NEAR-TIP STRESS FIELDS FOR CRACK IN COMPOSITE WITH NEGATIVE POISSON’S RATIO

It had been proved experimentally that Graphite(AS4)/Epoxy(3501-6) unbalanced laminates with inplane negative Poisson's ratio have higher fracture toughness and notch fracture strength. In this paper, a study is made of the near-tip stress fields for crack and the stress intensity factors in unbalanced laminates with inplane negative Poisson's ratio by the complex variable-variational method. The results obtained are compared with the results of halaneed lamlnates.Three layups, 0/15/75/15,0/25/65/25_s with negative Poisson's ratio and 0/60/90/-60_s with positive Poisson's ratio are analysed. Emphasis is put on research into the elations between principal stress's orientations and fiber's orientations as well as between stress intensity factors and fracture toughness. The calculation results show that these laminates with negative Poisson's ratio have higher notch fracture strength.