碳含量对超声波评价碳钢表层应力的影响

Influence of carbon content on surface stress evaluation of carbon steel by ultrasonic wave

基于超声波声弹性公式优化,探讨碳含量对碳钢超声波声弹性系数的影响规律。采用中心频率为5 MHz一发一收模式的超声波探头采集信号,通过互相关系数函数计算超声波信号间时间差,借助线性拟合函数计算超声波声弹性系数,利用SEM对试样断口微观形貌进行观察。结果表明:Q235钢超声波声弹性系数较大,低载荷阶段超声波信号间时间差波动较明显,信号间时间差-应力曲线的转折点载荷与Q235钢弹性极限载荷较接近,表层初始应力引起的试样表层不均匀塑性变形程度不同是导致上述结果的重要原因,超声波探头与试样间耦合状态也是影响超声波评价应力结果的因素之一。

Based on optimization of ultrasonic acoustoelastic formula,the influence of carbon content on ultrasonic acoustoelastic coefficient of carbon steel was discussed.Two ultrasonic transducers with the center frequency of 5 MHz were used to collect ultrasonic signal,the difference in flight time between the ultrasonic signals was calculated with cross correlation coefficient function,and the ultrasonic acoustoelastic coefficient of the carbon steel under tensile was obtained with linear fitting method.The tensile fracture morphology of the carbon steel was observed by SEM.The results show that comparing with 45 steel,the ultrasonic acoustoelastic coefficient of Q235 steel is higher,the difference in time of flight between the ultrasonic wave fluctuates more obviously.The difference between the turning point load of the experimental result and elastic limit load of Q235 steel is smaller.The difference in inhomogeneous plastic deformation of the specimen surface by initial stress is responsible for the above results,and coupling state between the ultrasonic transducer and the specimen also affects the results.