The longevity of materials under radiation conditions is a critical consideration in the design of nuclear components. One apparent effect of radiation is a reduction in ductility that occurs from radiation induced embrittlement. The testing of irradiated materials necessary to understand this effect can be expensive and introduces significant safety hazards. Smaller test specimens require less total radiation dose to impose the same damage and are therefore much safer to handle for post-irradiation evaluation (PIE). Thus, in order to facilitate the testing of smaller PIE specimens, there is a significant need for characterization techniques which can bridge length scales. One early ductility scaling law, proposed by Barba, describes the total elongation at failure as a combination of the uniform elongation (regardless of necking) and the non-uniform elongation (dependent on initial length, initial area, and a material constant). Traditionally, Barba’s Law is characterized by testing multiple specimens of different lengths and fitting a line to the data to obtain empirical material properties.

This work develops a novel variable extensometer method that fully characterizes Barba’s Law from a single specimen. The variable extensometer uses Digital Image Correlation (DIC) to extract full field displacement data during a tension test of Oxygen Free High Conductivity (OFHC) copper. The DIC data allows for selecting multiple different initial gauge lengths along the specimen.  The elongation for each of these lengths can then be tracked over time and line can be fitted to the obtained data to characterize the parameters for Barba’s Law. This provides two unique benefits. The first is the measurement resolution is limited only by the camera resolution and step size used during DIC. This produces a curve with thousands of data points from a single specimen rather than a handful points from the available specimen lengths. The second is that this measurement is taken in-situ and provides an understanding of how Barba’s law parameters develop over time. Traditionally, the final elongation is a postmortem measurement, but DIC allows for the development of Barba’s Law parameters through all phases of a tension test.

 Testing was performed with a Gleeble 1500D on specimens of OFHC copper with lengths of 40 mm, 60 mm, and 80 mm. Images were processed in VIC-2D, a commercial DIC software, then processed in Matlab to extract a time evolution of Barba’s Law parameters from images throughout the duration of each tension test. The results for each different length were compared against each other to validate the variable extensometer method.   


a Variable Extensometer Method for Characterizing the Multi-Scale Ductility of Ofhc Copper

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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