Comparison study of fixed and variable blade interfacial testing systems for the characterisation of thermoset composites
Topic(s) : Experimental techniques
Co-authors :
Beth MALONE (UNITED KINGDOM), Oscar REYNOLDS (UNITED KINGDOM), Rebecca LUNN (UNITED KINGDOM), James THOMASON (UNITED KINGDOM), Ross MINTY (UNITED KINGDOM)Abstract :
As the demand for composite materials for increasingly advanced applications grows, so too does the necessity to accurately predict their performance and optimise their properties. Composites have become a staple in aerospace and automotive industries due to their manufacturing flexibility and the ability to tailor their properties to the requirements of the load the component will experience. As such, extensive investment has gone into developing our understanding of the fundamental properties that contribute to the load-bearing capabilities of composites.
The optimisation of composite properties is intrinsically linked to the optimisation of the stress transfer capability of the fibre-matrix interface. One accepted mechanically measurable value which can be used to characterise the strength of the interface is the interfacial shear strength (IFSS). With interface strength being affected by the chemistry of the fibre surface and matrix system applied, the accurate quantification of the IFSS is vital to the tailoring of these properties [1].
The microbond test provides an estimation of the IFSS through the shear debonding of a droplet on a single fibre by means of a set of parallel blades with variable gap spacing [2]. Due to a lack of standardisation of the test, equipment and methodology differs between research groups, resulting in reduced confidence in the test. Furthermore, the test is prone to high scatter in results [3]. Prior research has attributed the blade placement as being a key source of error, with too large a gap between blades resulting in a normal force acting on the droplet rather than a shear force [3,4]. Whilst the effect of the placement of the variable blades has been widely reported, there remains a gap in the literature with respect to the efficacy of a fixed blade setup and the effect that such a system may have on the results.
In the present work, a direct comparison was established between the Dia-Stron LEX820 fitted with IFSS module with a fixed blade setup and a variable blade rig system in which the blade gap is controlled using a microvise. It was observed that the results from the variable blade system were more prone to overestimation of IFSS. The fixed blade system allowed for a gap width close to that of the fibre diameter, ensuring that a shear force was applied. Additionally, in removing the need to manually adjust the blades, the scope for user error was reduced. If the microbond test is to be seen as a reproducible method for characterising the fibre-matrix interface, it is essential that the methodology and equipment used is standardised, with the limitation of having to accurately control variable blades being removed.
The optimisation of composite properties is intrinsically linked to the optimisation of the stress transfer capability of the fibre-matrix interface. One accepted mechanically measurable value which can be used to characterise the strength of the interface is the interfacial shear strength (IFSS). With interface strength being affected by the chemistry of the fibre surface and matrix system applied, the accurate quantification of the IFSS is vital to the tailoring of these properties [1].
The microbond test provides an estimation of the IFSS through the shear debonding of a droplet on a single fibre by means of a set of parallel blades with variable gap spacing [2]. Due to a lack of standardisation of the test, equipment and methodology differs between research groups, resulting in reduced confidence in the test. Furthermore, the test is prone to high scatter in results [3]. Prior research has attributed the blade placement as being a key source of error, with too large a gap between blades resulting in a normal force acting on the droplet rather than a shear force [3,4]. Whilst the effect of the placement of the variable blades has been widely reported, there remains a gap in the literature with respect to the efficacy of a fixed blade setup and the effect that such a system may have on the results.
In the present work, a direct comparison was established between the Dia-Stron LEX820 fitted with IFSS module with a fixed blade setup and a variable blade rig system in which the blade gap is controlled using a microvise. It was observed that the results from the variable blade system were more prone to overestimation of IFSS. The fixed blade system allowed for a gap width close to that of the fibre diameter, ensuring that a shear force was applied. Additionally, in removing the need to manually adjust the blades, the scope for user error was reduced. If the microbond test is to be seen as a reproducible method for characterising the fibre-matrix interface, it is essential that the methodology and equipment used is standardised, with the limitation of having to accurately control variable blades being removed.