Measurement of existing prestressing force in concrete structures through an embedded vibrating beam strain gauge

A steel frame is designed to measure the existing prestressing force in the concrete beams and slabs when embedded inside the concrete members. The steel frame is designed to work on the principles of a vibrating wire strain gauge and in the present study is referred to as a vibrating beam strain gauge (VBSG). The existing strain in the VBSG is evaluated using both frequency data on the stretched member and static strain corresponding to a fixed static load, measured using electrical strain gauges. The evaluated strain in the VBSG corresponds to the existing stain in the concrete surrounding the prestressing strands. The crack reopening load method is used to compute the existing prestressing force in the concrete members and is then compared with the existing prestressing force obtained from the VBSG at that section. Digital image correlation based surface deformation and change in neutral axis monitored by putting electrical strain gauges across the cross section, are used to compute the crack reopening load accurately. (C) 2016 Elsevier Ltd. All rights reserved.

Effect of potassium present in stratum corneum during non-invasive measurement of potassium in human subjects using reverse iontophoresis

Purpose: Reverse iontophoresis (RI) is one of the potential techniques used to monitor the concentration of various analytes in body fluids non -invasively. Transdermal extraction of potassium is investigated using RI. In the present work, the effect of potassium on stratum corneum (SC) during RI, feasibility of RI for continuous monitoring of potassium, and use of potassium as internal standard in RI, are investigated. Methods: Tape stripping experiment is carried out to find potassium concentration in SC. RI is carried out continuously for 180 min without passive diffusion and after passive diffusion for 60 min. Skin impedance measurements are done at 20 Hz and 20 kHz. Results: Potassium is found to be in the range 300-650 nmol/cm(2) on SC by tape stripping experiment. Correlation coefficient between blood potassium and extracted potassium through RI after passive diffusion (R-2 = 0.5870) is more than without passive diffusion (R-2 = 0.5117). The skin impedance measurement shows that RI has more effect on SC than superficial layer of SC during RI. Conclusion: The present investigations conclude that it is possible to monitor potassium continuously through RI and using potassium as internal standard in RI.

Laboratory determination of coefficient of consolidation from pore water pressure measurement

In the recent past, many studies have been carried out on the determination of coefficient of consolidation (c(v)) from the time (t)-deformation (d) data obtained from conventional consolidation tests. Several researchers have also proposed different curve fitting procedures for determining cv from the t-d data. It is anticipated that the cv values obtained from the t-d data may be influenced by initial and secondary compressions. Nevertheless, the pore water pressure data measured during the consolidation process will be independent of initial and secondary compressions. In this study, the conventional Asaoka (1978) method is extended to evaluate cv and end-of-primary (EOP) consolidation from the pore water pressure data measured from laboratory experiments. Laboratory experiments were carried out on the modified one-dimensional consolidation apparatus on different remoulded clay samples measuring pore water pressure during the consolidation process. The cv and EOP computed from the proposed approach have been compared with the results of the t-d data and found to be in good agreement.

Damage assessment of composite plate structures with material and measurement uncertainty

Composite materials are very useful in structural engineering particularly in weight sensitive applications. Two different test models of the same structure made from composite materials can display very different dynamic behavior due to large uncertainties associated with composite material properties. Also, composite structures can suffer from pre-existing imperfections like delaminations, voids or cracks during fabrication. In this paper, we show that modeling and material uncertainties in composite structures can cause considerable problein in damage assessment. A recently developed C-0 shear deformable locking free refined composite plate element is employed in the numerical simulations to alleviate modeling uncertainty. A qualitative estimate of the impact of modeling uncertainty on the damage detection problem is made. A robust Fuzzy Logic System (FLS) with sliding window defuzzifier is used for delamination damage detection in composite plate type structures. The FLS is designed using variations in modal frequencies due to randomness in material properties. Probabilistic analysis is performed using Monte Carlo Simulation (MCS) on a composite plate finite element model. It is demonstrated that the FLS shows excellent robustness in delamination detection at very high levels of randomness in input data. (C) 2016 Elsevier Ltd. All rights reserved.

An out-of-plane linear motion measurement system based on optical beam deflection

Measurement of out-of-plane linear motion with high precision and bandwidth is indispensable for development of precision motion stages and for dynamic characterization of mechanical structures. This paper presents an optical beam deflection (OBD) based system for measurement of out-of-plane linear motion for fully reflective samples. The system also achieves nearly zero cross-sensitivity to angular motion, and a large working distance. The sensitivities to linear and angular motion are analytically obtained and employed to optimize the system design. The optimal shot-noise limited resolution is shown to be less than one angstrom over a bandwidth in excess of 1 kHz. Subsequently, the system is experimentally realized and the sensitivities to out-of-plane motions are calibrated using a novel strategy. The linear sensitivity is found to be in agreement with theory. The angular sensitivity is shown to be over 7.5-times smaller than that of conventional OBD. Finally, the measurement system is employed to measure the transient response of a piezo-positioner, and, with the aid of an open-loop controller, reduce the settling time by about 90%. It is also employed to operate the positioner in closed-loop and demonstrate significant minimization of hysteresis and positioning error.

