Fiber optic sensing for ultrasonic NDE

An innovative approach to nondestructive evaluation (NDE) using noncontacting optical sensors has demonstrated. In this effort a single mode optical fiber interferometer (OFI) was used to sense the presence and form of Rayleigh waves traveling along the surface of a steel test bar at a velocity of nearly 3mm/µs. Acousto-optic time-domain data was successfully used to detect the presence and locate the position of a test flaw (a machined slot) in the bar, and spectrum analysis was used to estimate its geometry and size. This approach has many potential applications in the ultrasonic evaluation of real flaws in structures with complex geometries. Coupled with the authors' earlier work demonstrating the feasibility of generating acoustic waves in metals using laser light pulses transmitted through the fiber optic probes, this latest achievement points to the development of a fully noncontacting, fiber optic based thermal-acousto-photonic (TAP) NDE system, with potential applications to the reliability testing of many important structures where composition, scale, geometry, or restricted access preclude the use of conventional NDE techniques.     

An overview of nondestructive evaluation methods

ondestructive evaluation is described as nondestructive testing (NDT), nondestructive inspection (NDI), and nondestructive examination (NDE). The activities associated with the evaluation include testing, inspection, and examination and primarily involve looking at (or through) and/or measuring some characteristic of an object. Frequently there is a desire to determine some characteristic of the object or to determine whether the object contains irregularities, discontinuities, or flaws. These examinations, inspections, or tests are used to determine the physical soundness of a material without impairing its usefulness. Nondestructive evaluation is a powerful tool that can help assure safety, quality, and reliability; increase productivity; decrease liability; protect the environment; and save money. In this article, nondestructive evaluation is represented by the acronym NDE.     

Remote nondestructive evaluation technique using infrared thermography for fatigue cracks in steel bridges

Long‐standing infrastructure is subject to structural deterioration. In this respect, steel bridges suffer fatigue cracks, which necessitate immediate inspection, structural integrity evaluation or repair. However, the inaccessibility of such structures makes inspection time consuming and labour intensive. Therefore, there is an urgent need for developing high‐performance nondestructive evaluation (NDE) methods to assist in effective maintenance of such structures. Recently, use of infrared cameras in nondestructive testing has been attracting increasing interest, as they provide highly efficient remote and wide area measurements. This paper first reviews the current situation of nondestructive inspection techniques used for fatigue crack detection in steel bridges, and then presents remote NDE techniques using infrared thermography developed by the author for fatigue crack detection and structural integrity assessments. Furthermore, results of applying fatigue crack evaluation to a steel bridge using the newly developed NDE techniques are presented.     

CFRP拉索预应力超高性能混凝土斜拉桥力学性能分析

为了探讨碳纤维复合材料(carbon fiber reinforced polymer,CFRP)和超高性能活性粉末混凝土(reactive powder concrete,RPC)在超大跨度斜拉桥中应用的可行性,以主跨1 008 m的大跨度钢主梁斜拉桥设计方案为例,采用拉索的等强度原则将原桥钢索替换成CFRP索,考虑截面刚度、截面应力和局部稳定等要求,将原桥钢主梁替换成RPC主梁,拟订了一座等跨度的CFRP拉索、RPC主梁斜拉桥方案。采用有限元法分别对两种方案结构的静力特性、动力特性、稳定性能以及抗风性能等进行了分析与比较。结果表明:从结构受力性能角度而言,采用超高性能混凝土主梁和CFRP拉索构成千米级跨度混凝土斜拉桥的结构体系是可行的。     

Displacement discontinuity method applied to nondestructive testing related stress problems

A numerical stress analysis technique using the displacement discontinuity method (DDM) is used to evaluate surface breaking and near surface flaws. DDM is described briefly, with the main body of the work devoted to exploring the use of DDM in a nondestructive evaluation (NDE) program. DDM is a subset of boundary element method technique, and it requires that only the boundaries of the problem be described. Two smooth subsurface voids are investigated. Results for two-dimensional circular and elliptical holes are presented. Comparisons with experimental and theoretical work are shown. The method of uneven element spacing is explored. The results are examined in the context of providing information for NDE inspection requirements and the definition of acceptable flaws. DDM is very well suited for examining the stress field around a surface crack. Surface cracks can be very dangerous and good NDE inspection techniques are required. A method of obtaining the stress intensity factors is developed and illustrated on angular surface breaking cracks. The results are compared with limited experimental and numerical results and interpreted in terms of NDE inspection requirements.     

