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Non-destructive inspection: the answer to controlling quality without sacrificing operation

11 November 2022
Article by Paulo Tavares, project manager in the area of Advanced Monitoring and Structural Integrity at INEGI.

All infrastructures and components have a lifespan established in mechanical design, which gives users a certain degree of confidence in their safety. However, in reality, not everything always goes as planned and there are defects - originating during production, installation or use - that change these projections.

Therefore, if not monitored, components may need to be replaced or undergo extensive repairs, failing which unsafe conditions and catastrophic failures can result. These components or infrastructures may still operate below their projected efficiency, with possible financial impacts for the owner, although this may not be evident.

However, testing this type of components or infrastructure can be a considerable challenge. How to inspect pipelines, bridges, railway lines, aircraft, trains, among others with high resolution, without interrupting your operation?

One of the answers is the use of non-destructive testing (NDT) techniques, an approach to the field of experimental mechanics that allows the analysis of displacement and deformation fields in real time, both in dynamic and in quasi-static applications, in measurements carried out without contact and processed directly on a computer.

This means that these techniques are fundamental for the evaluation of structural behavior, allowing the early detection of defects and anomalies.

At INEGI we have been working on the development and application of these inspection techniques, through the creation of measurement devices and laboratory and field applications. Based on this experience, we know that tests using NDT techniques apply to various sectors of the industry and are the most convenient as they allow simultaneously obtaining information from a surface and detecting possible anomalies without contact.

Inspection techniques apply to various sectors

In a laboratory environment, the inspection of the tail of a Eurocopter NH90 helicopter stands out, with the aim of detecting multiple defects in the panels, such as delamination, water absorption, take-off and inclusions. The entire inspection system, from the optical head to the image processing software, was designed by INEGI.

In industry, these techniques can support product-level developments. In this context, we highlight the collaboration with a tool manufacturing company that resulted in the development of tools to attenuate the operating noise in circular saws. For this purpose, a damping system and alteration of the geometry of the saw teeth was introduced, based on the study and measurement of the natural modes of vibration using interferometric techniques.

For different problems, different methods

There are currently several constructive solutions to apply these techniques in a laboratory context or directly in the industry. Speckle pattern electronic interferometry (ESPI) and shear interferometry are two of the techniques used in the inspection of different materials.

The electronic interferometry of speckle patterns allows the measurement of displacements that can be translated into strain fields and, later, into stresses, as long as the material behavior law is known, as well as the study of the vibration of objects and structures in non-destructive tests. The high sensitivity of the method requires some care in its use and the use of devices with high mechanical stability.

Shear interferometry (shearography) is used to measure strain fields. Given its robustness and sensitivity, the technique makes it possible to easily detect defects in a structure through the changes they cause to the surface. It is a technique widely used in the inspection of aeronautical structures, especially those that include composite components.

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