[Image: Dan Little Photography, © 2015 HRL Laboratories]

The Air Force has been researching additive manufacturing for military purposes for quite some time, with resources for both plastic and metal 3D printing. Now the Air Force is looking into ceramic additive manufacturing, with a specific purpose in mind – hypersonic flight vehicles. The Air Force Research Laboratory Aerospace Systems Directorate has entered into a Cooperative Research and Development – Material Transfer Agreement (CRADA-MTA) with HRL Laboratories to test 3D printed silicon oxycarbide (SiOC) materials.

HRL Laboratories developed the ceramic materials with hypersonic flight in mind, as they can withstand the extreme environments and high temperatures that hypersonic flight requires. The Aerospace Systems Directorate’s scientists began assessing the potential of HRL’s materials while searching for new thermocouple radiation shields. The SiOC materials were produced through an additive manufacturing process using a pre-ceramic resin. After the part is manufactured, it is subject to a heat treatment that converts it into a fully ceramic state.

“If a material can withstand those temperatures – roughly 3,200 degrees Fahrenheit – it could be used for hypersonic aircraft engine components like struts or flame holders,” said Jamie Szmodis, a hypersonic research engineer with the Aerospace Systems Directorate.

To get an idea of what hypersonic speed is, consider that current aircraft fly at Mach 1, or more than 768 miles per hour. That’s supersonic speed. Hypersonic speed exceeds Mach 5, meaning that aircraft would be flying at speeds of over 4,000 miles per hour. This would allow for faster military response times, more advanced weapons and much faster travel for both the military and commercial sectors.

The CRADA-MTA is a type of technology transfer agreement that allows for the transfer of materials for testing, meaning that the Air Force can now access HRL Laboratories’ ceramic materials for research purposes.

“Without the material transfer agreement, we would have purchased the samples to test them. We would have been a customer, as opposed to a collaborator,” said Szmodis. “With the agreement we are able to provide test results to HRL and provide feedback that is valuable to both parties.”

Under the agreement, the Aerospace Systems Directorate received five thermocouple radiation shields and 15 sample cylinders manufactured from the SiOC resin. Szmodis established a small team from various directorates and specialties to conduct the tests. Scientists from the AFRL Materials and Manufacturing Directorate, Structural Materials Division, Composite Branch, led by Dr. Matthew Dickerson, conducted materials analysis and heat treatments. The Aerospace Systems Directorate, Aerospace Vehicle Division, Structural Validation Branch scientists, led by Bryan Eubanks, performed mechanical analysis focusing on thermal expansion analysis at temperatures ranging from 500 – 3,500ºF. Scientists at the Arnold Engineering Development Complex’s Propulsion Research Facility performed analysis of the material’s characteristics in a high-enthalpy instrumentation test facility.

A sample of additively manufactured silicon oxycarbide (SiOC) material is tested at Arnold Air Force Base. [Image: Air Force]

The Air Force completed a final report of the results in March and delivered it to HRL Laboratories. The study pushed the 3D printed components far beyond their design envelope, and the data generated provided valuable information that is now being used to guide the production of next-generation 3D printed ceramics. These results, and further work by HRL, have the potential to produce materials that can meet hypersonic requirements.

“The extreme temperature testing that AFRL performed revealed the limits of our new material and challenged us to improve it,” said Dr. Tobias Schaedler, a senior scientist from HRL.

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[Source: Air Force]

 

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