Lightweight garage #9 Ceramic fiber composites as heat shield @ SHEFEX DLR

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Lightweight garage, News

The vehicle

As a lightweight manufacturer, our global goal is optimization and efficiency. In the end, it's not just about the kilograms saved. Optimization can also occur as a positive secondary effect, as innovative materials combine many positive material properties. One example of this is the use of oxide ceramic composites in the SHEFEX ("sharp edge flight experiment") project of the DLR, in which a sharp-edged re-entry vehicle was designed in three evolutionary phases and used for the first time in 2005 as SHEFEX I.

©DLR German Aerospace Center, Shefex II on launch pad @ Andøya Space Center, CC-BY 3.0

The follow-up project SHEFEX II celebrated its first success in 2011 with a re-entry speed into the atmosphere of 11,000 km/h. Basically, the project is about the realization of the sharp-edged contour of a re-entry body, which was created in the course of the discontinuation of the space shuttle project. The main advantage of the contour is the reduction in manufacturing costs, as the original curved heat shields require complex manufacturing processes. The new contour creates point loads at the joining edges, where ceramic fiber composites are used.

The technology

By combining a heat-resistant ceramic matrix with high-strength ceramic fibers to increase the strength and ductility of the composite, excellent material properties are created in terms of weight, electromagnetic transparency, dimensional stability and high-temperature capability.

Alexander Stirn, Detailed view of ceramic composite entrance sign Shefex II, CC BY-NC-ND 2.0

Thanks to the evolution of the ceramic composite plates in SHEFEX II, these can also be controlled by actuators, which leads to further functionality of the edge geometry. This integration means that control elements can be saved in other structural areas of the reentry body, which is a classic principle of functional lightweight construction. By means of this functional integration, weight can be saved in other areas.

The lightweight aspect

Since weight reduction is not the top priority in the SHEFEX project, but is the most important aspect for us as TGM, a direct comparison of steel and ceramics clearly shows the potential of thermally highly stressed ceramics. With half the density and about three times the heat resistance, ceramic fiber composites can achieve a savings potential of factor 6, which makes pure ceramics very interesting for lightweight construction applications.[1] The combination with ceramic fibers greatly increases the fracture toughness and thus enables the material to be used in a wide range of technical applications.

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