Durability of pultruded E-glass/vinylester under combined hygrothermal exposure and sustained bending

The effect of combined water immersion and sustained bending on the degradation response of E-glass/vinylester composites is characterized through mechanical testing (tension and short-beam-shear) and moisture uptake. It is seen that moisture uptake and coefficient of diffusion increase with levels of sustained strain and that uptake characteristics can be predicted with a reasonable level of accuracy using a model incorporating the free volume approach. Both tensile strength and short-beam-shear strength decrease with increasing periods of immersion and level of sustained strain. A transition in degradative response can be identified in terms of level of sustained strain. Comparisons of response with ACI-440 guidelines indicate that the use of stress limitations is essential in specifying design allowables since the use of ACI thresholds involving environmental exposure factors alone may be unconservative for long periods of service. It is emphasized that synergistic effects of sustained bending and water immersion are accelerative and that further research is needed on ascertaining the safe level of sustained loading for use in civil infrastructure.