PSI - Issue 17

Formiga J. et al. / Procedia Structural Integrity 17 (2019) 886–893 "Formiga J, Sousa L., Infante V." / Structural Integrity Procedia 00 (2019) 000 – 000

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equal to the modelled one. This distant results between numerical and experimental analysis shows that the model demands some improvements. In Fig. 8a chamfer failure modes are presented. Ply failure happened in the inner edge of the chamfer, almost separating it from the rest of the plate. Some manufacturing errors, including vacuum bag issues and incorrect distance could create stress concentration and lead to this because, according to the numerical analysis, this area has not higher composite failure. The overlap of the carbon fibre plies is observable, creating a thickness increase, as well as a small compression of the honeycomb core across the inner edge. Moving into the interior of the chamfer a lot of failure modes are observable. First, adhesive rupture happened between the outer ply and the honeycomb and in the area where the two plies join, due to bending. This bending opened fissures in the external laminate that went into ply de lamination. And finally, is observable a collapse of the plies below the backing plate. 5. Conclusions Different configurations to reinforce the load transmission zone of a monocoque chassis were studied, a finite element model was performed to improve several geometrical parameters of each studied configuration. The geometric study led to better understand how these parameters influence the final behaviour of sandwich structure, not only when used independently but also when included in a suspension quarter-car. The application of a failure criteria, based on Groenwold and Haftka (2008), aided to compare their failure probability. The improved geometry configurations were selected, and a laminate optimization was performed in order to get the most proper structure for each approach. Specimens associated to these structures were built, and pull-out tests were performed. The apparatus for these tests was improved to achieve consistent results. The experimental results were compared with the ones achieved by the numerical analysis and a correlation was obtained for both configurations. The inserts configuration presented exact results but revealed small variations between themselves, producing an average error of 7% which reflects a good agreement between the numerical and experimental results. Chamfers configuration showed precise results but different from the ones predicted by the finite element model. In this case, an average difference of 39% was achieved showing that the model needs some improvements. This discrepancy is justified by some manufacturing adaptations demanded to produce plates which are, in some order, different from the modelled ones. Overall, despite some results deviations, all specimens withstand the design load without failure which infers that both configurations are valid to be used. Acknowledgements The study was supported by FST Lisboa formula student team. This work was also supported by “Fundação para a Ciência e a Tecnologia” (FCT), through the Institute of Mechanical Engineering (IDMEC) under the Associated Laboratory for Energy, Transports and Aeronautics (LAETA), Project UID/EMS/50022/2019. References Gebhardt, J., Fleischer, J., 2014. Experimental investigation and performance enhancement of inserts in composite parts. Procedia CIRP 23,7-12. Roth, A., 2005. Strukturelles Nähen:Ein Verfahren zur Armierung von Krafteinleitungen für Sandwich-Strukturen aus Faser-Kunststoff-Verbund. Thompson, R., Matthews, F. 1995. Load attachment for honeycomb panels in racing cars, in. Materials and design vol.16, nº3. Space Engineering Insert Design Handbook. 2011. ESA Requirements and Standards Division. Heimbs, S., Pein, M., 2009. Failure behaviour of honeycomb sandwich corner joints and inserts. Composite Structures 89, 575-588. Song, K., Choi, J., Kweon, J., 2008. An experimental study of the insert joint strength of composite sandwich structures. Composite Structures 86, 107-113. Bunyawanichakul, P., Castanie, B., Barrau, J., 2005. Experimental and numerical analysis of inserts in sandwich structures. Applied Composite Materials 12, 177-191. Lim, J., Lee, D., 2011. Development of the hybrid insert for composite sandwich satellite structures. Composites Part A: Applied Science and Manufacturing 42,1040-1048. Wolf, J., Brysch, M., 2018. Validity check of an analytical dimensioning approach for potted insert load introductions in honeycomb sandwich panels. Composite Structures 202, 1195-1215. Kim, B., Lee, D., 2008. Characteristics of joining inserts for composite sandwich panels. Composite Structures 86, 55-60. Groenwold, A., Haftka, R., 2006. Optimization with non-homogeneous failure criteria like Tsai-Wu for composite laminates. Structural and Multidisciplinary Optimization 32, 183-190.