outstanding problems in the physics of deformation of polymers

1. outstanding problems in the physics of deformation of polymers Han E.H. Meijer and Leon E. Govaert Dutch Polymer Institute (DPI) Materials Technology (MaTe) Eindhoven Univ of Tech (TU/e) APST ONE, Advances in Polymer Science and Technology July 8 – July 10, 2009, Johannes Kepler University Linz, Austria

2. outline • introduction • predicting performance of present models • outstanding problems: • first question: origin of deformation kinetics • second question: origin of ageing kinetics • third question: origin of strain hardening • summary

3. localization of strain tough brittle • PC: necking • moderate localization • stable growth • PS: crazing • extreme localization • unstable growth

4. a comment on (solid state) rheology rheology: branch of fluid mechanics call themselves non-Newtonian but are Newton’s successors that are mathematically well educated and only deal with transient homogeneous shear flows it took them 50 years to arrive at a constitutive equation that is also valid in transient homogeneous extensional flows solid state rheology: branch of solid mechanics Hooke’s successors that necessarily have to deal only with transient inhomogeneous extensional flows

5. rejuvenation polystyrene PS

6. ageing mechanically rejuvenated moderate ageing severe ageing unstable localisation homogeneous deformation stable localisation brittle ductile ductile

7. ageing

8. from compression (intrinsic) to tension compression entanglement network intermolecular total ageing = + Mn tension increasing entanglement density

9. outline • introduction • predicting performance of present models • outstanding problems: • first question: origin of deformation kinetics • second question: origin of ageing kinetics • third question: origin of strain hardening • summary

10. from compression to tension compression tension

11. from compression to tension compression fit tension prediction

12. indentation and scratching mesh

13. indentation and scratching indentor type round a c a Berkovich b b flat punch c

14. indentation and scratching flat-ended cone angle: 60o diameter: 10.0 µm post-mortem visco-elastic visco-plastic

15. indentation and scratching line: experiment symbol: prediction flat-ended cone angle: 60o diameter: 10.0 µm post-mortem visco-elastic visco-plastic

16. indentation and scratching results are quantitative lines: experiments symbols: predictions ageing deformation rate ageing kinetics deformation kinetics

17. indentation and scratching strategy hybrid numerical/experimental method Fn v Ff polymer Ff experiments Fadh= Ff- Fdef ? simulations Fdef T,v,scale effects

18. indentation and scratching results: influence sliding velocity

19. indentation and scratching results: deformation only Fn=300mN v =0.1µm/s r =50 µm visco-elastic visco-plastic

20. indentation and scratching results: deformation only Fadh Fdef Ff = Fdef + Fadh

21. indentation and scratching results: influence interaction between indenter and polymer what about adhesion? most basic dry-friction model: Leonardo da Vinci (1452) Amonton (1699) - Coulomb (1781) stick: slip :

22. indentation and scratching results: influence interaction between indenter and polymer

23. indentation and scratching results: influence interaction between indenter and polymer Fn vx Ff A2 polymer Fsim A1 Ff = Fsim = Fdef Fadh = 0

24. indentation and scratching results: influence interaction between indenter and polymer Fn vx Ff A2 polymer Fsim A1 Ff = Fsim = Fdef + Fadh Fadh Fdef

25. indentation and scratching results: influence interaction between indenter and polymer Fn vx Ff A2 polymer Fsim A1 Ff = Fsim = Fdef + Fadh Fadh Fdef

26. indentation and scratching results: influence interaction between indenter and polymer

27. indentation and scratching results: validation using different tip Fn=150mN v =0.1µm/s r =10µm visco-elastic visco-plastic

28. indentation and scratching results: validation using different tip

29. indentation and scratching results: wear

30. outline • introduction • predicting performance of present models • outstanding problems: • first question: origin of deformation kinetics • second question: origin of ageing kinetics • third question: origin of strain hardening • summary

31. deformation kinetics rate dependence of PC

32. deformation kinetics rate dependence of PC

33. constant stress .  deformation kinetics constant strain rate response rate-dependent yield failure under constant strain rate and constant stress experiment governed by same kinetics

34. deformation kinetics time-dependent accumulation of plastic strain: plastic flow

35. deformation kinetics influence of thermal history on intrinsic behavior influence of thermal history on rate dependence

36. deformation kinetics and time to failure PC influence of thermal history on intrinsic behavior influence of thermal history on time-to-failure

37. deformation kinetics and time to failure strain rate dependence of yield stress stress dependence of time-to-failure

38. deformation kinetics and time to failure question 1: how does molecular architecture determine deformation kinetics

39. deformation kinetics and time to failure question 1: how does molecular architecture determine deformation kinetics and thus the long term behaviour asreflected in the time-to-failure

40. outline • introduction • predicting performance of present models • outstanding problems: • first question: origin of deformation kinetics • second question: origin of ageing kinetics • third question: origin of strain hardening • summary

41. ageing and ageing kinetics ageing ageing influence of thermal history on intrinsic behaviour influence of thermal history on rate dependence

42. ageing and ageing kinetics PS PS: brittle fracture within hours PC: necking returns within months

43. ageing and ageing kinetics ageing accelerated by temperature Arrhenius temperature dependence; ΔH 205 kJ/mol

44. ageing and ageing kinetics Isothermal creep loading master curve ageing accelerated by stress

45. ageing and ageing kinetics rate dependence of yield stress aged loading curve changes in thermal history captured by a single state parameter: Sa behaviour independent of molecular weight distribution

46. ageing and ageing kinetics yield stress increases with time

47. ageing kinetics: two domains temperature history received during processing temperature history received during product life • ~seconds • high temperatures • fast evolution • ~years • low temperatures • slow evolution evolution of yield stress in both domains governed by the same kinetics

48. ageing kinetics during processing

49. ageing kinetics during product life

50. ageing and ageing kinetics rate dependent yield stress long-term failure both short-term and long-term deformation kinetics are captured !