Elastic behaviour of circular composite plates transversely loaded at the centre

Static tests were carried out on moderately anisotropic, simply supported circular plates made of graphite fibre reinforced plastic laminates of various thicknesses, loading them at the centre by a hemispherical tup. A non-linear solution available for large deflections of isotropic plates was suitably modified to account for the Hertzian contact phenomena, and adopted to model the plate behaviour in the elastic field. From the experimental results, an unacceptable error is made in predicting the force-deflection curve up to first failure, if the non-linear portion of the deflection is neglected. This error is the more evident when thin laminates are concerned. For thick laminates, the Hertzian contact plays a significant role in affecting the plate behaviour. Taking into account both the local deformation and non-linearity due to large deflections, a very accurate prediction of the load-deflection curve was obtained. Only in the case of the thinnest composites tested, a divergence of the theoretical curve from the experimental data was observed at sufficiently high loads. The analysis of the failure modes revealed that the discrepancy is seemingly attributable to internal damage not resulting in clearly discernible discontinuities in the load-deflection curve.