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This study focuses on understanding and prediction of short-term thermal degradation of polymer matrix composites. One sided irradiation of two commercial composites (HexPly® 8552/IM7 and M18-1/G939) is carried out on specimens of various thickness (2, 4, 6 mm) at different heat fluxes (50 and 80 kW/m2) for various exposure times prior to ignition. The aim is to correlate the amount of the applied thermal energy with the heat damage and the residual mechanical strength. Among the two primary components of each matrix the epoxy resin is observed to degrade faster than the thermoplastic under thermal load, as measured by IR spectroscopy. A correlation is achieved between the interlaminar shear strengths and the relative amount of the residual matrix components. The interlaminar shear strengths and degradation processes are assessed in dependence of the applied energy per volume. The derived relationships and a chemometric analysis of IR spectra, can be used to rapidly estimate mechanical properties, as well as other properties of specimens with unknown thermal preload. Degradation processes are discussed in detail.

This work provides techniques to separately determine temperature and duration of a thermal pre-load on a polymer matrix composite with a focus on long-term load (max. 400 days) without massive polymer degradation. The aim is a non-destructive, rapid, robust and precise in-service method to characterize incipient heat damage. A commercially available composite 8552/IM7 is investigated. Infrared spectroscopy of the surface and bulk material traces thermal degradation of the polymer. A multivariate (chemometric) data analysis was performed. The reliability of the calculated values for time (AE19 d) and temperature (AE 12 C) is increased by including other parameters with various degradation velocities such as mass loss of the composite and color changes and binder degradation of a typical top coat. The residual strength of a composite with unknown thermal history can be predicted and thermal loads such as heating in an oven and hot air are compared.

The interdependence between the curing conditions, structure, and the mechanical properties of tow neat phenolic resin systems was investigated. Changes of the distribution of the void diameters were characterized by light-an scanning electron microscope analyses. Tensile tests and dynamic mechanical thermo analysis were performed to determine the influence of the hardener concentration and the curing temperature on the mechanical and the thermomechanical properties. The study reveals that the hardener concentration predominately influenced the microscopic structure, and thus the mechanical properties of the phenolic resin systems. By varying the postcuring times, it can be shown that independent from the microstructure of the phenolic resin system, the degree of cure has a strong influence on the mechanical properties.