Defects, application

Kenneth Zanio, Materials Preparation Physics Defects Applications... 

MSee for example Diam. Relat. Mater. 1997,6,1243-1571 (an issue dedicated to SiC characterization, crystal structure, defects, applications, bulk and epithaxial growth, and other related materials). 

This concludes our consideration of defect applications. Let us now consider a more mathematical approach to the description of point defects. 

QA is a rather costly activity (a component can cost much more if a stringent QA requirement is specified), therefore every QA requirement must be accurately weighed against its real need the approach must always be graded and proportionate. It has been known in some cases, for defective application of the method to have produced more paper than quality and this must, by all means, be avoided. 

Fig. 1 (a) Qualitative interpretation of spalling of masonry units due to defective application of deep rejointing, (b) A brick wallette tested in compression after iayer of... 

On industrial applications orientated detection of casting defects... 

The first results of computer-based assessment system application show that the benefits are obvious for repaired (without heat treatment) welds and complex defect configurations defect with height local increasing, group of defects, case analysis of defects interference and possible joining. 

In contrast to a direct injection of dc or ac currents in the sample to be tested, the induction of eddy currents by an external excitation coil generates a locally limited current distribution. Since no electrical connection to the sample is required, eddy current NDE is easier to use from a practical point of view, however, the choice of the optimum measurement parameters, like e.g. the excitation frequency, is more critical. Furthermore, the calculation of the current flow in the sample from the measured field distribution tends to be more difficult than in case of a direct current injection. A homogenous field distribution produced by e.g. direct current injection or a sheet inducer [1] allows one to estimate more easily the defect geometry. However, for the detection of technically relevant cracks, these methods do not seem to be easily applicable and sensitive enough, especially in the case of deep lying and small cracks. 

The application of eddy currents in non destructive testing was very developed during the recent years. Adding to the defects characterization, actual studies deal with the metallurgical evaluation of materials. Surface processing allow to increase the material endurance and consequently its life duration. 

The application of fundamentally new ECT (Russia patent Jf 2063025) has made it possible to provide high-efficiency defect control accompanied by detecting both small surface defects and more rough under-surface defects under non-magnetic metal layer of 7 mm thick, or surface defects under protection coatings, dye, corrosion, hermetic and other type of layer of 10 mm thick. 

Fig. 3 Examples of Zond VD - 96 application in detecting defects filed.

There are difficulties of detecting defects in axial canal because of solid sediment layer of 1. 2 mm thick on the canal surface. When using known defectoscope devices a preliminary labor-intensive mechanical treatment of the axial canal surface is needed. The experience of application of different methods of rotor axial canal control in multifunction automatic device ROTOR - K has pointed to the fact that the most effective method is eddy current one [1]. All the dangerous cracks were just detected by the eddy current method, the part of the cracks were not... 

Elaboration of a Physical Model by Eddy Current and Application in the Characterization of Long Defects in Hollow Cylindrical Products. 

It is easy to calculate tire value of e as an application of the MAXWELL S equations in the case of a symmetric tube without defect. 

Feiste, K. Hanke, R. Stegemann, D. R.eimche, W. Three Dimensional Analysis of Growing Casting Defects. International Symposium on Computerized Tomography for Industrial Applications, Applications II 20, Berlin, 1994. 

General hydrodynamic theory for liquid penetrant testing (PT) has been worked out in [1], Basic principles of the theory were described in details in [2,3], This theory enables, for example, to calculate the minimum crack s width that can be detected by prescribed product family (penetrant, excess penetrant remover and developer), when dry powder is used as the developer. One needs for that such characteristics as surface tension of penetrant a and some characteristics of developer s layer, thickness h, effective radius of pores and porosity TI. One more characteristic is the residual depth of defect s filling with penetrant before the application of a developer. The methods for experimental determination of these characteristics were worked out in [4]. 

Here a - surface tension pa - atmospheric pressure 9 - contact angle of crack s wall wetting by penetrant n - coefficient, characterizing residual filling of defect s hollow by a penetrant before developer s application IT and h - porosity and thickness of developer s layer respectively W - minimum width of crack s indication, which can be registered visually or with the use of special optical system. The peculiarity of the case Re < H is that the whole penetrant volume is extracted by a developer. As a result the whole penetrant s volume, which was trapped during the stage of penetrant application, imbibes developer s layer and forms an indication of a defect. 

The obtained results for the magnetic bench have allowed to note that defects situated at 12 mm of depth have been observed clearly. This is explained by the high power furnished by the bench, in addition its induction is double alternation rectified. Dimensions of the defect (height and width) are precisely estimated (figure 1). The defect detection at this depth is due to the application of a rectified field, so skin phenomenon is almost absent. 

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