Durability of Closed-End Pressurized GRP Pipes under Hygrothermal Conditions. Part I: Monotonic Tests

Abstract

Environmental factors are of extreme importance with respect to the ser-vice life of composite components based on polymeric engineering matrices. Part I deals with the role of matrix ductility and chemical environmental 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 composites are an E glass fiber reinforced polyester resin and an ECR glass fiber reinforced vinylester resin.

The mechanical behavior of the pipes before and after exposure to water for different duration is studied through internal pressurizing tests with closed end procedure. The results indicate that in the hoop direction, fibers carry the complete load while in the axial direction there is a substantial contribution from the matrix. The use of elasticity theory appears as an appropriate method to describe the mechanical behavior of the pressurized pipes under 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 mechanical properties are investigated. Experimental results show that the mechanical properties, the damage mechanisms and the failure mode of the pipes are changed by water uptake. Relations between the mechanical properties and the exposure duration based on physical considerations are assessed, allowing for the definition of a damage parameter related 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 axial modulus. This leads to the definition of two independent damage parameters.