非线性超声脉冲反转法在铝合金焊缝疲劳寿命预测中的应用
Nonlinear ultrasonic evaluation of fatigue life of aluminum alloy welded joint based on pulse-inversion technique
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摘要: 以不同疲劳寿命的铝合金焊缝为例研究了疲劳过程中的超声波非线性效应,同时建立了非线性参数与疲劳寿命的关系曲线(S-N曲线).采用脉冲反转法对非线性超声信号进行处理.结果表明,经过脉冲反转法获得的S-N曲线与经过滤波模块获得的S-N曲线相比谐波幅值提高了一倍,所以脉冲反转法可以提高非线性超声检测法表征疲劳损伤程度能力,而S-N曲线在疲劳过程中呈先缓慢增长后快速增长,最后下降的趋势,此趋势对应了材料疲劳的3个阶段,而金相组织验证了曲线的准确性,所以通过非线性超声脉冲反转法来预测疲劳寿命是可行的.Abstract: Fatigue is a common phenomenon in welded structures, therefore prediction of fatigue life of welded joints in-service is an on-going and unsolved challenge with conventional linear ultrasonic test method. In this paper, nonlinear ultrasonic distortion effect of the crack during the initiation and propagation process in different fatigue cycles of the aluminum alloy joints was studied and the curve of nonlinear coefficient and fatigue cycles was established simultaneously. The pulse-inversion technique was used for signal processing. The experimental results showed that the harmonic wave amplitude of S-N curves processed by pulse-inversion technique is increased one time compared with that by filtering module. Therefore, the pulse-inversion technique can improve the detection capabilities of nonlinear ultrasonic test technique. Experimental results showed that the S-N curve changes slightly in the fatigue crack initiation stage, then increases rapidly with the increase of fatigue cycles, and it begins to decrease when fatigue crack extends to the macroscopic crack. The experiments of microstructures verify the precision of curve. It can be concluded that the nonlinear ultrasonic technology base on the pulse-inversion can be effectively used to predict the fatigue life of aluminum alloy welded joint.
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