DFG UL 121/14-1 - EXPERIMENTAL AND NUMERICAL INVESTIGATION OF THE DAMAGE BEHAVIOUR OF SINGLE FIBRE COMPOSITES
DETERMINATION OF EFFECTIVE PROPERTIES OF FIBER-REINFORCED COMPOSITES BY HOMOGENIZATION BASED ON MICROMECHANICALLY MEASURED MATERIAL BEHAVIOR
The project investigates the damage of fibre-reinforced plastics. Therefor the concept of homogenisation is deployed, spanning three scales - micro, meso and macro. The methology to determine the properties of the fibres and the fibre-matrix-interface on the microscale was developed during the first period of the project. To characterise those properties, the comparison of simulations and experimental results of single fibre fragmentation tests (SFFT) and pullout test was used. Furthermore the viscoelastic properties of the matrix material were identified. During the second stage the rate dependend behaviour of the damaged matrix shall be modelled and parameterised by comparison with experiments. Thereby the behaviour of all constituents of the composite is identified. Based on this knowledge the effective behaviour of damaged composites on the macroscale will be determined by means of a two-stage computational homogenisation. This homogenisation includes the simulation of representative stochastic distributions of fibres and their strength on the microscale as well as the reinforcement structure consisting of rovings on the mesoscale. All simulations will be compared to experiments to calibrate parameters of the deployed models or to validate their predictions. Besides the mentioned experiments model composites with few fibres will be used to validate the interaction of interface and matrix damage on the microscale. Results of the homogenisation will be validated by experiments on unidirectional and multiaxial reinforced specimen. The proposed investigation is fundamental. Exemplary the material combination of E-glass and epoxy resin as well as the fibre geometry of the reinforcement are deployed. Nevertheless the results are of direct significance in the application of fibre-reinforced plastics. In comparison to materials like steel or aluminium their potential is exploited poorly due to a lack of quantification of their damage behaviour.
Specimen for a single fiber fragmentation test. Inside the epoxy tensile specimen a single glas fiber filament is molded. Testing such specimen allows for the characterization of fiber and interface properties, because due to lower strain to failure the fiber fractures before the epoxy resin.
Photoelastic picture taken during a tensile test.
Development of the number of fiber breaks in experiment and simulation for two types of fiber. Thin lines mark single experiments or simulations, whereas thick lines show the average.
Effective strain in an axial symmetric simulation of the single fiber fragmentation test. Six fiber breaks are visible due to an increase of effective strain at the lower side of the picture.