PSI - Issue 28

Florian Vlădulescu et al. / Procedia Structural Integrity 28 (2020) 637–647 Vl ă dulescu and Constantinescu / Structural Integrity Procedia 00 (2019) 000–000

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a) b) Fig. 7. Local values of relative lattice densities: a) lateral view; b) section of the bracket.

structure to be homogenized will play a role in establishing the variable lattice volume fraction, respectively variable density. This case sensitive attributes will closely modify the mass of the component and its fundamental frequency. 6. SMART crack propagation The SMART (Separating Morphing and Adaptive Remeshing Technology) feature can be used in ANSYS (2019d) for crack-growth simulation. An artificial crack of 50 mm was generated along the axis of symmetry and off-axis at angles of 30º and 60º. The main purpose of this analysis was to evaluate the variation of the stress intensity factors along the crack front and to monitor the crack path during propagation by using 3D crack models. Linear Elastic Fracture Mechanics (LEFM) is considered, that is plasticity effects, nonlinear geometry effects, load-compression effects, and crack-tip-closure effects are disregarded. SMART works only if finite element type Solid 187 (quadratic tetrahedral element) is used. Variation of material properties along crack front (e.g., due to temperature-dependency) is ignored, and therefore same Young’s modulus of 200 GPa as before is used for stress intensity factor SIF calculation at all crack front nodes. SMART offers two common fracture criteria for static crack-growth simulation and a crack will grow based on the user specified critical values of a given criterion: J-integral ₋ crack growth occurs when J = J c or SIF ₋ crack growth occurs when K I = K Ic . We chose a fracture toughness value K Ic = 800 MPa√mm (around 25 MPa√m� . As material properties the critical energy release rates for all three modes were considered as: G Ic = 2912 N/m; G IIc = G IIIc = 3000 N/m. By default, we considered plane stress at start and end nodes on the surface of the bracket and plane strain at all other nodes along crack front. In SMART the crack propagation angle is established by using the well-known maximum tensile stress (MTS) criterion. In Fig. 8 are presented in a lateral view of the bracket the initial positions of 50 mm cracks before propagation.

a) b) Fig. 8. Initial 50 mm crack position for SMART analysis: a) symmetric; b) 60º off-axis.