1. Prediction of the Flexural Modulus of Fibre Reinforced Thermoplastics as used for Kayak Paddle Blades.
P.D. EWART* AND CJR VERBEEK
The Department of Materials and Process Engineering.
The University of Waikato,
Hamilton, New Zealand.

2. Overview Introduction Composite materials and their interactions
The model accounting for the interfacial layer
Experimental
Results and discussion
Conclusion

3. Introduction A strong link between paddler
performance and paddle stiffness [1]
Modelling mechanical properties
of composite materials to aid product design
Inaccuracies inherent in theory due to assumptions

4. Introduction (cont) Discrete layers seen within a composite
An improved model accounting for a non-bonded layer at the interface

5. Composite materials and their interactions
Modelling component interaction
Surfaces between components, interface
Intermediate third layer, interphase
Three interphases and two interfaces
Non-contact region
to account for the
interface

6. The model with account for the interfacial layer
From previous work a model based on simple beam theory gave a reasonable prediction for flexural modulus [2]
To account for non-contact regions the equivalent section is reduce to an
effective section [3]

7. The model with account for the interfacial layer (cont)
Where;

8. The model with account for the interfacial layer (cont)

9. Experimental Test samples: Injection moulded, glass fibre/ LLDPE
wood fibre/ LLDPE
Kayak paddle blades, glass fibre/ PP
carbon/ PA

10. Results and discussion
The improved model shows similar trend to experimental values with excellent approximation for modulus values using 2μm non-contact depth

11. Results and discussion (cont)
Sample
Experimental modulus
Predicted modulus
Glass/ PP (Aplax)
5.8 GPa (σ = 0.02)
GPa
Carbon/ PA (Duralon)
20.2 GPa (σ = 1.35)
GPa
Manufacturers only provide limited data on many commodity materials
Non-contact values may be better gained by density measurement to account for voidage

12. Conclusion The assumption of perfect bonding using the
elemental approach is greatly improved when
some account is made for non-contact regions
The model shows sensitivities to
both non-contact value and elastic
modulus value.

13. References
Carreira, R.P., Q.H. Ly, and G. Lagante. A bicycle frame Finite Element Analysis: standard tests and common cycling situations simulation. in The 4th International Conference on the Engineering of Sport. 2002: Blackwell Science.
Ewart, P. D. and C. J. R. Verbeek (2005). Prediction of the Flexural Modulus of Composite Materials for Sporting Equipment. Asia-Pacific Conference on Sports Technology., Tokyo, Japan, Australian Sports Technology Alliance Pty Ltd.
Moore, D. R. and M. J. Ironman (1973). “The prediction of the flexural rigidity of sandwich foam mouldings.” Journal of Cellular Plastics 10 (5).
Throne, J. L. (1972). “A note on the mechanical strength of self-skinning foams.” Journal of Cellular Plastics 8(4).
Wu, J.-S. and Y. Tsong-Ming (1994). “Studies on the Flexural Modulus of Structural Foams.” Journal of Polymer Research (1):

14. Acknowledgments New Zealand Lottery Grants Board
Lottery Ministers discretionary fund
The Department of Materials Engineering
The University of Waikato, Hamilton, New Zealand.
Waikato Centre of Advanced Materials