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1、Effect of vibrations on void content in composite materials,Jelena Muric-Nesic Supervisors: P.Compston, N.Noble, Z.Stachurski,DERF June 2008.,2/16,Presentation Overview,Project to date aim method results discussion Current work Future Conclusions,Vibration Project, Jelena MN,Vibrations,3/16,Projects
2、 Aim,What? Good quality laminates Better mechanical properties Minimize defects Bubbles, fibre wetting Void content 2%,How? Vibrations: Suitable frequency Mode of vibration Position Transmission means,Vibration Project, Jelena MN,4/16,Projects Method I,Shaker 1-9000 Hz, signal generator, power ampli
3、fier and mould Hand lay-up of glass fibres (12 plies) and vinyl-ester resin Laminates (10x10x3mm) UV curing Optical microscope Top cover&Vacuum-later,Vibration Project, Jelena MN,5/16,Projects Method II,Changing Parameters Frequency and power of vibrations Time length Temperature Top cover plate Vac
4、uum bagging,Hypothesis Void mobility Stokes law Viscosity (Arrhenius) Energy-Amplitude: EA2 Pressure: PV=RT,Vibration Project, Jelena MN,.,Whats happening?!,Pressure and temperature variations internal pressure - external pressure = 2/r Buoyancy Coalescence/dispersion of voids,6/16,Vibration Project
5、, Jelena MN,Expansion,Shrinkage,- surface tension of a liquid r - radius of a bubble,7/16,Projects Results I,Optical micrograph (64x),Void sizes: 500 m,_ 100m,Vibration Project, Jelena MN,Distribution of bubble size cross section,8/16,Projects Results II,10 min,30 min,Vibration Project, Jelena MN,A.
6、 50 100 m B. 100 200 m C. 200 500 m D. 500 m,9/16,Projects Results III,Vibration Project, Jelena MN,A. 50 100 m B. 100 200 m C. 200 500 m D. 500 m,10/16,Projects Discussion I,Void percentage observed on 8 images of each laminates cross-section,Frequency Hz,Vibration Project, Jelena MN,11/16,Projects
7、 Discussion II,Good results from: Low freq (10-50Hz) Higher temperatures Top cover Vacuum,Void % decreased Properties still to investigate Is it good enough? Can it be better?,Vibration Project, Jelena MN,Hot water tanks, 50l,Pump,Water pot,Flexible hoses,Shakers,Lower chamber,Upper chamber,Silicone
8、 membrane,Schematic of the system,Current Work,Small machine?!? With vibrations Curing at elevated temperatures (80C) Heat transfer rate liquid/gas = 25 Vacuum Epoxy resin system,Vibration Project, Jelena MN,13/16,14/16,Future,Low frequencies High temperatures Vacuum Different fibre/resin 1 to 5 sha
9、kers,Optical microscopy and CT scan Mechanical testing ,Vibration Project, Jelena MN,15/16,Conclusions,Vibrations reduce void content (bubbles) Reduced void % leads to improved laminate quality ,Vibration Project, Jelena MN,Effect of vibrations on void content in composite materials,DERF June 2008.,Jelena Muric-Nesic Supervisors: P.Compston, N.Noble, Z.Stachurski,Thank you!,