Non-linear deformation in fibre-reinforced epoxies : micromechanical characterisation and modelling
(2024)
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- Authors
- Supervisors
- Pardoen, Thomas
- Abstract
- Fibre-reinforced polymer (FRP) composites are ubiquitous in structural applications requiring high stiffness or strength and low weight. While the fibres are responsible for the superior stiffness and strength, the matrix material, typically made from highly cross-linked epoxies, often plays a crucial role in the damage and failure mechanisms dictating the overall strength of the composite. Hence, over the past two decades, bottom-up multiscale approaches have been at the heart of the research on composite materials. The understanding of the mechanisms defining the deformation and failure of the constituents at the microscale is of prime importance. This thesis provides experimental characterisation and modelling of an epoxy matrix at this scale. Before entering into the micromechanical aspects, the macroscale properties of several highly cross-linked epoxies are compared and rationalised via the glass transition temperature. The aim is to determine if master trends exist in epoxies. (Non)-linear relationships between several mechanical properties, such as the yield stress, and the glass transition temperature are found, valid at different temperatures and strain rates. Then, the microscale mechanical response of the matrix in confined volumes between fibres in a unidirectional FRP is studied. To that end, a novel nano digital image correlation (DIC) method has been developed, relying on the deposition of a fine, dense and homogeneous speckle pattern with nanoscale particles. Nano DIC allows quantification of strain fields at the submicron level and identification of regions of strain concentrations. Using the nano DIC results, a strain gradient plasticity model has been added to the constitutive model for the matrix material. This model delivered accurate predictions of the matrix strains at the microscale and of the macroscale stress-strain response of the composite. Finally, nanoindentation was used to assess size effects within epoxies, namely the indentation size effect and the increase in the hardness of the matrix when in-between fibres of a composite. The influence of physical ageing and of the low strain rate response were carefully studied.
- Affiliations
Citations
Klavzer, N. (2024). Non-linear deformation in fibre-reinforced epoxies : micromechanical characterisation and modelling. https://hdl.handle.net/2078.5/248885