https://reports.aerade.cranfield.ac.uk/handle/1826.2/4522 2026-08-15T15:47:36Z https://reports.aerade.cranfield.ac.uk/handle/1826.2/4545 The use of a simple composite element to describe the creep properties of fibre reinforced composites The stress-strain relationship for a composite material is dependent on both the geometry and the stress-strain relationships of the component phases. This note describes a technique by which the stress-strain relationship can be calculated for any fibre reinforced composite where the matrix has linear viscoelastic properties and the fibres are linearly elastic. The distribution of fibres within the composite is assumed to be macroscopically homogeneous but the distribution of fibre orientation can take any configurations. The problem is solved initially for the case where both phases are linearly elastic. A simple composite element from which a composite can be built up is defined and the stress-strain relationship for this element is calculated using variational methods. By summing these elements assuming either uniform stress or uniform strain throughout the composite, upper and lower bounds to the stiffness matrix of the composite are obtained. Using the correspondence principle these bounds for the purely elastic case are transformed to give the bounds for the viscoelastic case. The theoretical answers obtained using this method are compared with those obtained using a more simple model for the mode of combination of the two phases. https://reports.aerade.cranfield.ac.uk/handle/1826.2/4548 Some microstructural features of fatigue in an aluminium alloy The microstructures produced by the heat treatment of a commercial age hardening At-4.4 Cu alloy have been examined by thin foil electron microscopy. Whilst there is similarity of the microstructures in the commercial alloy to those which have been reported for simple binary At-Cu alloys, there is a strong association of dislocation structures and incoherent precipitates with undissolved Mn bearing intermetallic particles. Fatigue tests made on the alloy at both 50 Hz and 20 kHz have shown that there are changes in microstructure during fatigue; more markedly at 20 kHz in which tests the heating effect has some importance. There is some evidence of both accelerated ageing and also the by-passing or resolution of coherent phases during fatigue, particular at 20 kHz. https://reports.aerade.cranfield.ac.uk/handle/1826.2/4547 A fracture of rubber in a state of finite torsional shear A solid rubber cylinder with metal end plates fractured in the rubber when a torsional deformation was applied 'which corresponded to a shear angle of 56° on the cylinder surface. The height of the cylinder was maintained accurately constant during the deformation. A comparatively smooth fracture surface was created in a direction perpendicular to the principal tensile stress and a rough surface was created perpendicular to the principal compressive stress. The markings on the smooth surface have some feature similar to a cleavage-type failure in a crystalline material. https://reports.aerade.cranfield.ac.uk/handle/1826.2/4546 Some further experiments in fatigue testing at 20 kH2 Considerations are made of the suitability of acoustic transformers applied to fatigue testing at 20 kH2. A suitable system has been constructed which allows the use of plain cylindrical specimens. The results of fatigue tests on an aluminium alloy are given and discussed in relation to structure and environment.