Abstract

The tensile strength of welded joints subjected to thermal stresses degrades with age. Tensile strength is generally assessed using tensile test, which is a destructive technique. This degradation measurement using the nondestructive testing (NDT) method has merit as specimens are intact even after the test. In situ NDT offers another significant advantage that testing of material can be performed without removing the sample from its service. Ultrasonic testing (UT) is a widely used NDT technique for material characterization and flaws detection. Motivated by this, we aim to investigate the tensile strength of mild steel post-weld heat-treated samples through advanced signal processing of the acquired ultrasonic signals through UT of mild steel heat-treated welded specimens. To this end, mild steel welded specimens were prepared for this study using electric arc welding with E6013 electrodes. After welding, specimens were heat-treated at different temperatures and then normalized. Ultrasonic signals were acquired using the pulse-echo technique on different samples, heat-treated at different temperatures, and later ultrasonic signal’s attenuation was measured. The acquired UT signals were then processed using advance signal processing techniques i.e., fast Fourier transform (FFT) and power spectral density (PSD). Measured attenuation of UT signals and discriminatory features computed through the application of signal processing techniques on acquired UT signals then correlated with the specimens’ tensile strength. Analysis of results showed that the tensile strength, FFT power of UT signals, and UT signals’ PSD energy decreases as UT signal attenuation, increases with an increase in heat treatment temperature. Results also revealed that there exists a relationship between FFT signals strength, PSD energy, and UT signals attenuation with respect to heat treatment temperatures. This study will help weld quality inspectors to use in situ UT for predicting the tensile strength of mild steel welded specimens using the relationship established through the proposed scheme.

中文翻译：

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用超声波检测热处理对低碳钢焊接接头抗拉强度的影响

摘要

受到热应力的焊接接头的抗拉强度随着时间的推移而降低。拉伸强度通常使用拉伸试验进行评估，这是一种破坏性技术。使用无损检测 (NDT) 方法进行的这种退化测量具有优点，因为即使在测试后样品仍完好无损。原位无损检测提供了另一个显着的优势，即可以在不从服务中移除样品的情况下进行材料测试。超声波检测 (UT) 是一种广泛使用的无损检测技术，用于材料表征和缺陷检测。受此启发，我们旨在通过对低碳钢热处理焊接试样的 UT 获取的超声波信号进行高级信号处理，研究低碳钢焊后热处理试样的抗拉强度。为此，本研究使用 E6013 焊条进行电弧焊制备低碳钢焊接试样。焊接后，试样在不同温度下进行热处理，然后正火。使用脉冲回波技术对不同样品进行超声信号采集，在不同温度下进行热处理，然后测量超声信号的衰减。然后使用先进的信号处理技术，即快速傅立叶变换 (FFT) 和功率谱密度 (PSD)，处理获取的 UT 信号。通过对获取的 UT 信号应用信号处理技术计算 UT 信号的测量衰减和判别特征，然后将其与试样的拉伸强度相关联。结果分析表明，UT信号的抗拉强度、FFT功率、和UT信号的PSD能量随着UT信号衰减而降低，随着热处理温度的升高而增加。结果还表明，FFT 信号强度、PSD 能量和 UT 信号衰减与热处理温度之间存在关系。这项研究将帮助焊接质量检查员使用原位 UT 来预测低碳钢焊接试样的抗拉强度，使用通过提议的方案建立的关系。