摘要在现代工业中，焊接技术在重型机械、汽车制造、石油管道、压力容器等领域得到广泛应用，焊接技术早已成为各大工业的必不可缺的核心技术。焊接结构的质量是保证推动焊接技术不断发展、应用领域不断扩展的关键。相关研究表明，影响焊接结构服役安全及其可靠性的因素众多，而焊接应力是其关键甚至决定性因素，焊接结构的质量是保证推动焊接技术不断发展、应用领域不断扩展的关键。 86176

鉴于此，本文以304L钢为例对焊接应力的超声波技术评价进行了研究，通过建立应力-信号间时间差关系实现应力的无损评价，因而信号间时间差计算结果对应力评价精度就显的极为重要。本课题采用互相关函数计算信号间时间差，探讨了互相关步长、信号起始点选择对信号间时间差计算精度的影响。

结果表明：距离焊缝位置越远，其超声波信号波形越平滑、信噪比越大，分析认为这是由试样微观组织结果引起的，焊缝位置组织中界面较多、组织不规则，因而超声波信号波形畸变明显。随互相关步长的增大，互相关函数曲线逐渐趋于稳定，互相关函数最大值逐渐趋于明显，当互相关步长达到1周期时，再随互相关步长的增大，互相关函数曲线及互相关函数最大值基本重合。互相关步长相同时，以信号过零点为信号起始点计算信号间时间差结果更好，随距离焊缝位置越远，其信号间时间差基本保持稳定，但略有起伏，焊缝附近区域位置的信号间时间差明显大于远离焊缝位置处的信号间时间差，焊缝中心的信号间时间差达到最大值，即应力达到最大值，这与理论结果是相符的。综合上述分析结果，认为采用本文研究方法可实现不锈钢焊接应力超声波技术评价。

毕业论文关键词：残余应力；互相关步长；超声波；信号间时间差

Abstract In modern industry, welding technology has been widely applied in the field of heavy machinery, automobile manufacturing, oil pipelines, pressure vessels, welding technology has become indispensable core technology of major industry。 Quality assurance of welded structures is crucial to promote the continuous development of welding technology, expanding applications。 Research shows that many factors affect the welding service safety and reliability of the structure, and even welding stress is a key factor in determining the quality of welded structures is the key to promote the continuous development of welding technology, expanding applications of assurance, for domestic and foreign welding stress evaluation techniques carried out extensive research。

In view of this, in this paper, 304L steel, for example for the technical evaluation of ultrasonic welding stress were studied by creating stress-between the signal time difference of relations between stress nondestructive evaluation, and thus inter-signal time difference calculations for stress evaluation of the accuracy on the obvious is extremely important。 This paper uses cross-correlation function to calculate the impact time difference between signals, discussed the cross-correlation step, select the starting signal for the time difference between the signal calculation accuracy。

The results show that the farther away from the weld location, the ultrasonic signal waveform smoother, the greater the signal to noise ratio, analysts believe that this is the result of the sample microstructure caused by weld position tissue interface more irregular organization, thus ultrasonic signal waveform distortion significantly。 With the cross-correlation step increases, the cross-correlation function curve gradually stabilized, the maximum cross-correlation function is gradually becoming more apparent, when the cross-correlation step of 1 cycle, and then with each other a long step increases related to cross-correlation function curve and the maximum cross-correlation function substantially coincide。 Cross-correlation step looks the same time, the signal zero-crossing signal is the starting point to calculate the time difference between signals better results, the farther the distance with the weld location, the time difference between its signal remained stable, but slight ups and downs, the location near the weld area signal significantly greater than the time difference between a position away from the weld between the signal time difference between the signal time difference weld center reaches a maximum that stress reaches the maximum value, which is consistent with the theoretical results。 The above analysis results that can be achieved using the method of this study stress ultrasonic welding stainless steel technology assessment。