Active thermography works by heating the component that is to be inspected in a controlled environment then using an infrared camera to record an image of the temperature differences across the object. The results of thermography inspection are recorded as high resolution images, making data easy to be stored. Some benefits of active thermography inspection include the speed of the test, data is easily stored, and the ability to inspect large areas. There are a few different types of active thermography inspection including pulse thermography, lock-in thermography, and vibrothermography. The methods differ mostly in how the component to be inspected is heated.
Pulse thermography is also referred to as flash thermography. With this method, a short pulse of energy in the form of light is applied to the measuring object. The part cools after flash heating, and any flaws present will cause changes in the cooling rate. The cooling rate is recorded by the infrared camera as an image. Differences in temperature are depicted in the image and reviewed to identify any flaws present in the test object. This method is commonly used on components with thin walls or layers. An advantage of pulse thermography is the inspection time is only a few seconds long, at most. Also, the depth of the flaw is able to be determined using pulse thermography.
During lock-in thermography inspection, the surface of the test object is energized with periodical harmonic-modulated energy. The source of this energy could be derived from a halogen lamp or hot-air blower. Heating of the test object with this method is more controlled because energy can be continuously applied to the object. Consistent heating ensures that the infrared camera will be able to pick up and record any temperature differences. With other active thermography inspection methods, the test object is not continuously heated. Therefore, the part may cool too quickly and the camera will not be able to capture a usable image. The measuring time for this method is slightly longer than other active thermography methods.
In vibrothermography inspection, power ultrasound is used as the energizing source. For this inspection method, the ultrasonic equipment must be in contact with the surface of the test object, and couplant must be applied to the test object before the start of inspection. The ultrasonic energy is converted into heat by rubbing on defect locations. This rubbing creates friction. Any defects present act as an internal heat source while the surface of the test object shows almost no increase in temperature. An advantage of this method is the defects are shown very clearly on the resulting image.
Hello! My name is Melanie Boop, and I am the Communication Specialist at AER.