School of Engineering and Materials Science
Research Student Awards
PhD Thesis: Characterisation of Kevlar-49 fibres and interfacial shear strength measurements in model composite materials, using laser Raman spectroscopy
Author: JAHANKHANI, Hamid
Supervisor(s): Costas Galiotis
Kevlar-49 fibres (Du Pont's trade name for aramid fibres), of three types (a) as-received, (b) mechanically conditioned and (c) surface treated, were fully characterised using Laser Raman Spectroscopy (LRS) and other techniques. LRS was subsequently used to evaluate the fibre/matrix adhesion of single short kevlar fibres embedded in epoxy based model composites. It was found that there was a linear relationship between Raman frequencies and strain upon loading a single kevlar-49 filament in the air. The 1615cm-1 Raman peak for all three types of kevlar-49 fibre could be adequately described by a Lorenzian curve while the broadening of this peak with applied strain was found to be symmetrical. The strain hardening or mechanical conditioning effect as a result of recycling of the as-received fibre was studied by LRS. It was shown that the slope of the linear relationship of Raman frequency as a function of strain, increased with number of cycles. This was attributed to the alignment of the constituent fibrils with applied external load resulting in a stiffer fibre. With regards to the chemical surface treatment used for roughening of the fibre surface through pore formation, it was found that it affected severely the mechanical performance of the fibre. The strain distribution in single fibre model composites was successfully monitored using LRS. The transfer length was measured at various levels of applied tensile load and the dependence of transfer length upon applied matrix strain was established. The interfacial shear stress (ISS) distribution along these embedded fibres was also obtained by balancing the tensile and the shear forces acting along the interface. The interfacial shear strength (IFSS) for the as-received fibre-epoxy system was found to be 848MPa at 1.1% matrix strain compared to 817MPa at 0.9% strain for the conditioned fibre system and 858MPa at 0.8% strain for the surface treated fibre.