Plate Impact Experiments for Studying the Dynamic Response of Commercial-Purity Aluminum at Temperatures Approaching Melt PDF Download

Author: Bryan Zuanetti
Publisher:
ISBN:
Category : Aluminum
Languages : en
Pages : 243

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Book Description
The mechanical properties of materials are known to be rate- and temperature-dependent. Owing to this, investigations aimed towards the exploration of material behavior (i.e. plasticity, strength, and failure) under thermomechanical extremes has been a subject of sustained interest. The extreme temporal and precise nature of these studies produces special experimental challenges, and as a consequence, knowledge regarding the dynamic response of materials, especially in thermomechanical extremes, is still limited by the deficiency of experimental data. The main objectives of the current study are to 1) develop a reliable experimental scheme for investigating the dynamic inelasticity of metals under thermomechanical extremes. In particular, the focus is on elevated temperature dynamic compressive and shearing resistance of metals at plastic strain rates in excess of one-million/sec and sample temperatures approaching melt. And, 2) to address the need for experimental data on the dynamic response of FCC metals in previously unexplored but important thermomechanical regimes, such as elevated temperatures and plastic strain-rates on the order of 10^5 – 10^9 /s. In order to conduct this research, the single-stage gas-gun facility at CWRU was modified to include a breech-end sabot heater system and a novel fully fiber-optics based normal and transverse motion diagnostics system, which enabled reverse geometry normal and pressure-shear plate impact experiments to be conducted on pure aluminum at elevated temperatures. Additionally, a full characterization of the WC anvil plates was performed. Using these capabilities, elevated temperature normal and combined pressure-shear plate impact experiments were carried out to better understand the high temperature dynamic compressive and shearing resistance of aluminum. These experiments were used to shed light on the temperature-dependence of the shock impedance of aluminum at pressures of around 1.0 – 1.6 GPa, and the temperature-dependence of shear flow stress at levels of strain approaching 50% and strain-rates in the order of 4 – 8 x 10^5 /s. The results showed an overall decrease in the shear flow stress with temperatures in the range of 23 – 593 ̊C, showing that temperature facilitates plastic flow of aluminum when deforming at strain-rates approaching 10^6 /s. Additionally, in an effort to better understand the relaxation behavior of this material at incipient plasticity at ultra-high strain-rates, a series of laser-driven shock compression experiments are carried out on pure aluminum films at temperatures ranging from 23 – 400 ̊C. The results are used to correlate the temperature-dependence of the rate-sensitivity of the Hugoniot elastic limit (HEL) of pure aluminum at strain-rates up to 10^9 /s. In contrast to the previous case (i.e. large plastic strains, and lower strain-rates), the results reveal a monotonic increase in the HEL with temperature for strain-rates in the range of 10^4 – 10^9 /s. This effect is shown to decrease with increasing strain-rate.