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Measuring the deflection of bridges in service is crucial for monitoring their structural health conditions. Recently, the image measurement method has been developed to measure the bridge deflection, wherein the camera for taking images is installed at a distant place where the target bridge can be seen. In this study, we developed a simple but effective optical method to measure the out-of-plane displacement of a bridge, which could not be done before, from the images captured with a camera installed under the bridge. The proposed method converts the virtual in-plane displacement evaluated from the sampling moiré measurement into the out-of-plane displacement under the assumption that the target bridge and the reference point move in the in-plane direction as a rigid-body deformation, or the in-plane displacement is absent or negligible. In field experiments to measure the deflection of a viaduct during the passage of a high-speed train (Japanese Shinkansen) with a speed of 320 km/h, we successfully measured the bridge deflection less than 1 mm from images recorded with a camera installed under the bridge floor. When comparing the difference in deflections measured from the proposed method and a conventional Laser Doppler vibrometer, the average absolute difference was less than 0.05 mm. Our developed method is simple and cost-effective, making this technique very efficient in structural health monitoring of elevated railway or road bridges. [ABSTRACT FROM AUTHOR]

Measuring accurate dynamic deformation distribution for large-scale structures inexpensively and efficiently is a crucial challenge of structural health monitoring. In this study, a simple technique for measuring the deflection and vibration frequency from a captured video, based on the sampling Moiré method is developed. The striking advantage over conventional measurement using sensors and other imaging techniques are that the developed technique allows accurate measurement of two-dimensional deformations at multiple locations as well as the natural frequency of the target structure. Joint Photographic Experts Group (JPEG)-formatted images encoded from the recorded video with Motion-JPEG (MJPEG) format reduced the file size significantly without degrading the measurement accuracy and applied to deformation measurement. The effectiveness of the developed technique was confirmed through a field experiment of an old bridge in Taiwan. The field experiment demonstrated that both deflection and natural frequency of the bridge were successfully measured with higher 0.1 mm displacement accuracy and 0.05 Hz frequecy comparable to a conventional microwave radar displacement sensor from 20 m distance. [ABSTRACT FROM AUTHOR]

Residual deformation evaluation of underfill (UF) materials in flip chips is crucial to improve the reliability of electronic packages. In this study, we propose to evaluate the residual thermal strain distributions using an inverse method based on the sampling moiré technique. Even if a grid pattern is fabricated on the specimen at room temperature, the residual strain distributions at an arbitrary temperature relative to the specimen formation temperature can be successfully calculated. The residual strain distributions relative to the free contraction state at an arbitrary temperature can also be measured when the coefficient of thermal expansion is available. A thermal chamber for flip chips was designed under a laser scanning microscope. Using the proposed method, the normal, shear and principal internal strain distributions and deformation characteristics of two kinds of UFs in flip chips were investigated relative to 150 °C. The strains of the UF with low glass transition temperature (UF-A) concentrate near the die material, especially at the die corner, while the strain concentration of the underfill with high glass transition temperature (UF-B) mainly occurs at the die corner and the buffer layer. The maximum principal strain of UF-A is greater than that of UF-B around the die corner. The residual maximum principal strain distributions relative to the free contraction state at 25 °C were compared with the simulation results by the finite element method. The residual strain distribution trends from experiments are consistent with those from simulations. [ABSTRACT FROM AUTHOR]

