Testing nondestructive

Testing yields basic information about any materials (plastics, steels, etc.), its properties relative to another material, its quality with reference to standards or material inspections, and can be applied to designing with plastics. Examples of static and dynamic tests are reviewed in Chapter 2. 

There are destructive and nondestructive tests (NDTs) (2). Most important, they are essential for determining the performance of plastic materials to be processed and of the finished fabricated products. Testing refers to the determination by technical means properties and performances. This action, when possible, should involve application of established scientific principles and procedures. It requires specifying what requirements are to be met. There are many different tests (thousands) that can be conducted that relate to practically any material or product requirement. Usually only a few will be applicable to meet your specific application. Examples of these tests will be presented. 

There is usually more than one test method to determine a performance because each test has its own behavior and meaning. As an example there are different tests used to determine the abrasion resistance of materials. There is the popular Taber abrasion test. It determines the weight loss of a plastic or other material after it is subjected to abrasion for a prescribed number of the abrader disk rotations (usually 1000). The abrader consists of an idling abrasive speed controlled rotating wheel with the load applied to the wheel. The abrasive action on the circular specimen is subjected to a rotary motion. 

Other abrasion tests have other type actions such as back and forth motion, one direction, etc. These different tests provide different results that can have certain relations to the performance of a product that will be subjected to abrasion in service. 

A method of evaluating the adhesive bond to a plastic coating substrate is a tape test. Pressure-sensitive adhesive tape is applied to an area of the adhesive coating, which is 

Nondestructive testing or evaluation (NDT or NDE) covers any type of evaluation of a product that leaves it 

Discontinuities in products result from inherent material characteristics and from the manufacturing method. For example, casting, as a generic process, is more likely to produce material containing voids (porosity) compared with hot worked product such as plate where the voids are closed up by the mechanical work used to shape the product. 

Selection of NDT technique, test parameters and definition of acceptance or rejection criteria are based on the following  

Not all discontinuities in materials are cause for rejection. The controlling specification or standard indicates the size and quantity of permissible discontinuities. When they exceed the threshold level, discontinuities are called defects and are cause for rejection. Do not over inspect because it adds unnecessary cost. 

Eddy-current Testing (ET) is an electromagnetic technique for measuring physical and mechanical parameters on 

Nondestructive testing (NDT), on the other hand, examines a specimen without impairing its ultimate usefulness. It does not distort the test specimen s configuration, but provides a different type of data. NDT allows suppositions about the shape, severity, extent, configuration, distribution, and location of such internal and subsurface defects as voids and pores, shrinkage, cracks, and the like. 

Radiography is the most frequently used nondestructive test method. X rays and ganuna rays passing through a structure are absorbed distinctively by flaws or inconsistencies in the material so that cracks, voids, porosity, dimensional changes, and inclusions can be viewed on the resulting radiograph. 

Infrared (IR) spectroscopy records spectral absorptions in the infrared region using pyrolysis, transmission, and surface-reflectance techniques. Exposing the sample to light in the infrared range and recording the absorption pattern yield a fingerprint of the material. 

Infrared spectroscopy is used for identification of plastics and elastomers, polymer blends, additives, surface coatings, thickness (see Fig. 9-12), and chemical alteration of surfaces [10-12]. 

This is one of the most common analytical techniques used with plastics. The easy operation and availability of this type of equipment have contributed to its popularity. Although the infrared spectrum characterizes the entire molecule, certain groups of atoms give rise to absorption bands at or near the same frequency, regardless of the rest of the molecule s structure. The persistence of these characteristic absorption bands permits identification of specific atomic groupings within the molecular structure of a sample. 

