THE EFFECT OF MOISTURE ON THE INTERLAMINAR FRACTURE TOUGHNESS OF CFRP LAMINATE

摘要

The effect of moisture on the mode I and mode II interlaminar fracture toughness of carbon fibre/epoxy laminates was studied experimentally with DCB (Double Cantilever Beam) and ENF (End Notched Flexure) tests. Unidirectional [0°]24 layup was used in the study. The material used in the specimens was AS4/35016 unidirectional prepreg tape. Three types of specimens were tested: 1) dry specimens, 2) environmentally exposed specimens, and 3) specimens at ambient humidity. The tests were performed with a servohydraulic test machine. A 0.5 kN load cell was used in the DCB tests. The DCB test procedure included two loading cycles making it possible to measure two separate crack initiation values and several crack propagation values. The ENF tests were performed with a typical three point bending jig. A higher mode I crack initiation value was obtained for an environmentally exposed (wet) laminate when interlaminar fracture toughness was measured from the delamination insert. When measured from the precrack, the crack initiation values showed lower dependence on moisture. The delaminationresistance curves were similar for all three types of specimens. Mode II values increased slightly with moisture. Increase in the insert crack initiation toughness was most likely caused by moisture related toughening of the resinrich area at the insert tip.