On superior buckling performance of flat plates through anisotropy

The behaviour of flat plates made from composite laminates with negative Poisson's ratios is investigated. The requirements for negative Poisson's ratio laminates is discussed and the maximum negative Poisson ratio and the stacking sequence was identified. For an eight layered laminate of the material considered this was a laminate with stacking sequence [75₃ 25]_S with a Poisson's ratio of -0.296. It is hoped that a negative Poisson's ratio would provide a transverse tensile stress during prebuckled loading if the plate was restrained such that transverse displacement was eliminated. Approximate closed form solutions were shown that accurately assessed the effects of extension/shear and flexural/twist anisotropy on buckling loads. Using this model the laminate [65₃ 15]_S was identified as that with the greatest buckling load. There was good correlation with linear finite element analyses (FEA). The effect of plate overhangs and restraining edges were found to significantly affect buckling loads and were modelled using FEA. The two laminates identified above in addition to [(90,0)₂]_S were made into flat plates (three of each) for subsequent buckling tests. Experimental buckling loads correlated well with FEA for the angle ply plates.