Novel ductile steel fiber composites: opportunities and challenges

Transcription

1 NANOFORCE Next generation nano-engineered Polymer-Steel/CNT Hybrids Novel ductile steel fiber composites: opportunities and challenges SIM User Forum November 19, 2014 Ghent Prepared by L. Gorbatikh on behalf of the NaPos consortium: I. Verpoest, M. Callens, M. Smet, B. Goderis, E. Bertels, S. Bals, M. Kurttepeli, D. Van Hemelrijck, B. Van Mele, A. Ghosh, G. Da Ponte, B. Verheyde, K. Allaer, J. Faes, W. Van Paepegem, J. Degrieck, K. Bracke, P. Persoone

2 NANOFORCE NANOFORCE Next generation nano-engineered Polymer-Steel/CNT Hybrids

3 Composites for structural applications today Advantages: Lightweight Excellent strength and stiffness Good durability (fatigue life, corrosion, impact resistance) Problem areas: Brittleness (due to fibers) Catastrophic failure without warning, material disintegration Weak out-of-plane properties Early onset of damage stress strain ~2% I. Taketa (PhD thesis, KU Leuven)

4 Next generation composites Properties of interest: - Ductile of pseudo-ductile behavior, gradual failure - No sacrifice in other properties Strategies to : - Fiber hybridization (combination of two or more fiber types) (a) (b) (c) Y.Swolfs, L. Gorbatikh, I. Verpoest, Fibre hybridisation in polymer composites: A review, Composites Part A, Development/ search for new fibers with intrinsic ductility

5 Fibers for use in composites Steel has a unique combination of High ductility Low stiffness M. Callens (PhD thesis, KU Leuven) Stiffness: 200 GPa ~= carbon fibres (> 230 GPa) 3x glass fibres (72 GPa), flax (60~70 GPa) Ductility: Failure strain adjustable without loss of stiffness High stiffness Low ductility

6 Challenges for steel fibers - High density (not for weight sensitive applications) - High stiffness mismatch between the fiber and the polymer (200GPa vs 2 GPa) debonding and cracks - Irregular cross-section (due to bundle drawing) additional stress concentrations - Additional challenges (identified during the project) Debonding in carbon fiber composite 7 µm M. Callens (PhD thesis, KU Leuven)

7 Engineering steel fiber composites Woven reinforcement Composite properties Tensile and compressive properties Impact resistance Fracture toughness Fatigue life Functional properties Matrix selection Epoxy, PA, PU, PP, nano-reinforced polymers Interface modification Plasma and wet chemistry treatments to tune interface strength (including nano-modifications) Composite production VARI, RTM, hot pressing, pre-pregging.. M. Callens, L. Gorbatikh, I. Verpoest, Effect of fibre architecture, Composite Structures (2014)

8 Effect of the matrix 7

9 Effect of the matrix Ductile polymers lead to higher failure strain of steel fiber composites Steel fiber fabric 5 mm Steel fibre composites Steel fibre/pa-6 Composite failure strain is ± 50% for a ductile matrix M. Callens, L. Gorbatikh, I. Verpoest, Ductile steel fibre composites.., Composites: Part A (2014)

10 Failure of steel fibers in a brittle matrix Applied deformation Local Ductile necking fiber failure of the fiber Crack in the matrix Local debonding M. Callens (PhD thesis, KU Leuven)

11 Failure in brittle and ductile matrices Brosse matrix = matrix breekt eerst Ductiele matrix = vezel breekt eerst Effect of the interface becomes important M.Callens, et al Tensile behaviour of stainless steel fibre/epoxy composites with modified adhesion, Composites: Part A (accepted)

12 Effect of the interface 11

13 Surface treatments - Wet chemistry (Department of Chemistry, KU Leuven) - Plasma process (VITO) - Characterization of the interface strength (VUB) - Effect on composite properties (UGent, KULeuven) Different types of silanes, deposition parameters, aging, etc were studied Transverse 3-point bending Ghosh et al., Optimisation of wet chemical silane deposition, Applied Surface Science, 2015 Da Ponte et al, Adhesion Improvement, Plasma Processes and Polymers, 2014

14 Effect of surface treatements (1) Wet chemistry treatments (Chemistry Department at KU Leuven) Developed treatments perform better than those found on the market 29% 46% Effect on composite failure strain 32% M.Callens, et al Tensile behaviour of stainless steel fibre/epoxy composites with modified adhesion, Composites: Part A (accepted)

15 Effect of treatments on damage development Damage development is hindered in composites with stronger interface M.Callens, et al Tensile behaviour of stainless steel fibre/epoxy composites with modified adhesion, Composites: Part A (accepted)

16 Other mechanical properties

17 In-plane properties of UD steel fibre composite laminates Matrix: Fibres: EPIKOTE Resin RIM 135 EPIKURE Curing RIM H 137 UD 316L - weft Fibre volume fraction: 42 % Allaer et al, CSTE 2014 K. Allaer, et al, On the in-plane mechanical properties of stainless steel fibre, Composites science and technology (2014)

18 Low velocity impact properties of UD steel fibre composites More energy absorbed by steel fibre laminate configuration Deformation energy Plastic behaviour Damage Damaged area ± equal for both materials

19 Penetration impact resistance M. Callens, L. Gorbatikh, I. Verpoest, Effect of fibre architecture, Composite Structures (2014)

20 Hybrid steel fiber composites 19

21 Remaining challenges High density Low yield strength M. Callens (PhD thesis, KU Leuven) Hybridisation with traditional fibres An increase in strength comes at the expense of the failure strain optimization is needed

22 Potential of hybridisation with steel fibres Hybridisation with self-reinforced PP Increase the stiffness of self-reinforced PP Without sacrificing the toughness/impact resistance Tensile behaviour M. Callens (PhD thesis, KU Leuven) Penetration impact resistance

23 Conclusions and outlook - Conclusions Steel fibres composites with high strain-to-failure - Ductility can be further improved through modification of: Matrix and interphase Hybridisation offers oppurtunities C- and G-fibres: additional strenght, but loss in toughness SRPP: no loss in toughness and higher stiffness than non-hybrid SRPP - Outlook Effect of the fibre diameter Partially annealed fibres Complex and dynamic loading (fatigue, open hole tension) Multi-functionality

24 Thank You!