There are other methods of NDI other than X-ray radiography. One of them is ultrasonic NDI. In this technique, ultrasonic waves are used to investigate the interior of a ceramic piece. An ultrasonic transducer placed on the surface of the ceramic piece sends the ultrasonic waves received by a sensor found either within the ultrasonic transducer or at another location on the surface of the ceramic piece. Ultrasonic waves are scattered emd reflected back finm the surfaces and defects within 

High Density Inclusion Ceramic Part Being Inspected 

With holographic techniques, the ceramic piece is imaged by coherent light or sound waves before and after it is stressed slightly. The holo- 

Microwaves are particularly useful for NDI because many ceramics are transparent to microwaves, allowing flaws to be detected. Metallic Si flaws fim in diameter within a reaction bonded Si3N4 piece can be detected with 91-98 GHz microwaves using a cross-polarized transmission techniques [13]. 

In addition, a very simple and low cost method can be used to detect surface flaws. This is the use of penetrants that are typically fluorescent dyes. Usually, a three-step procedure is used. The ceramic part is first soaked in a fluorescent dye. Then the part is dried and cleaned in a very controlled manner to remove the dye from smooth surfaces but not from the surface defects. When the part is examined under ultraviolet li t, the surface defects such as cracks and porosity retain the dye and show up brilliantly. This method is used widely for surface inspection of ceramics and is frequently included as part of a quality assurance certification. Penetrants are effective for nonporous ceramics. With open porosity, the penetrant will enter all the pores of the ceramic, giving fluorescence to the whole ceramic piece, thus preventing detection of surface flaws. Not all penetrants are fluorescent dyes. Radioactive krypton can be used as a penetrant. It is retained in cracks or other defects and can be detected by either a Geiger counter or by carefully wrapping the ceramic piece in photographic film. After development of the film, the location of cracks emd pores can be detected. 

---

Stegemann, D, Reimche, W. Schmidtbauer, J. Investigations of Light Metal Casting Processes by Real Time Microfocus Radioscopy. The European Journal of Nondestructive Testing, Vol. l,No. 3, S. 107117, Jan. 1992... 

The basic condition of the Standard application - the availability of stable coupled probabilistic or the multiple probabilistic relations between then controlled quality indexes and magnetic characteristics of steel. All the probabilistic estimates, used in the Standard, are applied at confidence level not less than 0,95. General requirements to the means of control and procedure of its performance are also stipulated. Engineers of standard development endeavoured take into consideration the existed practice of technical control performance and test at the enterprises that is why the preparation of object control for the performance of nondestructive test can be done during the process of ordinary acceptance test. It is suggested that every enterprise is operated in correspondence with direct and non-destructive tests, obtained exactly at it, for detailed process chart and definite product type, however the tests have long since been performed after development of the Standard displayed that process gives way to unification. 

B. A. Auld, F. G. Muennemann and M. Riaziat, Quantitative modelling of flaw responses in eddy current testing. In R. S. Sharpe (ed.), Research techniques in nondestructive testing, Vol. 7. Academic, London, 1984. 

The ultrasonic testing of anisotropic austenitic steel welds is a commonly used method in nondestructive testing. Nevertheless, it is often a problem to analyze the received signals in a satisfactory way. Computer simulation of ultrasonics has turned out to be a very helpful tool to gather information and to improve the physical understanding of complicated wave phenomena inside the samples. 

Nondestructive testing techniques for welded joints usually include visual, radiographic, magnetic particle, liquid penetrant, and ultrasonic testing methods. Of interest in this paper is the radiographic testing (RT) technique. 

Koshovy V. V. Methods of restoring of the acoustical images and their applications to nondestructive testing in civil engineering // Proc. Int. Symp. Non-Destructive Testing in Civil Engineering - Berlin, Sept. 26-28, 1995. - V.2. -P. 1153-1156. 

Gutkiewicz P. "Ultrasonic and eddy current nondestructive testing in Windows envirorunent , ZfP als Dienstleitung in einer veranderten Industriestruktur, Dresden, 5-7 Mai 1997, P 67... 

Nondestructive Testing Handbook Vol. 9, Special Nondestruetive Testing Methods , ASNT 1995... 

Luminescence IP s are fundamentally and theoretically utilizable for nondestructive testing if all of the recommended guidelines and operational recipes and appropriate systems are used. They are quite capable of producing image quality on a par with industrial radiography. 

