Measurement of small elastic anisotropy in solids using laser-induced ultrasonic pulses

Abstract

Nondestructive laser-induced short ultrasonic pulse generation (duration ≊10 ns) together with broadband detection is used to detect and measure the small elastic anisotropy in opaque solids quickly and precisely. This is demonstrated for an extruded aluminum alloy type 6061-T6. A single laser-induced acoustic pulse propagation measurement over a path length of 47 mm provides a longitudinal ultrasonic velocity measurement accuracy of 0.02%. The longitudinal velocities at ±45°from the extruding direction Z are found to be 2% larger than the velocity along Z, indicating that most of the aluminum crystallites are oriented with a principal axis parallel to Z. Thermal annealing of the sample results in a small increase in ultrasonic veolcity in all directions with the observed acoustic anisotropy remaining essentially unchanged.