Dynamic High-Temperature Characterization of an Iridium Alloy in Compression at High Strain Rates

Abstract

Iridium alloys have superior strength and ductility at elevated temperatures, making them useful as structural materials for certain high-temperature applications. However, experimental data on their high-temperature high-strain-rate performance are needed for understanding high-speed impacts in severe elevated-temperature environments. Kolsky bars (also called split Hopkinson bars) have been extensively employed for high-strain-rate characterization of materials at room temperature, but it has been challenging to adapt them for the measurement of dynamic properties at high temperatures. Current high-temperature Kolsky compression bar techniques are not capable of obtaining satisfactory high-temperature high-strain-rate stress-strain response of thin iridium specimens investigated in this study. We analyzed the difficulties encountered in high-temperature Kolsky compression bar testing of thin iridium alloy specimens. Appropriate modifications were made to the current high-temperature Kolsky compression bar technique to obtain reliable compressive stress-strain response of an iridium alloy at high strain rates (300-10000 s-1) and temperatures (750°C and 1030°C). Uncertainties in such high-temperature highstrain-rate experiments on thin iridium specimens were also analyzed. The compressive stressstrain response of the iridium alloy showed significant sensitivity to strain rate and temperature.

Dynamic high-temperature characterization of an iridium alloy in tension

“…In addition to the diagnostic issues in Kolsky tension bar experiments presented above, it is even more challenging when the Kolsky tension bar is used for high-temperature experiments. The concepts for high-temperature Kolsky compression bar techniques developed previously [7,8] cannot be used for high-temperature Kolsky tension bar tests. In previous high-temperature Kolsky compression bar experiments, the specimen was individually heated to high temperatures while the pressure bars were kept at room temperature.…”

“…The engineering stress and strain histories in the specimen, which were calculated with Eqs. (8) and (9), respectively, are shown in Fig. 18.…”

“…However, it has been challenging to dynamically characterize materials at high temperatures, particularly when the temperature is higher than 600°C [7]. Recently, Song et al [8,9] modified Kolsky compression bar techniques to characterize the dynamic stressstrain properties of a DOP-26 iridium alloy in compression at high strain rates (300 -10000 s -1 ) and high temperatures (750 and 1030°C). The iridium alloy showed significant strain-rate and temperature effects on the compressive stress-strain response.…”

Dynamic High-Temperature Tensile Characterization of an Iridium Alloy with Kolsky Tension Bar Techniques

“…However, current mechanical characterization of iridium alloys has been limited to relatively low strain rates (below 50 s -1 ) [2][3][4][5], which are not sufficiently high for their potential applications. Song et al [6,7] recently employed Kolsky compression bar testing, also known as split Hopkinson pressure bar testing, to characterize the compressive stress-strain properties of a DOP-26 iridium alloy at high strain rates (300-10,000 s -1 ) and high temperatures (750 and 1030°C). The iridium alloy showed significant strain-rate and temperature effects on the compressive stress-strain response.…”

“…Cold contact time (CCT) has been defined as the time during which the high-temperature specimen stays in contact with the room-temperature bars until being dynamically loaded [11]. The CCT is usually required to be as short as several milliseconds, and even within 1 ms when the specimen is thin [7]. Appropriate modifications have been made to Kolsky compression bars for generating short CCTs.…”