Electrical crack length measurement and the temperature dependence of the Mode I fracture toughness of carbon fibre 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°C to 120°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°C.