The Application Of Composite Load Technique In Infrared Thermal Wave Nondestructive Testing

Infrared thermal wave nondestructive testing (NDT) method is based on the thermal wave theory. Unlike the conventional thermograph that only monitor the surface temperature variations passively, the thermal wave NDT use various controllable heating sources,such as high energy flash lamp, ultrasonic wave, electromagnetism, hot wind etc. to actively excite detected material. The material's subsurface physical properties will change the thermal wave's conduction, and then the change will be shown on the surface's temperature field. The characteristics of the method are real time, fast, non-contact etc. It can be used as the additional and vicarious method of the conventional NDT.When using high energy flash lamp as thermal excitation source in the thermal wave NDT, one problem in the art relates to materials having high visible light reflection and low infrared emissivity. In this case it is necessary to do some surface treating to enhance the visible light absorption and infrared emissivity. But the information of some defects like tiny craze of objects can hardly be inspected, so it's necessary to look for an effective method to inspect this kind of defects in order to extend the application field of NDT.The composite load technique means we can inspect the defects with flash lamp to stimulate the objects in the state of vacuum, and the fundamental is to put one face of the object in the state of vacuum and the other face in the state of ordinarily air pressure. The defects can expand in small range as a result of the difference of air pressure, and this expand can be received by infrared thermal wave photography. Then we use computer to analyse and draw the information of the defects. In order to optimize the result of experiment, we use Matlab and VC to enhance the result to avoid the illegibility of edge drawed by three-dimensional thermal diffusion.This work also introduces the vacuum applications of the method, it improves the cover of the flash lamp based on the quondam system of infrared thermal wave of NDT. Moreover, an experimental sample with five kinds of defects which is differences from type, size and the rate of heat exchange inside is designed. Finally,we do some experiments on the designed sample and analyse the result of type and size about the sample which is examined in the state of composite load technique.