Non-destructive test methods

Munns, G.A. Georgiou, Non-destructive testing methods for adhesively bonded joint nspection - a review, INSIGHT, Vol 37, No 12, Dec 1995, pp 941-952... 

The use of tracers enables efficient and reliable measurements of oil, gas and water flow in industrial process units and pipe line systems under production conditions thus fundamentally being non-destructive testing methods. Typical problems which can be efficiently assessed by tracer studies include ... 

Non-Destructive Test Method for Defects in Propellant Rocket Motors (Ref 11)... 

The impact of thermal shock on the properties of a ceramic or a CMC is assessed by means of both destructive and non-destructive testing methods. Flexural or tensile (mainly for CMCs) tests of suitably-sized thermally shocked specimens are usually employed to measure retained mechanical properties as a function of the temperature difference. The temperature differential for which a significant drop in property values is observed is the A A- For monolithic ceramics and particle- or whisker-reinforced CMCs the property under investigation is usually strength, whereas in fibre-reinforced CMCs a drop in Young s modulus is usually a better indication of the onset of damage. 

After a further 48 hr the third and last stiffener is welded in the same manner as the second but using a preheat of 100 °C. After a further 48 hr the welds are examined, firstly by non-destructive testing methods and then by selective sectioning to establish whether cracking has occurred. This examination provides the fabricator with evidence to justify his use of either no preheat at all or a level below the recommended temperature of 60 °C. The evidence might, of course, justify the original prediction of 60 °C minimum. 

Munns. 1. J.. and Georgiou. G. A. (1995). Non-destructive testing methods for adhesively bonded joint in.spection--A review. Insight. Dec. 1995. 12. 941 9.S2. 

The chosen method depends on the geometry and properties of the article. Table 2.2 lists many of the available non-destructive test methods for composites for initial quality control and for assessing damage and repair [8]. The following discussion highlights just a few of the more important techniques. 

Different from other non-destructive testing methods AE analysis does not deal with a steady state but with a procedure that basically changes the condition of the structure. Therefore AE signals are unique they cannot be reproduced and recordings cannot be repeated. 

Like for all non-destructive testing methods there is a need to depict results in graphic form. Images have a large potential to discover both repetitions and abnormalities that would not be recogiuzed in a pure numerical analysis. Imaging techniques need according special skills. 

Ceramographic methods have proven indispensable in the characterization of thermally sprayed coatings, in which non-destructive testing methods for purposes of quality assurance have only limited applicability. Characteristic properties of a coating, such as its thickness, structure, porosity, and adhesion to the base material, as well as the hardness of individual phases or the overall composite, can be accurately evaluated by applying these ceramographic methods to the polished section. 

Non-destructive evaluation of reinforced concrete structures Volume 2 Non-destructive testing methods... 

Particular attention needs to be paid to establishing an effective system of quality assurance for adhesive connections. Non-destructive test methods based on ultrasound, X-rays or the measurement of electrical or thermal conductivity are available but only of limited value in practice. Specific data on adhesion cannot always be obtained by these methods. This section examines the issue of quality assurance from a practical point of view. Many years of experience have shown that only a quality assurance system that takes into account the specific features of adhesive bonding technology can produce consistently satisfactory results over an extended production period. The information outlined here should be viewed as a general checklist to be adapted to the specific requirements of each manufacturing environment. 

However, microscopic considerations are subject to the limitations of destructive test methods, i.e., only one particular condition of a sample can be characterized following a fatigue load. If the characterization of the damage curve is desired, several tests of various test specimens are required as well as subsequent microscopic examination. Non destructive test methods [130], such as... 

The most commonly used methods for evaluation of adhesive bonds are mechanical tests such as tensile shear and peel tests that determine the weakest link in a bonded assembly. Although these tests are useful in the development and quality control of adhesives, they are destructive and cannot offer failure prediction for in-service components. Ultrasonic inspection is the most commonly used non-destructive test method and can accurately assess de bonding in single adhesive bonds, providing that the sensor is perpendicular to the defect plane. However, ultrasound has some limitations in... 

Qualification services for in-service inspection systems may be required to verify that a proposed non-destructive testing method, technique or procedure and associated equipment are adequate for their purpose and that the inspection personnel is able to perform the assigned inspection duties. Any organization providing qualification services should be independent from any commercial or operational consideration. If the qualification bodies are part of the operating organization, they should satisfy specific independence criteria equivalent to those laid down in the appropriate international standards (e.g. EN 45004 for a type B inspection body). 

As mentioned above, a few non-destructive test methods do yield more information than merely the presence or absence of voids above a certain size. 

Two excellent reviews have been published recently, and readers are referred to them for a fuller account and references of non-destructive testing methods of adhesive joints. They are by Schliekelmann (1979) and Segal and Rose (1980). 

On page 25 of the November 2001 issue of Adhaesion, Kleben Dichten, the nuclear magnetic resonance contact technique was introduced as a new sort of method for non-destructive characterisation of polymers. This article uses examples from the area of epoxy resins and thick-layer bondings to give an impression of typical, potential applications for this new non-destructive testing method. 2 refs. 

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