Abstract:
Performing an elevated temperature post-cure procedure on glass reinforced plastic vessels
and components that are subjected to aggressive chemical environments enhances the
mechanical and chemical resistant properties of a laminate. This is a result of the
completion of the cross-link polymerisation reaction at an elevated temperature. The postcure
process is however the cause of matrix embrittlement and possibly also contributes to
crazing on the inner surface of the vessels or similar components.
To determine the cause of crazing at the inner surface this work investigates the stress and
strain development, resulting from post-cure, in chopped strand mat reinforced laminates
in the form of small bore tubes, small bore full face flanges and small diameter vessels.
The investigation consists of experimental measurements during post-cure procedures and
numerical simulations of these procedures on specified test specimens.
The numerical simulations consist of finite element analyses of models using commercially
available finite element analysis software. Material properties for the analyses are
determined using two different, but well-known approaches. The post-cure simulations are
conducted by applying laminate shrinkages, by analogy, as coefficients of thermal
expansion with a unit temperature difference in the finite element models.
Initially only the structural layers of the laminates were considered and analysed for postcure
shrinkage. However, the results obtained did not show any cause for crazing
occurring on the inner surfaces. The resin rich corrosion barrier, that is usually applied as
a first layer when manufacturing a vessel component, was added to the finite element models and analysed for post-cure stresses and strains. These results clearly indicate that
the corrosion barrier causes stress conditions at the inner surfaces that should be
unacceptable for the GRP vessel industry.
The experimental and predicted results are compared to determine the accuracy of the
finite element analyses.
Factors influencing the accuracy of strain gauge measurements on laminates constructed of
CSM are presented. The study investigates issues to be considered when finite element
analyses are required on composite material components to determine the residual
manufacturing stresses.
The study's relevance to industry is discussed and topics for further and additional studies
are recommended.
