| [ 1 ]
|| Fengler, B.; Schäferling, M.; Schäfer, B.; Bretz, L.; Lanza, . G.; Häfner, B.; Hrymak, A. & Kärger, L. (2019), "Manufacturing uncertainties and resulting robustness of optimized patch positions on continuous-discontinuous fiber reinforced polymer structures", Composite Structures, pp. 47-57. https://doi.org/10.1016/j.compstruct.2019.01.063
Discontinuous fiber-reinforced Sheet Moulding Compound (SMC) in combination with continuous carbon fiber patches provide a high design freedom in combination with good weight-specific properties. However, the application of these materials requires a strategic and exact positioning of the patches, necessitating the consideration of unavoidable manufacturing defects during the design phase. Therefore, a workflow is proposed to evaluate the robustness of multi-objective patch optimization results using two robustness measures, the degree of robustness and robustness index. An efficient calculation of the robustness measures is achieved by replacing computational expensive simulation models with a Kriging surrogate model. Typical manufacturing deviations occurring during the patch positioning and moulding process are determined from experiments using active thermography. Finally, the proposed workflow is applied to the multi-objective optimization of two patches on a demonstrator under four-point-bending load. The resulting robustness measures can be used as a decision criterion for the selection of the best Pareto optimal solution. Furthermore, they can be used for the determination of the maximum occurring objective variation as well as the largest permissible manufacturing tolerances.
| [ 2 ]
|| Bretz, L.; Hinze, T.; Häfner, B. & Lanza, G. (2019), "Evaluation of anomaly detection capabilities using a non-orthogonal camera angle in pulse-phase thermography". Procedia CIRP, eds. Kerrigan, K.; Mativenga, P. & El-Dessouky, H., pp. 308-313.
Pulse-phase thermography (PPT) is widely used to nondestructively inspect internal defects in fiber reinforced polymers. However, the challenges using PPT for complex shapes is poorly documented in literature. Only small changes in the object distance have been considered.
Complex parts can have significant variations in object distance and thus, in detected radiation. In this contribution, the effect of a non-orthogonal camera angle with respect to a flat sample, leading to varying object distances and an inhomogeneous sound background area in phasegrams, is investigated. Samples with artificial round and square defects of different sizes are positioned under varying angles with respect to the camera, representing geometric properties of complex parts. The construction of the thermographic system and the experimental setup to systematically vary the angle between camera and specimen is presented. We investigated the change of the signal-to-noise ratio (SNR) of artificial delaminations in PPT measurements under varying object distances. The SNR in a distance of 136 mm out of the focal plane is sufficiently high for image feature extraction. Phasegrams are exported to a colored representation, leading to a higher contrast in distinct color channels. An algorithm which extracts and merges defect information from three different color channels is developed. Challenging lighting conditions lead to a noisy background having artifacts. The developed filter performs better in defect detection and size quantification than a global or local threshold in grayscale phasegrams under those conditions.
| [ 3 ]
|| Bretz, L.; Häfner, B. & Lanza, G. (2019), "Funktionsorientierte Inline-Messtechnik von Faserverbunden", wt-online, pp. 816-821.
Hybrid fiber-reinforced plastics combine the advantages of their different fiber types and materials. During the expensive manufacturing process, production deviations with unknown influence on the part‘s performance may occur. The integration of inline measurement technology for quantitative measure-ment of the deviations and simulative evaluation of the mea-surement results at the functional level during the production process can reduce scrap and costs.