残余应力的超声横纵波检测方法

基于声弹性原理,研究板材厚度方向、螺栓轴向方向(以下简称z轴方向)宏观残余应力分布的超声无损检测方法。针对被测构件厚度不均匀对应力检测精度的影响非常大、检测原理繁杂不适合工程应用、拉伸实验中拉伸形变对应力系数测量精度的影响很大等问题,采取超声横波、纵波相结合的方法重新推导检测公式,并提出采用一发一收模式进行拉伸实验,通过对实验数据进行拟合,由公式计算出声弹性系数代替应力系数。然后结合插值、互相关等算法,采用VC++编制z轴方向残余应力超声检测软件并搭建检测系统。分别对性能为A2-70,4.8,8.8,长度依次为135 mm,100 mm,100mm的M20的螺栓进行拉伸实验,比对计算拉伸应力与检测拉伸应力,结果表明,该测量系统的绝对误差限为20 MPa,相对误差小于25%,且应力值较大时,相对误差有所减小,当应力值大于100 MPa时,相对误差小于5%,非常实用。 

Ultrasonic shear and longitudinal wave testing method of residual stress

Based on elastic theory,the ultrasonic nondestructive testing method of macroscopic residual stress distribution in plate thickness direction or bolt axial direction(hereinafter referred to as the z axis) is studied.A method of combining ultrasonic transverse wave and longitudinal wave to derive detecting formula is produced and pitch and catch mode is applied in the tensile test in order to reduce the influence on the stress testing accuracy of the detection principle,measured components' uneven thickness and measurement of stress coefficient.By experimental data fitting,the acoustoelasticity coefficient is re-calculated and is in place of stress coefficient.Afterwards,the software of ultrasonic testing residual stress in z axis direction is set up combined with interpolation and cross-correlation algorithm,then the detection system is also constructed.Tensile tests are conducted with the bolts in performance of A2-70,4.8 and 8.8,whose lengths are 135 mm,100 mm,100 mm,respectively.Comparing the computation and detection of tensile stress,the results show that the absolute error limit is 20 MPa and the relative error of the test system is less than 25%.As residual stress increases,the relative error decreases.When the stress increases to over 100 MPa,the relative error is less than 5%.It shows that the testing system is practical.