基于共线异向混频技术的不可见疲劳裂纹定位

对金属构件中不可见疲劳裂纹进行有效的检测是保证其安全服役的关键因素,本研究利用共线异向混频技术对不可见疲劳裂纹进行检测和定位。当两列共线异向超声波在金属构件内相遇时,会与疲劳损伤发生非线性相互作用。研究结果表明,随着试件疲劳裂纹长度的增加,混频非线性系数单调递增,这与材料内部微观结构的变化密切相关。此外,通过控制两激励信号的延迟时间,使两列激励信号的相遇位置沿试件的水平方向由左向右移动,利用和/差频信号幅值最大值所对应的延迟时间对不可见疲劳裂纹进行定位。因此,利用共线异向混频技术可以对金属构件内部的不可见疲劳裂纹进行有效的检测和定位。

Invisible Fatigue Crack Location Using the Collinear Heterotropic Mixing Ultrasonic Technique

In order to effective detect the fatigue cracks and damage in metal components ensuring their safe service, the collinear heterotropic mixing ultrasonic technique is applied to detect and locate the fatigue cracks in metal components. When two columns of collinear heterotropic ultrasonic waves meet inside a metal component, the nonlinear interaction with fatigue damage would be occurred, and a third column of ultrasonic wave can be generated, which is closely related to the fatigue damage degree at the meeting position. The experimental results indicates that the mixing nonlinear coefficient increases monotonically with the increase of fatigue crack length, which is concerned with the microstructure change of metallic material during the fatigue damage process. In addition, by controlling the delay time of two exciting signals in the process of experiment, different meeting positions along the length direction of components can be detected. The relationship between the amplitude of sidebands at difference or sum frequencies and delay time is obtained, and the delay time corresponding to maximum amplitude is applied to locate the fatigue crack along the length direction. The experimental results indicates the fatigue crack can be located in metallic components. It is concluded that the collinear heterotropic mixing ultrasonic technique can effectively detect and locate the invisible fatigue crack in metallic components.