Ultrasonic Evaluation of Acoustoelastic Parameters in Aluminum

Aluminum has become a structural material widely used not only in mechanical and aerospace engineering, but also, more recently, in civil engineering. Because of its structural properties—such as strength, lightness, durability, and fire safety—aluminum, in recent decades, has been increasingly applied to the mechanical and civil engineering industry, including automotive components and large structural constructions. The main objective of the research presented here is to assess aluminum elastic parameters through simple ultrasonic measurements that can be used for in situ civil engineering applications. Experiments were conducted to measure second- and third-order elastic parameters in 6061-T6 aluminum alloy specimens. All measurements were made with the application of simple through-transmission ultrasonic transverse and longitudinal waves in prismatic samples while uniform load was vertically applied. Measurements were taken with all waves transmitted perpendicularly to the applied load direction, shear pulses were polarized in the direction of the load and also perpendicularly to it. Even though the stresses due to the applied loading were relatively low (up to 140 MPa) consistent and continuous variation of the measured ultrasonic velocities with increasing stress was observed. Classical third-order acoustoelastic Murnaghan coefficients $l$, $m$, and $n$ were then calculated using the velocity measurements. In the experiments wave velocities were directly calculated from inquiring ultrasonic pulses transmitted and received using pairs of 500-kHz broadband transducers. The experiments showed the feasibility of applying simple ultrasonic apparatuses to assess third-order acoustoelastic parameters for field applications and can be applied in an axially loaded member of any structural material.