PSI - Issue 13

T.D. Joy et al. / Procedia Structural Integrity 13 (2018) 328–333 T. D. Joy et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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Fundamentally, A DAPCRACK 3D consists of two modules: NETADAPT3D and NETCRACK3D. The module NETADAPT3D deals with all the mesh adaptation required for the 3D Model during the simulation. NETADAPT3D generates a global model with the crack opened and a submodel on the crack front. Global model and submodel are generated with tetrahedral and hexahedra elements, respectively. Both these models are presented to the simulation software ABAQUS TM and then the results will be forwarded to the next module NETCRACK3D, where fracture mechanical evaluation of the model takes place. It includes calculating stress intensity factors, crack growth direction, new position of the crack front nodes, lifetime, etc. The comparative stress intensity factor is calculated in the software using σ 1 ’ criterion, se e Schöllmann et al. (2002). The newly calculated coordinates of the crack front nodes are forwarded to NETADAPT3D and the model is updated with the mesh adaptation algorithm to accommodate the new crack front. This process will continue till the failure of the structure or by reaching any defined termination criterion. To understand more about the simulation program A DAPCRACK 3D, a practical example – a bicycle stem – is considered. The idea stated by Brüggemann (2017) is to use a lightweight and strength-optimized bicycle stem. This stem has to withstand the static and cyclic test procedures declared in DIN EN ISO 4210-5:2014. A suitable material for the bicycle stem is Ti-6Al-4V alloy. Due to its good mechanical properties at medium density and the possibility of additive manufacturing by selective laser melting (SLM), this alloy offers great potential. The SLM-process allows a high degree of creative freedom because of the layered manufacturing. Using SLM, complex structures adapted to the force flow can be created. These lightweight-optimized structures can, for example, consist of filigree lattice structures, which can be both internal and external. The resulting changes in cross-section can act as a starting point for crack growth. Thus, the analysis of crack growth simulations is of great importance. A simulation is carried out considering this critical condition to find out the position with the highest value for the maximum principal stress according to N AVIER . As shown in Fig. 2 a there are two positions diagonally opposite to each other where the maximum principal stress is at its highest value in the bicycle stem. At one of these positions an initial crack is introduced and the model is submitted for simulation in A DAPCRACK 3D. The crack geometry at the 20 th step and the broken model after the 48 th step are shown in Fig. 2 b and Fig. 2 c, respectively. The crack inside the bicycle stem calculated by A DAPCRACK 3D is in Fig. 2 d. The results obtained from A DAPCRACK 3D are compared with that of the results obtained from experiments. The initial crack location, the crack path, the crack growth and fracture surface are in accordance with that of the results obtained from the experiment. The lifetime of the component is 264,572 load cycles as compared to the 218,113 load cycles obtained by the experimental tests. The experimental results considered for comparison are taken from Brüggemann (2018). Until now the models with mechanical loading conditions are simulated in A DAPCRACK 3D. The functionality of A DAPCRACK 3D is extended so that models that are having temperature as an extra boundary condition can also be simulated to study the crack growth behavior. As shown in the architecture in Fig 1 a pre-simulation is carried out on the model without crack in ABAQUS TM to obtain the temperature distribution in the model or the steady state temperatures in the nodes. This is then passed over to the global model created by NETADAPT3D. In this case, the pre-simulation to find the temperature distribution is performed only once and the results are used thereafter for all the following simulation steps. This method of simulation is successful because the outer geometry of the model being simulated will be identical all the time. Even though the global model changes in the successive steps due to crack growth, by using the temperature distribution from the pre-simulation and by interpolation, ABAQUS TM calculates the nodal temperature for all the nodes in the global model. 3. Additional boundary condition in A DAPCRACK 3D Fig. 2. (a) Highest maximum principal stress; (b) crack geometry at 20 th step; (c) model broken at 48 th step; (d) crack growth inside bicycle stem.