互相关函数步长影响超声波评价涂层应力的实验研究

以声弹效应理论为基础,结合力学拉伸实验,采用表面超声波法对涂层应力进行评价,并在互相关函数法的基础上计算应力引起的信号间时间延迟.结果表明:当涂层试样处于弹性变形范围内时,随着应力的增加,表面超声波在涂层中的传播速度逐渐变大,而当拉伸应力达到一定值使得涂层内部出现微裂纹时,随着应力的增加,伴随着裂纹的扩展超声波波速会出...

Study on Influence of Calculating Length on Evaluation Result of Stress by Surface Acoustic Wave for Coating

Based on the theory of acoustoelastic effect,using mechanical tensile experiment,the residual stress of coating was evaluated by the method of surface acoustic wave.The difference in time of flight among the ultrasonic signals caused by difference tensile stress is calculated on the base of cross-correlation function.The results show that when the tensile stress is less than elastic limit of coating,the velocity of surface acoustic wave is bigger and bigger with tensile stress increasing in coating,and when the tensile stress is bigger than a certain value,microcrack appears and expands gradually with the tensile stress increasing in coating,so the velocity of surface acoustic wave also changes correspondingly.The length of reference signal(n) is a vital factor for calculating result of cross-correlation function.The tendency of tensile stress and difference in time of flight is prone to linear increasing with value of n increasing.And when the value of n attains one cycle,the calculating result between tensile stress and difference in time of flight is basic similar with tensile stress increasing.By calculating the evaluation parameter of linear fitting result,the result of fitting value of cross-correlation function and root-square error also show that when the length of reference signal is one cycle,the calculating result of cross-correlation function is optimal for the evaluation of tensile stress.