Defects such as porosity are inherent in e.g. 3d printing or casting processes and may critically influence the mechanical properties of the manufactured components. Local stress concentrations around pores or other defects, might reduce the load bearing capacity and the fatigue performance. Therefore, it would be desirable to include a quantification of the detrimental effect of pores in the structural performance assessment of a component.
An application of classical FEM simulation to this problem requires a geometry conformant mesh which does not only represent the external surface of the component but also the much more complex internal surfaces resulting from the pores. Due to the potentially high number and small size of the pores, the time required to generate such a mesh and the computational effort for the simulation may quickly increase beyond practical limits. Recently, immersed-boundary finite element methods have been used to overcome this meshing problem. This approach is implemented in the Structural Mechanics Simulation module of VGSTUDIO MAX by Volume Graphics. It simulates local stress distributions directly on computed tomography (CT) scans which accurately represent complex material structures and internal discontinuities.
As a validation of this simulation approach, several studies were conducted for various types of 3D printed components to compare the simulation results with experimental tensile tests. In the experimental tensile tests, the load was increased up to the point where macroscopic fracture of the components was observed. Both the tensile strengths as well as the locations where the first cracks occurred were in good agreement between simulation and experiments.
The simulation approach presented here can be used to determine the influence of defects or shape deviations on the mechanical stability. This can be done by simulating the internal stress distributions for both a CAD model of the ideal component and one or multiple CT scans of prototypes or manufactured parts. Based on a numerical comparison of the results, it is possible to determine whether or not defects or shape deviations of the actual components lead to local stress peaks which are significantly higher than those found in the ideal component.