Correlation of micro- and macro-mechanical damage in continuous fibre-reinforced plastics
The damage behaviour of continuous fibre-reinforced plastics results from a complex interplay of failure mechanisms across different scales. At both the micro- and macroscopic levels, fibre breakage, matrix cracking, delamination and degradation at the fibre–matrix interface interact, leading to a nonlinear material response. In this research project, a three-dimensional shear-lag model (3D-SLM) was developed to numerically investigate the mechanical behaviour of unidirectional fibre-reinforced plastics (UD-FRP) under quasi-static and dynamic cyclic tensile loading.
The model accounts for both the plastic material behaviour of the matrix and interface debonding, thereby enabling multiple breakages along the fibres. To represent fibre strength, a two-parameter Weibull distribution is applied, with its parameters determined through micromechanical characterisation experiments. Although the model quantitatively underestimates the stiffness of the composite compared to experimental values, it provides a good qualitative approximation of the actual quasi-static and dynamic cyclic behaviour.
A detailed analysis of the numerical results reveals that the damage patterns associated with matrix cracking and interface debonding is reflected in the stress fields of both hydrostatic pressures and octahedral shear stresses. To investigate the stress state, a Principal Component Analysis (PCA) was implemented on the numerical models, thereby simplifying the description of the complex micromechanical stress state. The conversion from conventional PCA to a mesh-independent principal component analysis proved essential for ensuring consistency across various RVE models and establishing this method as a valuable tool for investigating the micromechanical stress state. The RVE simulations further indicate that the respective damage mechanisms leave a specific signature in the redistribution of the matrix stress field, providing a new and valuable numerical insight into the complex micromechanical damage behaviour that cannot be captured through experimental analyses.
Thus, the fatigue behaviour can be comprehensively examined, thereby laying the foundation for the development of new, damage-mechanism-based models that can be applied in the design of continuous fibre-reinforced structural components.
Project data and funding
We would like to thank the DFG for funding the project (funding code: HO 4776/78-1) and the project partners for their cooperation.
Project duration: 03.2022 – 04.2025
Funding:
