This presentation was made at the 2019 NAFEMS World Congress in Quebec Canada
Processing of polymer fibre composites has a remarkable influence on their mechanical performance. These mechanical properties are even more influenced when using recycled reinforcement. Therefore, we place particular attention on the evaluation of micromechanical models to estimate the mechanical properties and compare them against the experimental results of the manufactured composites from recycled carbon fibre material. For the manufacturing process, an epoxy matrix and carbon fibre production cut-offs as reinforcing material are incorporated using a vacuum infusion process. These types of cut-offs usually vary from each other in terms of quality, shape and size, and in the case of individual fibres, length variations are common. Thermally treated fibres (thermally recovered from end-of-life composites) are typically in the form of fluffy, which is a state difficult to handle, and often requires some additional treatments to allow for further application. Each carbon fibre waste type requires a different recycling strategy and resulting fibres often vary significantly in terms of quality. The main challenge of reusing thermally recycled carbon fibres is that their length or degree of degradation cannot be fully controlled. In addition, continuous textile reinforcement in combination with the epoxy matrix is used as reference material to evaluate the degradation of mechanical performance of the recycled composite.
In order to predict the properties of the manufactured composites, micromechanical models are used here to predict the elastic and strength properties of the composite. The stiffness models are chosen to consider the precursor as unidirectional short fibre composites and use respective methods such as the Cox shear lag model, rule of mixture and inverse rule of mixtures for elastic properties. Later they are used along with laminate analogy approach (LAA) for evaluation of the elastic modulus and strength of recycled short fibre composites with planar fibre orientation distributions. As of predictive models for strength properties, Cox shear lag model for unidirectional and quasi isotropic material is also used where the critical fibre length is calculated first for including the length factor and then experimental/environmental factors for each configuration were invoked into the rule of mixture.
The experimental results show higher degradation of the composite strength compared to the stiffness properties. Observations from the modelling also show the same trend as the deviation between the theoretical and experimental results is lower for stiffness comparisons than the strength calculations.
In order to analyse the mechanical performance of these material, an industrially common geometry was chosen and loaded in a three-point-bending cases. The material data from the models and the experiments were used to also see the structural performance and compare them together.
|Date||18th June 2019|
|Organisation||RISE SICOMP AB|