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为了探索超声红外热像检测技术对涂层下基体疲劳裂纹识别和评估的可行性,在Q235不锈钢试样中预置了拉伸疲劳裂纹,并采用火焰喷涂方法在试样表面制备了3Cr13合金涂层,使用25 k Hz低频脉冲超声波从涂层表面进行激励,研究了激励过程中涂层表面温度场的瞬态响应过程,以及裂纹区和非裂纹区的温度变化趋势;分析了表面喷涂层对基体裂纹开口处的生热机制的影响,提出了裂纹识别的最佳时间;通过二值化处理,基于MATLAB软件的数字图像处理功能,从热图中提取了裂纹骨架,并计算了裂纹长度。结果表明:超声红外热像法可实现对再制造毛坯涂层下基体疲劳裂纹的定性识别和定量检测。
In order to explore the feasibility of using ultrasonic infrared thermal imaging to detect and evaluate the fatigue crack under the substrate, a tensile fatigue crack was pre-set in the Q235 stainless steel sample and a 3Cr13 alloy coating was prepared on the sample surface by flame spraying Layer, using a 25 k Hz low-frequency pulsed ultrasonic wave to stimulate the surface of the coating, the transient response of the surface temperature field during the excitation process and the temperature trend of the cracked and non-cracked areas were investigated. Based on the digital image processing function of MATLAB software, the crack skeleton was extracted from the heat map and the crack length was calculated. The results show that ultrasonic thermography can realize the qualitative identification and quantitative detection of the fatigue crack under the remanufactured blank coating.