Development and Evaluation of Residual Stress/Strain Reduction Method in Thick CFRP Pipes

摘要

Carbon fiber reinforced plastic (CFRP) pipes are key elements of truss structuresrnin spacecrafts supporting heavy optical instruments. CFRPs are utilized due to its lowrncoefficients of thermal expansion and high stiffness, which enhance performance ofrninstruments. Recently, stiffness and size of CFRP components have been increasedrndue to increased size of optical instruments. In thick CFRP pipes, however, significantrnradial stress/strain arises during cure and low temperature operation, resulting inrndelamination failure. Thus, we have developed a fiber-optic-based monitoring systemrnthat directly measures radial strain. In this study, we demonstrate a residualrnstress/strain reduction method using asymmetric layup and evaluate its effect using therndeveloped monitoring system. First, we addressed the effect of stacking sequence onrnradial stress development using finite element analysis (FEA). The results proposed arnconcept that residual stress decreases when 90o layers having circumferential fiberrndirection are gathered and placed close to the inner surface. This is because thernasymmetric layup decreases the bending stiffness in the circumferential direction andrnsuppresses thermal deformation leading to residual stress. We then manufacturedrnsymmetric and asymmetric pipes to verify the concept using the developed monitoringrnsystem. The embedded sensor responses showed that residual stress was successfullyrnreduced in the asymmetric pipe, confirming the effect of the proposed concept. Finally,rna 50ply thick CFRP pipe in which delamination occurs using symmetric layup wasrnmade using an asymmetric layup. The sensor response embedded in the specimen andrncross sectional observation indicated no damage in the pipe, realizing a thick “crackfree”rnCFRP pipe. The concept developed would improve thermal stability of thickrnhigh modulus CFRP pipes and contribute to high performance of satellites.