Quantitative correlation of micro- and macromechanical parameters of endless fibre reinforced plastics

• Applicant: Professor Dr.-Ing. Christian Hopmann
• Subject Area: Polymeric and Biogenic Materials and Derived Composites ; Lightweight Construction, Textile Technology
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 471651330

Unidirectional continuous fibre-reinforced plastics (UD-FRP) have high weight-specific strength and stiffness as well as good energy absorption capacity and fatigue behaviour under fibre-parallel tensile load. For this reason, understanding the properties of FRP under fibre-parallel tensile load is of great importance. Due to the micromechanically heterogeneous structure, however, the consideration of composite properties is more complex than with metal materials and requires a deeper understanding of the damage behaviour and the underlying mechanisms. According to the literature, there are essential damage mechanisms for carbon fibre or glass fibre reinforcement with a thermoset matrix, e.g. fibre breakage, fibre debonding and matrix damage. Therefore, there are complex interactions between the mechanisms. In static, crash-relevant, and cyclic load cases, these micromechanical mechanisms are influenced differently by the fibre and matrix types and the properties of the fibre/matrix-interface, so that there is an optimum fibre/matrix combination for these load cases and their requirements. Although in the literature there are investigations on individual mechanisms and influencing factors, no studies on the interaction of all essential factors with uniform boundary conditions can be found. It is therefore not fully understood how the constituent properties influence the damage and the macro-mechanical parameters, such as tensile strength, and fatigue life. Various micromechanical models have been developed to investigate this topic, along with the three-dimensional Shear-Lag model (SLM) offers the greatest potential. The aim of this project is the further development of the Shear-Lag model for UD-FRP for different load cases (quasi-static load and fatigue) and the evaluation of the applicability of the model for different fibre/matrix combinations. A further goal is the prediction of the mechanical parameters by simulation so that the performance of UD-FRP can be optimized application-specifically by material selection.To achieve this goal, the shear-lag model will be further developed for these load cases. At the same time, the micro-mechanical input parameters of the model and the macro-mechanical parameters of different fibre/matrix combinations will be characterized experimentally. The predictive quality of the model will then be analysed to evaluate for which fibre/matrix combinations and which load cases the model is suitable. As a direct result of the applied project, a validated model for the prediction of the mechanical parameters will be developed. Furthermore, the understanding of the interaction between the influencing factors will be extended.

• DFG Programme: Research Grants