The final design was determined through a trade-off and further improved through an iterative process containing design-, optimization- and analysis-loops. The output was a composite 6 unit CubeSat structure utilizing the performance of Carbon-Fiber reinforced Epoxy pre-preg designed to be manufactured efficiently, and configured as a sandwich, with optimized weight to stiffness ratio.
A worst case analysis determined the sandwich panel as the most critical component and therefore the qualification section scoped to optimize and predict possible failure modes.
A stress map from a numerical finite-element model, verified by analytical stress calculation theories and ASTM test setups, was used as input for failure mode analysis. The study showed an indication of skin failure as the critical, but no break at the worst case load during launch. It was also noted that by using shell elements the finite-element model was no longer subject of "shear locking". Shell theory was studied through the Kirchoff-Love and Reissner-Mindlin theory. At larger thickness panels or shorter support distance, the shear deformation effect could result in a lower stress and deflection result compared to analytical results. The effect was assumed negligible in the panel proposed, and verified at different loads to indicate correlation between hand calculations and finite-element modeling. The recommendation based on the analysis is to use SHELL181 elements to gain a result as close to reality as possible.
A modal analysis determined natural frequency at mode 1 for the sandwich panel using NASA's plate theory. This was compared to a finite-element model with coinciding results. The model was deemed reliable, but far from the coupled system achieved when analysing a complex and flight ready structure.
As proof of concept a prototype was manufactured. With a saved mass of 49%, the hyptohesis was accepted.
|Publikationsdato||21. dec. 2019|
|Status||Udgivet - 21. dec. 2019|