Carbon Fibre Reinforced Magnesium and Aluminium Materials for Vehicle Structures

1. Carbon Fibre Reinforced Magnesium and Aluminium Materials for Vehicle Structures Towards Affordable, Closed-Loop Recyclable Future Low Carbon Vehicle Structures Hannah Constantin

2. Aim: to fabricate discontinuous carbon fibre reinforced magnesium composites for lightweight structures Objectives: Improve the creep resistance of unreinforced magnesium Incorporate recycled fibres Test feasibility of use of composite in powertrain applications

3. Overview Literature review Key challenges Improve wettability of molten Mg on CFs Reduce interfacial reactions Achievable volume fractions Experimental methods Fabricate composite coupons Characterisation and testing to identify further challenges Refining fabrication process Fabricate larger composites for further tests and realisation of components

4. Background • Significantly increased creep resistance • UD MgMC 30% volume fraction PAN CFs: • EL = 104 GPa, ET = 35 GPa (epoxy EL = 74.8, ET = 5.8) • Random MgMC 30% PAN CF: • E = 59 GPa • (epoxy 30 GPa) • Variety of fabrication routes

5. Estimated mechanical properties (2) CES Edupack 2009 200 100 50 20 10 Carbon steel as rolled Mg–4Al–30%GrF longitudinal Mg–2Al–30%GrF long. Mg–30%GrF long. Young’s Modulus (GPa) Commercially pure Al cast Mg AZ91 cast T6 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 Density (g/cc)

6. Pressureless Infiltration (1) • No external pressure • Does not require expensive equipment • Easy to control volume fraction • Reinforcement homogeneously distributed

7. Pressureless Infiltration (2) • Mg–9Al–1Zn + rCFs • 900oC • Ramp rate 20oC/min • Air cooled • Flowing Ar • Mg + C reactions • Al–10Mg + rCFs • 900oC • Ramp rate 20oC/min • Air cooled • Flowing Ar • No infiltration

8. Wettability • Contact angle θ < 90o • For Al on carbon fibres often > 140o • Depends on temperature • Sessile drop test

9. Fibre Coatings (1) TiN coating TiAlN coating Ti coating Al coating

10. Fibre Coatings (2) • Increase wettability • TiN, TiAlN, SiC, Al, Ti • PVD • Flat surface for experiments SEM image of TiN coated fibres 5000x magnification BSE image of TiN coated fibres BSE image of TiN coated fibres 2500x magnification 5000x magnification

11. Gas Pressure Infiltration 1 2 3 4 Demir 2004 Hufenbach 2006

12. Limitations of Volume Fraction 140 350 700 1400 Corresponding fibre length (μm) assuming fibre Φ 7μm

13. What’s next?

14. Random Sequential Adsorption Model

15. Mechanical Testing, Characterisation, Fabrication of Larger Samples and Working Components Effective plastic strain • SEM • Tensile tests • 3 point bend • Indentation tests • Shear tests • Corrosion tests • Creep tests

16. Summary • Done: • Researched C/Mg area • Identified key challenges • Next: • Experiments to try to overcome challenges • Fabricate a small sample • Use computer model • Later: • Testing and characterisation of sample • Fabrication of larger samples

17. Towards Affordable, Closed-Loop Recyclable Future Low Carbon Vehicles TARF-LCV Development of recyclable thermoplastic matrix composites for use in LCV body structures David Burn 19th January 2012

18. Objectives Development of recyclable polymer matrix composites (PMCs) for LCV body structure Develop an effective approach for using short rCF in PMCs Study the effects of thermoplastic matrices on the mechanical properties of discontinuous PMCs Determine feasibility of using discontinuous PMCs as semi-structural /structural parts for LCVs

19. Background • Fuel economy pushing towards lightweight vehicles • Composites suited to this application • ELV targets – 95% reuse and recovery of vehicle – 5% landfilled • Highest potential recovery from thermoplastic polymers

20. σ Stress concentrations at fibre ends σf Polymer Matrices CF/Epoxy CF/Thermoplastic? • Discontinuous fibre composites transfer stress through the matrix material • Properties more dependent on the matrix • TPs generally have higher elongation to failure than thermosets • Can a good fibre/matrix bond be achieved to enable stress transfer at the interface? • How will the increased strain to failure affect the failure mode? • Compare the data against toughened CF/Epoxies ε (lc/2) (lc/2) Kelly- Tyson Model

21. Specific Strength (x106 m2/s2) Price (GBP/kg)

22. Thermoplastic Selection

23. Material Formats • Pellets • Powder • Liquid • Film / Sheet • Commingled

24. Processing Routes

25. Processing Routes • Pellets cheapest polymer format • Melt impregnation and film stacking most viable options

26. Processing Routes • Film format more expensive than pellets due to processing • Film stacking with preform most viable option

