Elastic-constant variability in stainless-steel 304

Abstract

Variability of elastic constants in stainless-steel 304 was determined by measuring longitudinal and transverse ultrasonic velocities in 20 samples acquired randomly. Three kinds of variations—sample to sample, directional within a sample, and repeated measurements on a single sample—are reported for four elastic constants: the bulk modulus, Young’s modulus, shear modulus, and Poisson’s ratio. Because of surprisingly small variations, 1% or less, the principal problem became measurement sensitivity and reproducibility. To overcome this problem, a high-resolution measurement system was devised using general-purpose equipment augmented with a very simple impedance-transforming amplifier and an FET transmission gate. With this system the often-reported troublesome transit-time correction disappeared. Effects due to frequency and directionality were negligible.