Research And Detection Of Residual Stress Based On PEC Thermal Imaging Technology

Aerospace vehicles typically work in extremely demanding and high-temperature low-pressure environment, long-term withstand to high stress loads easily lead to metal fatigue and crack growth rapidly. With the rapid development of China’s aerospace industry, structural strength and fatigue stress testing of materials was put forward higher requirements. Related research using pulsed eddy current method to detect material stress remains less at home and abroad. Conventional eddy current probe method always low detection accuracy, low efficiency, and cannot detect the stress distributions in anisotropic metallic materials.Since the disadvantages of the conventional method of the eddy current, this paper proposed a new method based on directional pulsed eddy current heating and the principles of thermal conductivity can changed by stress of a metal material. Firstly, this article briefly describe the plane stress state based on elasticity, and the function of stress and thermal response peak of pulsed eddy current was obtained by analyzing Piezoresistive effect and the stress-strain relation. Further, the existence of a relationship between thermal conductivity and stress based on Weidmann-Franz’s law was got. Then the above relation was verified by finite element analysis and simulation use COMSOL.Finally, experiment of axial tensile was done use aluminum alloy, austenitic stainless steel and nickel alloy plate, surface temperature of the heating and heat transfer data was collected use infrared thermal imager. At the same time, the curve of uniaxial stress and thermal conductivity was got based on two-dimensional heat conduction differential equation, linear fit by one-dimensional. Also, stress of aluminum alloy specimens was measured with this fitting parameters, and a brief analysis was done for error causes.Compared to the method based on thermal response peak characteristic, calculation of thermal conductivity does not depend on the initial temperature distribution and incentives to lift-off and power change, also thermal conductivity of all units with heat transfer process can be calculated by excite once. As a result, stress detection method proposed in this paper have the advantages of good stability, high detection efficiency and can realize the stress testing of anisotropic material.