Ultrasonic measurements and

The objectives of this chapter are to introduce the basic concepts of ultrasonic propagation in materials, to describe some of the most important methods for measuring and interpreting ultrasonic measurements, and to outline existing and possible applications of the technique in the food industry. 

P. Martinoty et al. (Phys. Rev. E 1997) at the first-order SmC-SmF transition where nevertheless, fluctuations are observed by anomalies in ultrasonic measurements and H. Yao, T. Chan, C. W. Garland, Phys. Rev. 1995, E51,4584 at the first-order SmC-SmI critical point. See also [11]. 

This is identical with the Moseley equation (17), if the second term is negligible. The principle limitation of this method is that it measures the average orientation of the total sample. It has, however, been found that a good correlation exists between the orientation data derived from ultrasonic measurements and those obtained from birefringence measurements. ... 

The ASTM thermal cycling method (ASTM Cl 171-96) (3) combines ultrasonic measurements and modulus of rupture at ambient temperature on 150-mm X 25-mm x 25-mm bars to assess performance. In this case, comparisons are between two separate sets of test pieces. 

For the repetitive inspections the required hydrotest can only be performed for a limited number of the small cylinders, and even then the drums have to be removed from the line and the cylinders will be supported in defined distances for the weight of the water and the pressurisation. For the new and long cylinders even this is impossible, because they loose due to the additional weight of the water and the over-pressurisation their roundness and balances. Therefore the law in the most countries within and outside of the EU accept as a replacement of the hydrotest an additional application of different NDT methods, which were often done by an ultrasonic measurement of the wall thickness of the cylindrical part and a MT of the flat covers. 

In the near future the technique will be further evaluated using ultrasonic signals from natural defects, e.g., fatigue cracks. The performance measure and the parameter optimization procedure wilt also be refined in order to obtain a computationally efficient implementation, easy to use for a trained operator. 

Theoretical studies of the interaction between an ultrasonic beam and planar defects have been widely carried out and shown that the upper and lower tip diffraction echoes are characterized by phase inversion. In other words, the measurement of 180° phase shift between these two echoes proves the plane nature of the defect that has generated them. 

In general a thickness measurement using ultrasound is done by measuring the time of flight of the ultrasonic pulse and calculating the thickness of the objeet multiplying the time and the known constant sound velocity in the material. 

This paper presents solutions of two different NDT problems which could not be solved using standard ultrasonic systems and methods. The first problem eoncems the eraek detection in the root of turbine blades in a specified critical zone. The second problem concerns an ultrasonie thiekness measurement for a case when the sound velocity varies along the object surface, thus not allowing to take a predetermined eonstant velocity into account. 

Ultrasonic techniques are an obvious choice for measuring the wall thickness. In the pulse-echo method times between echoes from the outer and inner surface of the tube can be measured and the wall thickness may be calculated, when the ultrasonic velocity of the material is known. In the prototype a computer should capture the measuring data as well as calculate and pre.sent the results. First some fundamental questions was considered and verified by experiments concerning ultrasonic technique (Table I), equipment, transducers and demands for guidance of the tube. 

Based on the results from the initial experiments ultrasonic equipment and transducers for the scanning system were selected. Also a measuring chamber with transducer fixtures was constructed and manufactured for measurement on the tubes directly on the drawing bench. 

T. Leon-Salamanca and D. E. Bray, "Ultrasonic Measurement Of Residual Stress In Steels Using Critically Refracted Longitudinal Waves (L j )," R j". NDE 6(4) 1995 (in press). 

Figure 16.6 shows the general yield and fast fracture loci for a pressure-vessel steel and an aluminium alloy. The critical flaw size in the steel is =9 mm that in the aluminium alloy is =1 mm. It is easy to detect flaws of size 9 mm by ultrasonic testing, and pressure-vessel steels can thus be accurately tested non-destructively for safety -vessels with cracks larger than 9 mm would not be passed for service. Raws of 1 mm size cannot be measured so easily or accurately, and thus aluminium is less safe to use. 

