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Impact Damage in Carbon Fibre Composites
Mechanics of Impact
Vehicle Dynamics and Road Damage
Machine Elements
Vibration Damping of Composite Plates
Corrugation Prediction in Railway Lines
Stick-slip Motion in the Atomic Force Microscope
Mechanics of Musical Instruments
The Transmission of Vibration from Railways
Pipeline Inspection
Track Settlement Adjacent to Bridge Abutment
Fault Identification using Neural Networks
Wavelet Analysis
References
Dr W.J. Stronge
Laminated carbon fibre composite (CFRP) shells suffer local damage due to impact; for some states of stress, small levels of damage can reduce the strength of composites although the fractures and delaminations are subsurface and difficult to detect. A numerical method of predicting the dynamic response of orthotropic cylindrical shells to non-penetrating impact has been developed and is being used to evaluate failure stresses in CFRP pressure vessels struck by low speed missiles(F8).
Dr W.J. Stronge
Fundamental research is continuing into deformation processes during impact with the aim of obtaining a physical basis for parameters representing "rigid body" impact where deformations are small. This research is relevant to constraints on operation of mechanical linkages in high speed assembly operations, impact printers and sports mechanics. For mechanisms consisting of stiff bodies with compliant contacts the spread of impact effects throughout the mechanism has been shown to progress as a dispersive wave, with interactions depending on the gradient of relative compliance(F16). In collisions between hard bodies that are rough (i.e. where friction is not negligible) the energy absorbed during collision can be separated into part due to friction and part due to plastic deformation and elastic waves(F7).
Work continues on obtaining methods of assessing risk of perforation in metal structures subjected to impact by small sub-ordnance velocity fragments or missiles. Failure criteria representing kinematic constraints on deformation as well as material properties are being developed for oblique penetration and dishing of thin to moderately thick metal plates.
Dr D. Cebon
Research has continued on the use of advanced suspension technologies to improve heavy vehicle safety(F13), reduce road damage(F1,F2), and reduce energy losses. Considerable support in cash and kind has been received from the industrial members of the Cambridge Vehicle Dynamics Corsortium (Tinsley Bridge Limited, Meritor HVS, Koni BV, Dunlop Tyres, Volvo Trucks, DERA, Shell, Crane Fruehauf). This work is co-funded by two EPSRC grants. Research has also continued on an investigation of the use of multiple-sensor `weigh-in-motion' systems for measuring the weights of heavy vehicles travelling at highway speeds(K139). This project is funded by the EC.
Dr D J Cole and Dr D Cebon were awarded the 1996 Crompton Lanchester Medal for Automotive Engineering, and the 1996 Thomas Hawksley Gold Medal, by the Institution of Mechanical Engineers, for a paper on design of heavy vehicles to minimise road damage.
Dr J.D. Smith
A book on gear noise has been completed and will be published soon. Following the successful testing of the Smith Shock technique for monitoring scuffing on a medium size gearbox, it is proposed to test the technique on a large gearbox.
Further development of the manual trolley for measuring railway line corrugations has led to the method being proposed for a European standard for corrugation specification(F4). Current work is aimed at a system to fit underneath a train.
Dr J. Woodhouse
Earlier work on the vibration damping of thin orthotropic plates has been extended to the case of laminated plates(F16). The predictions of laminate theory were shown to give reasonably accurate agreement with measurements on carbon/epoxy plates with different lay-up details. It was also shown that laminate theory can be inverted to give accurate calibration information on the elastic and damping properties of a single ply of the laminate.
Dr J. Woodhouse
Professor K.L. Johnson
Two papers were reported last year on models for the growth of short-pitch corrugations on high-speed railway track, leading to so-called roaring rails. [Bhaskar, A., Johnson, K.L., Wood, G.D., Woodhouse, J. Wheel-rail dynamics with closely conformal contact. Part 1: dynamic modelling and stability analysis. Part 2: forced response, results and conclusions. Proceedings of the Institution of Mechanical Engineers: Part F, Journal of Rail and Rapid Transit, 211 , 11-26, 27-40 (1997). Annual Report 1996/97, E1 and E2.] These papers have been awarded two prizes by the Institution of Mechanical Engineers, the Stewartson-Dyer/Trevithick Prize and the Stephenson Prize.
Dr J. Woodhouse
Professor K.L. Johnson
Unsteady motion is sometimes observed during a steady traverse of the probe tip in the Atomic Force Microscope. This has been described as "atomic stick-slip". The behaviour has been analysed using continuum methods, to shed light on the physical mechanisms of friction, jump behaviour and energy dissipation in this system(F5). Predictions were made, which need to be tested by further experiments in the AFM.
Dr J. Woodhouse
The vibrational behaviour of musical instruments continues to provide challenging scientific problems. An extensive study has been conducted into the effect on the motion of a bowed string of the finite width of the ribbon of bow hair(F11,F12). A finite-width bow has been shown to behave quite differently from a point bow, such as has been studied extensively in the past. In particular, some parts of the bow may be sticking to the string while other parts are slipping. Such "differential slipping" produces clearly audible consequences. Simulations using a theoretical model have revealed detailed features which accord with observations.
