Developing a four point bend specimen to measure the mode I intralaminar fracture toughness of unidirectional laminated composites

The use of a four point bend test is investigated for the measurement of intralaminar toughness of unidirectional carbon fibre composites. A key element of the investigation is the process of producing a sharp pre-crack and the effect of this on the measured toughness. A method is presented in which the pre-crack is produced during the layup and cure process and this is shown to cause minimal distortion of the plies of the laminate. The test results show good consistency and low scatter.