# Further Development of 3D Crack Growth Simulation Program to Include Contact Loading Situations
## 2 3D Crack Growth Simulation Program--Adapcrack3D  
Adapcrack3D is a crack growth simulation program based on the Finite Element Method (FEM) to predict crack growth in structures and to estimate the residual service lifetime [3]. The architecture of the program is displayed in Figure 1. It is divided into three modules: (i) Netadapt3D, (ii) FE solver, and (iii) Netcrack3D. At first, the FE models of the structure and of the initial crack are submitted to the first module Netadapt3D. Thereby, the FE model of the structure contains the boundary conditions necessary to perform the crack growth simulation. The initial crack is modelled with a 2D mesh of the crack surface describing the shape and the position of the crack in the structure. Netadapt3D inserts the initial crack in the model and performs necessary mesh adaptations around the crack to generate an FE model of the structure with crack. The program uses the submodeling technique for the fracture mechanical analysis. Hence, the module Netadapt3D also generates a submodel along the crack front. The global model for the submodel is the previously generated model of the structure with crack. In the second module, both FE models generated by Netadapt3D are used for static stress analysis of the models, and the results obtained from the simulation are transferred to the third module Netcrack3D. This module performs the fracture mechanical evaluation, in which the strain energy release rates, \(G\), are first calculated using the modified virtual crack closure integral (MVCCI) [7; 30]. The fracture mechanical evaluation is carried out exclusively with the submodel. The module then determines the stress intensity factors (\(K_{\text{I}}\), \(K_{\text{II}}\), \(K_{\text{III}}\), and \(K_{\text{v}}\),) for all the nodes along the crack front. The crack propagation is calculated with mixed mode crack propagation criteria such as the criterion from [PERSON] [31; 32] or the \(\sigma_{1}^{\prime}\) criterion from [PERSON] et al. [33]. In those concepts, values such as the equivalent stress intensity factors, \(K_{\text{V}}\), and the crack kinking and twisting angles are calculated. If the crack is able to propagate, Netcrack3D calculates the coordinates of the new crack front nodes depending on the crack increment provided by the user. The load cycles for this amount of crack growth are computed thereafter. The newly calculated crack front coordinates are forwarded to the first module Netadapt3D, which inserts the extended crack front in the FE model and thereby generates FE models of the global model with crack and the submodel for the next step. This process will continue until a termination criterion defined in the program is reached, e.g., the equivalent stress intensity factor calculated at the crack front is equal or larger than the fracture toughness, \(K_{\text{IC}}\), of the material. If the crack is not able to grow, i.e., if the cyclic equivalent stress intensity factor, \(\Delta K_{\text{V}}\), is less than the threshold, \(\Delta K_{\text{th}}\), of the material, the program will end the simulation. In order to perform the fracture mechanical evaluation, the aforementioned fracture mechanical material parameters obtained from experiments have to be passed on to the module Netcrack3D. The crack growth rate curves obtained from the experiments are described mathematically with the help of equations such as Forman/Mettu [34] or Erdogan/Ratwani [35] to obtain fracture mechanical material parameters. This information, as well as the \(R\)-Ratio of the applied load, is given to Adapcrack3D for the fracture mechanical evaluation, to thereby estimate the load cycles. For FE models with temperature boundary conditions, the input model is simulated only with the thermal loading before inserting the crack in the model to obtain the temperature distribution in the model. This result will be used in all subsequent steps during the crack growth simulation.