Micro-mechanical modelling of lenght distributions in short fibre reinforced composites

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Examensarbete för masterexamen
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2021
Författare
Mentges, Noah
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Sammanfattning
The material behaviour of short fibre reinforced composites is dependent on several micro-structural properties, such as the fibre orientation distribution and the geometrical fibre properties. Hence, in order to accurately predict the mechanical response of these materials, micro-mechanical models are used. Those models estimate a homogenised material response for these rather heterogeneous materials. The length of the short fibres inside the composite is not uniform due to the manufacturing process of these materials. Hence, it is necessary to represent the distribution of fibre lengths inside a composite within the micro-mechanical model. In this work, a two-step Orientation Averaging model is extended to account for fibre length distributions for the linear elastic and elasto-plastic material behaviour. Three different methods for modelling the fibre length distributions are investigated and compared. Two of them are then implemented for further investigations. The first method uses Unit Cell simulations for different fibre length classes, which are combined to a composite behaviour in an additional averaging scheme. For the second method, a single representative fibre length is obtained from the fibre length distribution, and the two-step Orientation Averaging is applied with this single fibre length. For that, a novel method for a representative fibre length is presented with the stiffness-averaged fibre length. The predictions obtained with the models show good agreement with the experimental results as well as in comparison to each other. Due to the better computational performance, the method using a single representative fibre length is preferred and recommended for the ongoing investigations.
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Composite mechanics, Short fiber reinforced composites, Micro-mechanics, Orientation Averaging, Fibre lenght distribution, Elasto-plasticity, Fibre-matrix debonding
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