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Time Dependent Response of Polymers: PEEK Performance

Time Dependent Response of Polymers: PEEK Performance. By Andrew Darmawan. Supervisors. Prof. David Mckenzie. Dr. Rebecca Powles. Stress ( σ ). Copper. Elongation ( Δ ). Stress ( σ ) . Viscous Materials. Free molecules. Elongation ( Δ ). Weaker Inter-molecular forces.

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Time Dependent Response of Polymers: PEEK Performance

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  1. Time Dependent Response of Polymers: PEEK Performance By Andrew Darmawan Supervisors Prof. David Mckenzie Dr. Rebecca Powles

  2. Stress (σ) Copper Elongation (Δ) Stress (σ) Viscous Materials Free molecules Elongation (Δ) Weaker Inter-molecular forces Elastic Materials Crystalline atomic structure Strong Inter-atomic Forces

  3. When stress (σ) is instantaneously increased: • Instantaneous increase in strain • Continued straining with time at a non-constant rate (called creep) • When stress (σ) is instantaneously released: • Some instantaneous strain recovery • Delayed recovery Viscoelastic materials are those for which the relationship between stress and strain depends on time. E.g. Polymers. Illustration by David Zinn

  4. Pitch drop experiment • Started in 1927 by University of Queensland Professor Thomas Parnell. • A drop of pitch falls every 9 years Pitch drop experiment apparatus Pitch can be shattered by a hammer

  5. VentrAssist™ LVAS • Left Ventricular Assist System (LVAS) • Used as alternative to heart transplant or a bridge to recovery • Only one moving part

  6. 1. 2. 3. 4. Aluminium Titanium 5. ? Evolution of the heart pump Polymers • Why Polymers? • Easier manufacture (injection molding) • Cheaper • Density is a better match with the human body

  7. PEEK (Poly ether ether ketone) Properties • Why PEEK? • Biocompatible • Strong • Smooth Chain Structure ketone ether

  8. t Experiment 1: Newton’s Rings • Light is reflected from both sides of a thin film • Interference occurs • The interference pattern represents a contour map of the surface. Optical flat Reflective polymer Air film (made by indentation)

  9. Experiment 1: Newton’s Rings Camera Beam splitter Apparatus Sample with optical flat Laser Paper

  10. 10min 60min Results 480min 4300min

  11. Experiment 2: Surface Profiler Pin dragged across surface Produces a profile of the indentation. Tencor Alpha-step

  12. Recommended topics for further research: • Long term recovery of PEEK • Ways we can speed up recovery eg. Temperature • Cross-linking in PEEK and its effect on recovery properties • Use of surface profiling on other materials (viscoelastic or not) • Creep characteristic of PEEK • Instantaneous recovery of PEEK after indentation Non-cross linked polymer Cross-linked polymer Conclusions: Surface profiling is a useful method for measuring the time dependant response of polymers. PEEK has a time dependant response to indentation (appears to be exponential) (the sample recovered by approximately 8% in 87 minutes)

  13. Other applications…

  14. 2. Viscoelastic Materials 1.Elastic and Viscous materials Summary 3. Ventracor’s VentrAssist™ 4. PEEK 5. Experiment 1: Newton’s Rings 6. Experiment 2: Surface Profiler

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