Dr H.E.M. Hunt
Professor D.E. Newland
Methods to predict the levels of vibration in the ground and in buildings near railways are important for the design of the substructure of railway track and of vibration-isolating foundations for large buildings. Recent work focusses on vibration transmission from railway tunnels which is leading to improvements in the methods used to reduce vibration levels at source. Tunnels and buildings are modelled by means of repeating-element theory which, through the use of random-process theory, links in with existing structural models of infinite extent. The models are being validated by measurements in tunnels and in buildings.
Dr H.E.M. Hunt
Pipelines which are prone to developing leaks may be identified with a vibrating pig. The pig identifies areas of free-spanning and unsupported pipe. This kind of pipeline inspection, routine for oil and gas pipelines, is now being applied to problems which face the water industry.
Dr H.E.M. Hunt
Professor D.E. Newland
Experimental works to validate a computational model of the growth of track settlement adjacent to bridge abutments form the basis of an on-going collaboration with Netherlands Railways. The measurements are being made in Holland where track settlement is a serious problem. It has been found that sleeper impact due to voidage is the main cause of settlement.
Dr H.E.M. Hunt
Fault identification using finite-element updating methods does not work well for axisymmetric structures with closely-spaced resonance peaks. Neural-network methods are being developed based on the `committee of networks' approach and are to be evaluated by locating faults in the armatures of electromagnetic shakers.
Professor D.E. Newland
Signal decomposition by time-frequency and time-scale mapping is now used extensively in vibration analysis. Recent research has concentrated on comparing various different wavelet transforms with the short-time Fourier transform and the Wigner-Ville method. Harmonic wavelets have been found to be particularly suitable because of their simple structure in the frequency domain, but it is still difficult to produce high-definition time-frequency maps. Research has focused on improving harmonic wavelet transform algorithms and on utilising phase data which can be obtained from the complex harmonic wavelet formulation(F9,F10). Advice has been provided on a range of different applications, including biomedical signals, road vehicle test data, experimental earthquake simulations and NASA vibration monitoring test data.
F2. Cole, D.J., Cebon, D. Influence of tractor-trailer interaction on assessment of road damaging performance. Proceedings of the Institution of Mechanical Engineers, Part D, Journal of Automotive Engineering, 212, (1), 1-10 (1998).
F3. Genin, G.M., Cebon, D. Failure mechanisms in asphalt concrete. Cambridge University Engineering Department Technical Report CUED/C-MATS.TR.245 (June 1998).
F4. Grassie, S.L., Smith, J.D., Saxon, M. Measurement of irregularities underpins grinding criteria. Railway Gazette International, 154, (3), 163-166 (March 1998).
F5. Johnson, K.L., Woodhouse, J. Stick-slip motion in the atomic force microscope. Tribology Letters, 5, (2-3), 155-160 (1998).
F6. Kashtalyan, M., Stronge, W.J. On Saint-Venant's principle in two-dimensional theory of elasticity of anisotopic bodies. Dopovidi NatsionalnoiAkademii Nauk Ukrainy (Reports of National Academy of Sciences of Ukraine), 9, 62-66 (1997).
F7. Lim, C.T., Stronge, W.J. Normal elastic-plastic impact in plane strain. Mathematics and Computer Modelling, 28, (4-8), 323-340 (1998).
F8. Matemilola, S.A., Stronge, W.J. Low-speed impact damage in filament-wound CFRP composite pressure vessel. Transactions of the ASME, Journal of Pressure Vessel Technology, 119, (4), 435-443 (1997).
F9. Newland, D.E. Application of harmonic wavelets to time-frequency mapping. Proceedings, 5th International Congress on Sound and Vibration, Adelaide, Australia, Paper 260, 2043-2054 (December 1997). CD ROM ISBN 1 876346 06 X
F10. Newland, D.E. Time-frequency and time-scale signal analysis by harmonic wavelets. In: Signal Analysis and Prediction; Edited by A. Procházka, J. Uhlir, P.J.W. Rayner, N.G. Kingsbury, Chapter 1 (Birkhäuser, Boston, 1998). ISBN 0 8176 4042 8
F11. Pitteroff, R., Woodhouse, J. Mechanics of the contact area between a violin bow and a string. Part 1: reflection and transmission behaviour. Acustica/Acta Acustica, 84, (3), 543-562 (1998).
F12. Pitteroff, R., Woodhouse, J. Mechanics of the contact area between a violin bow and a string. Part 2: simulating the bowed string. Acustica/Acta Acustica, 84, (4), 744-757 (1998).
F13. Sampson, D.J.M., Cebon, D. An investigation of roll control system for articulated heavy vehicles. Proceedings, AVEC '98, 4th International Symposium on Advanced Vehicle Control, Nagoya, Japan (September 1998).
F14. Stronge, W.J. Mechanics of impact for compliant multi-body systems. Proceedings, IUTAM Symposium on Unilateral Multibody Dynamics, Munich, Germany (August 1998).
F15. Stronge, W.J. Newtons' cradle - sequential collisions in a compliant periodic system. Proceedings, 12th Vibro-impact Conference, Moscow-Zvenigorod, Russia, 17-21 (May 1998).
F16. Talbot, J.P., Woodhouse, J. Vibration damping of laminated plates. Composites Part A: Applied Science and Manufacturing, 28A, (12), 1007-1012 (1997).
F17. Zhang, T.G., Stronge, W.J. Rupture of thin ductile tubes by oblique impact of flat-nosed missiles: experiments. International Journal of Impact Engineering, 21, (7), 571-587 (1998).
Last modified: October 1999