针对金属疲劳裂纹检测研究不深入的问题，本文以金属平板疲劳裂纹为研究对象，搭建了超声红外锁相热像检测实验系统，分析了调制超声激励下裂纹生热及热信号频谱的规律。研究结果表明：裂纹区域温升以裂纹根部为圆心向外呈圆形辐射状分布，而且温升逐渐递减，但是在调制频率处，裂纹区域与正常区域的相位差和幅值差明显高于其他频率处的数值。进一步，基于实验方法揭示了预紧力和调制频率等检测条件对幅值差和相位差的影响。研究成果将为超声红外锁相热像技术的金属疲劳裂纹检测研究提供理论支撑。

Few studies have investigated techniques for effectively detecting fatigue cracks in metal. In this study, a metal plate is fatigue-cracked while being observed with lock-in vibrothermography, in order to extensively investigate crack heating under modulated ultrasonic excitation and obtain the frequency spectra of thermal signals. The crack root was centered in the sample, radiating circularly outward, with the rate of temperature increase observed in cracked areas decreasing with distance from the center. However, the amplitude and phases were different between cracked and uncracked areas at certain modulated frequencies. Moreover, the experimental method identified the influence of frequency modulation on the amplitude and phase differences. Further theoretical work will support the ongoing study of metal fatigue crack detection using lock-in vibrothermography.