PSI - Issue 46

Raviraj Verma et al. / Procedia Structural Integrity 46 (2023) 175–181 Raviraj Verma/ Structural Integrity Procedia 00 (2021) 000–000

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The reported experimental data of additively manufactured Ti alloy such as Yield strength (912 MPa) tensile strength (1147 MPa) are considered for predicting fatigue life using XFEM simulation. The fatigue properties such as hardening coefficient ( � ), 957 MPa, hardening exponent ( � ) 0.0167, fatigue strength coefficient ( � � )-1734 MPa, fatigue strength exponent ( ) -0.109, fatigue ductility coefficient ( � � ) 10.38, and fatigue ductility exponent ( ) -1.399 are accounted during the simulation. As far as fatigue crack growth and fracture toughness C(T) model are considered, the central-back edge is fixed, and loading is applied on both the pinholes as mode- Ⅰ requirements as shown in Fig. 1. For the discretization of specimen geometry, the 8-noded brick element is taken. Once the load is implemented, crack is initiated from the crack front and it is tracked by XFEM approach efficiently (Borrego et al. 2018). 3. Results and Discussion The 3-dimensional C(T) specimen model is loaded in mode- І for evaluating crack initiation and propagation. Once the LPBFed Ti alloy computational model is loaded, the crack front would be stressed, and it increases with increasing load. At critical stress value, the crack is nucleated on the peak stress-concentration location on the crack front, and it starts propagating. The von Mises stress distribution in the crack tip vicinity can be observed in Fig. 2(a) in 3D C(T) model for its approximate location. As observed on the crack front in Fig. 2(b), stress concentration sites are shown with the crack opening and its widening from center to edge location. Subsequently, it travels towards the specimen interior. The stresses on the crack surface and crack front are governed by 2 level sets in XFEM, i ) φ for tracking crack surface and ii ) ψ for the crack front. Fig. 2(c) also displays the delamination or crack opening from the center location on the crack initiation sites due to mode- І loading. The φ intensity confirms surface dissociation, which also validates Mises’s stress concentration, as shown in Fig. 2(b). This XFEM methodology follows the elastic and plastic response of materials as per experimental data to precisely simulate its deformation and failure mechanisms. It is important to note that crack tip location is identified through the above-mentioned material’s property, i.e., for LPBFed Ti-6Al-4V alloy, which is defined by crack tip enrichment function (Eq. (4)) and hence its behaviour is specific. This might be different for other materials.

Fig. 2. Fracture toughness evaluation domain through C(T) specimen where (a) applied loading induces stress in the vicinity of crack tip in C(T) specimen and von Mises stress distribution alongside. (b) Stress concentration on the crack front and corresponding crack nucleation sites are shown in (c) through opening/delamination from the center location.