Focused Practice

I. Answer the following questions:

1. Why are the measurements of beam profiles in contact tests very complex?

2. Why do many variations of the beam profiles occur?

3. What can transducer elements be made of?

4. What can the backing materials be?

5. What are the problems complicating the beam profiles in contact tests?

6. What are the reasons for the data scattering due to?

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

III. Speak on: The measurements of beam profiles in contact tests.

Unit 11 Grammar: The Infinitive. The Passive Voice Word List:

1. magnetic flux	магнитный поток
2. leakage field	поле рассеяния
3. field strength	напряженность поля
4. specimen	образец
5. prod	игольчатый электрод
6. heavy duty cable	кабель, несущий большой ток
7. to exploit	разрабатывать
8. iron filings	мелкие частицы, образующиеся при обработке железа
9. technique	технический прием
10. magnetic particle inspection (MPI)	магнитно-порошковая дефектоскопия
11. saturation magnetization	степень намагниченности

Review of Magnetic Methods for Nondestructive Evaluation (nde)

The subject of flaw detection in materials using magnetic methods has a long history, going back as far as Saxby in the last century. Systematic development of testing techniques based on perturbations of the magnetic flux in iron and steel due to the presence of defects did not begin, however, until after the chance discovery of Hoke that iron filings accumulated close to defects in hard steels while in the process of being ground.

Later, as the subject of flaw detection became more quantitative, additional methods were developed in which the leakage field in the vicinity of the flaw was measured with a magnetometer. Once the field strengths of the leakage fields were being measured on a routine basis, it became desirable to relate these to flaw size and shape, and therefore there arose the need for modelling the leakage fields from different crack geometries.

The technique of magnetic particle inspection was the first magnetic NDE method in widespread use. It was discovered accidentally by Hoke in 1918, but it was left to DeForest to develop the method further for practical use. DeForest’s work involved devising methods of generating a magnetic field of sufficient strength in any direction in a specimen. This he solved by proposing that electrical contact electrodes (known as ’prods’) with heavy-duty cables be used to pass large currents through test specimens in desired directions. Furthermore, he realized the need to use magnetic powders with uniform properties such as particle shape, size and saturation magnetization in order to obtain more reliable and reproducible results. DeForest and Doane formed the Magnaflux Corporation to exploit the MPI method in 1934. This company remains one of the principal suppliers of equipment for MPI.

The next stage of the evolution of MPI should be the development of expert systems, since even with automated measurement there are some disadvantages compared with a human operator. For example, an experienced inspector will know where flaws are most likely to occur and therefore can concentrate his efforts on that area. The transfer of this expertise to computer systems would be advantageous.