基于空腔辐射效应的钢索截面温度场分析

该文基于传热学基本理论及ABAQUS数值传热分析平台,以圆柱壁的截面径向导热热阻和空腔热阻代替平壁导热热阻,分别建立了四面受火工况下具有空腔几何特征的钢索截面升温理论及数值传热模型,得到考虑空腔辐射传热效应的无防火保护钢索截面升温历程,将其与具有等效截面圆钢的升温历程比较,研究表明:截面尺寸和空腔辐射效应对钢索截面升温历程有显著影响,空腔辐射效应在火灾升温初期加快了钢索截面的升温速率;最终在钢索热传导理论分析及数值模拟基础上,建议了钢索截面升温计算式,从而准确确定火灾升温历程中钢索材料性能衰减程度,正确评估预应力张拉结构中钢索的抗火承载力。     

斜拉桥中索-桥耦合非线性振动的理论研究

考虑拉索的垂度、大位移引起的几何非线性及空气动力对系统的影响,将桥面简化为等截面的连续梁,建立了索-桥耦合的非线性振动模型。得到了对不同拉索数值求解的结果,表明当桥面和拉索的振动频率比值在1:1和2:1附近的小区间范围内时,索-桥耦合系统将产生严重的内共振,并呈现拍振的特征,而拉索与桥面耦合的振动特性与索的振动频率、垂度、倾角、风速偏航角、风速大小和阻尼等因素有关,从而为桥梁的设计和计算提供了理论依据。     

表面损伤的斜拉索平均气动阻力特性的试验研究

斜拉索作为斜拉桥的重要受力构件,其风荷载设计在桥梁抗风设计中具有重要意义。斜拉索在生产、运输和安装过程中有可能受到损伤,针对不同程度表面损伤的斜拉索,利用风洞测力试验,研究了亚临界、临界和超临界雷诺数区域损伤程度对斜拉索气动阻力的影响,并得到了表面损伤斜拉索气动阻力的计算方法。结果表明:在一定的风向范围内,斜拉索表面损伤对其气动阻力影响显著,在亚临界区,表面损伤模型阻力系数大于光滑模型;进入临界区后,表面损伤模型的阻力系数则小于光滑模型;在超临界区,二者又比较接近。随着划痕的加深,临界区起始雷诺数提前,且在临界雷诺数区,随着雷诺数的增大,阻力系数减小。对不同损伤程度斜拉索的阻力系数进行拟合,得出相应的计算公式,以方便斜拉索气动阻力的估算。     

Signal Processing for In-Line Inspection of Gas Transmission Pipelines

Abstract

Gas transmission pipelines in the United States are primarily inspected using the magnetic flux leakage (MFL) nondestructive evaluation (NDE) technique. However, accurate analysis of the NDE signals in terms of the underlying defects requires a thorough knowledge of various operational parameters such as B-H characteristics of the pipe wall, the velocity of the scanning tool, etc. In certain situations, information about such operational parameters is either absent or hard to obtain. Appropriate signal processing techniques can be applied to the raw MFL signals to ensure that defect characterization is possible in spite of local variations in the test situation. This paper presents two such signal processing methods–one, to compensate the MFL signal for variations in pipe-material grade, and the other to remove the effects of signal distortion that occur due to the velocity of the scanning device.     

Signal processing for in-line inspection of gas transmission pipelines

Gas transmission pipelines in the United States are primarily inspected using the magnetic flux leakage (MFL) nondestructive evaluation (NDE) technique. However, accurate analysis of the NDE signals in terms of the underlying defects requires a thorough knowledge of various operational parameters such as B-H characteristics of the pipe wall, the velocity of the scanning tool, etc. In certain situations, information about such operational parameters is either absent or hard to obtain. Appropriate signal processing techniques can be applied to the raw MFL signals to ensure that defect characterization is possible in spite of local variations in the test situation. This paper presents two such signal processing methods—one, to compensate the MFL signal for variations in pipe-material grade, and the other to remove the effects of signal distortion that occur due to the velocity of the scanning device.     

