【作者】 刘锋；

【导师】 马宏伟；

【作者基本信息】 暨南大学 ， 工程力学， 2010， 硕士

【摘要】 管道运输业在经济建设和国防工业中发挥着越来越重要的作用,但管道腐蚀、裂纹等缺陷引起的泄露不仅造成经济上的巨大损失,且会污染环境影响生态平衡,因此对管道的损伤检测显得尤为重要。超声导波是近年来发展起来的一种能够进行快速、长距离、大范围、相对低成本的无损检测方法,受到无损检测领域的广泛关注。本文在前人对导波在管道中传播的理论基础上,重点对管道进行了损伤检测的实验研究。首先通过对激励信号的分析,发现信号周期数目越多,其频带越窄,更有利于频率的控制,但周期数越多,其在时域信号的持续时间越长,波形易叠加,所以选择经HANNING窗调制的20个周期的正弦信号作为实验的激励信号；然后对3米长钢管进行了裂纹损伤模拟,对5米长钢管进行了腐蚀损伤模拟,发现随着激发频率的增加,激励信号的能量幅值不断增加,但高频率下的能量更易损耗,所以选择70KHz做为激发频率进行实验。实验结果表明了纵向超声导波能很准确地定位单裂纹和双裂纹,并能成功地检测出占管道横截面积3.7%的小损伤,且随着缺陷的扩展,导波遇到缺陷后的能量反射率单调递增,而能量透射率单调递减。当导波经过端面和缺陷时,除了发生反射之外,还会发生一定程度的模态转换,且转换模态幅值与入射导波频率有关。适当地选取激发频率,能很好地抑制转换模态幅值。最后探索了超声导波在4米长的PVC-U管道中的传播规律,发现纵向导波在PVC管道中传播时,其能量大幅度地衰减,传播距离大约为1米,远小于其在钢管中传播的距离,说明了管道材料的性质会极大影响导波的传播距离。更多还原

【Abstract】 Pipeline transportation business plays a much important role in the economy construction and national defence industry, but the leakage of the pipe defects, corrosion and cracks can not only make the huge damage to the economy, but also pollute the environment and affect the balance of the ecology, so it is very important to detect the pipes. Ultrasonic guided waves technique has not only good command of efficiency and low cost, but also can inspect the whole wall thickness of pipe. Therefore, ultrasonic guided wave technique is paid more attention in pipe NDT area.Based on previous study on the guided wave propagated in the pipeline, the main of this paper is to do experimental study on damage detection in pipes using ultrasonic guided waves technique. First of all, based on the analysis of the excitation signal, it’s found that the more the number of cycles, the band becomes narrower, more conducive to control the frequency, but the signal lasts longer in the time domain and it is easier to superipose, so select the sinusoidal signal of 20 cycles which modulated by window of HANNING as the excitation signal in the experiment. And then to 3-meter-long steel pipe to simulate the crack damage, the 5-meter-long steel pipe to simulate the corrosion damage was found that increase with the excitation frequency, the energy amplitude of the excitation signal increased, but easier the energy of high-frequency loss, so select 70KHz as the excitation frequency of the experiment. The results showed that the longitudinal ultrasonic guided waves can be very accurately locate a single crack and double cracks, and can successfully detect the small defect which account for 3.7% of cross-sectional area of pipe, and with the expansion of defects, the reflectivity of guided wave energy increase monotonically, while the transmittance of guided wave energy decrease monotonically. When the guided wave propagate through the end of the pipe and defects, in addition to reflection occurs, but also a certain degree of mode conversion, and the amplitude of conversion mode has something with the frequency of the excitating guided wave. Selecting the appropriate excitation frequency can well inhibit the conversion mode amplitude. Finally the rules of ultrasonic guided waves propagate in the 4-meter-long PVC-U pipe were explored and found that the energy of longitudinal guided wave was greatly attenuated, spreading about 1 meter distance, far less than the transmission distance in steel pipe, it indicates that the nature of the pipe material will significantly affect the guided wave propagation distance.更多还原