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

摘要

The effect of moisture on the mode I and modernII interlaminar fracture toughness of carbonrnfibre/epoxy laminates was studiedrnexperimentally with DCB (Double CantileverrnBeam) and ENF (End Notched Flexure) tests.rnUnidirectional [0°]24 layuprnwas used in thernstudy. The material used in the specimens wasrnAS4/35016rnunidirectional prepreg tape. Threerntypes of specimens were tested: 1) dryrnspecimens, 2) environmentally exposedrnspecimens, and 3) specimens at ambientrnhumidity.rnThe tests were performed with a servohydraulicrntest machine. A 0.5 kN load cell wasrnused in the DCB tests. The DCB test procedurernincluded two loading cycles making it possiblernto measure two separate crack initiation valuesrnand several crack propagation values. The ENFrntests were performed with a typical three pointrnbending jig.rnA higher mode I crack initiation valuernwas obtained for an environmentally exposedrn(wet) laminate when interlaminar fracturerntoughness was measured from the delaminationrninsert. When measured from the precrack, therncrack initiation values showed lowerrndependence on moisture. The delaminationresistancerncurves were similar for all threerntypes of specimens. Mode II values increasedrnslightly with moisture.rnIncrease in the insert crack initiationrntoughness was most likely caused by moisturernrelated toughening of the resinrichrnarea at therninsert tip.