Multiscale modelling of fiber composites - Investigating micromechanics of constituents' interaction
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The objectives of this thesis have been to develop a script for a multiscale method based on first order homogenisation, to investigate estimation of properties and behaviour of unidirectional (UD) fiber composites. To model composites on the microscale, an algorithm that generates periodic representative volume elements (RVE) geometries from controllable parameters and a pseudo random factor was developed. The output of this algorithm (fiber populations) was used to create heuristic RVE models in the Finite Element Analysis (FEA) software, Abaqus 6.14-4. These heuristic RVE models consist of fibers, matrix and an interface. The fibers in the models were assigned linear elastic material properties and the matrix and interface were assigned elastic, plastic and damage material properties. To simulate deformations and loads, macro strains were imposed on the heuristic RVE models through constraint equations. As the properties of the RVE varied with the distribution of the fiber populations, the creation of RVE models was automated to perform multiple iterations to calculate estimations of the average properties and the statistical dispersion of these. The effect of design parameters on stiffness estimations was investigated. To get insight into the local stress field in the RVE models, the maximum principal stress and maximum shear stresses were found for normalized linear elastic load cases. The strength of the RVEs was predicted by simulating nonlinear behaviour with different assigned material models. Consistent macrostrains for the non-linear analyses were maintained by an iterative backward force balancing procedure.The results showed that the stiffness estimations generally follow micromechanical approximations based on the rule of mixture. For the strength estimations, the produced results correlate with comparable methods and results found in the literature. This suggests that the method is feasible for microscale modelling of an RVE of UD fiber composites. Further development into material models, damage models and confirmation and calibration of results with empirical data should be investigated before using such a tool for design estimates.