Some Aspects of Evaluation of GFRP Composite Depending on Its End Use

Abstract

The present work is an attempt at evaluating E-glass fibre reinforced epoxy resin matrix composites when exposed to various environmental severities including temperature fluctuations. The conditions to which the representative sample of the Glass fibre reinforced polymer (GFRP) composite is exposed in the present investigation, include hydrothermal and hygrothermal conditioning with up and down thermal shock; sea water immersion followed by up and down-thermal shock; flowing of sea water in a GFRP pipe with temperature fluctuations and gamma irradiation. The performance of the material is thus, thoroughly investigated and on the basis of the findings, an effort is made to comment on the life-span of the GFRP composite for its safe use under the environmental severities.
The mechanical properties of the composite are noticeably altered as the material picks up moisture. When exposed to sea water on immersion/flow of sea water in a GFRP composite pipe; it is observed that the intake of moisture is low as compared to an exposure to distilled water through immersion/exposure to moisture laden atmosphere. Different salts present in the sea water penetrate to different depths in to the composite matrix; this order being Ca > Mg > K > Na; as dictated by catalytic effects and the growth of micro-organism on the composite surface. It is also observed that low intensity gamma irradiation is more harmful to the composite as compared to high intensity irradiation which may be due to cross-linking of polymer network of the epoxy resin due to free radical reactions. Glass transition temperature (Tg) for all exposed composites decrease in general under the influence of the adverse factors.
The deteriorating effect under hygrothermal and hydrothermal exposures is time dependent. Hygrothermal exposure causes more deterioration of the property of the composite in comparison to hydrothermal exposure. ILSS decreases 26.6 MPa to 20.08 MPa after 90 days of hygrothermal exposure, correspondingly, Tg decreases from 1200C to 98.080C. For both up and down-thermal shocks, the hygrothermal and hydrothermal exposures bring in greater deteriorations, the ILSS decreasing up to17.62 MPa and 18.12 MPa respectively. More significant results have been presented for the GFRP composite pipe allowed for 1 year of sea water flowing. ILSS of GFRP pipe sample decreases up to 23% of as-cured sample after 1 year of exposure to flowing sea water. Tg for such treated pipe sample decreases to 93.270C from 1200C for as-cured one. Depth of penetration of the salt components of sea water is more for ‘Ca’ compared to other salt components showing 750 .
It is further observed that the rate of variation of the mechanical properties like inter laminar shear strength (ILSS), stress and strain at rupture of the material diminishes with lapse of time indicating a safe suitable use of the material over prolonged periods.
The modes of failure as revealed from the scanning electron microscope (SEM) fractographs include fibre/matrix debonding, fibre pull out, fibre breaking, matrix cracking as well as crazing, etc.