An Ultrasonic Technique for Measuring the Elastic Constants of Small Samples

Using instrumentation designed for the ultrasonic measurement of thickness, a technique has been devised for measuring the isotropic elastic constants of small samples, i.e., samples 1 mm in thickness and a minimum of 5 mm in other dimensions. Young's modulus, the shear modulus and Poisson's ratio are calculated from measurements of density and ultrasonic shear and longitudinal wave velocities. Samples of valve train materials, including chill cast iron, low alloy steel, tool steel, stainless steel, a nickel-base superalloy, and a powder metal alloy were machined from components and analyzed. The magnitude of the measured values of the elastic constants are reasonable when compared with published values. The measurement error on all the constants is estimated to be less than 1 %. Moduli determined by this method can be used in finite element analyses to improve designs. When material properties are different near a surface, elastic constants characteristic of the surface layer can be measured. When the material properties are a function of the fabrication process, e.g., small castings or powder metal components, reliable elastic constants can be found. Metal stampings can be analyzed in a through-thickness direction. The elastic properties of non-metallic materials - ceramics, glasses and plastics - can also be measured.