After a satisfactory verification film is produced, an assembly may be fabricated specifically for destructive inspection to validate that the verification film was accurate. This correlation allows the use of verification film rather than more expensive destructive inspection for future changes such as duplicate tool fabrication and tool or detail modification. Simple assemblies are usually not destructively inspected because of high confidence that the verification film is entirely representative of the expected bondlines. Complex or large parts may not be destructively inspected because of the cost of the details and assembly time. In these cases other means of validating the verification film are used. Meticulous pre-bond detail and post-bond assembly thickness measurements may be sufficient to prove bondline thickness control. Ultrasonic inspection and X-ray photography (discussed previously) may be sufficient to prove that details are in the correct places and bonds are good. 

The caliper is used to correct the density and neutron porosity measurements for borehole effects and also can be used as a borehole stability indicator. Figure 4-289 shows an example of comparison between the MWD ultrasonic caliper and the four-arm wireline caliper run five days later. 

Miscellaneous methods. Other techniques, although used much more rarely, can sometimes be helpful. Among these techniques dynamic thermochemical analysis295, measurements of electric conductivity297, of ultrasonic absorption298, and of dielectric constant299,300 should be mentioned. 

Winter T. G., Hill G. L. High-temperature ultrasonic measurements of rotational relaxation in hydrogen, deuterium, nitrogen and oxygen, J. Acoust. Soc. Am. 42, 848-58 (1967). 

The most significant results obtained for complexes of iron(II) are collected in Table 3. The data derive from laser Raman temperature-jump measurements, ultrasonic relaxation, and the application of the photoperturbation technique. Where the results of two or three methods are available, a gratifying agreement is found. The rate constants span the narrow range between 4 x 10 and 2 X 10 s which shows that the spin-state interconversion process for iron(II) complexes is less rapid than for complexes of iron(III) and cobalt(II). 

Interfacial area measurement. Knowledge of the interfacial area is indispensable in modeling two-phase flow (Dejesus and Kawaji, 1990), which determines the interphase transfer of mass, momentum, and energy in steady and transient flow. Ultrasonic techniques are used for such measurements. Since there is no direct relationship between the measurement of ultrasonic transmission and the volumetric interfacial area in bubbly flow, some estimate of the average bubble size is necessary to permit access to the volumetric interfacial area (Delhaye, 1986). In bubbly flows with bubbles several millimeters in diameter and with high void fractions, Stravs and von Stocker (1985) were apparently the first, in 1981, to propose the use of pulsed, 1- to 10-MHz ultrasound for measuring interfacial area. Independently, Amblard et al. (1983) used the same technique but at frequencies lower than 1 MHz. The volumetric interfacial area, T, is defined by (Delhaye, 1986)... 

Turbidity of the sonicated (30 min), control and boiled samples were measured and given in Table 9.19. As could be seen, the turbidity increased gradually, as the volume of solution or of CH3COONa increased in all solutions (control, sonicated and boiled). When 20 ml of Al3+ was sonicated for 30 min with 5 ml of CH3COONa, turbidity did not appear, but when a solution containing, 10 ml of Al3+ and 2.5 ml of CH3COONa was sonicated for the same duration, the turbidity appeared, indicating the role of ultrasonic power which decreased to about half as the volume of the solution increased. 

The viscosity coefficients at dislocation cores can be measured either from direct observations of dislocation motion, or from ultrasonic measurements of internal friction. Some directly measured viscosities for pure metals are given in Table 4.1. Viscosities can also be measured indirectly from internal friction studies. There is consistency between the two types of measurement, and they are all quite small, being 1-10% of the viscosities of liquid metals at their melting points. It may be concluded that hardnesses (flow stresses) of pure... 

We wish to note that 0D can also be calculated from the measured ultrasonic velocities, and data should be equal to those obtained from specific heat measurements. The Debye s temperature evaluated from data of ultrasonic velocity is (see e.g. [14,15]) ... 

L. S. Wilson and D. E. Robinson, Ultrasonic measurement of small displacements and deformations of tissue, Ultrason. Imaging, 1982, 4, 71-82. 

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