Other Nondestructive Methods

The finite element method, as applied to an engineering structure, consists of dividing the structure into distinct nonoverlaping regions known as elements the elements are connected at a discrete number of points along the periphery, known as nodal points. For each element the stiffness matrix and load vector are calculated, by assembling the calculated stiffness matrix and load vector of the elements, one obtains the overall stiffness and vector of the system or structure the resulting simultaneous equations for the unknown displacement components of the structure (unknown nodal variables) are solved and the stress components are evaluated for the elements. 

Computations involving this method are now available in the form of commercial software with many examples of engineering models.58 Some typical problems considered are  

Fluid flow over a flexible structure in a channel 

Conjugate heat transfer and natural convection within an enclosed system 

Heat transfer from sodifying concrete blocks 

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Pipeline systems shall be tested after construction to the requirements of this Code except for pretested fabricated assemblies, pretested tie-in sections, and tie-in connections. The circumferential welds of welded tie-in connections not pressure tested after construction shall be examined by radiographic, ultrasonic, or other nondestructive methods in accordance with para. PL-3.19.2. 

The most efficient approach to measuring intimate contact of a multiple ply composite laminate would probably be to first use the C-scan technique or some other nondestructive method to determine the location of any flaws in the panel. The cross-sections of the panel that contain the flaws can then be examined by preparing optical micrographs of those areas, and the interply interface examined for complete contact. 

Following initial screening measurements, samples that showed elevated levels of U or Pu were measured by other nondestructive methods, such as NAA (for F and Cl content), before being submitted for chemical dissolution and further destructive analysis. Care was taken in the chemical treatment of the samples to minimise the danger of contamination. The primary methods used for the determination of U... 

Physical methods Physical methods include photometric absorption and fluorescence and phosphorescence inhibition, which is wrongly referred to as fluorescence quenching [1], and the detection of radioactively labelled substances by means of autoradiographic techniques, scintillation procedures or other radiometric methods. These methods are nondestructive (Chapt. 2). 

Nondestructive Detection Using Other Physical Methods 2.5.1 Spectral Phenomena... 

Nondestructive Dection Using Other Physical Methods 43 Table 7. Nondestructive detection of lipophilic substances with water as detecting reagent. 

Nondestructive Dection Using Other Physical Methods... 

Other techniques that can support predictive maintenance include acoustic emissions, eddy-current, magnetic particle, residual stress and most of the traditional nondestructive methods. 

A rapid, nondestructive method based on determination of the spatial distribution of ATP, as a potential bioindicator of microbial presence and activity on monuments, artworks, and other samples related to the cultural heritage, was developed [57], After cell lysis, ATP was detected using the bioluminescent firefly luciferin-luciferase system and the method was tested on different kinds of surfaces and matrices. Figure 3 reports the localization of biodeteriogen agents on a marble specimen. Sample geometry is a critical point especially when a quantitative analysis has to be performed however, the developed method showed that with opti-... 

Nondestructive hyphenated methods of analysis require follow-on spectro-photometric methods. The most common spectrophotometric analysis is FTIR, and it is most commonly associated with GC. It is, however, possible to combine it with other separation methods under specific conditions. 

In comparison with other measurement methods, NMR has important strengths. Its great virtue is its noninvasive nature, allowing one to obtain spatially resolved metabolic profiles and to investigate metabolomics in vivo. 10 There is little or no sample preparation. It is nondestructive. It is information-rich with regard to the determination of molecular structures because it can detect different chemical groups of metabolites simultaneously. 

Near infrared spectroscopy (NIRS), a technique based on absorption and reflectance of monochromatographic radiation by samples over a wavelength range of 400-2500 run, has been successfully applied for food composition analysis, for food quality assessment, and in pharmaceutical production control. NIRS can be used to differentiate various samples via pattern recognitions. The technique is fast and nondestructive method that does not require sample preparation and is very simple to use compared too many other analytical methods such as HPLC. The drawback of NIRS, however, is that the instrument has to be calibrated using a set of samples typically 20-50 with known analyte concentrations obtained by suitable reference methods such as FIPLC in order to be used for quantitative analyses. Simultaneous quantification of the... 

