Bulletin of the American Physical Society
21st Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 64, Number 8
Sunday–Friday, June 16–21, 2019; Portland, Oregon
Session J4: MS: Strength & Spall III |
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Chair: Kathy Prestridge, LANL Room: Pavilion West |
Tuesday, June 18, 2019 11:00AM - 11:15AM |
J4.00001: Constraining flow stress models at high strain-rates through in-situ imaging of hole closure under dynamic compression Jonathan Lind, Andrew Robinson, Matthew Nelms, Nathan Barton, Mukul Kumar The stress at which a material plastically flows depends on the current state of the material, strain-rate, and microstructure among other quantities. Experimental tests at high strain-rates (\textgreater 10$^{\mathrm{3}}$/s) often use measurement of shape change to infer flow stress behavior and are facilitated by comparisons with advanced simulations. A new plate-impact experimental test will be described consisting of in-situ x-ray imaging the closure of a cylindrical hole in a sample during the passage of a pressure pulse of controlled amplitude and duration. Experiments on tantalum aims to test the validity of present flow stress models within the experimental uncertainty. Results will be compared with direct numerical simulations using several flow stress models. We will discuss the results, the sensitivity of this new experimental test, and the implications for informing models. [Preview Abstract] |
Tuesday, June 18, 2019 11:15AM - 11:30AM |
J4.00002: Effect of stress triaxiality on damage behavior of AM pure copper in a wide range of strain rate Gianluca Iannitti, Andrew Ruggiero, Nicola Bonora, Martina Riccio, Michele Antolotti, Gabriele Rizzi, Mariano Zarcone, Diego Corona In this study, the effect of stress triaxiality on ductile damage of additive manufactured pure copper were investigated in a wide range of strain rate (from 10$^{-3}$ to 10$^4$ 1/s). Round notched bar and Rod-on-Rod (RoR) specimens were manufactured by means of Sisma MYSINT100 machine, based on Selective Laser Melting (SLM) technology. The specimens were heat treated in order to obtain the same average grain size of wrought annealed pure copper. Tensile tests on round notched bar specimens were performed in a wide range of strain rates to determine the failure strains at different stress triaxiality. Bonora Damage Model was calibrated and used to assess the velocities at which incipient and fully developed damage occur in RoR specimens. Tests at selected velocities were carried out and soft-recovered specimens were sectioned and polished to observe the developed damage. Nucleated voids maps were compared with numerical simulations results of RoR. Finally, the comparison with wrought annealed pure copper was also reported. [Preview Abstract] |
Tuesday, June 18, 2019 11:30AM - 11:45AM |
J4.00003: ABSTRACT WITHDRAWN |
Tuesday, June 18, 2019 11:45AM - 12:00PM |
J4.00004: Strength Characterization of Ductile Materials in Dynamic Tension from SHTB Data Avishay Lindenfeld, Yehuda Partom Using a Split Hopkinson Tension Bar (SHTB) to test ductile materials with high strain to failure (of the order of \textasciitilde 50{\%}), poses some challenges. 1) Interpretation of SHTB tests is not straight forward due to neck formation, which causes non-uniform stress and strain distributions along the specimen. 2) Neck location varies with specimen geometry and loading conditions, and it is not clear if this may influence the strain to failure. 3) To cause failure of a long specimen requires a long loading pulse, and this may be practically limited by the maximum striker's length possible for a given system. We address the latter problem by using a technique that practically doubles the duration of the loading pulse without changing the striker's length. We address problems 1 and 2 by using full numerical simulations (including the striker, the bars and the specimen) to predict the test results. In this way we are able to calibrate the strength model, taking into account necking, neck location and plastic heating. [Preview Abstract] |
Tuesday, June 18, 2019 12:00PM - 12:15PM |
J4.00005: Development of tensile SHPB system and properties of AM Maraging steel. Christopher Braithwaite, David Williamson, Nicholas Taylor Additively Manufactured (AM) materials have great industrial potential, but remain relatively under-studied, particularly at high strain rates. This paper describes the modification of a tensile SHPB system in order to study the properties of an AM Maraging steel and a comparison with the equivalent wrought material. Results demonstrate an unexpected level of ductility in the AM steel, as well as good levels of reproducibility. This reproducibility speaks both to the consistency of manufacture in the specimens but also the reliability of the apparatus used. [Preview Abstract] |
Tuesday, June 18, 2019 12:15PM - 12:30PM |
J4.00006: Is there an upturn phenomenon in the strength of metals at strain rates of 10$^{\mathrm{3}}$-10$^{\mathrm{4}}$ s$^{\mathrm{-1}}$? Yechezkel Ashuach, Zvi Rosenberg, Roman Kositski, Alon Malka-Markovitz In this paper we focus on the controversy surrounding a claim, made by many authors, that the flow stresses of various materials experience a very large increase (the "upturn" phenomenon) at strain rates in the range of 10$^{\mathrm{3}}$-10$^{\mathrm{4}}$ s$^{\mathrm{-1}}$. This claim was contradicted by other workers who did not find such "upturn" behavior for the same materials. We identify some possible reasons for this controversy, focusing on the differences between the dynamic loading techniques, which were used in these studies. Our conclusion is that these differences may result in problems with data interpretation, which can lead to the controversies surrounding the "upturn phenomenon". In order to enhance our claim we performed Kolsky compression bar tests on two materials for which an upturn was found in previous works, namely, copper and a tungsten heavy alloy. We found no upturn in these materials at strain rates of 10$^{\mathrm{3}}$-10$^{\mathrm{4}}$ s$^{\mathrm{-1}}$ which covers range in which the upturn was found in those works. [Preview Abstract] |
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