Detection on cracks in blades with complex profile based on ultrasonic infrared thermal imaging

It is difficult to detect the defects in blades with complex profile due to the complex structures, thus nondestructive testing on this type blade has attracted abundant attentions around the world. In this paper, based on the frictional heat generation model of the defect-containing medium under ultrasonic excitation, the heat flow conduction was analyzed and the surface temperature field of the simplified model about cracked blades was derived. For the heat generation in cracked fields of blades with complex profile, finite element method was applied to numerical simulation. According to the simulation result, the longer the excitation time was, the greater the temperature rise in the crack defect field was; the rate of temperature rise presented a trend that the rate rose first and then fell with time. The steam turbine blade with a crack was tested by the detecting platform of ultrasonic infrared thermal imaging. The result of test shows that the heat generation field is most obvious in the cracked field and the result is most clear for the crack in this blade when the preload is from 100 N to 150 N. According to the numerical simulation and test, ultrasonic infrared thermal imaging technology can efficiently detect cracks defect in blades with complex profile, it has a definite guiding significance on engineering and a broad application prospect.