DURABILITY OF CLOSED-END PRESSURIZED GRP PIPES UNDER HYGROTHERMAL CONDITIONS .2. MONOTONIC TESTS

Environmental factors are of extreme importance with respect to the se rvice life of composite components based on polymeric engineering matr ices. Part I deals with the role of matrix ductility and chemical envi ronmental degradation on the composites mechanical properties. Part II is concerned with the lifetime prediction of GRP filament wound pipes under low pressure levels and hygrothermal conditions. There composit es are an E glass fiber reinforced polyester resin and an ECR glass fi ber reinforced vinylester resin. The mechanical behavior of the pipes before and after exposure to water for different duration is studied t hrough internal pressurizing tests with closed end procedure. The resu lts indicate that in the hoop direction, fibers carry the complete loa d while in the axial direction there is a substantial contribution fro m the matrix. The use of elasticity theory appears as an appropriate m ethod to describe the mechanical behavior of the pressurized pipes und er monotonic loading conditions. In the hoop direction the behavior is governed by the fibers one whereas in the axial direction damage must be accounted for in the elastic law. Chain scission effects on the me chanical properties are investigated. Experimental results show that t he mechanical properties, the damage mechanisms and the failure mode o f the pipes are changed by water uptake. Relations between the mechani cal properties and the exposure duration based on physical considerati ons are assessed, allowing for the definition of a damage parameter re lated to hygrothermal degradation. Environmental effects (swelling and chain scission) mainly affect the yielding pressure and the pressure to failure, whereas load condition and initial defects affect the axia l modulus. This leads to the definition of two independent damage para meters.