Mechanism of breakdown in the interface region of glass reinforced polyester by artificial weathering

Laboratory studies were conducted to elucidate the mechanism of breakdown in the interface region of glass-fibre reinforced polyester (GRP) composites on outdoor weathering. GRP composites were subjected to the effects of moisture, temperature and radiation. Breakdown in the interface region occurred when the GRP sheets were aged in the presence of water and physically-induced stress (thermally and/or by moisture). The stresses involved are complex, the most predominant being axial shear stresses. Fracture characteristics of breakdown produced during laboratory ageing were very similar to those occurring on outdoor weathering.According to the mechanism proposed, the resin in the interface region is subjected, during environmental ageing, to a stress-fatigue resulting from the differential dimensional changes between glass and matrix induced by moisture and/or temperature cyclic variations. Under the influence of alternating cyclic stresses and in conjunction with the chemical degradation of the matrix, the interface region undergoes cracking, fracture and fibre delamination. This type of breakdown may be referred to as environmental stress cracking.