CRACK-FOLLOWING FOR ACCURATELY DETERMINING FRACTURE-TOUGHNESS

Current standard fracture-mechanics methods encourage sudden, explosive and total testpiece fracturing in which one catastrophic event produces one set of measurements. By demanding conformance to the overall elasticity requirement while relaxing thickness and crack-length specifications and following a slow crack-growth sequence, series of simultaneous measurements were made on single testpieces. From these measurements independent values of the Mode-I critical stress-intensity factor and strain-energy release rate were determined. Polyethersulphone injection-moulded discs were prepared as round-compact testpieces. The crack grown from a chevron-notch was propagated under control, slowly. A large number of measurements were made as the crack extended. The fractures were smooth, square to the body of each disc and had a stable crack path across the diameter. The independent fracture-toughness values were small but their derived modulus agreed well with directly measured values of Young's modulus, thus confirming the elastic integrity of the test.