Measurement of the in situ ply fracture toughness associated with mode I fibre tensile failure in FRP. Part II: Size and lay-up effects

The in-plane size, thickness and lay-up effects on the measured fracture toughness associated with fibre tensile failure were investigated for a T300/920 laminated carbon/epoxy material system. Compact tension specimens were tested with scaled in-plane size, increased thickness, and having various proportions of plies orientated at 0° and 90° to the loading direction. No in-plane size effects were discovered; however, testing revealed a thickness dependence. It was found that the ply toughness is significantly dependent on the thickness of the 0° layers. Propagation values of toughness were measured to be 132 kJ/m² for specimens made up of 90/0₂] sub-laminates and between 57 and 69 kJ/m² for all other configurations. Investigation of the fracture surfaces using SEM revealed that the increase in measured toughness for specimens with thicker 0° plies was due to an increase in the amount of pulled-out 0° fibres.