The ultrasonic C-scan technique is the most widely used nondestructive method of locating defects in the composite microstructure. The through transmission C-scan is easy to implement and a large composite panel can be scanned in a matter of minutes. The problem with this technique is that a C-scan cannot reveal the type of defect present. Hence, there is no way to determine if a flaw detected by the C-scan is due to incomplete contact of an interply interface or some other type of defect in the composite microstructure. 

In the round-robin analysis, a minimum of five samples each of coal, fly ash, gasoline, and fuel oil were analyzed. The NBS Probable Certified Value for certain elements are shown in Table IX along with PBR values. Since no data were reported on gasoline, there are no comparisons. The most inconsistent comparison was for mercury. Only four laboratories reported mercury by INAA in coal, three by INAA in fly ash, and two by INAA for fuel oil. Most other laboratory results reported were based on atomic absorption spectrometry. With one exception, all mercury values reported by INAA (a nondestructive method) were higher than... 

Although the high sensitivity of activation analysis is perhaps its most striking advantage, there are a number of other favorable aspects as well. Activation analysis is basically a multielemental technique. Many elements in the sample will become radioactive during the irradiation and if each of these elements can be isolated chemically or instrumentally, their abundances may be determined simultaneously. Activation analysis can be a nondestructive method of analysis. Numerous tests have shown that with careful experimental manipulation, activation analysis is an accurate ( 1% accuracy) and precise ( 5% precision) method of measuring elemental concentrations. 

Because NMR is a nondestructive method, the NMR samples can be used for the preparation of samples for other analytical techniques. (Note that in some cases the deuterated solvent may deuterate the chemicals of interest affecting their detection, for example by GC/MS.)... 

It is evident from the above considerations that the use of the physisorption method for the determination of mesopore size distribution is subject to a number of uncertainties arising from the assumptions made and the complexities of most real pore structures. It should be recognized that derived pore size distribution curves may often give a misleading picture of the pore structure. On the other hand, there are certain features of physisorption isotherms (and hence of the derived pore distribution curves) which are highly characteristic of particular types of pore structures and are therefore especially useful in the study of industrial adsorbents and catalysts. Physisorption is one of the few nondestructive methods available for investigating meso-porosity, and it is to be hoped that future work will lead to refinements in the application of the method -especially through the study of model pore systems and the application of modem computer techniques. 

Theories and instrumentation of Fourier transform IR spectroscopy and electron spectroscopy for chemical analysis are briefly reviewed. The possibility of using these techniques in detection and analysis of acid impurities distributed at surfaces of paper documents produced during the period from 1790 to 1983 is demonstrated. Results show that all of the papers tested contained carboxylic groups. The carboxylic acids found in the paper of 1790 are the results of oxidation and aging. Acids in other papers are due to fiber oxidation as well as the presence of rosin acids. These techniques show promise as nondestructive methods for elucidating chemical characteristics of surfaces of paper documents. 

Despite the high cost of the equipment required and the time taken for sample preparation and spectra acquisition, MAS-HR NMR provides invaluable stmctural information about the species present in a reaction. Only a few milligrams of resin beads are required and they can be recovered as the technique is nondestructive. The complementarity of the technique with other analytical methods is clear MALDl-TOP cannot discriminate among compounds with the same MW and depends on the ionization properties of the resin-bound compound, while PTIR depends on the presence of selected functional groups in the molecule. MAS-HR NMR can be used independently from the nature of the performed reaction and the functional groups formed or lost during the SPS step. Additionally, two-dimensional MAS techniques such as 2D-COSY (correlated spectroscopy) and TOCSY (total correlated spectroscopy) (171) or 2D-SECSY (spin echo correlation spectroscopy) (181) can provide more detailed information that may be useful in specific cases. 

Much more information can be obtained by examining the mechanical properties of a viscoelastic material over an extensive temperature range. A convenient nondestructive method is the measurement of torsional modulus. A number of instruments are available (13—18). Afore details on use and interpretation of these measurements may be found in references 8 and 19—25. An increase in modulus value means an increase in polymer hardness or stiffness. The various regions of elastic behavior are shown in Figure 1. Curve A of Figure 1 is that of a soft polymer, curve B of a hard polymer. To a close approximation both are transpositions of each other on the temperature scale. A copolymer curve would fall between those of the homopolymers, with the displacement depending on the amount of hard monomer in the copolymer (26—28). 

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