摘要Q235钢是工业生产中应用最为广泛的原材料之一。而应力是造成各种金属行业设备出现问题、损坏的很大因素之一。对于焊接件更是如此，焊接后的金属设备在使用过程中的应力大小和种类对设备的使用影响很大。因此对于焊接件的焊缝质量评价的研究就显得尤为重要。超声波法是目前应力评价方法研究领域热点之一，因而本课题以不同应力下不同晶粒尺寸的Q235钢的组织反应为研究对象，探索影响超声波评价应力的因素及其规律。86841

超声波法是基于超声波声弹性效应实现应力评价的一种技术，通过建立应力-信号间时间差关系实现应力的无损评价。基于此，本课题选取Q235钢为材料，对不同晶粒尺寸的试样进行等幅加载拉伸实验，并同时测其超声波信号。计算得到该信号与参考信号的信号时间差和各晶粒尺寸对应的超声波声弹性系数。最终建立了超声波声弹性系数和晶粒尺寸的关系，并结合断口形貌进行了理论分析。并在Q235对接接头中得到了应用验证。

结果表明：随应力增大，超声波在Q235钢中通过相同距离所需时间逐渐变大，当应力达到一定值时，超声波在Q235钢中通过相同距离所需时间呈不规律变化。与此相似，随应力增大，超声波信号间时间差基本呈线性规律变大，当应力分别达到一定值时，超声波信号间时间差达到最大值，而再随应力的增大，超声波信号间时间差呈不规律变化。随晶粒尺寸增大，Q235钢超声波声弹性系数逐渐减小。分析认为以上结果是由试样微观组织结果引起的，随着应力和晶粒尺寸的增加，超声波信号的畸变增大，因而在传播过程中越不稳定。综合上述分析结果，认为采用本文研究方法可实现不同晶粒尺寸对超声波声弹性系数影响的应力的评价。

毕业论文关键词：Q235钢；晶粒尺寸；声弹性；应力评价

Abstract Q235 steel is widely used materials in industrial production。 A variety of metal equipment problems were caused by the stress, so the welding seam is。 The size and type of the stress in the metal equipment after welding does a great impact in it’s use。 Therefore, it is particularly important to study this aspect。 Ultrasonic method is the widely used method in research of stress。 So this topic will research the Q235 steel tissue of different grain under different stress, and explore the regularities and factors which impact the evaluation of stress in use of ultrasonic method。

Ultrasonic method is a kind of technique to fulfill stress evaluation based on ultrasonic acoustoelastic effect, and it can realize nondestructive evaluation of stress by establishing the time difference between stress and signal。 Based on this, Q235 steel is selected, and it is carried out in loading tests with different grain sizes, and the ultrasonic signals are measured simultaneously。 The time difference of signal between is calculated, and the corresponding ultrasonic acoustoelastic coefficient of each grain size is calculated。 Finally, the relationship between the ultrasonic acoustoelastic coefficient and the grain size was established, the fracture morphology was analyzed。 It has been verified in the Q235 butt joint。

The results show that the time of ultrasonic going through Q235 steel gradually become larger with the increase of stress。When the stress reaches a certain value, the time required of the same distance changes erratically。 With the stress increases, the ultrasonic signal time difference is basically linear law。 When the stress reached a certain value, time difference of ultrasonic signal reached the maximum value, then ultrasonic signal time difference changes erratically。 The ultrasonic changes erratically of Q235 steel decreases gradually with the increase of grain size。 The analysis shows that this is caused by the microstructure of the samples, with the increase of the grain size and stress the distortion of ultrasonic signal is increased, so it is not stable in the process of propagation。 Based on the above analysis results, it is considered that the stress of different grain sizes can be realized by the method of this research。