变径厚壁管周向兰姆波检测方法及实验研究

发布时间：2018-06-13 06:55

本文选题：变径厚壁管 + 周向兰姆波　；参考：《南昌航空大学》2017年硕士论文

【摘要】：变径厚壁管在核电、石油化工、军工等特种设备领域应用的越来越广泛。传统上变径管损伤的分析方法,一是化学成分;二是通过模拟实验,对变径管在某些环境中容易产生裂纹、腐蚀等缺陷进行剖析;三是采用数值计算或实验的方法,直接分析变径管的应力、强度等材料特性。以上方法虽然能够分析变径管的强度及材料性能是否合格以避免由变径管损伤引起的相关事故,但对变径管的质量状况不能进行快速检测。研究变径管的有效无损检测技术,实现变径管缺陷的快速检测具有重要意义。与轴向导波相比,超声周向导波更适合用于厚壁管道的检测,沿着管道轴向移动超声导波换能器,可实现变径厚壁管的全面扫查。本文研究了变径厚壁管的检测方法,为有关变径厚壁管检测技术标准的制定,提供基础性实验数据和可行性方法。本文首先对变径厚壁管中周向兰姆波的频散特性进行了分析,给出了周向兰姆波的频散方程的推导过程,运用等效替代法,把变径厚壁管等效成不同径厚比等径厚壁管,通过求解频散方程和波结构,得到壁厚不变、不同径厚比管道所对应群速度曲线以及波结构。对比在0~1MHz频率范围内的频散曲线可知,随着变径厚壁管外径减小,各个模态在处于较优频散特性时的群速度也都依次减小,且模态阶数越高,整个变径厚壁管全部外径所对应群速度曲线都处于较优频散特性所需要的激励频率越大;在激励中心频率不变的情况下,随着变径厚壁管外径不断减小,能够检测整个壁厚所需要的导波模态阶数越高;根据频率与入角度的关系,选择合适的激励角度,有望激励出较少模态的周向兰姆波。其次,开展了变径厚壁管周向兰姆波传播特性及在缺陷上反射的数值模拟研究,利用有限差分方法模拟了周向兰姆波在壁厚30mm、大管径250mm、小管径100mm、轴向长度600mm的变径厚壁管上的传播特性和散射特性。研究了采用压电晶片30°、45°和60°斜入射时,变径厚壁管中声场的分布规律,并检测了不同尺寸的位于外壁、中壁和内壁的缺陷。此外,还进一步研究了周向兰姆波在不同倾斜度变径厚壁管中的传播特性。研究结果表明:对于周向兰姆波,不同入射角会影响变径厚壁管中声场的覆盖范围,角度过大会使得内壁声场较弱,角度过小时频散现象严重;周向兰姆波在变径厚壁管中不同大小的缺陷反射时会产生不同效果,缺陷尺寸太小,效果很弱,当内壁圆孔缺陷半径大于3mm时,效果变化显著;通过对比周向兰姆波在等径厚壁管、变径厚壁管、45°变径厚壁管、60°变径厚壁管上的传播特性可知,变径厚壁管倾斜角度越大,周向兰姆波越难以在其中传播。再其次,基于数值模拟的结果,选取中心频率为500KHz的压电晶片,设计了楔块角度为37°、45°、55°的有机玻璃楔块,制作了中心频率为500KHz的角束斜探头以激发周向兰姆波。确定了周向兰姆波在变径厚壁管中传播时,形成稳定幅值的周向兰姆波的周向距离是300mm。在此基础上,利用连续小波时频分析得到周向兰姆波在这三种角度斜入射时,群速度与频率的关系曲线,分析了主要的传播模态。最后,开展了变径厚壁管缺陷周向兰姆波检测实验研究,针对壁厚30mm、大管径250mm、小管径100mm、轴向长度600mm的变径厚壁管,在外壁、中壁、内壁不同位置加工了一系列缺陷,研究了不同角度探头对不同位置、不同大小、不同类型缺陷的检测,以及变径厚壁管不同径厚比周向兰姆波的反射波能量问题。实验检测结果表明:变径厚壁管周向兰姆波的检测灵敏度为长1mm、宽1mm、高1mm的缺陷;当检测变径厚壁管中、外壁缺陷时,楔块角度55°的周向兰姆探头所激励的导波检测效果最好,当检测内壁缺陷时,选择楔块角度45°的探头更适合;周向兰姆波在变径厚壁管中的传播具有较强的指向性,了解周向兰姆波在变径厚壁管中反射波能量有利于对缺陷进行定位分析。
[Abstract]:The variable diameter thick wall tube is becoming more and more widely used in the fields of nuclear power, petrochemical, military and other special equipment. The traditional analysis method of the variable diameter tube damage is chemical composition. Two through the simulation experiment, the defects of the variable diameter tube are easily analyzed in some environment, such as crack and corrosion, and the three is the method of numerical calculation or experiment. The above method can analyze the strength of the variable diameter tube and whether the material performance is qualified to avoid the related accidents caused by the variable diameter tube damage, but the quality condition of the variable diameter tube can not be detected quickly. The effective nondestructive testing technology of the variable diameter tube is studied and the fast tube defect is realized quickly. The speed detection is of great significance. Compared with the axial guided wave, the ultrasonic circumferential wave guide wave is more suitable for the detection of the thick wall pipe. The ultrasonic guided wave transducer is moved along the axial direction of the pipe to realize the comprehensive scanning of the variable diameter thick wall tube. This paper studies the detection method of the variable diameter thick wall tube, which provides the basis for the formulation of the technical standards for the variable diameter thick wall tube detection. The basic experimental data and the feasibility method. Firstly, this paper analyzes the frequency dispersion characteristic of the circumferential Lamb wave in the variable diameter thick wall tube, gives the derivation process of the frequency dispersion equation of the circumferential Lamb wave, and uses the equivalent substitution method to equip the variable diameter thick wall tube into a thick wall tube with different diameter and thickness ratio, and obtains the wall by solving the dispersion equation and the wave structure. The group velocity curve and wave structure corresponding to the diameter thickness of the pipe are not constant, and the frequency dispersion curve in the 0~1MHz frequency range shows that with the decrease of the diameter of the variable diameter thick wall tube, the group velocity of each mode in the better dispersion characteristic decreases in turn, and the higher the modal order, the whole diameter of the whole variable diameter thick wall tube corresponds to the group. The faster the velocity curve is in the better frequency dispersion characteristic, the