Development and assessment of a novel resin injection repair procedure for impact damaged composites

Composites are finding increasing use in structural applications due to their high specific properties. However, while significant research has taken place into the manufacture and design of composite structures, relatively little research has focused on their repair. Impact damage is of particular concern due to the low through-thickness strength of composites in comparison to metals. To allow the continuing expansion in use of composites, the development and assessment of a novel resin injection repair method was investigated.

A carbon fibre epoxy resin pre-impregnated material, HTA6376, was examined. The use of cyanoacrylates (CAs) as the repair resin was investigated due to their very low viscosity. The strength of the bond formed between the fracture surfaces of HTA6376 and CA was examined in both Mode I and Mode II conditions. Experimental tests were performed at both the micro- and macro-scale. The strength of the bond formed between the fracture surfaces of HTA6376 and CA was found to be greater than the original interlaminar strength. Micro-scale specimens were found to have failed due to adhesive failure in contrast to macro-scale specimens which failed due to cohesive failure.

A repair rig requiring only common workshop materials and a repair procedure suitable for CA were developed. The compressive and flexural strength of impact damaged specimens were successfully restored as a result of the developed resin injection repair procedure. Repairs performed with toughened CA were not as successful as repairs performed with standard CA due to their higher viscosity. Tensile strength was not restored as a result of this repair method although the use of patches resulted in an increase in tensile strength.

Overall, it was found that the developed repair procedure can successfully restore the compressive and flexural strength of damaged composites when the impact damage consists of breakout where the plies close to the impacted surface are not fractured.