RESIDUAL-STRESSES ARISING FROM PARTIAL IN-SERVICE POSTCURE OF GRP STRUCTURES

Strain gauge measurements on glass fibre-reinforced plastic (GRP) spec imens subjected to elevated temperatures indicated that shrinkage asso ciated with post-curing is such that, should it be restrained in any w ay, stresses of reasonable magnitude can be developed. Laboratory test s on a thick-walled GRP tube and field tests on a GRP thermosiphon eva porator showed that such restraint can be developed by partial post-cu ring of the material due to the temperature gradients developed in ser vice. Under these conditions residual tensile stresses are developed o n the laminate side subjected to the elevated temperature and, most pr obably, the chemical environment. With environmentally assisted cracki ng being sensitive to tensile stress level, it is likely that the resi dual tensile stresses can contribute to the premature failure of equip ment not subjected to a full post-cure prior to commissioning.