Abstract
Three-point bend tests were performed on two 32-layer balanced symmetric laminates. The advanced composite material is HI-TEX 46–8B carbon fibre in epoxy resin E7K8T, with a 59.5 % fibre volume fraction. A graphical technique based on classical beam theory was used to measure specimen longitudinal flexural and out-of-plane shear moduli. Likely sources of error were examined. A special case of the classical lamination plate theory was found to give excellent predictions of the flexural modulus. Comparison with the experimental data demonstrated that omission of the in-plane coupling stiffness had a more profound effect than omission of the shear coupling stiffnesses. To provide the engineer with a design tool a high-order analytical technique was developed. Its purpose is to predict shear deformation in multi-layered symmetrical strips, subjected to three-point bending. Exact elasticity solutions for specially orthotropic examples were used to establish its potential performance. Measured moduli for the two laminations established the shear contribution to the central displacement. Comparison with the computational model was found to be excellent for thin strips. As the span was reduced the numerical predictions gave higher displacement from shear. For the two laminations tested, shear effects can be neglected for span-to-thickness > 40. The work presented confirms the safe use in the composite community of spans 30 to 40 times the specimen thickness.
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