- Composite Materials Group, Material Science Department, KU Leuven
- Title of the dissertation:
- Development of ductile stainless steel fibre composites
- Promoter: Prof. Dr. Ir. Ignaas Verpoest
- Co-promoter: Dr. Larissa Gorbatikh
- Advanced structural composites such as carbon and glass fibrereinforced polymers have a limited ductility. This is due to intrinsic brittleness of the high performance fibres. The composite ductility can be enhanced by choosing fibers with a higher strain-to-failure, but most known ductile fibres (e.g. some natural and polymer fibres) have a low stiffness. The aim of this work was to investigate a new fibre type for application in composites – annealed stainless steel fibres. The unique property of these fibres is that they combine a high stiffness (±193GPa) with a strain-to-failure which can be tailored up to 20%. The strain-to-failure is as high as that of a silk fibre and up to 10 times higher than that of a carbon fibre. An extensive experimental program, supported by modelling investigations, was performed to understand the mechanical behaviour of polymer composites made of these fibres. The influence of the matrix ductility, fibre architecture and interphase properties on the damage development and composite properties was investigated. Additionally steel fibre hybrids in combination with carbon fibres, glass fibres or drawn polypropylene tapes were studied.
- Date of Defense: October 20, 2014
Amit Kumar Ghosh
- Physical Chemistry and Polymer Science Group and Department of Materials and Chemistry, Vrije Universiteit Brussel
- Title of the dissertation:
- The Interphase in Stainless Steel-Polymer Hybrids: Characterisation and Optimisation of Interfacial Interaction via Surface Treatment and Nanomodification of the Polymer
- Promoter: Prof. Dr. Ir. Bruno Van Mele
- Co-promoter: Prof. Dr. Ir. Danny Van Hemelrijck
- Stainless steel (SS)/polymer hybrids are recently explored for composite applications due to the unique combination of high strength and stiffness of SS with the low density and other functionalities of the polymer. These hybrids offer a higher strength-to-weight ratio and impact resistance, better dimensional stability, more design freedom. However, SS combined with a polymer matrix generally suffers from a low interfacial strength. Clearly, enhancing the interfacial strength will open new perspectives for real life applications. Pull-off testing was used to measure the interfacial strength of the hybrids (mechanical characterisation). A pull-off testing methodology was optimised in case of thin SS plates (<1 mm). A methodology based on differential scanning calorimetry and microcalorimetry (physical-chemical characterisation) was developed to study the interactions in the interphase between the metal and a thin polymer film (< 25 μm) of a thermoset or a thermoplastic. Two strategies were followed to influence/improve the interaction and the interfacial strength between SS and the polymer: (i) the SS surface was modified by silane coupling agents. Two deposition routes were used, i.e. wet chemical deposition (WC) and atmospheric plasma deposition (AP); (ii) nano-modifications of the matrix were carried out, using organoclays and carbon nanotubes. Clear correlations were found between the silane WC or AP deposition conditions and the interfacial strength of the SS-polymer hybrids. A significant effect of nano-modification of the polymer on the interfacial strength was seen. In addition, a strong effect of surface treatment and nano-modification on epoxy cure kinetics and on nylon 6 crystallisation kinetics was observed. The content of this thesis is relevant for both industry and the scientific community to develop new composites with improved properties.
- Date of Defense: March 4, 2015
- Department: Physics/Universiteit Antwerpen
- Title of dissertation: Carbon based materials and hybrid nanostructures investigated by advanced transmission electron microscopy
- Promotor: Prof. Dr. Sara Bals
- Summary: Carbon based materials have been investigated intensely in the materials science community for decades owing to their exceptional electrical, physical, chemical and mechanical properties. One of the main trends in this research field is to synthesize allotropes of carbon, such as carbon nanotubes, via a templated approach, which can lead to enhancements in their morphologies. Another popular trend is to use allotropes of carbon (such as carbon nanosheets and carbon nanotubes) as templates for the deposition of different metal/metal oxide layers in order to form hybrid nanostructured films for a wide range of materials applications. In both cases, the interaction between carbonaceous species with their coatings/templates plays a vital role in the final structure and morphology of the material. Investigations of the carbon based materials and hybrid nanostructures are therefore crucial to understand their properties, which may lead to their use in actual applications. In this respect, transmission electron microscopy is a powerful technique to study materials at the atomic level. The combination of conventional transmission electron microscopy techniques with more advanced ones, such as electron tomography, enables one to obtain valuable structural and chemical information, both in two- and three-dimensions. Moreover, through the instrumental developments, such as aberration correction, the characterization of carbon based materials and hybrid nanostructures using transmission electron microscopy has become of increasing interest. In this regard, this thesis focuses on the structural characterization of carbon based materials and hybrid nanostructures performed by transmission electron microscopy. The thesis is divided into two main parts. The first part is devoted to the systematic investigation of structures obtained using a method based on a templated approach which aims to produce large areas of highly ordered, isolated, well-aligned and long carbon nanotube bundles. The second part focuses on the structural characterization of carbon nanosheets and carbon nanotubes which are used as templates for the synthesis of various metal/metal oxides for different materials applications. Combining conventional and advanced transmission electron microscopy techniques, the structural transitions and the interaction between coatings/templates and carbonaceous species have been revealed.
- Date of defense: December 14, 2015