Video Gauge Research Articles

Cracking and deformation of cuboidal sandstone with a single nonpenetrating flaw under uniaxial compression

To get a good understanding of the cracking mechanism of a nonpenetrating flaw, digital carving technology was employed to pre-cut a nonpenetrating flaw within a rock block. Uniaxial compression tests were conducted on the specimens containing a single nonpenetrating flaw. A strain measuring system was employed to monitor the local microstrain near the flaw tips. Meanwhile, the failure process of specimens was recorded simultaneously using a video camera and the noncontact video gauge. Based on the experimental results, the crack propagation behaviors and the fracture characteristics of the nonpenetrating-flaw sandstone specimens during uniaxial loading were presented. Also, the relationship between peak strength and pre-existing flaw angle was shown. Furthermore, numerical models containing a penetrating or nonpenetrating flaw were developed using 3D particle flow code to investigate the crack propagation mechanisms under uniaxial compression. By comparing the contact force distribution and the principal stress distributions around pre-existing nonpenetrating or penetrating flaw just before crack initiation, the crack initiation and propagation of sandstone specimens containing a single nonpenetrating flaw was explained from the microscopic point. It is found that (a) the average peak strength increases with the growth of nonpenetrating flaw angle and reduced by 21.8% for 0°, 16.0% for 30°, 13.0% for 45°, 4.7% for 60°, and 0.5% for 90° comparing with the peak strength of the intact specimen; (b) the crack first appears at the flaw tip on the front surface and then a new crack appears in the middle of the flaw on the back surface, the tensile stress gradually decreases from the front to the back; (c) the local strain at the front surfaces of the pre-existing flaw tip is greater than that at the same position on the back, the flaw tip of the model front is prone to stress concentration; (d) the final failure pattern relies on the pre-existing flaw angle and as the pre-existing flaw angle increases, the failure mode changes from mixed tension and shear failure to shear failure.

Experimental research on the aerodynamic responses of a long-span pipeline suspension bridge

The aerodynamic stability performance of a long-span pipeline suspension bridge is studied based on a 1: 25 full-bridge aeroelastic model using wind tunnel tests. The influences of initial angle of attack, pipeline diameter, pipeline number, and turbulence intensity on the aerostatic and buffeting displacements of the girder, and on the wind cable tensile forces are comprehensively investigated. The aerodynamic displacements of the girder along the span were measured by using a video gauge. Analytical expressions are derived to construct the displacements of three-degree-of-freedom motions from the recorded signals, and the differences between the derived formulas and the conventional ones are demonstrated. Recommendations are offered to reduce or even eliminate the potential errors of the convenient habitual formulas. The testing results show that the aerodynamic displacements and wind cable tensile forces of the bridge may depend remarkably on the initial angle of attack, pipeline diameter, pipeline number, and turbulence intensity. Research results of the present work can provide beneficial references for evaluating the wind-resistant performances of bridges of the similar type.

The application of track deflection measurements made by video gauge

This paper presents direct track deflection data measured using a video gauge (VG) (a digital image correlation (DIC) method) to determine track stiffness characteristics remotely. Two cases are discussed. First, the deflection performance of two novel ballastless trackforms are coupled with an analytical model to assess their stiffness properties for known train loads. Second, the performance of a bridge transition is evaluated under live train passages by the VG; the traffic loads are assumed based on train type to allow track stiffness interpretation from a number of train passes. A track deflection bowl is assessed to show the performance of the transition. The paper initially discusses the DIC technique and the importance and assessment of track stiffness. It then presents the VG deflection data, the global support stiffnesses and deflection bowls. These novel methods are shown to be consistent with other approaches of track stiffness evaluation. The paper concludes with a discussion of how this methodology can be utilised in the railway industry for assessing the trackbed performance of critical zones without the need for track possessions.

Application of the Non-Contact Video Gauge on the Mechanical Properties Test for Steel Cable at Elevated Temperature

As the limit of traditional contact measurement, it is difficult to precisely measure the steel cables twisted by a branch of wires especially at elevated temperature. In this paper the strain-stress relationships of S355 and S690 structural steel, 1860 MPa steel cable twisted by seven wires have been measured by the strain gauge, extensometer and non-contact video gauge at ambient temperature and elevated temperature, respectively. Comparison of the stress-strain curves gotten by different measuring technology, it indicates that the non-contact video gauge can provide a more efficient and reliable database than the strain gauge as well as extensometer, especially at an elevated temperature. It is worth noting that the non-contact video gauge can capture not only the full range of stress-strain curves of steel cables, but is also efficient for the specimens with a complex shape.

Experimental tools for railway crossing condition monitoring (crossing condition monitoring tools)

Two experimental tools to measure the railway crossing dynamic responses are presented. One system is ESAH-M equipped with a 3-D accelerometer and a speed detection sensor that featured for crossing instrumentation and characterised by fast installation/uninstallation, automatic data recording and processing. The other system is a Digital Image Correlation (DIC) based Video Gauge System (VGS) that record the dynamic displacements of the rail/sleepers. A number of measurements have been performed aiming to explore the feasibility of these experimental tools, establish the relation between the measured dynamic responses and condition of the monitored crossings and estimate the effectiveness of crossing maintenances.The measurements based on crossing instrumentation show that the crossing degradation process can be described using the dynamic responses. The wayside monitoring in different problematic track sections have shown the capability of detecting and quantifying ballast conditions. Both systems will be further applied in long-term monitoring of railway crossings.