greater the frequency of the exciting frequency, and the higher the number of the guided waves needed to detect the thickness of the whole wall with the constant decrease of the diameter of the variable diameter thick wall tube, and the less modes are expected to be encouraged according to the relationship between the frequency and the angle of entry and the choice of the appropriate excitation angle. Secondly, the propagation characteristics of the circumferential rimbo wave and the numerical simulation of the reflection on the defect are carried out. The propagation and scattering characteristics of the circumferential Lamb wave on the wall thickness 30mm, the diameter of the tube 250mm, the diameter of the tube 100mm and the axial length 600mm are simulated by the finite difference method. The distribution of sound field in a variable diameter thick wall tube at 30, 45 and 60 degrees, and the defects in the outer wall, the middle wall and the inner wall of different sizes are detected. Furthermore, the propagation characteristics of the circumferential Lamb wave in different inclined variable diameter thick wall tubes are further studied. The results show that the different incidence angles are different for the circumferential Lamb waves. It will affect the coverage of the sound field in the variable diameter thick wall tube, and the angle over the assembly makes the inner wall sound field weak and the angle over hourly dispersion phenomenon serious; the circumferential Lamb wave can produce different effects when reflecting the defects of different sizes in the variable diameter thick wall tube. The defect size is too small and the effect is very weak. When the radius of the inner hole defect is larger than 3mm, the effect changes obviously. By comparing circumferential Lamb waves in equal diameter thick wall tube, variable diameter thick wall tube, 45 degree variable diameter thick wall tube and 60 degree variable diameter thick wall tube, it is known that the larger the inclined angle of the variable diameter thick wall tube is, the more difficult the circumferential Lamb wave is to propagate in it. Secondly, based on the numerical simulation results, a piezoelectric chip with the center frequency of 500KHz is selected and the wedge is designed. The angle of the block angle is 37, 45 and 55 degrees. The angle beam probe with the center frequency of 500KHz is made to stimulate the circumferential Lamb wave. The circumferential distance of the circumferential Lamb wave, which forms the stable amplitude, is 300mm. on this basis, and the continuous wavelet time frequency analysis is used to obtain Zhou Xianglan. When these three angles are oblique incidence, the relationship curves of group velocity and frequency are analyzed, and the main propagation modes are analyzed. Finally, an experimental study on the circumferential Lamb wave detection of variable diameter thick wall tube defects is carried out. The wall thickness 30mm, the diameter of the tube 250mm, the diameter of the tube 100mm, the axial length 600mm of the thick wall tube, are processed in different positions in the outer wall, the middle wall and the inner wall. A series of defects are studied, and the detection of different positions, sizes and types of defects and the reflection wave energy of different diameter thickness ratio circumferential ram wave are studied. The experimental results show that the detection sensitivity of the circumferential Lamb wave of the variable diameter thick wall tube is 1mm, wide 1mm, and high 1mm. In a thick wall tube, when the outer wall is defective, the guide wave excited by the circumference of the wedge angle of 55 degrees is the best. When the inner wall defect is detected, the probe which selects the wedge angle of 45 degrees is more suitable. The propagation of the circumferential Lamb wave in the variable diameter thick wall tube has strong directivity, and the reflected wave energy of the circumferential Lamb wave in the variable diameter thick wall tube is understood. It is beneficial to the location and analysis of the defects.
【学位授予单位】：南昌航空大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG115.285

【参考文献】