Lightweight Garage #9 Ceramic composites as heat shield @ SHEFEX DLR

October 14, 2021 from Micha Clauß

©Bernulius/stock.adobe.com

The Vehicle

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

©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 its re-entry body, which came up by the termination of the space shuttle project. The main advantages of the contour are the reduction in manufacturing costs, since the original curved heat shields require complex manufacturing processes. The new contour creates concentrated loads on the joining edges, on which ceramic fiber composites are used.

The Technology

The combination of a heat-resistant ceramic matrix with high-strength ceramic fibers to increase the strength and ductility of the composite, creates excellent material properties in terms of weight, electromagnetic transparency, stability, and high temperature resistance.

©Alexander Stirn, Detail view on ceramic composite entrance sign Shefex II, CC BY-NC-ND 2.0

Due to the evolution of the used flat ceramic composite panels in SHEFEX II, the panels now can also be controlled by actuators for steering, which leads to an additional functionality of the edge geometry. This integration allows control elements to be saved in other structural areas of the re-entry body, which is a classic functional lightweight construction principle.

The Lightweighting

Since weight reduction is not top priority in the SHEFEX project, but it is for us as lightweight engineers, a direct comparison of steel and ceramics makes it clear what potential there is in ceramics that are subject to high thermal loads. With half the density and about three times the heat resistance, ceramic fiber composites can achieve a saving 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, which enables the material to be used in a wide range of technical applications.

 

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