Co-authors​ :

 Jasmine BONE (UNITED KINGDOM), Hannah ZHANG , Stefanos GIANNIS (UNITED KINGDOM) 

This research focuses on the micromechanical property characterisation of carbon fibre epoxy composite materials subjected to water uptake, employing nanoindentation as a tool to quantify the property changes through the thickness of the material. Both carbon and glass fibre epoxy composites are extensively used in marine and offshore structural applications, and their performance can be significantly affected by exposure to environmental factors, such as moisture. To ensure the durability of these polymer composite materials, the degradation mechanisms that occur upon exposure to moisture absorption must be characterised, and the correct parameters measured to ensure valid predictive modelling. While many test methods exist for the accelerated ageing of polymers and polymer composites at the laboratory scale [1], they do not fully identify the mechanisms by which moisture causes material degradation. Previous work has demonstrated that degradation at the fibre-matrix interface is significant in reduction of mechanical properties such as strength and modulus [2].
Nanoindentation may be employed as a localised technique to measure changes in hardness, modulus, and viscoelastic behaviour at the microscale [3]. In this research, specimens of a unidirectional carbon fibre epoxy composite pultrusion were subjected to an accelerated ageing regime, using immersion in water at elevated temperature. Testing through the thickness was then conducted using nanoindentation on different locations through the cross section of the composite material. The nanoindentation results are complemented by macroscale mechanical testing (four-point bend flexure) and optical microscopy to correlate changes in mechanical properties with variations at the microstructural level, through the thickness of the material, as well as compared between materials exposed for increased exposure times. Specimens have also been dried to assess the reversibility of property degradation due to moisture uptake and evaluate the permanent effects of ageing on degradation of the composite materials over time.
Results will be presented on the micromechanical response of carbon fibre epoxy composites to water uptake, offering a more nuanced understanding of the underlying degradation mechanisms. This improved understanding is required for the development of predictive models for the mechanical performance of these materials in moist environments, aiding in the design and optimization of composite structures for enhanced durability.