EXPERIMENTAL CHARACTERIZATION OF VISCOELASTIC MATERIAL PROPERTIES AND NUMERICAL IMPLEMENTATION FOR ESTIMATING LONG-TERM STOWAGE BEHAVIOR OF DLR'S CFRP BOOMS

Abstract

This paper addresses an experimental approach for determining the viscoelastic material properties of DLR's CFRP (carbon fiber reinforced polymer) booms and implementing them into a finite element model in order to estimate the mechanical degradation of the booms after long-term stowage. Based on an accelerated creep test, a master curve for the relaxation modulus of the CFRP material is derived using time-temperature-superposition principle. This master curve describes the viscoelastic behavior of the boom material over its life time and shows a reduction of about 22 % in relaxation modulus after 20 years. For subsequent numerical analyses a mathematical description of the master curve is realized using a PRONY series. Furthermore this study illustrates, by the example of the ADEO-2 de-orbiting subsystem, the effect of long-term stowage on the performance of the booms. A finite element model of the ADEO-2 boom is presented and the residual deformation of the boom after 20 years of stowage show a reduction of about 11.5 % in boom height. The reduction in mechanical performance of the boom after 20 years of stowage is predicted in a subsequent buckling load analysis for different boom lengths and load directions.