Probing Compressive Behaviour and Failure in Single Carbon Fibre Composites: an In-depth Analysis using in-situ Laser Raman Spectroscopy
Topic(s) : Special Sessions
Co-authors :
Cameron WOODGATE (UNITED KINGDOM), Richard S. TRASK (UNITED KINGDOM), Milo S. P. SHAFFER (UNITED KINGDOM), Stephen J. EICHHORNAbstract :
Unidirectional carbon fibre-reinforced polymer composites often exhibit lower compressive strengths than their tensile strengths, which is a limitation in composite design [1]. To enhance compressive strength, a comprehensive understanding of the mechanisms governing compressive failure is needed. Compressive failure of fibres in unidirectional composites is often characterised by microbuckling and the formation of kink bands [2]. Developing insight into the behaviour of reinforcing fibre and the fibre-matrix interface before, during, and after failure is crucial for enhancing compressive performance.
Direct mechanical testing of single fibres faces challenges due to scale and aspect ratio considerations [3]. Additionally, characterising interfacial behaviour in compressive loading lacks a direct quantitative method. Raman spectroscopy provides a non-contact approach to revealing both micromechanical and interfacial responses of single fibres undergoing compressive loading. Raman spectroscopy is effective in measuring local stress states in graphitic materials such as carbon fibres, and is able to generate spatially resolved stress maps with a maximum resolutions of 0.5-2 μm [4]. It involves collecting inelastically scattered light (Raman scattering) and comparing the frequency of the scattered light to the elastic scattering (Rayleigh scattering), enabling the investigation of vibrational information about the atomic structure of the sample, and deriving local stresses and strains based on shifts in the positions of these vibrations.
This study employs in-situ laser Raman spectroscopy to generate spatially resolved stress maps of single carbon fibres during compressive loading, enabling the characterisation of fibre micromechanical behaviour and the derivation of interfacial shear stresses. Two experimental setups utilising Raman spectroscopy capabilities are discussed: a four-point bending setup (Fig. 1a) for static, single-point Raman analysis to derive micromechanical behaviour (Fig. 1d), and uniaxial compression (Fig. 1b), utilised to produce spatially resolved stress maps of model composites (Fig. 1d). The experimental procedures, capabilities of the techniques, and an investigation into the compressive performance of both intermediate and high modulus fibres are discussed. The study also demonstrates the use of high-resolution Raman stress maps, scanning electron microscopy, and confocal laser scanning microscopy to characterise the evolution of high modulus fibre failure.
Direct mechanical testing of single fibres faces challenges due to scale and aspect ratio considerations [3]. Additionally, characterising interfacial behaviour in compressive loading lacks a direct quantitative method. Raman spectroscopy provides a non-contact approach to revealing both micromechanical and interfacial responses of single fibres undergoing compressive loading. Raman spectroscopy is effective in measuring local stress states in graphitic materials such as carbon fibres, and is able to generate spatially resolved stress maps with a maximum resolutions of 0.5-2 μm [4]. It involves collecting inelastically scattered light (Raman scattering) and comparing the frequency of the scattered light to the elastic scattering (Rayleigh scattering), enabling the investigation of vibrational information about the atomic structure of the sample, and deriving local stresses and strains based on shifts in the positions of these vibrations.
This study employs in-situ laser Raman spectroscopy to generate spatially resolved stress maps of single carbon fibres during compressive loading, enabling the characterisation of fibre micromechanical behaviour and the derivation of interfacial shear stresses. Two experimental setups utilising Raman spectroscopy capabilities are discussed: a four-point bending setup (Fig. 1a) for static, single-point Raman analysis to derive micromechanical behaviour (Fig. 1d), and uniaxial compression (Fig. 1b), utilised to produce spatially resolved stress maps of model composites (Fig. 1d). The experimental procedures, capabilities of the techniques, and an investigation into the compressive performance of both intermediate and high modulus fibres are discussed. The study also demonstrates the use of high-resolution Raman stress maps, scanning electron microscopy, and confocal laser scanning microscopy to characterise the evolution of high modulus fibre failure.