The use of the direct impact Hopkinson pressure bar technique to describe thermally activated and viscous regimes of metallic materials
The influence of strain rate over domains involving the thermal activation and the viscous drag behaviour of the dislocations is discussed. While it is recognized that the Koslky–Hopkinson technique or split Hopkinson pressure bar technique can generate data up to the upper strain-rate limit of the thermal-activated regime, it is necessary to use a direct impact Hopkinson pressure bar technique to access the viscous regime. Data generated with this technique are presented for a series of metals, including steel, nickel, copper and tungsten alloys. The motivation to generate such data is provided through three industrial applications.
On the importance of recrystallization to reproduce the Taylor impact specimen shape of a pure nickel
Taylor tests are a mean to investigate the dynamic plastic and failure behaviour of metals under compression. By taking in account the strengthening occurring at high strain rates, the Taylor final diameter of a pure nickel impacted at 453 m/s have been numerically reproduced by 13%. Through post-mortem observations of the specimen impacted at 453 m/s, a recrystallization process has been found to occur resulting in a softening of the pure nickel. Subsequent numerical simulations taking in account this softening have been found to reduce the difference between experimental and numerical diameter by 10%.
Energy
Energy is often defined as the ability to do work. There are many forms of energy. A few examples include; Gravitational energy, Kinetic energy (energy of motion), Thermal energy (heat energy), Potential energy. Potential energy is the energy something has based on its position in the universe. A stretched elastic band has potential energy. A rock held up in the air has potential energy based on its position.