ELECTRICAL CRACK LENGTH MEASUREMENT AND THE TEMPERATURE-DEPENDENCE OF THE MODE-I FRACTURE-TOUGHNESS OF CARBON-FIBER REINFORCED-PLASTICS

The conventional optical crack length measurement in fracture toughness testing is unsuitable for tests carried out in a chamber, like temperature tests. An electrical method has therefore been developed which determines the crack length on the basis of a change of electrical resistivity. Compared with optical measurements this method has proved to be very accurate. With this method the Mode I fracture toughness of a carbon fibre reinforced epoxy composite was determined over the temperature range from -55-degrees-C to 120-degrees-C. It was found that the fracture toughness rises with increasing temperature. At low temperatures the values were constant or increased slightly, with minimum at about 0-degrees-C.