The results show that with the increase of load, 45 steel and Q235 steel ultrasonic signal time difference increases linearly increases, which are consistent with the sonic elasticity theory, but compared with the theory of ultrasonic signal, the time difference between the fluctuation of load curve slightly obviously, and the time of ultrasonic signal difference increases with load increasing rate decreased slightly and gradually stabilized, compared with low load stage of 45 steel and Q235 steel ultrasonic signal with the time difference between the load change rule of 45, fluctuation time difference between large steel ultrasonic signal, cause different results and theoretical results is the process of static tension in 45 steel and Q235 steel surface uneven deformation。 The coefficient of sound elasticity can be obtained by linear  fitting of the  stress time difference curve of the     two

samples。 As the grain size of the material is the same, the factors that affect the elastic coefficient of the material are the carbon content of the material。 So the relationship between the  sound  elasticity  coefficient   and the  carbon content  is  finally obtained。

Keywords: Ultrasonic wave; Stress; Nondestructive evaluation; Carbon content; Acoustoelastic  theory

目 录

第一章 绪论 1

1。1  课题研究背景及意义 1

1。2  超声波评价应力研究现状 2

1。3  超声波信号间时间差计算方法研究现状 5

1。3。1  基于相关分析的时间延迟估计方法 5

1。3。2  基于高阶统计量的时间延迟估计方法 5

1。3。3  基于分数低阶统计量的时间延迟估计方法 6

1。3。4  小波变换计算时间延迟 6

1。3。5  基于时频分析的延迟估计方法 6

1。3。6  阈值法 6

1。4  课题主要研究内容 7

第二章 实验材料与实验设备 8

2。1  实验材料 8

2。2  实验设备 8

2。2。1 CMT 5205 型静载拉伸实验设备 8

2。2。2  超声波评价应力系统 9

2。2。3 WZS-20 型双室真空烧结炉 10

2。2。4  材料金相显微镜 10

2。2。5 JSM-6480 型扫描电子显微镜 11

第三章 实验结果与分析 12

3。1  超声波声弹性理论 12

3。2  超声波信号的采集步骤 13

3。3  实验结果分析 15

3。3。1  试样超声波信号分析 15

3。3。2  超声波信号间时间差-应力曲线 17

3。4  理论探讨 20

3。5 本章小结 22

第四章