Ultrasonic measuring techniques available for material testing
In this article:
The Core Purpose of Ultrasonic Testing: How UT is used to detect internal discontinuities and analyze material properties through wave interference.
Wall Thickness Measurement Techniques: Methods for accurately measuring thickness using pulse transit time or resonance-based systems.
Determining Elastic Properties of Materials: How sound velocity relates to modulus of elasticity, shear modulus, and Poisson’s ratio.
Stress Analysis Using Shear and Surface Waves: Techniques for measuring stress in materials during elastic deformation.
Ultrasonic Structural Examination: How variations in sound velocity and attenuation reveal internal structure in metals, ceramics, and concrete.
Hardness and Viscosity Measurement Applications: How ultrasonic damping and contact impedance are used to assess hardness and fluid viscosity.
Recommended Equipment for Ultrasonic Testing: Waygate Technologies provides rugged, high-performance ultrasonic tools ideal for precise flaw detection and material evaluation in industrial settings.
What ultrasonic measuring techniques are available for material testing?
Ultrasonic testing (UT) is a widely employed non-destructive evaluation (NDE) method used primarily to detect and assess discontinuities within materials. By utilizing high-frequency sound waves and analyzing their interactions with the internal structure of materials, ultrasonic testing offers a precise and versatile approach to quality control and material characterization.
Beyond simple flaw detection, ultrasonic methods have evolved to support a broad range of measurement techniques that exploit the relationship between sound wave behavior and material properties. These include determining wall thickness, elastic constants, residual stresses, structural composition, and even hardness. This blog explores the core principles behind these ultrasonic measuring techniques and highlights their practical applications across materials science, metallurgy, and production environments.
The main purpose of the ultrasonic testing of materials is looking for and evaluating locations in materials which contain discontinuities and whereby advantage is taken of the interference to the wave propagation by such locations. At the same time a large number of measuring methods develop which take advantage of the numerous relationships in the interaction effects between sound waves and the material for a more accurate determination of the properties of material, from the physics of solids up to the production control. From this range outside the flaw locating, and which is somehow un- justly called “ultrasonic measuring techniques” various methods have gained practical significance.
The basics for all methods are either the influencing of the sound velocity (sound transit time) or the sound attenuation through the material in which the sound wave travels.
1. The wall thickness measurement uses the known sound velocity to determine the wall thickness. For this there are pulse transit time instruments with either analogue or digital displays e. g. D-Meter. Or a resonance method is used. The development of electronic components for the direct determination of the transit time allows a high level of measurement ac- curacy, for which interferometers or corresponding phase super- position methods were previously required.
2. Elastic constants of materials are very closely related to the sound velocities of longitudinal and shear waves. By transposing in equations (3) and (4) in chapter 5 one obtains the following relationships for the modulus of elasticity E, the shear modulus G as well as the Poisson ratio μ. In addition to the sound velocities cshear and clong (m/s) all that is needed is the density ⍴ of the material (in kg/m3):
3. Stress measurements during elastic deformation can also be carried out by measuring the speed of sound of shear or surface waves.
4. Structure examination is an important application of ultrasonic measuring techniques— especially with castings, concrete or ceramics and where sound velocity and sound attenuation are measured.
The sound velocity is influenced by the graphite content and formation. Similarly, with castings, ductility and hardness are related to the sound velocity.
For determining the mechanical characteristics however, the sound attenuation is often of greater advantage than the sound velocity because it reacts with far more sensitivity to the changes in the structure. In metallurgy and solid- state physics one can confirm deformation in the plastic and elastic ranges by changes in the sound attenuation.
5. Measuring hardness ultrasonically is based on the different damping of the oscillations of a metal rod in an UCI hardness meter, if the Vickers indenter on top of the rod is pressed to the sur- face of the test specimen. (Ultrasonic contact impedance) (fig. 85). The viscosity of fluids can be determined in a similar manner.
In Summary
Ultrasonic measuring techniques extend far beyond traditional flaw detection, offering powerful tools for analyzing the physical and mechanical properties of materials with high accuracy and efficiency.
By leveraging variations in sound velocity and attenuation, engineers and scientists can gain valuable insights into wall thickness, elasticity, internal stresses, and material structure. These methods are especially advantageous in fields requiring precise quality control and non-invasive analysis, such as metallurgy, manufacturing, and civil engineering. As advancements in electronics and signal processing continue to evolve, ultrasonic testing will remain an indispensable part of modern material evaluation and production monitoring.
A comprehensive listing of all the applications with ultrasonics can be used es given in:
[18] H. D. Tietz: Ultraschall-Meßtechnik (Ultrasonic measuring techinques), VEB Verlag Technik, Berlin (1974)