Dynamic yield-strength determination at elevated temperatures after nanosecond pulse heating

An experimental method is described that has been used to determine the yield strength of 6061-T6 aluminum after extremely short times at elevated temperature. The method combines electron-beam pulse heating and onedimensional stress-wave loading. A 3.5-MeV pulsed electron-beam source (pulse width of 70 nanoseconds) is used to deposit energy uniformly through the thickness and along a limited region of a slender aluminum rod. An axial compressive stress wave, produced by projectile impact on one end of the rod, propagates into the heated region a few microseconds after energy deposition. The nanosecond electron-beam pulse increases the internal energy of the material before it can expand to equilibrium dimensions at the elevated temperature. Additional time is therefore required for the specimen to equilibrate mechanically through the propagation of radial release waves which originate at the stress-free boundary of the sample. The deformation produced by these radial relief waves is coupled with microstructural changes that also contribute to a reduction in the yield strength of the material at elevated temperature, as well as at room temperature following electron-beam heating.