Valery Lisin / Shutterstock
Non-destructive testing (NDT) methods include a wide array of high- and low-technology solutions for evaluating materials, systems, and components without damaging them. This has become an essential part of many industrial processes in recent years, as well as in medicine where the evaluation subject – a human patient – must, of course, not be harmed by imaging.
In materials analysis, NDT methods are used to determine the physical properties of materials so that designers, engineers, and manufacturers can properly use them in interaction with various other materials or environmental factors. One useful NDT method in this regard is infrared thermography (IRT).
IRT utilizes specialist thermographic cameras to detect radiation in the 9–14 µm range of the electromagnetic spectrum (the long-infrared range). They rely on the fact that any material with a temperature above absolute zero emits thermal radiation, and detect this to produce thermograms (color representations of that radiation).
Due to differences in emitted temperature radiation of many objects in the physical environment, thermograms can produce a usable image even in the absence of any light radiation. For this reason, IRT has been incredibly useful in military, nature observation, and surveillance applications for many years.
There are two kinds of IRT – active and passive. Passive IRT is the kind used to create night vision cameras in the above applications and detects the emitted thermal radiation from objects with no interference. Active IRT applies thermal radiation to the image subject with an external source, such as a heat lamp.
Infrared non-destructive testing (IRNDT) of materials is an example of active IRT. IRNDT uses a halogen lamp, flash lamp, ultrasonic horn, or other devices to cause excitation in the subject material. This then makes the material show a thermal response (heating up), which is recorded using an IRT camera.
Defects in the material cause temperature radiation to pass through the material at a homogeneous rate, and these differences are picked up by the IR camera. In this way, IRNDT can detect defects under the surface of a material – or even minuscule defects on the surface, such as cracks or uneven mixtures.
The excitation source and procedure, the infrared camera, and the evaluation method can all be specialized for different materials in various settings.
The images produced by IRNDT can be evaluated either by human operators or automated computer image sensors, and this evaluation enables the detection of surface and internal defects in the material. The wide range of IRNDT methods can be employed either at separate testing facilities or as part of production processes and quality control inside manufacturing plants.
While inspection depth and the orientation and dimensions of detected defects pose limitations on IRNDT, its full availability and relatively low expense of components, non-contact and non-destructive features, and its high speed of detection are all significant advantages that have led to widespread adoption in material analysis for several industries.
For these reasons, IRNDT is commonly used to evaluate welded plastic parts and systems. Other possible NDT methods for this kind of analysis (X-ray tomography and metallographic cut microscopic analysis) cannot be used in routine measurement due to their relatively slow turnaround time and need for more expensive equipment.
Not only plastic welded parts but carbon steel, stainless steel, aluminum and its alloys, copper, and titanium are all commonly inspected using IRNDT methods for defects. This is important, as laser-welding these materials has become common practice in the automotive industry, and weld failure would cause serious accidents if not detected. IRNDT’s speed allows for inspection in real-time factory conditions, ensuring car manufacture can remain profitable for automotive companies.