Development of a lifetime prediction concept of continuous fibre-reinforced plastics based on time-temperature-superposition by using NIR-spectroscopy.

• Applicant: Dr.-Ing. Wilfried Liebig
• Subject Area: Polymeric and Biogenic Materials and Derived Composites
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 469043941

Fibre-reinforced plastics show a time and temperature dependent material behaviour. These dependencies are related since both arise from molecular motions and rearrangements. This correlation is known as time-temperature superposition and is mainly used in dynamic-mechanical analyses to determine mechanical properties of (fibre-reinforced) plastics in a wide time and temperature range while reducing the experimental effort. The aim of the proposed research project is to apply the time-temperature superpostion in the context of fatigue experiments. A testing methodology will be developed with the aim to predict the temperature and frequency dependent fatigue lifetime of continuously fibre-reinforced plastics as well as stiffness degradation curves. Experimental inverstigations on coupon level will be carried out on pure resin specimens as well as laminates built from multiple glass fibre-reinforced plies with varying orientations. The influence of internal heating owing to dissipation effect on the materials degradation behaviour is examined indepenantly from a purely mechanical load. The methodology is validated by means of suitable long-term experiments and the limitations of the concept are discussed. Near-infrared (NIR) spectroscopy measurements are carried out in the course of the experiments to determine the specimes absorption spectra. These spectra show a correlation with the mechanical and thermal loading history since different kinds of loads give rise to different molecular motions and molecular rearrangements. The NIR spectra can thus serve as a measure for the degradation of (fibre-reinforced) plastics. The quantitative relations between mechanical and/or thermal loads as well as the NIR spectra will be investigated in detail in the course of the proposed research project. A concluding result of the project will be the determination of the remaining service life of a fibre-reinforced plastic by means of NIR measurements without knowing the materials loading history. NIR spectroscopy shall thus be established as a method for fatigue lifetime prediction thereby eliminating or reducing the need for expensive stiffness and crack density measurements.

• DFG Programme: Research Grants
• Major Instrumentation: NIR-Spektroskop
• Instrumentation Group: 1830 Fourier-Transform-IR-Spektrometer
• Co-Investigator: Professor Dr.-Ing. Peter Elsner (†)