced due to dislocation recovery after heat treatment. The dislocation recovery also influences the materials potential for work hardening and it can be seen that the 700 °C heat treatment samples exhibit a higher degree of work hardening than the as-built samples. 3.1. Material Model