Development of a holistic fatigue damage approach for FRP-structures for the analysis of instabilities due to delamination growth

• Applicants: Professor Dr.-Ing. Maik Gude; Professor Dr.-Ing. Raimund Rolfes
• Subject Area: Lightweight Construction, Textile Technology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 567203965

In practice, high-performance components made of fiber-reinforced plastic composites (FRP) are subjected to cyclical stresses in particular over the course of their service life. Stresses with alternating load directions between tension and compression also occur regularly. In the damage process of fatigue-loaded FRP with various oriented layers, inter-fiber failures (IFF) usually represent the initial damage mechanism. If the intralaminar IFF meet layer boundaries, the formation of delamination may occur. As a result, the stability behavior of the structure becomes more important, as delamination greatly reduces the buckling stiffness of the laminates. The interaction of distributed IFF growth with strong stiffness degradation of the laminate and discrete delamination growth resulting in stability failure due to fatigue loading with compression has not yet been sufficiently investigated and understood. For safety reasons, FRP structures are therefore usually loaded far below their actual bearable loads. Improved utilization of the potential of lightweight construction for real FRP structures therefore requires sound knowledge of the variable stability behavior due to IFF and delamination growth under fatigue loading with compressive components. Based on extensive experimental analyses on the formation, growth and influence of delamination on the stability behavior of FRP test specimens, a profound understanding of the damage phenomenology is in focus of this research approach. This includes the specific investigation and quantification of the damage mechanisms IFF and delamination using new methods that enable a separate analysis of the influence of the respective damage mechanism on the stability behavior. The experimental findings will be used to develop a new simulation method for simulating fatigue-induced stability behavior. This simulation method is based on a coupled numerical description of inter-fiber failure and delamination-induced degradation due to fatigue. In contrast to existing homogenizing approaches, the project aims to develop a holistic fatigue damage model that differentiates between the damage components of IFF and delamination. For this purpose, a continuum damage model, which calculates the stiffness degradation due to fatigue caused by IFF, is to be coupled with a cohesive zone model, which describes the fatigue-induced delamination growth. The coupling of the two models will be realized in the form of a hybrid cohesive zone element, that also enables the stability analysis in addition to the damage analysis of the numerical models. The proposed project thus provides well-founded experimental findings and a novel numerical description of the influence of IFF and delamination on the stability behavior of FRP.

• DFG Programme: Research Grants