The fracture toughness of repaired composite

The fracture toughness (K'IC) at the interface formed between a composite substrate and more recently placed composite has been measured to determine the strength of the repair. The substrate material was 24 h old at the time of the repair and the fracture toughness of the repair was measured 24 h later. Five composite products were selected for repair by using either that particular product or one of the others. Repairs were made to clean fractured surfaces, and these after contamination with artificial saliva. The fracture toughness factor of any repair was significantly less than that for the respective control. The effect of surface contamination proved highly significant and reduced the fracture toughness. An interaction existed between adherend (substrate) and adhesive (addition) materials. Compatibility between these for matrix and initiation chemistries did not appear to be significant.