Integrated high-performance thousand-metre scale cable-stayed bridge with hybrid FRP cables

To overcome the limitations of conventional steel stay cables in a thousand-meter scale cable-stayed bridge, hybrid basalt and carbon (B/C) FRP cables were investigated to achieve integrated high performances in the bridge of this scale as a replacement for steel cables. First, the material properties of different cables were discussed, and static and dynamic analyses on the entire bridges with different cables were conducted by means of finite element method. Moreover, the aerodynamic stability of different cables was studied in terms of the Scruton number. Results show that (1) hybrid B/CFRP with a 28% volume proportion of carbon fibres exhibits relatively high stiffness, economical cost, a small sag effect and sufficient fatigue resistance, which was proven suitable for stay cables; (2) based on the stiffness principle, the cable-stayed bridge with hybrid B/CFRP cables exhibits linear L–D behaviour and higher stiffness compared to the bridge with steel cables under the static load, and this advantage would become more apparent with the elongation of span; (3) the hybrid B/CFRP cable processes much higher natural frequencies than steel cables, which could lower the possibility of resonance between stay cables and the bridge deck. Furthermore, the aerodynamic stability of hybrid B/CFRP cables is superior to other cables due to its designable inherent damping.     

大跨度钢桁梁铁路斜拉桥刚度参数敏感性分析

针对某大跨度钢桁梁铁路斜拉桥方案,采用变化结构刚度方法研究梁、索、辅助墩等构件刚度对桥梁结构及行车性能影响。结果表明,增大桁宽能显著增加桥梁横向抗弯刚度,但对车辆走行性影响有限;增加桁高或斜拉索面积能显著提高桥梁竖向基频、降低车桥竖向响应;桥面系对桥梁结构整体刚度贡献不大,对车辆响应影响有限;设置辅助墩可提高斜拉桥竖向刚度、降低车辆竖向加速度及梁端竖向折角等。     

Development of High-T c SQUID System for Nondestructive Evaluation

Nondestructive evaluation (NDE) system with high spatial resolution power based on high-T _c superconducting quantum interference device (SQUID) has been developed. The SQUID is fabricated by YBCO thin film and mounted in vacuum at the end of a cold finger fixed at the inner wall bottom of the dewar, which is filled with liquid nitrogen (77 K) to cool the SQUID sensor. The sensor faces a thin flat sapphire window on the outer wall of the dewar and is thermally isolated from it by a vacuum space at a distance of less than 1 mm. The magnetic field sensitivity of SQUID is about 40 pT/ Hz in magnetically unshielded environment. This NDE system was used to detect the flaws buried into materials. The remnant magnetic field inducted by the local damages in a stainless steel sample was measured. Incorporated a gradiometric double-D excitation coil, the eddy current NDE was carried out. Small cracks in the aluminum below the surface can be detected effectively in unshielded environment.      

亮化灯具对既有斜拉索风致振动影响的试验研究

为了装点城市夜景,对既有大跨度斜拉桥进行光彩亮化改造已成为一种趋势,但是安装照明灯具将显著改变斜拉索的气动形状,影响结构气动稳定性。为保证结构的安全及耐久性,通过风洞试验研究了安装灯具后斜拉索的抗风性能,评价亮化灯具对既有斜拉索产生的影响。以三种不同管径斜拉索为研究对象,制作了几何缩尺比为1∶1的节段模型,开展了测力和测振的风洞试验。研究结果表明:灯具的存在将显著改变斜拉索的气动外形,提高其背风侧漩涡脱落的频率,使斜拉索在更低的来流风速下就具备发生涡激共振的可能性。此外,灯具对斜拉索风雨激振的影响较为有限,对斜拉索干索驰振有一定的抑制作用。     

钢管混凝土拱桥施工过程中考虑温度效应的预抬高量二阶分析

依照千斤顶斜拉扣挂悬拼架设钢管混凝土拱桥的施工工艺,采用力矩平衡原理推导出扣索索力表达式;在分析温度效应时考虑二阶效应,导出了预抬高量与扣索变形之间的关系。最后,以广西邕宁县邕江大桥为例,采用多个温差段分析温度对预抬高量的影响。研究表明,温差较大时对预抬高量有一定的影响,但二阶效应可略去。     

