Residual stresses associated with post-cure shrinkage in GRP tubes

Laminates made with polyester or vinyl-ester resins can undergo substantial shrinkage when subject to an elevated-temperature post-cure after room-temperature polymerisation. In composite tubes, restraint on free shrinkage, which results in residual stresses, arises because the in-plane shrinkages tend to be substantially smaller than the through-thickness shrinkages and also because of differences in the shrinkages of adjacent layers of different constructions. This paper presents the results of a theoretical investigation of the associated residual stresses. The Rayleigh-Ritz method is implemented in predicting the residual stresses and results are presented for a range of cases representative of practical materials, constructions and geometries. It is shown that inner-wall tensile residual stresses of sufficient magnitude to promote environmentally assisted cracking can readily be induced. Furthermore, the results indicate that the widely specified +/- 55 degrees laminate construction tends to give rise to particularly unfavourable residual stress states. (C) 1997 Elsevier Science Limited.