PSI - Issue 18

Tintu David Joy et al. / Procedia Structural Integrity 18 (2019) 287–292 T. D. Joy, G. Kullmer / Structural Integrity Procedia 00 (2019) 000–000

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Subsequently both these models will be simulated in A BAQUS TM and the results are transferred to the module N ETCRACK 3D. The fracture mechanical evaluation in N ETCRACK 3D calculates the stress intensity factors (SIF), crack growth direction, new crack front coordinates, crack propagation lifetime, etc. If the crack is able to grow, then new crack front coordinates are calculated and are then transferred back to the module N ETADAPT 3D. N ETADAPT 3D inserts the new crack front in the FE-Model, re-meshes the model and then generates the global model and the submodel for the next step. This process continues until any of the termination criteria defined in the software is fulfilled. In the past, several models were simulated successfully in A DAPCRACK 3D. Some examples are the simulation of a single edge notch specimen in Buchholz et al. (2005), crack propagation in the frame of a hydraulic press in Fulland et al (2006) and crack propagation in fast train (ICE) wheel tire in Richard et al (2008). The results obtained from the simulations demonstrated good agreement with the crack propagation in the real structure. Earlier, all the models simulated in A DAPCRACK 3D had only mechanical loading conditions. One such practical example is shown in Fig. 2 a where the crack growth in an additively manufactured bicycle stem is simulated, see Joy et al. (2018). Recently, a new feature was implemented in A DAPCRACK 3D to carry out simulations of models that also have constant temperature boundary conditions. In this feature, the user-provided FE-Model without any crack will be simulated in A BAQUS TM before the beginning of the crack growth simulation to obtain the temperature distribution in the input model. This step is performed only once in the complete crack propagation simulation and there after the result obtained from this simulation is used for all the following steps. The details of the process and simulation results are described in Joy et al. (2018) in which the FE-Model selected for the crack growth simulation is that of a Y Strainer. One of the crack growth simulation results in the Y-Strainer is shown in Fig 2 b.

Fig. 2. (a) Crack growth in a bicycle stem and the residual forced fracture surface; (b) Crack growth in a Y-Strainer.

3. Crack Initiation in A DAPCRACK 3D

A module named C RACKINT 3D is newly introduced in the software A DAPCRACK 3D which has the function of automatically initiating a crack in the input Model and also to calculate the lifetime required for this crack initiation. The new architecture of A DAPCRACK 3D integrated with the module C RACKINT 3D is shown in Fig. 1. The two inputs that are required for the module C RACKINT 3D are: a 3D model of the structure created in A BAQUS TM CAE (Complete Abaqus Environment) and the FE-Model of the structure generated in A BAQUS TM . The 3D model has the geometrical information of the structure and will be referred to as A BAQUS TM CAE model in this paper. Python scripts are also integrated within the module C RACKINT 3D to access necessary data from the A BAQUS TM CAE model or to modify it. These python scripts make use of the application programming interface (API) provided by A BAQUS TM (Abaqus (2014)) to help in achieving the aim of inserting the initial crack surface in the model which is required by A DAPCRACK 3D to start a crack propagation in the model, as explained in section 2. The procedure to initiate a crack in module C RACKINT 3D begins with a simulation of the user-provided FE-Model in A BAQUS TM . The results from the simulation provides the stress distribution in the model according to N AVIER and C RACKINT 3D retrieves the maximum principal stresses on the nodes from it. Afterwards, a Python script is invoked on the A BAQUS TM CAE model to obtain the nodes that are only on the outer surface (boundaries) of the A BAQUS TM CAE model. This step is performed because of the assumption that a crack is most likely to initiate at notches or at sharp edges that appear generally on the boundaries of the structure. The stress tensors for these boundary nodes are also retrieved from the simulation results of the FE-Model.