Fast and accurate deformation measuring techniques show promising potential for monitoring high-temperature piping and other machinery in the energy sector, such as in thermal, steam, or nuclear power plants. Optics-based, nonintrusive, and real-time monitoring systems are critical for preventing high-temperature steam leaks, unexpected accidents, explosions, and other failures that can have catastrophic consequences for the power supply, the workers, and the public. In this study, a dynamic thermal deformation measurement technique utilizing the sampling Moiré method and grating magnets is developed for large-scale, high-temperature piping in a thermal power plant. Because of the high temperature of the piping of nearly 300 °C several 100 mm by 100 mm ferrite magnets were placed to select locations of the high-temperature piping. In each ferrite magnet, a regular, two-dimensional binary grating pattern with a pitch of 15 mm was painted on the surface, and the grating magnets were used as the reference grating to analyze the small in-plane displacement distribution using the sampling Moiré method. A compensation method of misalignment angle is also proposed to improve the measurement accuracy. The effect on vibration remove, mirage due to conversion in air, wide angle of camera lens, and compensation of misalignment angle, are discussed. The experimental results showed that our measurement technique is suitable for evaluation of high-temperature, large-scale infrastructure. [ABSTRACT FROM AUTHOR]

Measuring accurate displacement distributions for large-scale structures is an important issue and a very challenging task. Recently, a simple and accurate phase measurement technique called sampling moiré method [Exp Mech 50-4:501-508, ()] has been developed for small-displacement distribution measurements. In this method, the phase distribution of moiré fringes can be analyzed from a single grating image by simultaneously performing down-sampling image processing and intensity-interpolation to generate multiple phase-shifted moiré fringe images. In addition, the phase of the original grating can also be obtained from the phase of the moiré fringe by adding the phase of the sampling grating. In this study, the measurement accuracy of the sampling moiré method was analyzed through computer simulations and a displacement measurement experiment. Four factors of the sampling moiré method were investigated, including the sampling pitch, the order of the intensity-interpolation, random noise, and the form of grating. The results show that determining the optimal sampling pitch is an important factor for obtaining better results but it is not critical. In addition, a practical application of the sampling moiré method is presented that involves a deflection measurement on a 10-meter-long crane. The experimental results demonstrate that submillimeter deflections of the crane can be successfully detected. [ABSTRACT FROM AUTHOR]

In this paper, a novel accurate deformation distribution measurement technique by using sampling moiré method is proposed. The basic principle and an experimental result of a steel beam in symmetric three-point bending are reported. In this method, the measurement area of a target is attached with an adhesive tape of a known pitch grating firstly. An ordinary CCD camera is installed on a fixed point to record the image during deformation. The captured image is analyzed by performing easy image processing, i.e., thinning-out and linear interpolation, to obtain the multiple phase-shifted moiré patterns. Then, the phase distribution of the moiré pattern can be calculated using phase-shifting method. Finally, the deformation distribution is calculated by the grating pitch times the phase difference of before deformation and after deformation. The experimental results in symmetric three-point bending test show that the displacement of the steel beam at loading point agree well with those obtained by an accurate displacement sensor. The average error of displacement measurement is less than 4 μm when 2 mm grating pitch is used, and it corresponds to 1/500 of the grating pitch accuracy. This indicates that noncontact deformation distribution measurement is possible by simple and easy procedure with high accuracy, high speed, and low cost for the structural evaluation of infrastructures. [ABSTRACT FROM AUTHOR]

DMD (Digital Micro-mirror Device) is a new device, which has hundreds of thousands of micro-mirrors in one chip. We developed a DMD reflection-type CCD camera that we call ‘DMD camera’ previously. In this optical system of the DMD camera, each mirror of the DMD is corresponded to each pixel of the CCD. As a result, each DMD mirror works as a high-speed controllable shutter of the corresponding CCD pixel. However, corresponding each mirror of the DMD to each pixel of the CCD cannot readily be done since the pixel sizes of DMD and CCD are very small. In this paper, a pixel-to-pixel correspondence adjustment method, which can perform accurate adjustment of the DMD camera optical system by moiré methodology is proposed. The proposed method is easy and visual by observing the moiré pattern. This method enables DMD camera to adjust pixel-to-pixel correspondence less than one pixel accuracy of the CCD. An experiment of phase analysis to demonstrate the improvement of the resolution and accuracy was performed. [ABSTRACT FROM AUTHOR]