The fracture toughness of composite laminates with a negative Poisson's ratio

Two sets of carbon fibre laminate configurations have been designed, manufactured and examined. The first consisted of one in‐plane auxetic ( i.e. having a negative Poisson's ratio) and one with matched elastic moduli, but a positive in‐plane Poisson's ratio. The second consisted of three laminates, again with matched elastic moduli, but with negative, near zero and positive thru‐thickness Poisson's ratio. Fracture toughness is predicted to be enhanced if a negative thru‐thickness Poisson's ratio is present. This study also shows that more energy is required to propagate a crack in the auxetic laminate and that it is less notch sensitive than its conventional counterpart for the negative in‐plane Poisson's ratio.