Volker Trappe

Protecting the structural integrity of composites in fire: Intumescent coatings in the intermediate scale

The fire behaviour of light-weight material used in structural applications is regarded as the main challenge to be solved for mass transportation. The task is to perform realistic experiments, including a mechanical test scenario under fully developed fires, to improve the material’s reliability in structural applications. Our approach utilises an intermediate-scale test set-up (specimen size 500 × 500 mm) to apply realistic compressive loads and fully developed fires directly to one side of a carbon-fibre-reinforced sandwich composite. Three different intumescent coatings were applied to sandwich structures and compared to a bench-scale study. The results emphasise intumescent coatings as a promising method to sustain fire resistance, multiplying the time to failure. Nevertheless, the realistic intermediate-scale test using severe direct flame application underlines the extremely short failure times when the actual composite components are tested without any additional insulation.

Structural integrity of sandwich structures in fire: an intermediate-scale approach

A test set-up in intermediate scale was conceived to investigate the structural integrity of materials under fire. The task was to develop a realistic test scenario targeting component-like behaviour. Carbon-fibre-reinforced sandwich specimens (500 × 500 × 20 mm) were used to examine failure mechanisms, times to failure and critical failure loads under compression. Fire tests were performed with fully developed fire applied to one side of the specimen by an oil burner. In a first test series, the applied load was varied, but the fully developed fire remained unchanged. In general, times to failure were short. Decreased load levels resulted in prolonged times to failure and led to a different failure mechanism. Results obtained in the test series were compared with a bench-scale study (150 × 150 × 20 mm) investigating identical material. The comparison clearly revealed the influence of size on the time to failure and the load-bearing capacity.

Bestimmung des Zwischenfaserbruchversagens in textilverstärktem Glasfaserkunststoff mittels der Röntgenrefraktionstopografie

Kurzfassung Moderne Leichtbaustrukturen (Luftfahrt, Eisenbahn, Automotive) aus Faserverbundwerkstoffen (FVW) sind hohen mechanischen und klimatischen Beanspruchungen ausgesetzt. Aussagen über die Lebensdauer und Funktionssicherheit der FVW-Bauteile können eher aus Untersuchungen der mikromechanischen Eigenschaften gewonnen werden als aus der globalen Festigkeit. Die Röntgenrefraktionstopografie ist ein Verfahren zur zerstörungsfreien Bestimmung von inneren Oberflächen in Werkstoffen. Angewendet auf FVW lassen sich Aussagen über die Faserorientierungen, die Fertigungsqualität sowie über Faser-Matrix-Ablösungen und Matrixrisse infolge mechanischer Beanspruchung gewinnen. Nachfolgend wird ein neues Verfahren zur Bestimmung des Zwischenfaserbruchversagens am komplexen Laminat vorgestellt. Hierbei wird das Röntgenrefraktionsverfahren “online” bei Zug-Belastung der Probe angewendet.

Micro-mechanical properties of fiber composites characterized by X-ray refraction (Invited Paper)

Fiber Reinforced Plastics (FRP) are increasingly applied in transportation systems (aircraft, railway, automotive) and infrastructure industries due to the good specific properties of high strength at low weight. Advanced FRP structures have to endure high mechanical and environmental loading. Therefore the durability and reliability depends much more on the micro mechanical properties as on the global strength. X-ray refraction topography is a powerful tool for the characterization of inner surfaces in materials. Applied to fiber composites the presented investigations give information about the mean diameter of the fibers, orientation and the quality of impregnation. Strong correlations were found between fiber matrix debonding and micro cracking and the stress state due to mechanical loading. Additionally a new method for a quantitative determination of transverse and shear strength in a complex laminate is presented. Therefore the X-Ray refraction technique is applied on-line during tensile load of specimens.