27. Processing Routes • Powder more expensive than pellets • Powder coating and resin infusion most viable processing routes

28. Thermoplastic Matrix - Filament Processing Routes Carbon fibre reinforcement Plied Matrix Tow Commingled Tow Cowoven Fabric • Commingled tows most expensive • Chopping into a mat most viable option

29. Processing Routes • ‘Total’ weighted mainly towards quality of part and ease of manufacture • In-situ polymerisation, chopped commingled preforms and film stacking have the highest totals

30. Processing Routes – Random Materials

31. In-Situ Polymerisation • PA, PC, PEEK, PPS and PI all have reactive processing routes (in-situ polymerisation) • However, limited supply of materials • Avimid K and Avimid N (PI) • NyRIM (PA-6) • Cyclics CBT (PBT) • Carried out trials to characterise Cyclics CBT • Very small processing window • Polymerised CBT (pCBT) properties poor, especially elongation to failure ~3% • Interest from EPL – currently using a liquid CBT resin • Supply chain for CBT unavailable • Need a supplier to continue research

32. Differential Scanning Calorimetry – Cyclic CBT Holding at 190ºC Cooling at 5ºC/min Reheating at 10ºC/min Heat Flow (W/g) Peak due to crystallisation, polymerisation occurs simultaneously at this point Melting of the polymerised CBT Crystallinity calculation: • Low crystallinitygenerally gives better mechanical properties Time (min)

33. Differential Scanning Calorimetry – Cyclics CBT • Processing temperature • Polymerisation and crystallisation simultaneous or consecutive based on temperature • Temperatures <190ºC, polymerisation incomplete and resulting ‘polymer’ is unusable • Processing temperatures above 200ºC causes crystallisation to occur during cooling • Degree of crystallinity can be controlled • Holding time • Small effect on the degree of crystallinity • Polymerisation cannot complete in less than 20mins • Cooling rate • No significant effect on the degree of crystallinity • Pre-drying CBT • Decreases crystallinity of final polymer by approximately 5% • Slightly delays polymerisation and crystallisation

34. Current Work • Polypropylene / DCFP preform • 500gsm preform – 17% Vf • Polymer flows around preform • Poor encapsulation • Polypropylene / Recycled CF mat • Uniform mat – guaranteed global Vf • 100gsm recycled fibre mat – 13 – 20% Vf • Polymer penetrates mat • Incrementally increasing Vf to find limit • To date highest Vf is 20% • 25% Vf reported in the literature • 3 point bending - flexural modulus of around 6-7GPa for random mat • Rule of mixture equation predicts 14GPa

35. Current Work • Limited Vf due to film stacking approach • Initial stacking resulted in dry sections • Processing was modified to produce ‘composite film’ • These were stacked and pressed • Optical microscopy shows good wet-out • Fibres still appear dry on the fracture surface • SEM needed to assess encapsulation • Matched-die mould required to improve properties • Vacuum assisted • Improve fibre encapsulation

36. Vacuum Take-up Roll Carbon Fibre Spool Squeeze Rollers ResinBath Infra-red Oven Take-up Roll Tow Spreader Carbon Fibre Spool Balance Bars Future Work Air Quench Device Tm of Resin • Commingled • Drag fibre through bath • Co-extrude • Powder coating • Fluidised bed • Prepreg route • Similar to HexMC • Use a UD fabric and chop to make high Vf SMC • Further studies with in-situ polymerisation and low viscosity polymers • Working with Davide de Focatiis and Derek Irvine Ionised Air Porous Plate Dry Air Input Charging Medium

37. Future Work • Need repeatable processing route • Test other polymers • What are the effects of high strain to failure of the matrix? • How is the composite affected by cyclic testing? • Fatigue endurance • Creep behaviour • Crashworthiness • Ballistic impact testing • What are suitable applications based on the Vf achievable? • Cost modelling to assess new processing routes • Demonstrator part • May need some industrial partnership • EPL interested in CBT

38. Future Work • WP1 – Feasibility study • 1.1 – Find repeatable method for processing composites • 1.2 – Process PP using UniFilo, DCFP and fabrics • 1.3 – Process and compare selection of TPs • 1.4 – Use data from processing to validate model • WP2 – Development of model and characterisation of thermoplastic matrices • 2.1 – Develop FE model for TP composites • 2.2 – Study the effects of binder/sizing/surface treatments on interfacial adhesion • 2.3 – Joining of thermoplastics • 2.4 – Carry out work to develop processing of low viscosity TPs??? • WP3 – Demonstration of technology • Demonstrator Part • Would need some industrial support

39. Thank you for your attention. Progress Report David Burn