Velocity Constants for Ultrasonic Stress Measurement in Prestressing Tendons

Abstract

There is currently widespread use of high-strength steel tendons for prestressing and post-tensioning of concrete structures and as suspension cables for long-span bridges. Tendons normally consist of one or more seven-wire, helically wound steel strands or solid rods. There are more than 130,000 prestressed bridges in the United States that contain these tendons, and approximately 3,000 new bridges are constructed each year. The prestressing tendons are critical structural elements because the forces in the tendons counteract tensile stresses in the concrete that result from loads acting on a bridge. The tendons are frequently inaccessible for visual inspections and there is currently no accepted nondestructive evaluation technique to assess the condition of these tendons. The goal of this research is to examine ultrasonic stress measurement techniques for the condition assessment of prestressing tendons. This information could be used to compare the actual force in the tendon with its design values to determine if the tendon is performing below expectations. The focus of this paper is the characterization of the relationship between ultrasonic wave velocity and stress level in prestressing tendons. Measurements were made to determine constants that relate the change in ultrasonic velocity to the change in stress. The effects of dispersion in prestressing tendons, which act as circular waveguides for ultrasonic waves, are evaluated.     

A Precision Ultrasonic Phase Velocity Measurement Technique for Liquids

Present paper reports the design and developmental aspects of a new technique for ultrasonic phase velocity measurement in liquids, which is based on the studies carried out on frequency dependence of ultrasonic velocity in pure, binary and ternary liquids/mixtures. The design and developmental aspects of the experimental set up are reported along with optimisation of data acquisition software developed in LabVIEW. Finally, the developed technique is used to measure phase velocity in water (W), aqueous solution of mannitol (M), binary mixture of tertiary butyl alcohol (TBA) in water and a tertiary mixture of TBA + W + M. The results are reported within frequency bandwidth from 3 to 7 MHz. The main reason for selecting these liquids was to identify some of the liquids which can be used as reference liquids for metrological applications. Although, reporting the systematic studies to find out the reference liquid is beyond the scope of the present paper due to obvious reasons, and will be dealt separately, but the studies certainly demonstrate that the technique can successfully be used for phase velocity measurement as a function of frequency and temperature.     

A Method for Determining X-ray Elastic Constants for the Measurement of Residual Stress

Abstract: The X-ray diffraction method is arguably the most convenient method of measuring residual stresses in terms of cost, spatial resolution, measurement time and the accuracy of measurement. The normal methods for calibrating X-ray diffractometers are not conveniently applied to automated scanning systems, however, and so a new approach is required. In this study, a scanning X-ray diffractometer was calibrated and the X-ray elastic constant for a steel alloy was determined using a customised four-point bending rig. The bending rig, in turn, was calibrated by dead loading. This study also described a simple alternative method for determining the X-ray elastic constant, without the use of specialised software. After calibration, the error band of the diffractometer was found to be less than ±10 MPa. As this is ±5% of the yield stress for a typical steel, this level of accuracy was deemed to be acceptable for the measurement of residual stress.     

Ultrasonic Measurement of Stress in Pin and Hanger Connections

Pin and hanger connections are used in bridges to suspend an interior span from the outer spans. The connections can sometimes lock up due to corrosion. If lockup occurs the stresses in the connection are cycled due to thermal expansion and contraction of the bridge; fatigue cracking and failure may occur. We constructed an apparatus to simulate a locked-up pin and hanger connection. We performed proof-of-concept tests of a method to detect stresses in pin and hanger connections. The method uses the stress-induced changes in sound velocity of shear waves polarized parallel and perpendicular to the hanger axis. The birefringence is the normalized difference in these shear wave velocities. We measured the birefringence at opposite sides of the hangers, at midsection. We simulated three scenarios: continuous monitoring of hanger status; intermittent monitoring from a known initial state; measurement with no a priori knowledge of hanger status. Good agreement with strain gauge data was obtained for all three scenarios.     

