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 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

4/16 Project’s Method I  Shaker 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

5/16 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≈A 2  Pressure: PV=RT Vibration Project, Jelena MN.

What’s happening?!  Pressure and temperature variations internal pressure - external pressure = 2  /r  Buoyancy  Coalescence/dispersion of voids 6/16Vibration Project, Jelena MN Expansion Shrinkage  - surface tension of a liquid r - radius of a bubble

7/16 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 Vibration Project, Jelena MN Distribution of bubble size cross section

8/16 Project’s Results II 10 min 30 min Vibration Project, Jelena MN A. 50 – 100 μm B. 100 – 200 μm C. 200 – 500 μm D. > 500 μm

9/16 Project’s Results III Vibration Project, Jelena MN A. 50 – 100 μm B. 100 – 200 μm C. 200 – 500 μm D. > 500 μm

10/16 Project’s Discussion I Void percentage observed on 8 images of each laminate’s cross-section No cover [%] Top cover [%] + vacuum [%] NO Frequency Hz Vibration Project, Jelena MN

11/16 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

Hot water tanks, 50l Pump Water pot Flexible hoses Shakers Lower chamber Upper chamber Silicone 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 MN13/16

14/16 Future  Low frequencies  High temperatures  Vacuum  Different fibre/resin  1 to 5 shakers  Optical microscopy and CT scan  Mechanical testing  … Vibration Project, Jelena MN

15/16 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 Jelena Muric-Nesic Supervisors: P.Compston, N.Noble, Z.Stachurski Thank you!