A. R. Hutchinson

Adhesive systems for structural connections in timber

Adhesives can be used to form load-bearing joints in timber structures, both in repair and in new-build applications. An efficient and cost-effective method of making joints is to use rods or dowels, bonded into pre-drilled holes in timber elements, for transferring structural loads between such elements. This paper reviews the important issues in bonded-in rod technology, the adhesives and reinforcing materials used, the results of theoretical and experimental studies, and the steps involved in design and specification.

Resin repairs to timber structures

Abstract Resin methods to repair timber structures are relatively new with a history of use of approximately 25 years. Architects and engineers have mixed feelings about their use with reservations such as: (1) unknown or unreliable structural performance, especially with timber at high moisture contents, and (2) unproven durability and inability to conform to conservation recommendations. This paper discusses tests carried out to assess the performance of resins used in timber repair and discusses conservation recommendations which also prevent more widespread use of the technique.

EFFECT OF TIMBER MOISTURE CONTENT ON BONDED-IN RODS

Abstract Concealed bonded-in rods represent one example of an efficient joining method for modern structural timber composites and structures, exhibiting properties such as good joint stiffness and strength, reduced end-grain splitting, greater fire resistance and they have the added advantage of being more aesthetically pleasing than other joining methods simply because there is no visible joint. However, the effect of the timber moisture content (MC), at the time of bonding, on the strength of these connections is at present unknown. This paper describes the effect of MC on concealed bonded-in rod connections using ash and oak specimens. It was found that both strength and, in particular, the failure modes of the various specimen combinations were significantly influenced by the MC of the timber at the time of bonding.

The use of flame ionisation technology to improve the wettability and adhesion properties of wood

Flame ionisation technology has been used in an attempt to enhance the performance of exterior surface coatings with timber through an improvement in the wettability of the wood. Preliminary surface energy data indicate that total surface energy values can indeed be improved by an increase in the polar component of the energy. Flame treatment is not affected by surface preparation prior to treatment, although the response of the surface may be influenced by the amount of polar extractives in the timber.

Carbon-fibre-reinforced plastic (CFRP) strengthening of aluminium extrusions

Abstract The flexural behaviour of compound beams in which unidirectional carbon-fibre-reinforced plastic (CFRP) is externally bonded to extruded aluminium box-sections, is discussed. Simple transformed-section analysis and elastic buckling theory have been adapted to predict improvements in stiffness and strength with single-layer reinforcement. Close correlation between theory and experiment is observed and maximum gains in stiffness and ultimate strengths of 75% and 63%, respectively, are demonstrated with only a 7% weight increase. It is shown that the effects of the adhesive can be neglected when predicting the performance of the hybrid beam. Shape optimisation has been successfully applied to illustrate the potential of this technique for ‘new-build’ applications. Initial findings have produced weight savings of 33% in comparison to an all-aluminium optimised box-section.

A Review of Adhesion Promotion Techniques for Solid Timber Substrates

The use of primers, coupling agents, and other surface treatments to enhance adhesion is now common in the aerospace, automotive, and plastics industries, where they are used to develop highly durable bonds to metals, advanced composites, ceramics, and plastics. However, such treatments are virtually non-existent in the wood products industry although they could solve important adhesion problems. In particular, adhesion promoters can enhance the environmental durability of epoxy bonded joints, and they can enhance the reliability of bonds to timber treated with wood preservatives. A review of current findings is provided that attempts to gather the scarce and disperse information available in the literature about adhesion promotion techniques for bonded solid timber joints. A general overview of the research needs on this topic is also given.

Factors affecting electric vehicle energy consumption

Internal combustion (IC) engines waste a majority of the energy they consume, with only 20% actually going into moving the vehicle. The drivetrains of electric vehicles (EVs) can operate at over 80% efficiency which shows that they have great potential in reducing the transportation energy demand. This paper initially quantifies the energy needed to run an EV, having similar dimensions and performance to modern IC vehicles. Simple range and cost calculations were used to establish the advancements needed in battery technology to match the ranges of IC vehicles. Factors affecting EV energy consumption are then addressed, with the aid of MATLAB® simulations, to ascertain what variations can be expected in real-world situations and the benefits of optimising vehicle parameters. The results are then compared with conventional and hybrid IC vehicles. It is shown that an optimised EV can achieve a 63% ‘tank-to-wheels’ energy reduction over the best conventional IC vehicles available, and 60% over hybrids. The effects of either a badly optimised EV, hard acceleration during the driving cycle, or constant large accessory power draws, such as heaters and demisters, are each shown to increase the EVs energy consumption by 70%/km. To achieve the performance and practicalities comparable with modern IC vehicles, new battery technologies with specific energies of >300 Wh/kg are required.

Prediction of Brittle Failure of Notched Graphite and Silicon Nitride Bars

High stress gradients occur at metal-to-ceramic joints due to the different thermal and mechanical properties of the materials. In some cases, the magnitude of the highly localized stresses lead to failure thus compromising the structural integrity of such joints. The study of notched ceramic bars with high stress gradients can assist with the prediction of failure of metal ceramic joints. Experiments and fracture mechanics analysis were performed on notched and un-notched POCO E.D.M 3 graphite and AS800 Silicon Nitride bars with different notch parameters. The twoparameter, multi-axial Weibull statistics method and a brittle fracture criterion based on the average stress over an area approach were used to predict the failure of the bars and the results obtained were compared with experimental results. The brittle failure criterion appears to give much better correlation with experimental results than the multi-axial Weibull statistics approach. The findings also appear to highlight the limitations of the Weibull’s statistics method in cases involving very high stress gradients.

Sealing and resealing of joints in buildings

Abstract Sealants play a vital role in joints in maintaining the weather-tightness of buildings and engineering structures. This paper outlines the nature of joint movements and the requirements of sealants to fulfil this role. Aspects of economics, joint design, sealant system selection and joint preparation are then discussed, both in the context of new sealing and resealing. Important new guidance is also given in terms of resealing of joints. Finally, the requirements of a detailed contract specification are outlined.

Development of a Novel Test Rig for the Evaluation of Aircraft Fuel Tank Sealant

A key concept for the future evaluation of sealant materials for commercial aircraft is to expose realistic sealed joint systems to typical dynamic and environmental parameters representative of actual flight conditions. The development of a mechanism to undertake the full range of test parameters for the evaluation of sealants for current and future aircraft is described in this paper. This mechanism, or model sealed system (MSS), consists of an axial stress machine into which vibrational fatigue, high and low temperatures and pressures can be programmed for automatic operation. The test coupons, within the MSS, can be stressed to simulate flight conditions along with the flight pressures and temperatures. The MSS is described and the results of sealant evaluation to date are presented.