Inspection of Quebec Street Bridge in Denver, Colorado: Destructive and Nondestructive Testing

Nondestructive testing techniques have been historically and commonly used to evaluate the quality of existing concrete structures. Several traditional nondestructive testing techniques were applied to the pier caps of the Quebec Street Bridge over Air Lawn Road, constructed in 1971, which is located in Denver, Colorado. The techniques utilized included visual inspection, hammer sounding, Schmidt hammer rebounding, and ultrasonic pulse velocity testing, including tomographic imaging. Results of the nondestructive tests were used to determine areas to be tested with local destructive tests. These tests included concrete compressive strengths, chloride testing, and petrographic testing. This paper presents the application and interpretation of common nondestructive testing techniques and the consequent repair, rehabilitation, and maintenance decisions. The overall results indicate that inside cores of all the pier caps are healthy, sound concrete. On all of the pier caps, extensive exterior concrete layer rehabilitation needed to be completed.     

X光影像仪光采集系统的研制

X光影像仪的光采集系统是X光影像仪的核心。本文介绍了X光影像仪的光采集系统的原理以及在提高光采集系统的荧光收集率和采集信号的信噪比和提高图像处理质量方面的努力。     

DR图像缺陷检测的彩色合成方法

数字式X射线(DR)图像难以用一幅灰度图像同时显现不同壁厚部件的缺陷。为此,提出用一幅合成彩色图像显现缺陷的方法。对DR系统扫描铸件得到的浮点型数据,采用分段灰度拉伸的方法转换为3幅灰度BMP图像,其中,不同灰度段的图像含有被测铸件不同壁厚部件的缺陷,再将这3幅灰度图像合成为一幅彩色BMP图像。对其应用彩色C-V(Chan-Vese)模型分割缺陷,实验结果证明,该彩色合成方法能较好地分割出被测铸件不同壁厚部件的缺陷。     

铁路铸件DR图像缺陷的亚像素测量方法

根据DR图像目标边缘模糊、对比度低的特点,将小波多尺度分解与基于水平集演化的CV模型相结合,由此加快主动轮廓线向缺陷边缘收敛的速度,通过改进亚像素线性插值方法,使分割精度从整像素级提高到亚像素级,从而实现缺陷的亚像素测量。仿真结果表明,该方法的测量精度优于传统方法,对实际铸件DR图像的实验结果验证了其高效性。     

固体火箭发动机切线照相的漏检率研究

给出固体火箭发动机切线照相漏检率的计算方法，并阐明了在实际切线照相中脱粘弧长和脱粘宽度与漏检率的关系。     

Imaging by using proton-induced quasi-monochromatic X-ray emission

Quasi-monochromatic X-ray emission induced by MeV-proton bombardment onto metallic targets was applied to radiography of small samples. The X-ray energy was adjusted in the range of ≈4–23 keV by changing the target material. The radiograms were recorded on an imaging plate. A small phantom made of Lucite was prepared for the test of photography using a contrast medium (RuCl₃·H₂O; ruthenium chloride). To clearly observe the image of the contrast agent, the photon energy was chosen to be 23.17 keV (Cd Kα) which is slightly above the K-absorption edge of Ru at 22.12 keV. Only the image of the contrast agent was successfully extracted by subtracting the image taken by 21.18-keV X-rays (Pd Kα) from that obtained by the 23.17-keV photons. Also images of a small fish sample were taken using a point-like X-ray source excited by a proton microbeam with a diameter of ≈10 μm. In this experiment, the X-ray energy was adjusted to 4.51 keV (Ti Kα) to obtain a strong attenuation by Ca in the bones. A fine structure of the bones in the thin caudal fin (<100 μm) was highly contrasted by this method. The spatial resolution of the picture was ≈20 μm. Performance of the above technique based on the proton-induced quasi-monochromatic X-ray emission is discussed in comparison to conventional methods.     

Quantification and Simulation of Particle Kinematics and Local Strains in Granular Materials Using X-Ray Tomography Imaging and Discrete-Element Method

Microfeatures of granular materials have significant effects on their macrobehaviors. Unfortunately, three-dimensional (3D) quantitative measurements of microfeatures are rare in literature because of the limitations of conventional techniques in obtaining microquantities such as microdisplacements and local strains. This paper presents a new method for quantifying the particle kinematics and local strains for a soft confined compression test using X-ray computed tomography and compares the experimental measurements with the simulated results using the discrete-element method (DEM). The experimental method can identify and recognize 3D individual particles automatically, which is essential for quantifying particle kinematics and local strains. 3D DEM simulations of the soft confined compression test were performed by using spherical particles and irregular particles. The simulated global deformations and particle translations that were based on irregular particles showed better agreement with the experimental measurements than those that were based on spherical particles. The simulated movements of spherical particles were more erratic, and the material composed of spherical particles showed larger vertical contraction and radial dilation.     

Design of a stereoscopic X-ray imaging system using a single X-ray source

The design of a prototype binocular stereoscopic X-ray imaging system for a security screening application is presented. This is based on an innovative technique [Evans JPO, Robinson M, Godber SX. A new stereoscopic imaging technique using a single X-ray source: theoretical analysis. NDT&E International 1996;29(1):27–35] utilising a single X-ray source and a pair of linear X-ray detector arrays. The image data is collected whilst the object under inspection is linearly translated past the X-ray detectors. The machine constructed enables approximately one cubic metre of object space to be imaged in five seconds. The resultant images may also be used for the extraction of three-dimensional coordinate information.     

钛合金焊缝X射线照相底片黑度对灵敏度的影响

分析了钛合金焊缝Ｘ射线照相底工对度灵敏度的影响,试验表明,底片的黑度应限制在比标准要求要窄的范围内。     

Effect of Fine Particle Migration on the Small-Strain Stiffness of Unsaturated Soils

The paper presents the results of an experimental investigation of fine particle migration from pore body to the pore throat and toward the contact between particles and its effect on skeleton stiffness of granular materials. We hypothesize that the suspended colloids in the pore fluid migrate and deposit on the contact surface between the skeleton-forming particles and change the magnitude of the soil stiffness. Three specimens were prepared using uniform spherical glass particles that were saturated with deionized water and kaolinite or silt-base slurries. The specimens were drained by evaporation which retained the fines in the soil while increasing the matric suction. Changes in soil dynamic stiffness were evaluated using piezoelectric transducers while the migration of fines and the changes of the properties of the pore fluid were monitored using synchrotron X-ray microcomputed tomography (SMCT) on identical specimens. The wave propagation experiments show that the stiffness of the tested specimens increased at different rates during the drying processes. These measurements were complemented with SMCT scanning analysis that shows an increase in mass density of the remaining slurry as the pore fluid concentrated near the particle contacts. The results indicate that the soil stiffness increase due to the alteration of the pore fluid at the particles’ contact and changes caused at the contact behavior itself. These results provide an insight about parameters that influence soil stiffness which may help in better predictions of stiffness changes in compacted soils during moisture changes.