Лако-красочные материалы — производство

For quality assurance purposes in the aircraft and car manufacturing industries, it has been a matter of particular concern to develop methods for the nondestructive testing of adhesive bonds. However, these tests do not all provide significant results and are relatively easy to use in practice. Yet, at the same time, due to increased product quality expectations, they are expected to be more and more performing.

In both the literature and in industry, there is a body of different quality assurance methods. The National Materials Advisory Board (NMAB) Ad Hoc Committee on Nondestructive Evaluation adopted a system that has classified the different methods into six major categories: visual; penetrating radiation; mechanical vibration; ther­mal; magnetic-electrical; and chemical-electrochemical (Figure 7.17).

Each method can in turn be characterized in terms of five principal factors: energy source or energy medium; nature of the signals; image or signature resulting from

interaction with the test object; means of detecting or sensing resulting signals; method of indicating or recording signals; and basis for interpreting the results [6].

7.6.1

Visual Techniques

Although, visual or optical techniques are the best technology available for nonde­structive testing, their usefulness is rather limited for the testing of adhesive bonds. For example, when used for the control of bead application these tests do not yield any information about the quality of the bond, since delaminations or adhesion failure are not detected. Visual techniques are relatively inexpensive; whilst the behavior of a component under load can be tested by means of speckle interferometry, detailed information about the physical properties of the bond cannot be obtained from these tests.

Another available optical method is shearography, which is based on the differ­ences between the deformational states of an unloaded and a loaded component. The load is applied by different means depending on the component to be tested, for example, by deformation through vacuum or by twisting of the component. Until now it has not been possible to detect adhesion flaws satisfactorily with shearography, whereas it is possible to detect a position error of the bead. But even here, a high degree of practice and experience are needed to correctly interpret the results [7].

7.6.2