Accelerated ageing of a pultruded FRP composite PA6/GF: Characterisation and modelling of hygrothermal ageing
Topic(s) : Material and Structural Behavior - Simulation & Testing
Co-authors :
Hussein CHEBBO (FRANCE), Romain LÉGER (FRANCE), Arnaud REGAZZI , Didier PERRIN , Patrick IENNYAbstract :
Mobility is a major factor in economic development and is now undergoing numerous transformations driven by the need to reduce carbon footprint. The objective of the INFRAlight project is to provide an environmentally friendly, sustainable and recyclable, fibre reinforced polymer composite railway infrastructure. Among the materials considered for this type of application, a pultruded PA6/Glass fibre composite is proposed. The rails are subjected to severe natural and mechanical weather conditions such as temperature variations, relative humidity, UV radiation, as well as fatigue loads resulting from repeated train passage on the rail. Therefore, the study of durability under severe service conditions is essential to an industrial exploitation of these materials.
Pultrusion is a continuous process for producing composite profiles with uniform cross-sectional areas. Literature shows that the durability of pultruded composite materials is still an understudied topic. However, several studies have shown that PA6 polymers are sensitive to moisture, which leads to a decrease in their mechanical properties and changes in their physicochemical properties. This was demonstrated by Taktak et al, who showed a loss of approximately 60% in tensile strength and 74% in Young's modulus of PA6 specimens subjected to hydrothermal ageing at temperatures between 70°C and 90° [1]. Additionally, a decrease in Tg from 65.2°C to 2.3°C was observed by Lei et al after hydrothermal ageing at T=90°C [2].
In this study, hygrothermal ageing at (50°C < T < 70°C) and (50% < RH < 80%) was applied to the PA6/GF pultruded composite. During ageing, gravimetric monitoring, dimensional changes, and viscoelastic properties analysis through vibrational analysis were performed. Additionally, several techniques such as DSC, DMA, ATG, IRTF, XRD, and mechanical tests were conducted to characterise the evolution of the composite’s thermophysical properties during ageing. Initial results (Figure 1) show a decrease in mechanical properties for samples with fibre orientations at 90° and 45°, while properties are conserved in the 0° orientation. These tests will be complemented by a study at different temperatures and humidity levels to investigate the variation of diffusion kinetics depending on temperature and the saturation rate depending on relative humidity.
A morphological analysis of SEM images (Figure 2) has also been performed to assess the distribution of fibres within the matrix, and subsequently define a representative elementary volume to simulate the macro-homogeneous hygro-mechanical behaviour of the materials and predict its durability in service conditions.
Pultrusion is a continuous process for producing composite profiles with uniform cross-sectional areas. Literature shows that the durability of pultruded composite materials is still an understudied topic. However, several studies have shown that PA6 polymers are sensitive to moisture, which leads to a decrease in their mechanical properties and changes in their physicochemical properties. This was demonstrated by Taktak et al, who showed a loss of approximately 60% in tensile strength and 74% in Young's modulus of PA6 specimens subjected to hydrothermal ageing at temperatures between 70°C and 90° [1]. Additionally, a decrease in Tg from 65.2°C to 2.3°C was observed by Lei et al after hydrothermal ageing at T=90°C [2].
In this study, hygrothermal ageing at (50°C < T < 70°C) and (50% < RH < 80%) was applied to the PA6/GF pultruded composite. During ageing, gravimetric monitoring, dimensional changes, and viscoelastic properties analysis through vibrational analysis were performed. Additionally, several techniques such as DSC, DMA, ATG, IRTF, XRD, and mechanical tests were conducted to characterise the evolution of the composite’s thermophysical properties during ageing. Initial results (Figure 1) show a decrease in mechanical properties for samples with fibre orientations at 90° and 45°, while properties are conserved in the 0° orientation. These tests will be complemented by a study at different temperatures and humidity levels to investigate the variation of diffusion kinetics depending on temperature and the saturation rate depending on relative humidity.
A morphological analysis of SEM images (Figure 2) has also been performed to assess the distribution of fibres within the matrix, and subsequently define a representative elementary volume to simulate the macro-homogeneous hygro-mechanical behaviour of the materials and predict its durability in service conditions.