10. Contamination-Induced Degradation/Enhancement of Interfacial Toughness and Strength in Polymer-Matrix Composite Interfaces

This study explores the effect of environmental contamination on the interfacial toughness and strength of polymer-based interfaces. Double cantilever beam, end-notched flexure, and single lap joint tests are utilized to examine the contaminated bond line behavior under different fracture modes. A typical adhesive/adherend material system exposed to a common aviation hydraulic fluid at varying contamination concentrations is examined. The mode-I fracture tests reveal a significant degradation in mode-I fracture toughness and strength with increasing contaminant concentration, whereas mode-II fracture properties are found to be insensitive to the contamination level. To the contrary, single lap joint shear strength exhibits an enhancement with increasing contaminant concentration. Such contradictory result can be attributed to nucleation vs. propagation of interfacial cracks. Contamination weakens the interfacial bonding and thereby reduces the interfacial adhesion while shielding plastic dissipation within the bond line. Whereas, contamination also reduces the plastic flow stress of the bond line and thereby increases local plastic dissipation in the SLJ geometry.