J. T. Mottram

Manufacture and compression properties of syntactic foams

Abstract A study has been made of the processability, bulk density and uniaxial compression properties of a syntactic foam system with varying volume fractions of phenolic microballoons. Short-term compression tests showed that the compression yield strength and initial tangent modulus of elasticity were linearly dependent on the bulk density (and the volume fraction of microballoons). The microballoon concentration and resin binder composition was found to be crucial to the ease of manufacturing syntactic foams.

Lateral-torsional buckling of a pultruded I-beam

Abstract Measured short-term critical loading for linear elastic lateral-torsional buckling of a pultruded I-beam has been compared with theoretical predictions. In the buckling experiment, an E-glass reinforced polymer I-beam was simply supported about the major axis, and supported at both ends such that lateral deflection, warping and twist were restrained. It was subjected to a central point load applied to the top compression flange. The experimental evidence for critical loading is shown to compare favourably with the predictions using a finite difference method. The finite difference approach is used to solve the governing differential equation derived using thin-walled theory. Through the finite difference and other analytical models, it is shown that the classical one-dimensional isotropic theories can be adapted, by suitable substitution for the moduli parameters, to predict the buckling load for composite beams made from orthotropic panels. For the case where the load is applied at the centroid of the I-section, the design procedure given in an American design manual is shown to be conservative, providing the assumed boundary conditions at the supports are met.

Lamb wave tomography of advanced composite laminates containing damage

Abstract Ultrasonic techniques have been used to image damaged regions in two polymer composite plate samples. The two thin laminate samples studied consisted of 16 layers of carbon-fibre reinforced epoxy with a quasi-isotropic lay-up configuration and had been previously loaded in a biaxial test method until failure. The resulting damage, in the form of fibre failure, matrix cracking and delamination, has been imaged using a novel Lamb wave immersion tomography technique. Images created with this method were correlated with images obtained from C-scan techniques. Both C-scans and Lamb wave tomography were able to identify clearly regions of damage in the two samples.

Thermal conductivity of fibre-phenolic resin composites. Part II: Numerical evaluation

Abstract Measured thermal diffusivity data presented in Part I of this report are converted to thermal conductivity using specific heat and density data. Available models for the prediction of thermal conductivity of one- two- and three-dimensional composites are reviewed and evaluated. Perpendicular to the fibres the generalised dispersion approach of Bruggeman which allows porosity to be taken into account is considered to be the most appropriate. This enables fibre conductivities to be predicted and allowed the thermal conductivity of arbitrary fibre-phenolic resin arrangements to be predicted.

State-of-the-art review on the design of beam-to-column connections for pultruded frames

A review and commentary is presented on the research to understand and develop practical beam-to-column connections for pultruded frames. Experimental moment-rotation curves for isolated connections are presented and their properties used in a commentary on frame design. Current design recommendations for pinned connections are given, with reasons why research is still necessary to understand their complete structural behaviour, and that of practical semi-rigid connections. The paper introduces a new analytical method to predict the static behaviour of linear elastic plane frames having real connections, second-order deflections and shear deformable members. The beam-line method and the frame analysis are used to show the potential benefits of treating frame design as semi-rigid. Results using these analytical models are shown to provide useful information in our quest to optimize the performance of semi-rigid connections and frames.

Short- and long-term structural properties of pultruded beam assemblies fabricated using adhesive bonding

Abstract Two beam assemblies fabricated using simple pultruded sections and adhesive bonding have been tested to determine their structural properties. The test configuration was three-point bending to simulate the most severe loading in a proposed application. Short-term stiffnesses are compared with those predicted using known section properties and linear elastic beam theory. Accelerated creep test data are used to determine long-term behaviour using Findleys linear viscoelastic theory. For the purpose of structural design, Findleys model is used to estimate the increase in maximum deflection due to a constant design loading of 1 week, 1 year and 10 years.

Thermal conductivity of fibre-phenolic resin composites. Part I: Thermal diffusivity measurements

Abstract Measurements have been made on the thermal diffusivity of fibre-phenolic resin composites between 20 and 400°C. The matrix material was the phenolic resin SC-1008 manufactured by Monsanto. Two composite systems were considered: a two-directional composite reinforced with carbon fibres woven into an eight-harness satin weave, and a silica fibre composite orthogonally reinforced in three mutually perpendicular directions. One-directional composites were also prepared using the same fibres. To assist mathematical modelling of the thermal conductivity ( Part II of this report ) heat capacity, density, and volume fraction of constitutents were also determined, together with weight and length change during the diffusivity measurement. The problems and uncertainties in obtaining component data are discussed.

Lateral-torsional buckling of thin-walled composite I-beams by the finite difference method

Abstract The finite difference method has been used to solve the differential equation for the critical loading associated with a specific lateral-torsional buckling test configuration. The linear elastic analysis is valid for thin-walled composite doubly symmetric I-beams made from mid-plane symmetric, fibre-reinforced laminated panels. Here, the test configuration has an I-beam with specially orthotropic panels. It is subjected to three-point bending, and supported at each end such that the only degree of freedom is rotation about the major axis of the beam. For the modelling case where the central load is applied at the shear centre (centroid) of the cross-section there is a favourable comparison between the finite difference results and those results presented by Timoshenko and Gere (1961, Theory of Elastic Stability 2nd edn, McGraw-Hill, New York), which were originally generated for isotropic beams. A favourable comparison has also been found between the finite difference analysis and experimental evidence using an E-glass fibre-reinforced polymeric pultruded I-beam, where the central load is now applied to the top compression flange. The various theoretical models presented in the paper are used to show that the critical loading for buckling in real composite I-beams will be strongly dependent on both the support boundary conditions and the height of the loading relative to the centroid (shear centre).

Buckling characteristics of pultruded glass fibre reinforced plastic columns under moment gradient

Abstract The authors present the results of 10 full-size tests designed to investigate the behaviour of eccentrically loaded columns of pultruded glass fibre reinforced plastic. The major axis tests were carried out on 203 × 203 × 9.53 mm wide flange profiles at a single column height of 4.8 m. The choice and magnitude of the moment gradients are described, together with details concerning the design and operation of a purpose-built test rig. Salient results are given for loads, deflections and strains, and conditions at failure are described. The results are assessed for the their relevance to the development of design procedures suitable for manuals or design codes.

The ultrasonic impulse response of unidirectional carbon fibre laminates

Abstract The impulse response of unidirectional carbon fibre reinforced polymer laminates has been determined, using a pulsed laser to generate the impulse and a broadband capacitance transducer to detect the normal component of surface motion. Waveforms were recorded at a series of positions along lines both parallel and perpendicular to the fibre axis. Velocity profiles of major arrivals have been determined, and shown to correspond to the expected group and phase velocities for the quasi and pure bulk-wave modes respectively. The elastic stiffness constants for the material have been calculated using measured phase velocity surfaces for pure modes and the reconstructed phase velocity surfaces obtained from measured group velocity data for quasi-modes.