Damage evolution and characterisation of crack types in CF/EP laminates loaded at low temperatures

Tensile testing of CF/EP AS4/8552 cross-ply laminates at room (RT) and cryogenic (around - 150 degrees C) temperatures has been performed to study the effect of temperature oil damage (intralaminar cracking) evolution. microscopy studies of the specimen edges showed a significant difference ill damage pattern for the two different temperatures. At the low temperature (LT), more complex Crack types were obtained that could not be found ill specimens tested at the RT. The effect of these crack types oil the laminate tensile modulus was studied by FEM. Ill analytical stiffness modelling complex shape crack was replaced by an effective normal (straight) crack with all effective crack opening displacement (COD) that leads to the same reduction ill laminate stiffness. A crack efficiency factor was introduced to characterize the significance of complex crack shapes for stiffness reduction. The reduction of tensile modulus for a laminate damaged at low temperature was measured and compared with model predictions. (c) 2007 Elsevier Ltd. All rights reserved.