To enable the tests required for development work to be performed with maximum efficiency, the Zwick Roell Group (ZwickRoell) – a global supplier of materials testing machines based out of Ulm, Germany – developed a materials testing machine that can be equipped with both a temperature chamber and a high-temperature furnace.
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The ZwickRoell AllroundLine testing machine operates with an alternating current drive that requires extremely low maintenance when compared to large hydraulic drives and associated fluids. The AllroundLine attains maximum forces up to 250 kilonewtons in the tensile and compression directions and constant velocity characteristics at very low speeds.
The temperature chamber is designed for temperatures between -80°C and +300°C, but can be used down to -150°C with liquid nitrogen to simulate the below-freezing-temperatures found at commercial airline cruising heights. The high-temperature furnace operates from 200°C to 1,600°C, with is a choice between one- and three-zone versions and an air or vacuum environment. Temperature this high could reflect the temperatures that occur in and around aerospace turbines.
Strain measurement for all the above temperature ranges is handled by a non-contact laserXtens extensometer consisting of two measuring heads with digital cameras and laser light sources mounted on motorized carriages. This laser-optical method eliminates the need for material specimen marking in tensile tests, and instead uses light-generated virtual gauge marks on the material, the movement of which is tracked in real time.
This testing envelope is suitable for a wide variety of applications, such as tensile, compression, and flexure testing to determine aerospace material heat resistance, re-crystallization temperature, and thermo-elastic behavior.
Flexible testing stretched beyond original limits
Among the organizations taking advantage of this flexible testing system is KRP Mechatec GmbH of Munich, Germany. KRP Mechatec uses a ZwickRoell AllroundLine testing machine for testing additive manufactured aluminum and titanium structures for space launch vehicles at temperatures as low as -269°C.
The liquid hydrogen fuel tanks aboard launch vehicles need to hold fuel at a stable temperature of -253°C while being subjected to extremely high loads during take-off. Additive manufacturing methods such as laser melting afford a great amount of design freedom and therefore offer huge potential for weight minimization – one of the most important issues regarding launch vehicles.
Cyrostat installed in KRP Mechatec’s Zwick AllroundLine (Source: KRP Mechatec)
The objective of the test program at KRP Mechatec is to maximize the potential of lightweight construction for additive manufacturing while maintaining fuel tank structural integrity.
Because of the limited amount of material quantity, ZwickRoell readily helped KRP Mechatec develop a special fixture, which pushed past the original equipment’s limit of -150°C and allowed simultaneous materials testing to be performed efficiently and economically.
Tensile, compression, shear, and hole-widening tests were all performed in a cryostat pre-cooled to -196°C using liquid nitrogen and then cooled to a final temperature of -269°C with liquid helium.
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William Kucinski is content editor at SAE International, Aerospace Products Group in Warrendale, Pa. Previously, he worked as a writer at the NASA Safety Center in Cleveland, Ohio and was responsible for writing the agency’s System Failure Case Studies. His interests include literally anything that has to do with space, past and present military aircraft, and propulsion technology.
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