Focused Practice

I. Answer the following questions:

1. What was an experimental study conducted for?

2. What resulted in drastic reduction of hard zones at DMWs fabricated with EniCrFe-3 electrodes?

3. Can hard zones in DMWs be eliminated?

4. What is the optimum welding electrode composition?

5. Why have DMWs been used as transition joints for many years?

6. Where are the joints often made?

7. What can fabrication and metallurgical drawbacks of DMWs lead to?

8. What is the most troublesome drawback of DMWs?

II. Analyse the grammar structures underlined in the above text.

III. Speak on: Fabrication and metallurgical drawback of DMWs.

Unit 10 Grammar: The modal verb. The Passive Voice Word List:

1. propagation of longitudinal waves	распространение продольных волн
2. hear wavers	звуковые волны
3. mode conversion	изменение типа волны
4. damping factor	коэффициент затухания
5. pulser receiver response	чувствительность приёмника к импульсам от генератора
6. transducer	преобразователь, датчик
7. backing	подложка
8. curing temperature	температура затвердевания
9. couplant	спаренный, сопрягаемый, граничный
10. material velocity variations	изменение скорости прохождения импульса в твердом теле
11. interference	наложение волн друг на друга
12. diffraction	огибание волной препятствия
13. spread	разброс
14. surface roughness	чистота обработки поверхности
15. discontinuity	сосредоточенная неоднородность
16. search unit frequency spectra	частотные спектры исследуемых устройств

Measurement and Analysis of Ultrasonic Beam Profiles in a Solid

To accurately measure the size and shape of discontinuities in a structural material by contact ultrasonic testing (UT), the beam profile used for the interrogation must be known. To ensure a correct signal in use, the beam profile must be determined under a condition similar to the actual inspection conditions.

The measurements of beam profiles in contact tests, in general, are very complex, because we often encounter problems such as the mixture of signals due to the propagation of longitudinal waves, hear waves, mode conversions at odd boundaries, interference, and diffraction. In addition, many variations of the beam profiles occur due to the wide spread of search unit frequency spectra, damping factor and phase, the pulser receiver response, and the configuration and dimensions of the test blocks. The variance in performance of different ultrasonic search units cannot be neglected. There are many types of transducer elements and construction methods. For example, the element can be made of quartz, lead-meta niobate, lead-titanate-zirconate, barium titanate, lithium niobate, or other new ceramic materials. The backing materials can be different proportions of tungsten powder with epoxy at different curing temperature and length of time. Different probe shape, size, and search unit types (straight beam, focused, delay line, dual element, angle beam, angle beam focused, angle beam dual element, etc.) all generate different beam profiles.

Other problems complicating the beam profiles in contact tests include surface roughness, couplant variations, material velocity variations (caused by coarse grain structures or specific material properties), and variability in operators performing hand-held methods. Those problems are relatively minor when compared to the previously mentioned, since these problems can usually be controlled by selecting a homogeneous material for the test blocks, controlling the surface smoothness, providing plenty of compatible, couplant conditions and having the test performed by experienced operators. It is commonly observed that the results given by immersion tests are repeatable, whereas the ultrasonic signal amplitudes in contact tests are scattered. The reasons for the data scattering have been largely thought to be due to surface roughness, variations of couplant conditions, different construction of the search units, etc.