THE USE OF ELEVATED-TEMPERATURE IN THE STRUCTURAL TESTING OF FRP COMPONENTS FOR SIMULATING THE EFFECTS OF HOT AND WET ENVIRONMENTAL EXPOSURE

The natural process of moisture absorption in epoxy resin matrices is normally slow and this makes it is very difficult to achieve a realistic degree of moisture-related degradation in an FRP structural test element in a practical time. One of the effects of absorbed moisture is to lower the glass transition temperature of the matrix, thereby causing a reduction in the temperature-related properties. It is postulated that an increase in test temperature, equivalent to that of the change in the glass transition temperature, could be used to represent the degradation due to moisture. Experimental evidence to support the use of such an alternative is presented. The evidence comprises an examination of three matrix-dependent mechanical properties and their failure modes. Results show that the compression strength, the +/- 45 degrees tension strength and the interlaminar shear strength, together with the failure mode characteristics of the hot-wet structure, can be duplicated using a temperature increment over and above the normal temperature requirements for airworthiness clearance to achieve an equivalent effect of moisture.