微观组织及测量信号对超声横波评价材料硬度影响

Microstructure and measurement signal influences based on ultrasonic shear wave for applied hardness determination

硬度是材料力学性能的重要指标之一,采用超声无损检测方法评价材料硬度指标目前还存在诸多挑战。通过搭建高精度声时测量系统,采用横波直探头脉冲反射回波法测量不同热处理45钢试件厚度方向超声横波传播声时和底面反射回波幅值,分别计算横波声速和衰减系数;在测量超声横波声时,改变测量声时门信号的测量方式,研究不同微观组织及测量信号对超声横波声速的影响,通过构建材料硬度-微观组织-超声横波声速及衰减系数之间的映射关系,建立超声横波评价45钢试件硬度指标的标定模型,并对标定模型进行验证。研究表明,横波声速可以作为评价45钢试件硬度的评价参数,测量误差满足工程应用误差10%的要求;测量横波衰减系数与材料硬度之间的变化没有明显的映射关系,不能作为评价45钢试件硬度指标的评价参数。

Hardness is one important parameter to assess the performance of mechanical materials.There are many challenges to evaluate the hardness by ultrasonic nondestructive testing methods. In this paper, the high-precision acoustic measurement system was built.The shear wave reflection echo amplitude and propagation time in the thickness direction of different heat treated 45 steel specimens are measured by pulse reflected echo method using shear wave straight probe.The shear wave attenuation coefficient and velocity are calculated respectively. The gate signalof measurement shear wave propagation time is also changed.Then, the effects of different microstructures and measuring signals for the shear wave velocity are studied by building mapping relationships of hardness, microstructure, ultrasonic shear wave velocity and attenuation coefficient. Besides, the calibration model for evaluating the hardness of 45 steel specimens by shear wave velocity is formulated.Experimental results show that shear wave velocity can be employed to evaluate the 45 steel specimen hardness and its measurement error can meet 10% requirementof the engineering application. There is no obvious mapping relationship between the shear wave attenuation coefficient and the hardness.Hence,the attenuation coefficient cannot be used as the evaluation parameter to evaluate the hardness of 45 steel specimen.