PSI - Issue 28

Thomas Bergmayr et al. / Procedia Structural Integrity 28 (2020) 1473–1480

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C.V. Thomas Bergmayr et al. / Structural Integrity Procedia 00 (2020) 000–000

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Fig. 4. The results of the displacement in z -direction of the global finite element model and the designed submodel, at the buckling analysis step and the load analysis step with the implemented imperfection.

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Fig. 5. The figure shows the displacement of the submodel of the idealized spoiler model with respect to the z -axis (direction of the loads). Whereas the left side ( x < 0) shows the DIC results and the right side ( x > 0) shows the numerical results.

5. Results

To validate the numerical FE-model several experiments are performed with the DIC system. Fig. 5 shows the comparison of the displacements along the z -coordinate of the numerical and experimental results. The relative error between the displacements are approximately five percent. This comparison as well as the strains with respect to the x -axis depicted in Fig. 6 clearly shows that the results from the DIC system correlate well with the numerical results. Nevertheless, the depicted strains in Fig. 6 shows that the signal to noise level is very low caused by the large monitored area. To calculate the zero-strain directions β 1 , 2 according to equation 2 the simulation results are transferred to Matlab. The implemented algorithms uses the command ’stream2’, a function which computes the streamlines from direction vectors and the function ’griddata’ to fit the FE-data. However, at the beginning the zero-strain trajectories at the pristine structure are calculated at the whole spoiler model, depicted in Fig. 7. On the partial model according to the submodel depicted in Fig. 4 the strain profile of ten ZST are calculated at various damage states, i.e., debonding sizes (c.f.,Tab.2). Subsequently, the strain profile along these trajectories are calculated at the considered five damage state. The strain results of the horizontal and vertical ZST are plotted and compared to each other in the diagrams, depicted in Fig. 8. The results show that the strain measurements along the horizontal zero-strain trajectories are more sensitive than the vertical ones for the considered debonding damage. However, these diagrams shows that an inflicted damage