The Physical Mechanisms Responsible for the Weathering of Epoxy Resins and GFR Epoxy Resins.

The technique of using high intensity light emitting diodes to produce optical images of ultrasonic wave trains has been applied to two aspects of the work. In experiments preliminary to fundamental studies of resinglass interfaces, the technique has been refined to the stage where clearly resolvable fringes can be reproducibly observed in glass and in epoxy resin, and in experiments to assess the techniques potential as a NDT tool capable of detecting flaws in real composites, ultrasound has been successfully transmitted through composite slabs to give readable fringes in a glass visualising block. Accelerated water exposure tests and natural weathering tests on epoxy resin composites have continued. Chemical analysis has confirmed the impression gained from microstructural examination of fracture surfaces that, even when apparently fully cured, these materials contain unreacted resin and hardener, dissolution of which by diffused water is no doubt partly responsible for generation of the pockets of pressure believed to be the cause of disc-shaped internal cracks. Author