Ultrasonic Measurement of Stress Using a Rotating EMAT

Abstract

The acoustic birefringence method is primarily used to measure differences of principal stresses in regions where principal stresses coincide with material symmetry axes. To determine the differences of principal stresses also requires knowledge of the unstressed birefringence at the measurement locations. Consequently, variability in texture can introduce errors in stress determination. In contrast, the ultrasonic measurement of shear stress is independent of texture. The shear stress causes a rotation φ of the pure-mode polarization directions of the SH waves used in our experiments. We constructed a motorized electromagnetic-acoustic transducer (EMAT) and used it to measure phase as the EMAT is rotated. We developed an algorithm to determine φ and the birefringence B. We measured the shear stress along parallel scanlines in a residual-stress specimen with known stress state. We calculated the shear stress gradient and used it in the stress-equilibrium equation to determine the normal stress acting along the scanline direction. The other plane stress component was determined from an acoustoelastic relation between B and the difference of normal stresses. Good agreement was obtained with theoretical stress values.     

Ultrasonic Measurement of Stress Using a Rotating EMAT

The acoustic birefringence method is primarily used to measure differences of principal stresses in regions where principal stresses coincide with material symmetry axes. To determine the differences of principal stresses also requires knowledge of the unstressed birefringence at the measurement locations. Consequently, variability in texture can introduce errors in stress determination. In contrast, the ultrasonic measurement of shear stress is independent of texture. The shear stress causes a rotation φ of the pure-mode polarization directions of the SH waves used in our experiments. We constructed a motorized electromagnetic-acoustic transducer (EMAT) and used it to measure phase as the EMAT is rotated. We developed an algorithm to determine φ and the birefringence B. We measured the shear stress along parallel scanlines in a residual-stress specimen with known stress state. We calculated the shear stress gradient and used it in the stress-equilibrium equation to determine the normal stress acting along the scanline direction. The other plane stress component was determined from an acoustoelastic relation between B and the difference of normal stresses. Good agreement was obtained with theoretical stress values.     

管道冲刷腐蚀缺陷对超声测量流体速度的影响

针对管道内流体冲刷腐蚀管壁变薄最终导致管内流体泄漏的问题,采用超声多普勒检测法测量管道内流体速度分布以判断管壁的损伤程度。建立带有缺陷的管道内流体模型,通过CFD数值模拟分析了不同雷诺数以及不同缺陷下管道内流体状态。利用含有不同预制缺陷管壁厚度的有机玻璃作为实验测量对象,超声多普勒检测法测量参量分别为入射频率8MHz,入射角10°。CFD数值模拟以及UVP实验结果均表明,在缺陷不同位置处的流体速度分布具有较大区别,具体表现为在缺陷位置处缺陷越大流体速度分布越平缓;在缺陷临界点位置处产生了涡流现象,随着缺陷的增大和流量的增大,涡流现象将更加明显;在远离缺陷位置后的流体速度分布与缺陷位置前的区别并不明显。     

用声速法在线测量强酸溶液的浓度

超声波技术为化工溶液浓度的测量提供了可能。由于强酸中超声波速度在一定浓度上存在着极值现象，因此超声波测量溶液浓度的技术只适用于某些浓度范围。作者根据超声波速度与强酸溶液浓度的关系提出了一种用声速法测量强酸浓度的方法，该法特别适用于化工厂生产液的在线测量。     

Fiber-Optic Sensor for Web Velocity Measurement

The design and development of a new fiber-optic sensor for measuring the velocity of a continuous material (also called a web) in material processing systems is described. The development of the proposed sensor is based on the dual beam laser Doppler velocimetry technique and the unique properties of different types of optical fibers. The developed sensor is capable of measuring the true web transport velocity as opposed to the existing methods which infer web transport velocity based on the roller angular speed. Since the sensor design utilizes fibers, signal processing can be performed away from the measurement area, and as a result the sensor can be used in harsh environments within the web processing line. The proposed sensor has been constructed and experiments have been conducted on an experimental web platform. The performance of the sensor is evaluated for a range of web velocities and different web materials. Sensor design, its construction, and a representative sample of the results are presented and discussed.     

声学法测量复合绝缘子弹性常数

提出了一种实用的声学法测量复合材料弹性常数的方法.依据复合材料中声波速度与材料弹性常数之间的本构关系,测量不同传播方向的少数几个声速,就可以得到其弹性常数矩阵.以复合绝缘子为测量样品,为提高测量横波的精度,根据超声波在边界上的波型转换条件,使用常规纵波探头对由掠入射纵波产生的横波进行测量.     

