This document discusses how aramid fibers behave under dynamic loading conditions compared to static conditions. It finds that the modulus and elongation at break of aramid fibers can change under dynamic loading, with the modulus generally decreasing and elongation increasing. Testing was done on yarn and cord samples under different loading amplitudes and cycles. The document also compares the tension-tension fatigue life of aramid fibers to steel wires, finding that aramids would significantly outperform steel for applications involving cycling between lower load levels like a ferris wheel cable.
1. Teijin Aramid Engineering with aramid fibers Dynamic loading effects on aramid fibers Matthijs van Leeuwen Business Development Manager Linear Tension Members, Oil & Gas MTS IRTW 2011, College Station 23 rd March, 2011
5. Measuring material properties (2) Strength EAB Modulus calculated 300-400mN/tex Specific conditions: Twistlevel, temperature, moisture level, yarn length, clamp type, speed Standard yarn test according to ASTM D885
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7. Measuring material properties (4) The modulus can be measured according to the standard method at different temperatures. standard temperature
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10. Dynamic loading – Changing properties (3) Test setup (load controlled): cycling at 20°C amplitude 2,5% of BS 5-40% & 5-80% in 2,5% increm. Measuring dynamic modulus (‘storm stiffness’)
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12. Dynamic loading – Changing properties (4b) Modulus is slope of Force-elongation curve. Static modulus Dynamic modulus
13. Dynamic loading – Changing properties (5) Standard Modulus = 72 GPa EAB = 3,6% ~0,4% deformation due to 40% load ~0,4% deformation due to 80% load ~0,8% total deformation due to 80% load
14. Dynamic loading – Changing properties (6) Standard Modulus = 58 GPa (-20%) EAB = 4,5% (+24%) ~0,5% deformation due to 40% load ~0,5% deformation due to 80% load ~1,0% total deformation due to 80% load (+25%)
15. Dynamic loading – Changing properties (7) Standard Modulus = 11 GPa EAB = 14% ~1,9% deformation due to 40% load ~1,6% deformation due to 80% load ~3,5% total deformation due to 80% load
19. Dynamic loading – Mooring (1) Dynamic modulus Static modulus 3-ply cord 3-ply cord yarn yarn * 60% according to API x 75% rope efficiency 134 GPa (-6%) 83 GPa (-12%) @ 45% MBL * 142 GPa 93 GPa
20. Dynamic loading – Mooring (2) Twaron 2300 PET-HT * 60% according to API x 75% rope efficiency 134 GPa (1.6x static) 25 GPa (2.3x static) Dynamic modulus @ 45% MBL * 83 GPa 11 GPa Static modulus
21. Dynamic loading – Mooring (3) Normalised dynamic modulus Kr D is rope stiffness: Highest dynamic stiffness: At max. allowed load level (API 60% MBL). Elongation Δ L is the 2x amplitude of the waves. The stiffness Kr D is therefore proportional to a minimum applicable length of a mooring line: This means that Kr D,PET : Kr D,Aramid = L min,PET : L min,Aramid
22. Dynamic loading – Mooring (4) Twaron 2300 PET-HT * 60% according to API x 75% rope efficiency Kr D = 43 Kr D = 25 ‘ Normalised storm stiffness’ @45% MBL *
29. Conclusions Aramid fibers offer great advantages. Dynamic properties are known and can be used for engineering to estimate value in use. Aramids offer cost reduction in ultra deepwater mooring applications due to smaller dimensions and lower installation costs. Aramid ropes are 2x stiffer than PET ropes. The worlds of synthetics and steel are still way apart, but it is time for change! Let’s start talking the same language.
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31. Measuring material properties (4) 20°C 50°C 95°C Long-term load ability can be modeled for Twaron, which is useful for engineering purposes, studying static failure modes. 140°C
32. Dynamic loading – Changing properties (9) Dynamic modulus Aramids show a constant stiffness at a certain elongation, even after loading. Elongation at zero load changes.
33. Dynamic loading – Changing properties (9) Dynamic modulus Once yarn/rope is loaded at working level, the dynamic modulus will not change up to working load until higher loads are applied.
35. Dynamic loading – T-T (5) – Twaron Maximum load (LTBL line) High freq Low freq Damaging / abrasion effect of going from very high to very low load Miner’s rule Minimum load Maximum load
36. Dynamic loading – T-T (6) Ferris wheel ~2 cycles/hr ~20,000 cycles/yr Tension between 50% and 25% of MBL Steel wire has design life of ~10 years What about Twaron?
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38. Dynamic loading – T-T (8) – Steel vs Twaron Maximum load (LTBL line) Static loading 100k cycles 10M cycles Great wheel case (~1 cycles / hr) steel Twaron ® * The given numbers are only indicative, but based on reality Number of cycles with average load &12,5% amplitude * steel Number of cycles with upper load at 50% MBL * Twaron ® Lower load at 25% MBL *
