Ultrasound material testing

Medical ultrasonography (Inge Edler and Carl H. Hertz) Edler and Hertz adapt an ultrasound probe used in materials testing in a shipyard for use on a patient. Their technology makes possible echograms of the heart and brain. 

When ultrasound is used, a probe containing both transmitting and receiving transducers is placed on the object to be investigated (for materials testing Figure 16.2) or above the patient s bed (for medical use). 

Figure 16.2 The principle of materials testing with ultrasound. A flaw or a pore in a weld may be detected and the position of the defect is shown. (From B. A. Custafsson, Materiallara, Almqvist Wiksell, Stockholm, 1992. With permission.)...

In this paper, the performanees of laser-ultrasound are estimated in order to identify lacks of weld penetration. The laser-ultrasonic technique is applied to cylindrical metallic strucmres (few mm thick) in a single-sided control. The results obtained for different materials (gold-nickel alloy and tantalum) are presented by B-sean views for which the control configuration is discussed with regard to the thermal effects at the laser impact. This testing is performed for different lacks of weld penetration (up to 0.5 mm for a thickness of 2 mm) even in the presence of the weld bead, which corresponds to an actual industrial problem. 

Material Veloeity. Defines the velocity, in metres/sec, of ultrasound in the material of the test piece used to convert A-scan signal time to distances within the test piece. 

In this paper we propose a multivariable regression approach for estimating ultrasound attenuation in composite materials by means of pulse-echo measurements, thus overcoming the problems with limited access that is the main drawback of through-transmission testing. 

Staff Metallic and Inorganic Coatings Metal Powders, and Sintered P/MStructural Parts, American Society for Testing Materials, West Conshohocken, PA, 2001. Sushck, K.S. "Ultrasound Makes a Hit with Metal Powder, Advanced Materials... 

In practice ultrasound is usually propagated through materials in the form of pulses rather than continuous sinusoidal waves. Pulses contain a spectrum of frequencies, and so if they are used to test materials that have frequency dependent properties the measured velocity and attenuation coefficient will be average values. This problem can be overcome by using Fourier Transform analysis of pulses to determine the frequency dependence of the ultrasonic properties. 

Solids usually have larger ultrasonic velocities and acoustic impedance, than liquids, which have larger values than gasses. Air has a very low acoustic impedance compared to liquids or solids which means that it is difficult to transmit ultrasound from air into a condensed material. This can be a problem when ultrasound is used to test dry materials, e.g., biscuits or egg shells. A small gap of air between an ultrasonic transducer and the sample to be tested can prevent ultrasound from being transmitted into the material. For this reason coupling materials (often aqueous or oil based) can be placed between the transducer and sample to eliminate the effects of the air gap, or alternatively soft-tip ultrasonic transducers can be used. 

Mechanical and viscoelastic behaviour of materials can be determined by different kind of instrumental techniques. Broadband viscoelastic spectroscopy (BVS) and resonant ultrasound spectroscopy (RUS) are more commonly used to test viscoelastic behavior because they can be used above and below room temperatures and are more specific to testing viscoelasticity. These two instruments employ a damping mechanism at various frequencies and time ranges with no appeal to time-temperature superposition. Using BVS and RUS to study the mechanical properties of materials is important to understanding how a material exhibiting viscoelasticity will perform. 

The density of aluminum is 2.7 g/cra . Density is a property that can be used to identify an unknown sample of matter. Every sample of pure aluminum has the same density. How It Works at the end of the chapter explains how ultrasound testing relies on the variation in density among materials. 

These are fundamental considerations and are of interest not just to electrochemists and sonochemists, but care must be taken in correctly attributing an apparent shift in an experimentally observed potential under ultrasound. As already mentioned, system parameters and other factors may influence an observation beyond the effect under investigation. Thus there have been reports on the use of the titanium tip of the sonic horn itself, suitably electrically insulated, as the electrode material [50]. Dubbed the sonotrode , this is a clever idea to combine the two active components of a sonoelectrochemical system the authors noted the expected enhancements in limiting currents and an alteration in the morphology of copper electrodeposited from aqueous solution on to the titanium tip, which was the reaction under test. However, although titanium is widely used in sonochemistry because of its low-loss characteristics under vibration, it is not a common electrode material for electroanalysis because of its inferior electron transfer characteristics... 

Later the magnetic stirrer is operated in a defined manner and dispersion begins. The graph plotting transmission versus time provides a measure for dispersion velocity. When the transmission curve reaches a plateau the best possible (stationary) dispersion obtainable with this device has been reached. By applying ultrasound to the liquid the degree of dispersion can be further increased in most cases. The test results may be used to define several characteristic dispersion conditions of the material e.g. the ratio of transmission at a given time to transmission at stationary dispersion or final dispersion due to ultrasound. 

---