1. Fracture and Fatigue Crack Propagation in Injection-Molded Short Fiber-Reinforced Thermoplastics
József Karger-Kocsis
2017

2. Outline Toughness assessment Microstructure due to injection-molding
Fracture behavior
Fatigue crack propagation (FCP)
Outlook

3. Toughness Determination Methods
Standards
Fracture mechanics (partly also “standardized”)

4. Standardized Toughness Testing Methods: Differences
Different stress states in specimens
Different loading rates (frequency effect)
Unnotched and notched samples
“Notchology”

5. Why Fracture Mechanics?
- Yields an inherent material parameter
- Allows the direct comparison of toughness
Standardized toughness determination methods:
Charpy (with and without notching; with various notch shapes
(v-, u-,double v-); with various notching (direct injection molding, cutting…)
Izod (with and without notching)
Dynstat
Gardner
Falling dart etc.
the related toughness data can only be compared when exactly the same method and testing conditions were used

6. Why Fracture Mechanics?
Driving force:
Determine an inherent material parameter, i.e. independent
on specimen size and configuration
Linear elastic (stress-related):
- Kc, Gc (ASTM E , ISO 13586; 17281; 15850)
Non-linear elastic (energy-related):
J-integral (ASTM E , -87)
JR-Curves (ASTM E )
C(T)OD (ASTM E 1290, BS 5762)
Essential work of fracture (EWF)

7. Is it Possible to Determine the Toughness of Polymers by Fracture Mechanics?

8. Possibile Toughness Definitions

9. Factors Infuencing the Mechanical Response of Polymers and Polymeric Composites

10. then it should depend on structural
Molecular and Microstructural Dependence of Fracture Mechanical Parameters
If there is an inherent toughness parameter for polymers,
then it should depend on structural
(i.e. molecular, morphological, microstructural) terms!
How to determine possible correlations?
Select the right fracture mechanical test method
Use well characterized polymers
Separate effects controlled by the initial structure from
those affected by the loading (loading-induced structural
changes)

11. Fiber Structuring in an Injection-Molded LGF-PP (LGF content: 40 wt.%)

12. Structure Development due to Injection Molding

13. Microstructural Parameters of Injection-Molded Discontinuous Fiber-Reinforced Composites

14. Cutting of CT-Specimens to Study their LEFM Response

15. Fracture Surface of a T-L Type CT-Specimen of Injection-Molded SGF-PP ( 40 wt.%)

16. Individual Fiber- and Matrix-Related Failure Events

17. Local Failure Events
E. Belmonte et al.: Composites B, 113 (2017),

18. Effects of “Fiber End”

19. Relation between Fiber Orientation and Effective Fiber Orientation
K. Friedrich: Compos. Sci. Techn., 22 (1985), 43-74

20. Reinforcing Effectiveness of Discontinuous Fiber-Reinforced Injection-Molded Composites
J. Karger-Kocsis and K. Friedrich: Compos. Sci Techn., 32 (1988),

21. Relative Fracture Toughness vs. R for S(L)GF-PP Composites
M= a + n.R

22. Relative Fracture Toughness vs. Reinforcing Effectiveness (R)
Effect of matrix toughness
J. Karger-Kocsis et al.: Polym. Bull., 27 (1991),

23. Fatigue or Fatigue Crack Propagation?
Is any inherent „notch/crack” in
injection-molded composites?

24. Static and Cyclic Fatigue as Assessed by Fracture Mechanics
J. Karger-Kocsis in „Wiley Enyclopedia of Composites” (Ed.: L. Nicolais), 2012, pp

25. Fatigue Testing S-N; Wöhler diagram
V. Altstädt: Adv. Polym. Sci., 188 (2005),

26. Fatigue Crack Propagation (FCP)
Frequency change during test
V. Altstädt: Adv. Polym. Sci., 188 (2005),

27. Failure Map: Injection-molded GF/CF-PPS
Target:
Material development
Instead of many quasistatic
tests, only one FCP
J. Karger-Kocsis and K. Friedrich:
J. Mater. Sci., 22 (1987),

28. Typical Fatigue Crack Propagation (FCP) Behavior

29. Effects of MW and Orientation of the Skin-Core Structure on the FCP of Injection-Molded PP

30. Specimen Preparation for FCP PPS+30 wt% CF
K. Tanaka et al.: Eng. Fract. Mech., 123 (2014), 44-58

31. Crack Growth During FCP PPS+30 wt% CF
K. Tanaka et al.: Eng. Fract. Mech., 123 (2014), 44-58

32. Effects of Volume and Length of GF on FCP of GF-PP-Composites

33. FCP as a Function of Content and Aspect Ratio of Reinforcement

34. FCP Rate as a Funcion of the Microstructural Efficiency (M)

35. Difference between Static and Cyclic Fatigue as Assessed by Fracture Mechanics
Test option

36. Stable Delayed FCP in Discontinuous GF-PP Composites: Cyclic Fatigue

37. Stable Delayed FCP in Discontinuous GF-PP Composites: Static Fatigue
J. Karger-Kocsis et al.: Sci. Eng. Compos. Mater., 2 (1991), 49-67

38. Creep Superimposed to FCP-Behavior

39. Future R&D Activities on Injection-Molded Thermoplastic Composites
Fracture
Microstructure assessment, description and modeling:
μCT (computer tomography)
mold filling models
- Nanocomposites:
microstructure – toughness relationship
in situ use of additional techniques:
acoustic emission, infrared thermography, digital image correlation… …
Fatigue crack propagation (FCP)
Crack initiation threshold:
effects of aging and environments
Nanocomposites:
Estimation of fatigue life time:
using FCP results

40. Thank you for your attention! E-Mail: karger@pt.bme.hu
J. Karger-Kocsis