The effect of moisture on the failure locus and fracture energy of an epoxy–steel interface

Experimental studies have been undertaken that provide the fracture energy of an epoxy-steel interface that has been exposed to various uptake levels of moisture. The test configuration used for these studies is the mixed mode flexure (MMF) test. The specimens have been exposed to the moist environment as open-faced specimens. The results provided by the test show a steady degradation in the interface fracture energy with increasing moisture content. Surface characterisation techniques such as X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to characterise the nature of the failure surfaces. Both of these analyses show a reduction of adhesive fragments and carbon overlayer thickness on the steel fracture surface with increasing moisture levels. The variation of carbon overlayer thickness with moisture exhibits a similar trend as the fracture energy, indicating that the two may be related.