Life Cycle Monitoring of Thick CFRP Pipes for Spacecraft Structures

Abstract

CFRP pipes are key elements for truss structures supporting heavy optical telescopes in spacecrafts. CFRPs’ low coefficients of thermal expansion and high stiffness improve the instrument performance. In thick CFRP pipes, however, significant through-thickness tensile stress arises in curing and operation in a low temperature environment like in space, resulting in delamination failure. Though several systems are established to clarify the failure mechanism in composite pipes, the developed systems could not directly measure the through-thickness strain and could not detect signs of the damage. Hence, in this study we established a fiber-opticbased system for monitoring through-thickness strain throughout life-cycle. A fiber Bragg grating (FBG) sensor was embedded at the through-thickness center of a CFRP pipe and through-thickness strain change was measured using the birefringence effect of the sensor. The FBG sensor could continuously monitor strain development throughout the life-cycle (i.e., curing and simulated operation in a low temperature environment). Furthermore, the sensor successfully detected delamination from discontinuous strain change. Additionally, FEA and comparison with a plate specimen confirmed the validity of the measurement. This technique enables to avoid premature delamination failure, resulting in improvement of reliability of CFRP pipes.