Experimental Studies On The Applications Of Ultrasonic Pulse Thermography And Ultrasonic Burst Phase Thermography In NDT

The ultrasonic infrared thermography is a new nondestructive testing technique. It is remarkably sensitive and convenient for detection of small fatigue cracks in metals. Because ultrasonic wave can spread quickly in the sample, the crack in the sample can usually be detected less than 1s. It has the obvious advantage compared with some traditional technologies, such as whirling current, X-radial, and so on. It requires no fluid or magnetic particle intrusion, and requires no penetrating radiation. The speed and convenience of testing are much higher.Ultrasonic Pulse Thermography uses an ultrasonic pulse to excite the sample. If there are surface or subsurface defects (delamination or cracks) in the sample, it will cause the friction between the interfaces of the cracks, or thermoelastic effect and hysteresis effect. Because of the direct conversion from mechanical to thermal energy, heat is released at locations where defects such as cracks and delamination are located. An infrared camera is used to collect the thermal information of the surface, and show the thermal image with a computer.Ultrasonic Burst Thermography uses an ultrasonic burst whose duration typically ranges from 50ms to 1s to excite the sample. The signals emitted by the defects contain a lot of frequencies. Then the original thermal image sequences are processed by Fourier transformation, to obtain the amplitude and phase information of the defects in the material. The phase information can show the defects more obviously because it can not be disturbed by optical character of the surface and initial conditions.In this paper, ultrasonic infrared thermography was employed to test some kinds of cracks and fatigues. The defects of four kinds of materials excited by the ultrasonic were showed intuitively by the thermal image. Several laser welded stain plates were tested in this method, and the quality of the welded plates was evaluated by the thermal image and infrared radiation curve. Through comparing the position and shape of the defects with the results of the flash pulse method, some corrosive samples of civil aviation were tested for the feasibility of corrosive defects of aluminum materials. Trying to use ultrasonic burst phase thermography to process the original thermal sequences by FFT in VC++ in some of the experiments, the advantages of using ultrasonic as heat source and the feasibility of ultrasonic burst phase technology were proved by analyzing the phase information.