Preliminary creep test for estimating the long term stowage behavior of DLR's CFRP booms

Kurzfassung

In recent years DLR developed several mechanisms for boom and membrane deploying spacecrafts. Most of these concepts are using thin shell CFRP (carbon fiber-reinforced plastic) booms with a double omega shaped cross section to deploy the membranes. These CFRP booms provide a very volume efficient way for stowing by first flattening and then coiling them up onto a spool. Depending on storage time, up-reeling radius and storage temperature creep resulting from flexure loading might occur in the CFRP material, which could be a potential risk for the functionality of the deployable CFRP booms. This paper addresses the issue of long-term stowage of DLR’s CFRP booms by the means of a preliminary creep test. The test is conducted with flat CFRP specimens made out of the same material as used for the booms. The specimens are reeled on cylinders of different radii and stored under different temperatures, to represent the different thermal loading that can occur and to investigate different hub dimensions for boom stowage. At certain time intervals the specimens are unreeled and the curvature is scanned with an optical system and analyzed. The measured results show that temperature has a greater influence on the residual deformation of the specimens than the up-reeling diameter. Furthermore an estimation of the degradation of the relaxation modulus after 20 years of stowage at room temperature shows that the influence of creep can not be neglected.