Magnetic particles is one of the most used nondestructive testing techniques in industry. It allows detection and localization of surfacic and subsurfacic defects of ferromagnetic pieces by making conspicuous leakage fields by a magnetic developer. 

A. Gurvich und G. Passi Comparison of non automated systems for the acoustic nondestructive testing of welded joints, Defektoskopiya, 1991, No 2, p 3-9 (in Russian)... 

Lange, Yu V. Low Frequency Acoustic Methods and Means for Nondestructive. Testing of Multilayer Structures. Moscow, Mashinostrojenije, 1991, 272 p. (in Russian)... 

This presented approach to the development of the procedure for nondestructive testing is corresponding to special requirements specified in EAL -G15 to similar procedures. 

The first full text NDT Journal on www.ndt.net, the Online Journal of Nondestructive Testing Ultrasonics, is on the Internet and each month provides new information as well as a comprehensive overall reference - access is free since it is sponsored by the NDT online exhibition. 

The Canadian Society for Nondestructive Testing, http //www.csndt.org/... 

With the availability of such a SQUID system the question arises what it brings to nondestructive testing. One has to check if existing methods can be improved by using this systems. And, one has to check if this system allows for powerful new NDT methods. 

Brasche, L, Smith, K Engine Titanium Consortium An Overview of the Contaminated Billet Study, Fall Conference of the American Society of Nondestructive Testing, Oct. 20-24, 1997, Pittsburgh, USA... 

It has developed a real time method to compare successive non-destructive inspections of the steam generator tubes in nuclear power plants. Each tube provides a safety barrier between the primary and secondary coolant circuits. Each steam generator contains several thousands of tubes whose structural integrity must be ensured through the lifetime of the plant, Therefore, Laborelec performs extensive nondestructive tests after each plant outage. 

Laser-based profilometry systems have also been applied for nondestructive testing and measurement of both smooth-bore and rifled gun tubes. Working through Small Business Innovation Research program, the U.S. Army has developed laser-based profilometry systems for the inspection of the 120mm cannon used on the MI-Al Abrams main battle tank. Systems have also been built to measure the erosion of 25 mm and 155 mm rifled gun tubes. 

Doyle, J. L., Bondurant P. D., Johnson, R. F., (1994) Laser-Based Profilometry Point Triangulation Technology forNDE Applications, Nondestructive Testing Handbook, Special Nondestructive Methods, Vol. 9, pp. 141-157. 

Doyle, J. L., Wood, G. R., and Bondurant, P. D. Using Laser-Based Profilometry to Locate and Measure Corrosion Fatigue Cracking in Boiler Tubes, Materials Evaluation, D The American Society of Nondestructive Testing, Inc., Vol. 51, No. 5, pp. 556-560 (1993). 

Portions of the preceding paper have been reprinted with the permission of the American Society of Nondestructive Testing. 

S. Natansohn in A. Vary andj. Snyder, eds.. Nondestructive Testing of High Peformance Ceramics, The American Ceramic Society, Westerville, Ohio, 1987, p. 73. 

Handbook for Standardisation ofi Nondestructive TestingMethods, Vols. 1 and 2, MIL. HDBK-33, Dept, of Defense, Washington, D.C., 1974 R. E. Englehardt, "BibHography of Standards, Specifications and Recommended Practices," ia Nondestructive Testing Information Mnalysis Center Handbook, Nondestmetive Testing Information Analysis Center, Texas Research Institute, Austin, Tex., Mar. 1979, p. 212. 

Nondestructive Testing. Nondestmctive inspection of an explosion-welded composite is almost totally restricted to ultrasonic and visual inspection. Radiographic inspection is appHcable only to special types of composites consisting of two metals having a significant mismatch in density and a large wave pattern in the bond interface (see Nondestructive evaluation). 

R. C. McMaster, ed.. Nondestructive Testing Handbook, The Ronald Press Co., New York, 1959, 1963, The American Society for Nondestmctive Testing, Columbus, Ohio, 1977, 1979. 

---