Single fibre tensile testing: analysing the influence of fibre misalignment to reduce uncertainties in properties identification
Topic(s) : Experimental techniques
Co-authors :
Anouk CHEVALLIER (FRANCE), Florian BOUTENEL (FRANCE), Violaine GUICHERET (FRANCE), Cédric CLEVY , Vincent PLACETAbstract :
To facilitate the broader application of fibre-reinforced composites in structural applications, it is crucial to accurately predict their mechanical performances. For this purpose, knowledge and understanding of the mechanical behaviour of single fibres are essential. Tensile testing on single fibres stands out as one of the most commonly employed techniques to assess their strength and stiffness.
However, fibres are small, typically measuring a few tens of micrometres in diameter. Throughout the test, the forces and displacements measured fall within the range of one hundred milliNewtons and a few tens of micrometres, respectively. This makes the tensile testing on single fibre challenging.
Numerous sources of uncertainties and scattering arise during the tensile testing of a single fibre [1], linked to the fibre preparation and its handling (with potential damage from these operations), the fibre positioning and alignment [2], the determination of its length and its cross-section area, the positioning of the force and displacement sensors relatively to the fibre, as well as the set-up’s compliance [3]. Quantification and minimisation of these uncertainties are crucial for achieving reliable and reproducible characterisations and therefore more accurately determine the intrinsic variability of the tensile properties of fibres, especially plant fibres [4].
This study focuses on analysing the impact of fibre misalignment during tensile testing. Specifically, when an angle exists between the fibre and the tensile axis, it results in an overestimation of strain, impacting the accurate determination of the Young's modulus. Furthermore, the introduction of a multiaxial stress field induces stress concentration at the jaws' tip, elevating the likelihood of failure in this area and subsequently introduces an underestimation of the stress at failure of the fibre.
In this study, the influence of an angle between the fibre and the tensile axis is quantified using analytical and numerical models. For instance, considering beam theory, for a millimetre length transverse isotropic fibre, an angle of 10° leads to an underestimation of 4.48% of the longitudinal Young’s modulus (cf. Figure 1). This will be compared with the results obtained by finite element model (cf. Figure 2).
To complete this approach, a tensile test setup dedicated to single fibres is currently under development. This micro-mechatronic setup features a three-dimensional force sensor positioned in close proximity to the fibre, enabling the consideration of misalignment errors when identifying the Young's modulus and stress at failure.
However, fibres are small, typically measuring a few tens of micrometres in diameter. Throughout the test, the forces and displacements measured fall within the range of one hundred milliNewtons and a few tens of micrometres, respectively. This makes the tensile testing on single fibre challenging.
Numerous sources of uncertainties and scattering arise during the tensile testing of a single fibre [1], linked to the fibre preparation and its handling (with potential damage from these operations), the fibre positioning and alignment [2], the determination of its length and its cross-section area, the positioning of the force and displacement sensors relatively to the fibre, as well as the set-up’s compliance [3]. Quantification and minimisation of these uncertainties are crucial for achieving reliable and reproducible characterisations and therefore more accurately determine the intrinsic variability of the tensile properties of fibres, especially plant fibres [4].
This study focuses on analysing the impact of fibre misalignment during tensile testing. Specifically, when an angle exists between the fibre and the tensile axis, it results in an overestimation of strain, impacting the accurate determination of the Young's modulus. Furthermore, the introduction of a multiaxial stress field induces stress concentration at the jaws' tip, elevating the likelihood of failure in this area and subsequently introduces an underestimation of the stress at failure of the fibre.
In this study, the influence of an angle between the fibre and the tensile axis is quantified using analytical and numerical models. For instance, considering beam theory, for a millimetre length transverse isotropic fibre, an angle of 10° leads to an underestimation of 4.48% of the longitudinal Young’s modulus (cf. Figure 1). This will be compared with the results obtained by finite element model (cf. Figure 2).
To complete this approach, a tensile test setup dedicated to single fibres is currently under development. This micro-mechatronic setup features a three-dimensional force sensor positioned in close proximity to the fibre, enabling the consideration of misalignment errors when identifying the Young's modulus and stress at failure.