A material model, that translates into a stiffness matrix, the second order fiber orientation tensor, described by Advani and Tucker, and the stiffness matrix of a composite with aligned ellipsoidal inclusions, has been implemented in a FE programme and validated. The stiffness of a SMC panel with known state of fiber orientation is calculated using FEM. The influence of process induced fiber orientation is analysed. The fiber orientation for a realistic charge pattern for the panel has been obtained through mould filling simulation in a separate project. It is found that the fiber orientation has a rather small impact on the global stiffness. Only 0.8% lower stiffness compared to isotropic material model is obtained taking into account the fiber orientation distribution. The main reason for the low impact of the process induced fiber orientation is that the charge is symmetrically placed in the mould leading to a symmetric fiber orientation distribution.
SUMMARYA model accounting for linear viscoelasticity and microdamage evolution in short fibre composites is described. An incremental 2D formulation suitable for FE-simulation is derived and implemented in FE-solver ABAQUS. The implemented subroutine allows for simulation close to the final failure of the material. The formulation and subroutine is validated with analytical results and experimental data in a tensile test with constant strain rate using sheet moulding compound composites. FE-simulation of a four-point bending test is performed using shell elements. The result is compared with linear elastic solution and test data using a plot of maximum surface strain in compression and tension versus applied force. The model accounts for damage evolution due to tensile loading and neglects any damage evolution in compression, where the material has higher strength. Simulation and test results are in very good agreement regarding the slope of the load-strain curve and the slope change.
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