Non-destructive testing
Various analytical methods for testing materials or components during which the material of the item inspected is not damaged are termed non-destructive testing (NDT).
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Options for non-destructive material testing
at Quality Analysis
At Quality Analysis, we assist you with non-destructive test methods and analytical methods such as industrial computed tomography, X-ray inspection as well as optical metrology. Industrial metrology is also used from time to time to test surfaces. We adapt optimally to your requirements and undertake the necessary analyses in our accredited laboratory or on site in your facility – even in ongoing production.
Are you unsure as to which analytical method best suits your requirements? No problem, we would be pleased to advise you. Once you have decided, we undertake the necessary analyses and compile all the results in a practical, comprehensible test report that provides you specific answers to your questions.
Which types of non-destructive testing are available?
Non-destructive test methods can be categorised in various ways. The most obvious is classification into different measuring principles (chemical, electrical, electromagnetic, magnetic, mechanical, optical, thermal). Also the dynamic behaviour is a further aspect for classification: if an electrical or magnetic field is measured, the method is static. On the other hand, if the amplitude of a wave is measured, the method is termed dynamic.
X-RAY inspection and computed tomography
During this method, the workpiece is subjected to X-ray radiation; the resolution in a CT is significantly higher than in classic X-ray equipment. With modern nano-CTs, it is possible to detect details with a size of approx. 0.2 µm. Although X-ray inspection delivers a lower resolution, it is excellently suited to inspection in series production due to its speed. Radiographic inspection also uses X-rays or gamma rays.
3D computed tomography
3D computed tomography provides a non-destructive look inside the components. This aspect makes this method ideal for the verification of shrinkage cavities, pores and wall thicknesses. It is also possible to acquire complete components digitally. Limiting factors for computed tomography are the density of the material and the size of the component. Materials with a very high density cannot be penetrated by X-rays.
2D X-RAY inspection
With 2D X-ray inspection, non-destructive testing of components is also possible during ongoing series production. Automated X-ray inspection (AXI) is often used, e.g. if the realtime detection of defects during the production of printed circuit boards or assemblies with BGA ICs is required.
Other methods for non-destructive testing
Along with the methods described above, there is another whole string of methods for non-destructively analysing components or complete units. The following short description is therefore limited to a few selected examples.
Visual inspection
Visual inspection is one of the oldest inspection methods. It is often used during the final inspection of products. Depending on the application, the inspection is undertaken with the aid of mirrors, endoscopes or cameras. Depending on the task, this apparently simple method can place the highest requirements on the specialist knowledge and experience of the inspector. The lack of automation, however, makes visual inspection very susceptible to human error, e.g. due to waning concentration.
Ultrasonic inspection
Ultrasonic inspection is based on the varying speed with which sound waves propagate in different media. The waves are deflected or reflected at the boundary surfaces. This method makes it possible to detect defects that are not visible externally. Because most metals and alloys are suitable for inspection using ultrasound, this analytical method is of major importance.
Magnetic powder inspection
Using magnetic powder inspection, it is possible to verify cracks in the surface of ferromagnetic materials. For this purpose a magnetic field is generated in the test specimen and the component then sprayed with a liquid in which iron oxide powder or similar is dissolved. Any cracks present form a stray field. Fluorescing colour pigments are attached to the particles of magnetic powder so that the deposition of the magnetic powder is particularly easy to observe.
Penetration test
Penetration or dye penetration testing is used to verify fine hairline cracks. For this purpose, the item inspected is wet using a contrast agent with good penetrating properties; the surface then cleaned such that penetration agent is only left in capillary cracks and pores. A developer is used to make the damaged areas visible.
Eddy current test
Electrically conductive materials can also be non-destructively tested using eddy current testing. For this purpose, eddy currents are generated in the item inspected using an exciter coil and the amplitude and the phase shift in relation to the exciter signal measured. From this information it is possible to draw conclusions about the microstructure, the coating thickness and existing cracks.
What is limited non-destructive material testing?
Material testing also includes limited non-destructive testing. This term refers to test methods during which the surface of the component tested may be changed – by definition therefore destroyed – however the damage is so slight that it has no effect on subsequent use. This is the situation, for example, during numerous methods for testing hardness.
Summary: non-destructive testing
During the use of a method from the spectrum of non-destructive testing, the analysis and evaluation of a component is undertaken without damaging the material. This analysis can be undertaken, e.g. with the aid of ultrasound, with X-rays, for example using industrial computer tomography, optical metrology, using camera systems and in exceptional cases also with tactile metrology.
