Volume 26, Issue 3 (May 1998)
Ultrasonic Wave Measurements of Elastic Moduli E, G, and μ for Product Development and Design Calculations
A technique is presented to measure the isotropic elastic constants of small specimens using instrumentation designed for the ultrasonic measurement of thickness. Specimens as small as 5 mm × 5 mm × 0.5 mm can be measured. Shape is not critical as long as the major faces are plane and parallel. Young's modulus E, the shear (stiffness) modulus G, and Poisson's ratio μ are calculated from measurements of density and ultrasonic shear and longitudinal wave velocities. Samples of automotive valve train materials and of brake drum materials were machined from components, measured, and analyzed. Specimens included gray cast iron during stages of a development process, chill cast iron, hardened cast iron, low alloy steel, tool steel, stainless steel, a nickel-based superalloy, and a powder metal alloy. The magnitudes of the measured values of the elastic constants are reasonable when compared with published values available for some materials. The measurement error for each of the constants is estimated to be less than 1%.
Moduli determined by this method can be used in finite element analysis to improve design. When material properties are different near the surface, elastic constants characteristic of the surface layer can be measured. The development of new fabrication, alloying, or treatment processes can be monitored to assure the production of the desired material properties if modulus or some property correlated with modulus is desired. 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. “Small” is relative to the practicality of cutting tension bars and torsion rings from parts, so “Small” may seem rather large in some cases. Metal stampings can be analyzed in a through-thickness direction. The elastic properties of nonmetallics—ceramics, glasses, and plastics—can also be measured.