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Composites on the Move: The Need for Dynamic Testing

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Evaluate what is "new and exciting" in the composites testing world.

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Composites on the Move: The Need for Dynamic Testing

  1. 1. P. B. S. Bailey, PhD Manchester Conference Centre, November 2015 Composites on the Move: The Need for Dynamic Testing
  2. 2. 2 “New and Exciting”? • Frequent improvements in resins and fibers • Various “revolutionary” new processing techniques • Many effective test methods • Too many? • Or too few… • Established structural composites market for 30 years
  3. 3. 3 New and Exciting • Primary structures • High-volume products • Truly composite-specific design Aluminum CFRP
  4. 4. 4 Early Fiber Composites in UK Transport • Cost-Efficient Body Materials • 1936 Vickers Wellington • 1940 De Havilland Mosquito • 1946 Jowett Bradford • 1957 Ford UK Thames Trader © Crown Copyright: IWM Source: Redsimon at English WikipediaSource: Les Chatfield, Brighton, England
  5. 5. 5 UK Innovation Pedigree • Fiber Processing - 1779 spinning jenny – Samuel Crompton - 1784 power loom – Edmund Cartwright - 1792 mechanised braiding • The foundations of the industrial revolution
  6. 6. 6 Leaders in Science and Engineering • Testing & Materials Physics - 1858 Iron & Steel Testing, 1874 Testing Works - David Kirkaldy - Fatigue & Fracture - 1849 HM Govt procures research report from E. Hodgkinson - 1903 J.A. Ewing – origin of fatigue failure - 1920 A.A. Griffith - 1950s G.R. Irwin, R.S. Rivlin, A.G. Thomas Source: Richard Rogerson
  7. 7. 7 Why the History Lesson? • There is a huge weight of evidence behind metals design • Fibre technology has been around for a while too! • Structural composites have caught up a lot in just a few decades • But they are still some way behind…
  8. 8. 8 Catching Up with Metals Metals Tests Metals Theory Metals Design Composite Tests Composite Theory Composite Design Static       Impact       Fatigue     ? ? Strain rate    ?   Crack propagation     ? 
  9. 9. 9 How Does Testing Fit into this Now? On Measurements of Small Strains in the Testing of Materials and Structures Source: J. A. Ewing, Proceedings of the Royal Society of London, Vol. 58 (1895), pp. 123-142 AVE2 Video Extensometer Instron, 2014
  10. 10. 10 What Do You Think About Testing? • Costly? • Difficult? • Interesting? • Useful for R&D? • Central to your business success? • Critical?
  11. 11. 11 Yes …To All of Those! • Testing composites is critical to the continued success of the sector • Testing and design methods need to fully address the effects of dynamic behavior
  12. 12. 12 Fatigue • “Between 80% to 90% of ALL mechanical service failures can be attributed to fatigue.” (ASM – Metals Handbook 2008) • >186 years of observation! • Do we have enough data to make a comparison for composites?
  13. 13. 13 Fatigue: Early Industry Adoption • Lead by wind turbine industry • Recognition of the problem • Need for minimal cost • Lower regulation
  14. 14. 14 Fatigue: Early Compromises • Tension-tension tests only • Sinusoidal loading • Minimal temperature control
  15. 15. 15 Is this Representative? • Incomplete, but not incorrect… • Where all science starts out! • What is the next step? • Compression or reversed loading would be more aggressive and more realistic • Constant / fixed strain rate would give more comparable characterization
  16. 16. 16 The Thermal Problem • Cyclic heating effect • Severe test temperature change • Symptom/cause of break at grip? t = 0 2 min 8 min 25°C 30°C 35°C 26°C 27°C 28°C
  17. 17. 17 (Non-)Isothermal Behavior • Traditionally assume constant temperature • Reason for very-low, quasi-static test speeds on composites • Not an accurate description • Representative test?
  18. 18. 18 Strain Rate Testing • Materials exhibit different mechanical behavior at different strain rates • Viscoelastic behavior in polymers • Geometric & friction effects in textiles • Crack propagation mechanisms • Quasi-static data are insufficient to model crash behavior • Even for metals
  19. 19. 19 Very High-Speed Servohydraulic Test
  20. 20. 20 Significant Effects of High Strain Rate • Cold rolled steel
  21. 21. 21 Renewed Interest • Organic growth of research in: • Composites performance • Composites modelling • 2010 onwards • Automotive: • Before 2014, interest… • Now converted to urgent need
  22. 22. 22 High Strain Rates on Composites 0.00044 s-1 0.044 s-1 4.4 s-1 0.44 s-1 44 s-1 * Gude et al, Mech. Comp. Mat., Vol.45, No.5 High on-axis stiffness Off-axis stiffness low in static, but increases with strain rate… 2.5x Strength increases by factor of 2 in “crash” condition strain rate Woven Glass Fibre Reinforced Epoxy – modulus measurement ** Schloßig et al, Polymer Testing, Vol.27, p893-900
  23. 23. 23 Measurement Challenges • Strain rates over 100-s • At >10 m/s this is a very fast test • Looking at events on order of sound speed • Resonance ≠ Signal Noise • Careful interpretation needed • Effective fixturing must be highly tailored
  24. 24. 24 Recent Test Development • High rate compression & crushing • Measuring the critical properties for crash structures in composite • Servohydraulic • Drop weight • In drafting for ASTM method • Barnes et al at Engenuity Ltd.
  25. 25. 25 Crushing Data Good Stable Crush Performance Intermediate Performance Poor Crush Performance
  26. 26. 26 Successful Implementation
  27. 27. 27 Is That All We Need? • Good news or bad? • This is all that design methods can handle yet… or nearly • But there is plenty of headroom in measurement technology
  28. 28. 28 Where are We Heading? • What is the next level? • More data-rich tests • Crack propagation? • Low-cycle fatigue? …somewhere in Dallas, Texas, USA
  29. 29. 29 New Analyses • Quantifying “Failure” • Digital Image Correlation • Thermoelastic Stress Analysis Images reproduced by courtesy of the University of Southampton Crump et al, Engineering Integrity, No.35. 2013. T.S.A. Stressmap D.I.C. Strainmap
  30. 30. 30 Experiments with TSA Few Cycles Damage Onset? “Failure”? (images courtesy of J E Thatcher, University of Southampton)
  31. 31. 31 It’s Not all Bad News • Developing Effective Modelling • AMSCI Datacomp project • Engenuity Ltd. • Industry Investment in Test Capability • Automotive (Germany) • Aerospace (e.g. Boeing, COMAC…) • Materials (e.g. Hexcel, Borealis…) • Developing Tests and Theory
  32. 32. 32 We have the tools… What do you want to test? What do you need to measure?
  33. 33. 33 Questions? Contact: Peter Bailey, PhD Senior Applications Specialist Instron peter_bailey@instron.com +44 7880 187 716

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