One of the most important parts of assessing a buildings structural decline is to examine and monitor the development of cracks in the materials the building is constructed from. However most sensing methods that are used to evaluate the structure without causing damage are limited in some way. When only one method of analysis is used whether it be optical, radiographic, sonic, electrical, thermal or magnetic there will be some information that is missing and often will be insufficient for a full analysis of the materials defects. of course the simple answer is to fuse some of the more complementary methods together in order to gather the greatest range of information.
Some combinations that have been tried out are electromagnetic and acoustic; optical and magnetic; and infrared and thermal. The method that today’s paper talks about is a combination of electric, magnetic and thermography and can only be applied to conducting materials (which luckily many building materials are). Defects in the material can cause eddie currents to form when electricity is passed through or a change in flux leakage when a magnetic field is applied. These effects can be detected and mapped using thermal imaging. This method was shown to be effective through a series of experiments performed on a piece of defective train rail. It was also shown that the induced heating effect could reveal cracks in the metal and with the imaging taken from multiple angles reveals how the cracks show a different rate of heating then the surroundings. One of the things that still needs work on is how fast the material around the crack responds to the current, magnetic field or heating. This could give more details about the exact nature of the crack and hopefully further research will be performed on this topic in the future.