Strategies for Reducing Stress in Ultrasonic Cutting Systems

Abstract:  Ultrasonic cutting is an established technology in the cutting of food products. As the high-cost components of an ultrasonic cutting system are the ultrasonic generator and transducer, some designs have concentrated on running several cutting blades from a single power source. This strategy is undoubtedly economic, but problems remain with reliability. Blade failure during cutting is a common problem in ultrasonic systems and therefore strategies are proposed to reduce stress levels at the failure locations. Many alternative blade profiles are investigated using finite element (FE) models, which are validated by experimental modal analysis (EMA) using a 3D laser Doppler vibrometer (LDV). Combining three strategies can reduce the stress level at the failure location on cutting blades. The first investigates the blade profile at the failure location with the aim of incorporating sufficient gain at reduced stress levels. The second concentrates on detuning the block horn and blades in order to move the longitudinal node away from the highest stressed section of the blade. Finally, a redesign of the block horn is studied in order to eliminate the effects of blade flexural vibrations in the longitudinal cutting mode.     

Accuracy Estimation of Propagation Velocity in Variable Path Ultrasonic Interferometer for Liquids

MAPAN - In this article, we describe the effects and the degree to which they cause error in the measurement of propagation velocity. Various effects include nonlinearity in path measurement,...     

激光干涉测速用光电开关

介绍激光干涉仪应用特点及对光电开关的要求。研制了一种普克尔开关和相应的控制系统。开关上升时间 4μs,效率 2 0 0∶ 1,全开时间可按实验要求调整     

Precision Measurement of Fundamental Constants Using GAMS4

We discuss the connection of high-energy gamma-ray measurements with precision atomic mass determinations. These rather different technologies, properly combined, are shown to lead to new values for the neutron mass and the molar Planck constant. We then proceed to describe the gamma-ray measurement process using the GAMS4 facility at the Institut Laue-Langevin and its application to a recent measurement of the 2.2 MeV deuteron binding energy and the neutron mass. Our paper concludes by describing the first crystal diffraction measurement of the 8.6 MeV ³⁶Cl binding energy.     

医用超声诊断仪检定中的问题和探讨

探讨检定医用超声诊断仪声强输出的测量方法,以及如何获得宽频探头的最佳深度和分辨力。     

Ultrasonic Instrumentation for Measuring Applied Stress on Bridges

The measurement of applied stress on bridges can provide valuable information on the condition of the structure. The conventional technique for measuring applied stress is with a strain gage. However, strain gages can be time consuming to install because first the surface must usually be prepared. On a bridge, paint removal will most likely be necessary as part of this surface preparation. When dealing with lead-based paints, which are considered hazardous waste, many time consuming removal procedures are required. Because of these factors, a device that measures applied stress without requiring paint removal could be useful. While a “clamp-on” strain gage can also be used to measure applied stress without requiring paint removal, this type of strain gage can not be used on some bridge details, such as webs of I-beams and tops of box girders. An ultrasonic technique using non-contact electromagnetic transducers provides a possible method for applied stress measurement which is not limited by the same factors as those with conventional strain gages. The transducers operate through nonconductive and conductive (lead-based) paint and work on rusted, pitted surfaces. Our previous research developed a technique for measuring applied stresses on bridges with EMATs and included many laboratory tests. This paper describes field applications of the technique on actual bridge structures, as well as additional system testing and instrument calibration in the laboratory.     

射频同轴电缆衰减常数测量不确定度评定

本文探讨了按照国标GB/T17737.1[1]确定的测量原理、定义和测量方法对射频同轴电缆衰减常数进行检测时产生的测量不确定度的评定,对该检测方法的测量不确定度评定提出了自己的意见和看法,供检测实验室同行参考.     

Texture of Metal-Matrix Composites by Ultrasonic Velocity Measurements

Abstract

An ultrasonic method is developed for the nondestructive characterization of texture in metal-matrix composites. In this approach, it is assumed that the presence of reinforcement particles changes the elastic properties of the composite but only the texture of the matrix. The method utilizes the measurements of the six independent ultrasonic velocities V _ij and the formulation given by Bunge. The examined composites are the silicon carbide (SiC)-particle-reinforced aluminum 8091, 7064, and 6061 metal-matrix composites. The fourth-order expansion coefficients of the orientation distribution function are determined as a function of the SiC content in these composites. The results show that the expansion coefficients change with the presence of SiC where the coefficients C₄ ¹¹ and C₄ ¹³ increase as the volume fraction of SiC is increased and the coefficient C₄ ¹² is zero in all composites examined. The analysis of these results indicates that ultrasonics can provide a promising technique for the texture characterization of metal-matrix composites.