A New Test Method for Characterizing Low Temperature Structural Materials
Tensile tests were carried out at high speed loading in order to reduce the thermal component in plastic flow. The specimens were circular in cross section and notched around the girth by Electro Discharge Machining (EDM). The deformation to failure was performed within about 50 ms corresponding to a strain rate of the reduced section of ca. 50 s-1. The test temperature could be varied between 295 and 7K. Signals of the load cell and of two extensometers were acquired with a digital acquisition board at high sampling rate (20 kHz/channel). The area under the load-displacement curve provides the Fast Failure Energy Absorption (FFEA) of the specimen. The cryogenic structural materials investigated were 316LN-, CSUS JN1-, 310S-, and 03Cr20Ni16Mn6N- austenitic stainless steels, but also a selected Ti-alloy and an electrolytic tough pitch copper. For the high strength and high toughness austenites the FFEA-values versus temperature showed a sharp transition at a characteristic low temperature. Comparing the measured fracture toughness KIC values at 77 and 4K with the dynamic FFEA-data, a linear relationship was obtained. This suggests that the new method is able to give a quick estimate of the fracture toughness of a variety of materials over a wide range of temperatures.
KeywordsFracture Toughness Austenitic Stainless Steel Charpy Impact Notch Root Plate Material
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