Thermal Properties Measurement of Micro-Electromechanical System Sensors by Digital Moire Method

The thermal properties of a micro-electromechanical system sensor were analysed by a novel digital moire method. A double-layer micro-cantilever sensor (60 mu m long, 10 mu m width and 2 mu dm thick) was prepared by focused ion beam milling. A grating with frequency of 5000 lines mm- I was etched on the cantilever. The sensor was placed into a scanning electron microscope system with a high temperature device. The observation and recording of the thermal deformation of the grating were realised in real-time as the temperature rose from room temperature to 300 degrees C at intervals of 50 degrees C. Digital moire was generated by interference of the deformed grating and a digital virtual grating. The thermal properties including strain distribution of the sensor and the linear expansion coefficient of polysilicon were accurately measured by the phase-shifted moire patterns.

Temperature measurement of reflected shock wave by using chemical indicator

This report describes a new method for measuring the temperature of the gas behind the reflected shock wave in shock tube, corresponding to the reservoir temperature of a shock tunnel, based on the chemical reaction of small amount of CF4 premixed in the test gas. The final product C2F4 is used as the temperature indicator, which is sampled and detected by a gas chromatography in the experiment. The detected concentration of C2F4 is correlated to the temperature of the reflected shock wave with the initial pressure P-1 and test time tau as parameters in the temperature range 3 300 K < T < 5 600 K, pressure range 5 kPa < P1 <12 kPa and tau similar or equal to 0.4 ms.

DPIV and Interferometry Technique for Velocity Field and Concentration Fields Measurement in Crystal Growth

The property of crystal depends seriously on the solution concentration distribution near the growth surface of a crystal. However, the concentration distributions are affected by the diffusion and convection of the solution. In the present experiment, the two methods of optical measurement are used to obtained velocity field and concentration field of NaClO₃ solution. The convection patterns in sodium chlorate (NaClO₃) crystal growth are measured by Digital Particle image Velocimetry (DPIV) technology. The 2-dimentional velocity distributions in the solution of NaClO3 are obtained from experiments. And concentration field are obtained by a Mach-Zehnder interferometer with a phase shift servo system. Interference patterns were recorded directly by a computer via a CCD camera. The evolution of velocity field and concentration field from dissolution to crystallization are visualized clearly. The structures of velocity fields were compared with that of concentration field.

Interferometric Measurement of Density in Nonstationary Shock Wave Reflection Flow and Comparison with CFD

We present density measurements from the application of interferometry and Fourier transform fringe analysis to the problem of nonstationary shock wave reflection over a semicircular cylinder and compare our experimental measurements to theoretical results from a CFD simulation of the same problem. The experimental results demonstrate our ability to resolve detailed structure in this complex shock wave reflection problem, allowing visualization of multiple shocks in the vicinity of the triple point, plus visualization of the shear layer and an associated vortical structure. Comparison between CFD and experiment show significant discrepancies with experiment producing a double Mach Reflection when CFD predicts a transitional Mach reflection.

High resolution cortical bone thickness measurement from clinical CT data.

The distribution of cortical bone in the proximal femur is believed to be a critical component in determining fracture resistance. Current CT technology is limited in its ability to measure cortical thickness, especially in the sub-millimetre range which lies within the point spread function of today's clinical scanners. In this paper, we present a novel technique that is capable of producing unbiased thickness estimates down to 0.3mm. The technique relies on a mathematical model of the anatomy and the imaging system, which is fitted to the data at a large number of sites around the proximal femur, producing around 17,000 independent thickness estimates per specimen. In a series of experiments on 16 cadaveric femurs, estimation errors were measured as -0.01+/-0.58mm (mean+/-1std.dev.) for cortical thicknesses in the range 0.3-4mm. This compares with 0.25+/-0.69mm for simple thresholding and 0.90+/-0.92mm for a variant of the 50% relative threshold method. In the clinically relevant sub-millimetre range, thresholding increasingly fails to detect the cortex at all, whereas the new technique continues to perform well. The many cortical thickness estimates can be displayed as a colour map painted onto the femoral surface. Computation of the surfaces and colour maps is largely automatic, requiring around 15min on a modest laptop computer.

Real-Time Measurement on Deformation Fields of Hole-Excavated Samples under Impact Tension

In this paper, the real-time deformation fields are observed in two different kinds of hole-excavated dog-bone samples loaded by an SHTB, including single hole sample and dual holes sample with the aperture size of 0.8mm. The testing system consists of a high-speed camera, a He-Ne laser, a frame grabber and a synchronization device with the controlling accuracy of I microsecond. Both the single hole expanding process and the interaction of the two holes are recorded with the time interval of 10 mu s. The observed images on the sample surface are analyzed by newly developed software based on digital correlation theory and a modified image processing method. The 2-D displacement fields in plane are obtained with a resolution of 50 mu m and an accuracy of 0.5 mu m. Experimental results obtained in this paper are proofed, by compared with FEM numerical simulations.