中文摘要：

针对超声波声速随钢轨应力变化而改变的特征,采用测量时间差的方法获得速度信息,设计开发了基于FPGA和USB接口的超声波传播时间精确测量系统.通过巴特沃斯低通运算去除信号中的噪声,基于互相关算法得到了超声波的传播时间差,并通过三次样条插值方法提高了时间差的测量分辨率.基于钢轨拉压实验平台,测量了不同应力状态下超声波在钢轨中的传播时间,获得了超声波在钢轨中的声弹性常数.实验表明：在钢轨中超声波的传播速度随应力的改变成线性变化,通过测量钢轨中超声波的传播速度,结合温度补偿算法,可实现钢轨应力的实时在线监测.

英文摘要：

In order to study the method to measure the stress level in a rail by means of acousto-elastici- ty, a FPGA （Field-Programmable Gate Array） and USB based system to measure the ultrasonic trans- mitting time in a rail is designed. The Butterworth low pass filter is used to remove the noise from sig- nals, ultrasonic propagation time is obtained with cross-correlation algorithm and the cubic spline inter- polation method is used to improve the time resolution. Different stresses are applied on the rail through a tension and compression testing platform. After getting the transmitting time in the rail of certain length, an acousto-elastie coefficient for the rail is acquired. The experiments show that the propagation time of ultrasonic waves in the fixing distance rail varies linearly with the stress. It is fea- sible to measure the stress level in a rail by means of measuring changes of the transmitting time com- bined with temperature compensation algorithm.