Electric current injection NDE using a SQUID magnetometer

We built a portable low-cost superconducting quantum interference device (SQUID) magnetometer to be used as the sensing element of an electric current injection NDE system. Using this system, we measured the magnetic fields associated with aluminum plate with single flaws in the millimeter range (2 to 8 mm), at lift-off distances up to ten times the size of the flaw, with injection currents in the order of a few amps. Because the system is at a relatively large distance from the test plate, the signal generated by the flaw is masked by the sinal generated by the edges of the plate. This is independent of the amount of current injected. Due to this, visual inspection is difficult when the distance from the sensor to the flaw exceeds five times its size. To intensify the magnetic field disturbance due to the flaws, we used digital image-enhancement techniques. Applying the enhancement algorithm, magnetic field disturbances were visualized at distances up to ten times the size of the flaw.     

缠绕螺旋线斜拉索气动性能的数值模拟

为研究螺旋线对斜拉索气动性能的影响,采用Fluent软件的LES模块对光拉索和缠绕螺旋线拉索进行数值模拟。首先,建立了光拉索和缠绕螺旋线拉索的数值计算模型,并在拉索轴向布置9个截面的风压和风速监测点;然后,采用Fluent软件的大涡模拟模块进行了数值计算;最后,在数值模拟数据的基础上,研究了螺旋线对拉索平均阻力系数、脉动升力系数、旋涡脱落频率、风压和风速的轴向相关性、绕流流场等的影响。研究结果表明:在风雨激振发生的雷诺数范围内,缠绕螺旋线能减小拉索的平均阻力系数;破坏规则的旋涡脱落,减小脉动升力系数,降低气动力在拉索轴向方向的相关性。     

Modeling and Experimental Studies on 3D-Magnetic Flux Leakage Testing for Enhanced Flaw Detection in Carbon Steel Plates

ABSTRACT

For enhanced detection of flaws in engineering components using magnetic flux leakage (MFL) technique, measurement of the leakage magnetic field components along the three perpendicular directions is beneficial. This article presents the three dimensional-magnetic flux leakage (3D-MFL) modeling and experimental studies carried out on carbon steel plates. Magnetic dipole model has been used for the prediction of MFL signals and images. Sensitivity of the MFL signals peak amplitudes of tangential (H_X), circumferential (H_Y), and normal (H_Z) components with respect to flaw length, width, depth and lift-off have been studied. A 3D-GMR sensor has been used for simultaneous measurement of all the three components of leakage magnetic fields from surface flaws in 12 mm thick carbon steel plates. The experimental MFL images have been compared with the model predicted MFL images. The sensor has shown the capability to detect and image 0.9 mm deep surface flaws with a signal to noise ratio of 8 dB. Principal component analysis (PCA)-based image fusion has been performed for fusion of the 3D-MFL images to obtain a geometrical profile of the flaws. Study reveals that 3D-GMR enhances the capability for detection of flaws having irregular geometries.     

桥面侧振引起的斜拉索空间耦合振动分析

基于Hamilton原理,建立了斜拉索由桥面侧振引起的非线性振动方程,并运用多尺度法求得该方程的近似解析解。结合具体的工程实例,讨论了激励幅值、激励频率、阻尼等参数对拉索振动响应的影响,并与数值方法解进行了对比。研究结果表明,桥面侧振会引起拉索的大幅振动,拉索振动表现出多值性、跳跃等非线性特性。     

Dipole Modeling of Magnetic Flux Leakage

In this paper, we present an analytical model to represent the 3-D magnetic flux leakage (MFL) field due to the occurrence of a surface-breaking defect in a ferromagnetic specimen. This situation is frequently encountered in the nondestructive evaluation (NDE) of energy pipelines using the MFL technique. The model is derived from first principles, and utilizes the concept of dipolar magnetic charge induction to yield the 3-D MFL field in terms of surface integrals. The magnetic flux density in the specimen is assumed to be in the saturation region, and the permeability is assumed to be locally constant in the vicinity of the defect. The model uses just two geometric parameters and is capable of reproducing results that have been obtained experimentally in the literature. 3-D MFL field simulations obtained from the model facilitate a better understanding of the effect of a surface-breaking defect on the magnetic field in its vicinity. Furthermore, we simulate and analyze the 3-D MFL field in the 3-D space around the defect. This analysis yields numerous properties regarding the spatial characteristics of the three orthogonal components of the MFL field of the defect.