Experimental Testing and Characterization of High Velocity Impacts on Novel Ultra High Strength Steels
Avalos, Alba (2015)
2015
Teknisten tieteiden tiedekunta - Faculty of Engineering Sciences
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Hyväksymispäivämäärä
2015-06-03
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tty-201505201387
https://urn.fi/URN:NBN:fi:tty-201505201387
Tiivistelmä
The main aim of this work was to study the performance against high velocity impacts of two novel ultra high strength steels. Different impact velocities and testing conditions were studied to recreate the actual working environment. Lubrication and low temperature tests were performed and compared to dry-conditions impact testing. The effect of surface work hardening taking place during service was studied as well.
Mechanical behavior of the materials was studied at strain rates ranging from 10-3 to 3600 s-1 using a quasi-static testing machine and the Split Hopkinson Pressure Bar technique. High velocity impact tests were performed at different conditions using spherical projectiles at different velocities for a constant impact angle of 30°. The influence of impact energy and environmental conditions were studied. Wear was analyzed based on volume loss taking into consideration also the material plastically deformed and cut-off from the surface through the cutting-to-plasticity ratio. The energy dissipated during the impact was also studied. Characterization of the impact craters and their cross-sections was performed to identify failure and damage mechanisms.
Impact wear was found to be strongly dependent on impact energy and testing conditions. Higher impact energies lead to higher wear rates likely caused by the appearance of adiabatic shear bands. Lubrication was observed to lead to higher volume loss due to more material cut-off from the surface instead of plastically deformed. Work hardening prior to testing produced an increase of hardness of 45-80 %, which resulted in a decrease of wear rate except in the case of the highest impact velocities. Adiabatic shear bands were more present on dry-impact testing than in any other type of test case.
Mechanical behavior of the materials was studied at strain rates ranging from 10-3 to 3600 s-1 using a quasi-static testing machine and the Split Hopkinson Pressure Bar technique. High velocity impact tests were performed at different conditions using spherical projectiles at different velocities for a constant impact angle of 30°. The influence of impact energy and environmental conditions were studied. Wear was analyzed based on volume loss taking into consideration also the material plastically deformed and cut-off from the surface through the cutting-to-plasticity ratio. The energy dissipated during the impact was also studied. Characterization of the impact craters and their cross-sections was performed to identify failure and damage mechanisms.
Impact wear was found to be strongly dependent on impact energy and testing conditions. Higher impact energies lead to higher wear rates likely caused by the appearance of adiabatic shear bands. Lubrication was observed to lead to higher volume loss due to more material cut-off from the surface instead of plastically deformed. Work hardening prior to testing produced an increase of hardness of 45-80 %, which resulted in a decrease of wear rate except in the case of the highest impact velocities. Adiabatic shear bands were more present on dry-impact testing than in any other type of test case.