1. The Mechanical Testing of Polymersand their Composites By Gordon Williams

2. Introduction • Standard methods are vital in ensuring reliable data • True in all fields – Thus ASTM & ISO • If a property is to be claimed it must be backed by 1) a method and 2) statistical analysis ( means ,SD) • For materials science ;materials development must be supported by proper results.

3. Introduction • e.g. Toughened polymers (PA,PE), • Filled polymers; glass filled ;particle filled • Nano Composites • Recent confusion in “Nano” field is often a result of poor data.

4. Test Types • A range from direct product testing to basic properties ,e.g. Drop tests to Young’s Modulus. • Intermediate type, Testing special plaques or bowls. • Basic Tests measure material properties independent of size and method.

5. Test Types • Two Main Types • Deformation behaviour; to find Young’s Modulus ,Yield stress ,Poisson’s Ratio ,Elongation*,Strength*. • Fracture Behaviour; to find Toughness,K1c,Izod*, Charpy*. • All use Tension, Compression or Bending Tests. • * See later; not usually a good idea.

6. Testing Machines • A long history e.g. 1880 • Originally to test steel, e.g. Harbour Bridge • Machines in Civil Eng. Dept. from 1908 • All work in a similar way • Load applied via a screw ( Instron) or hydraulic rams (Servo Hydraulic) • Load measured by load cells (must calibrate)

7. Test machine  Instron 4302

8. Test machine  Instron 1195

9. Test machine  MTS 810

10. Testing Machines • Deformations; Cross head ,Gauge length? Extensometers, videos. • Modern machines are speed controlled, i.e. constant or exponential. • Polymers are rate dependent, i.e. are visco-elastic.

11. Deformation Properties • Measured in; Tension ,compression or bending. • Tension; simplest but; end effects (dog bones) ,gripping (slipping) ,accurate strains difficult. • Compression; no gripping problems • However ,friction . • Necessary for some yield stress tests.

12.  Stress,  y F E y F 2% 0 Strain,  Definition of Deformation

13. b W  l Illustrations of Deformation Tension: E= /=(F/)(l/bW) =F/bW = /l

14. Illustrations of Deformation Compression:

15. F  b W l Illustrations of Deformation Bending: E= /=(F/)(l/bW)(l 2/4W2)

16. Deformation Properties • Bending • Good for Modulus (magnification) • However; variable strain , inhomogeniety (flexural modulus) • Interpretation of curves. • Young’s Modulus; elastic property ,polymers are visco-elastic ,rate dependent ,unloading and hysterysis .Usually non- linear.

17. Deformation Behaviour • Yield Stress; onset of permanent deformation, hard to define. 2% offset ,maximum stress. • “Correct” or “definable” ? • Fracture stress/strain ,strength .Variable (surface finish) .A property? • Fracture Mechanics!! See next week.