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Effect of vibrations on void content in composite materials

Explore how vibrations impact void content in composites, aiming for defect-free laminates with improved mechanical properties. Learn about the methods, results, and future work of the research, examining vibration frequencies, modes, and positions. Discover the impact of vibration parameters on void mobility and void sizes, leading to reduced void percentages and enhanced laminate quality.

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Effect of vibrations on void content in composite materials

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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. Presentation Overview Project to date aim method results discussion Current work Future Conclusions Vibrations… Vibration Project, Jelena MN

  3. Project’s 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. Project’s Method I Shaker 1-9000 Hz, signal generator, power amplifier 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. Project’s Method II Changing Parameters Frequency and power of vibrations Time length Temperature Top cover plate Vacuum bagging Hypothesis Void mobility Stokes law Viscosity (Arrhenius) Energy-Amplitude: E≈A2 Pressure: PV=RT . Vibration Project, Jelena MN

  6. What’s happening?! • - surface tension of a liquid r - radius of a bubble Expansion Shrinkage • Pressure and temperature variations internal pressure - external pressure = 2/r • Buoyancy • Coalescence/dispersion of voids Vibration Project, Jelena MN

  7. Project’s Results I Optical micrograph (64x) Void sizes: <50 μm not observed A. 50 – 100 μm B. 100 – 200 μm C. 200 – 500 μm D. > 500 μm __ 100μm Distribution of bubble size cross section Vibration Project, Jelena MN

  8. Project’s Results II 10 min A. 50 – 100 μm B. 100 – 200 μm C. 200 – 500 μm D. > 500 μm 30 min Vibration Project, Jelena MN

  9. Project’s Results III A. 50 – 100 μm B. 100 – 200 μm C. 200 – 500 μm D. > 500 μm Vibration Project, Jelena MN

  10. Project’s Discussion I No cover [%] Top cover [%] + vacuum [%] 10 1.005 0.477 0.104 30 2.124 0.040 0.018 50 5.656 1.076 0.543 NO 8.374 4.502 1.363 Void percentage observed on 8 images of each laminate’s cross-section Frequency Hz Vibration Project, Jelena MN

  11. Project’s 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

  12. Current Work Small machine?!? • With vibrations • Curing at elevated temperatures (80C) • Heat transfer rate liquid/gas = 25 • Vacuum • Epoxy resin system Hot water tanks, 50l Upper chamber Silicone membrane Flexible hoses Shakers Lower chamber Water pot Pump Schematic of the system

  13. Vibration Project, Jelena MN 13/16

  14. Future Low frequencies High temperatures Vacuum Different fibre/resin 1 to 5 shakers Optical microscopy and CT scan Mechanical testing … Vibration Project, Jelena MN

  15. Conclusions Vibrations reduce void content (bubbles) Reduced void % leads to improved laminate quality … Vibration Project, Jelena MN

  16. Effect of vibrations on void content in composite materials DERF June 2008. Thank you! Jelena Muric-Nesic Supervisors: P.Compston, N.Noble, Z.Stachurski

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