Mixed mode fracture properties of GFRP-adhesive interfaces based on video gauge and acoustic emission measurements from specimens with adherend fibres normal to the interfaces

Mixed-mode bending tests were performed on fifty-three GFRP-adhesive-GFRP specimens. In each specimen the pre-crack was located near the GFRP adherend with fibres normal to the GFRP-adhesive interface, so as to encourage crack propagation along this interface rather than through the GFRP. The other GFRP adherend contained fibres parallel to the interface, leading to asymmetry of GFRP material (but not of specimen geometry) with respect to the adhesive layer in each specimen. This switching, across the adhesive layer, between normal and parallel fibres in the adherends, reflects a T-joint detail considered for a wave energy device. All tests used a video gauge system to measure crack propagation. Some tests also employed an acoustic emission (AE) system. Comparisons between the AE results and the video gauge-based crack propagation data strongly suggest that the AE energy vs time curve is a much clearer indication of crack initiation than is the widely used AE hit count vs time curve. Increase in Mode II ratio during the tests led to fewer but larger post-peak load drops. Williams's approach, based on beam theory for asymmetric sections with correction factors for large displacements and shear deformation included, led to fracture toughness (G(c)) values in the range 0.3-2.8 kJ/m(2), with a trend of increasing Gc values as pure Mode II is approached. The ASTM approach, developed only for symmetric specimens, gave much lower Gc values. (C) 2017 Elsevier Ltd. All rights reserved.

Hyperelastic polymer material models for robust fatigue performance of automotive LED lamps

The object of this paper is to determine the statistics of parameters of hyperelastic models specific to Polybutylene Terephthalate filled with 30% glass fibre (PBT GF30) and Polymethyl Methacrylate (PMMA) materials used in automotive lamps. The hyperelastic behaviour of both materials, a semi-crystalline and an amorphous, is modelled using appropriate hyperelastic models. The stress-strain curves of the materials were measured under uniaxial tension using a non-contact video gauge. Five samples each were tested to measure the effect of manufacturing variability. The model parameter statistics were determined, the mean value of the model parameters were used to construct average stress-strain behavior, which is then compared to the experimental stresses. Among all the models and their associated parameters studied, the 3-parameter Mooney-Rivlin model provided the most accurate prediction of the behaviour for both materials. The model showed excellent stability and is therefore the most appropriate model to represent variations due to the manufacturing process. The detailed study of the correlation of the model parameters provided a good understanding of how the parameters are related to each other, enabling construction of complete probability distribution functions for further analysis.

Potential for external reinforcement of insulated rail joints

This paper aims to investigate the alternative ways of reducing the deterioration and failure of insulated rail joints of railway tracks. Joints deteriorate faster than rails due to the presence of structural discontinuity. This weakness results in extra displacement due to the applied load and dynamic force that results as a consequence. Overtime, this situation worsens as the impacts and applied stresses damage and soften the ballast and the supporting subgrade under the joint. This study initially presents a static finite element model designed to simulate the mechanics of insulated rail joints, and then a comparison is made between the plain rail and a suspended insulated rail joint under various support stiffnesses. The product design options of the reinforced insulated rail joints are then chosen as input variables of the model. The results of the model are compared with the field and laboratory data acquired via the Video Gauge, which is a new high-resolution optical measurement technique. The results show that the use of strap rails or more robust I-beam sections in the vicinity of the insulated rail joint to stiffen the support structure can significantly reduce the displacement and the subsequent dip angle seen in an insulated rail joint. This potentially presents a means of improving the behaviour of the insulated rail joints. Their impact becomes more significant for soft support conditions. Although these results are indicative of new conditions for insulated rail joints, the field measurements indicate that the magnitude of deflection of insulated rail joints is a result of the structural discontinuity of the rails, the dynamic P2 force, the wheel condition, the degraded ballast and it significantly increases with time under repeated load. Thus, it is recommended that a careful field implementation and testing will indicate the effect of an external enhancement on the timely degradation of insulated rail joints.

Failure Mechanism of Foamed Concrete Made with/without Additives and Lightweight Aggregate

It has been reported that owing to a densification of the internal structure of concrete, adding mineral admixtures leads to a more brittle behaviour. Therefore, with the intention of modifying (increasing the strength of) foamed concrete to make it suitable for structural purposes by means of admixtures and lightweight aggregate addition, the effect of these additions on the failure mechanism under compressive and tensile loading using different techniques is evaluated and discussed in this paper. Eight different mixes, made using a pre-formed foam, were investigated with varying density (different foam volumes), nominally 1300, 1600 and 1900 kg/m3, without/with admixtures (silica fume, fly ash and superplasticizer) and lightweight aggregate. The Digital Image Correlation (DIC) technique was adopted to measure the deformations and strains on the surface of a specimen under uniaxial compressive load. Meanwhile, a Video Gauge technique was used to measure the horizontal deformation of discs during a splitting tensile test. From elasticity, fracture and fractal points of view, it was found that, for the same density, brittleness increases with many of the additives while it reduces with inclusion of lightweight aggregate. However, for all mixes, the lower the density (higher added foam volume), the higher the ductility.

Uncertainty analysis of displacement measurement with Imetrum Video Gauge

Imetrum Video Gauge is a commercial image-based two-dimensional displacement measurement system which has been widely used. Its uncertainty analysis is presented in this paper. First, the procedure to use Video Gauge is introduced. Then, based on the measurement model, two major sources of uncertainty are identified: (1) the uncertainty associated with the calibration procedure u(C) which is composed of the uncertainty of the known length used in calibration u(L) and the uncertainty of the projection of the known length in the image u(D) and (2) the uncertainty associated with the measurement system itself u(P). Following the Guide to the Expression of Uncertainty in Measurement, the uncertainties can be quantified. In the end, 60 experiments are performed to analyze the relationship between the measurement uncertainty and the working parameters, which are working distance, acquisition frequency and focal length of the lens. In order to ensure the validity of the calculation, two calculation methods are used. The main results of this paper are as follows: (1) the displacement measurement uncertainty increases along with working distance and decreases with the increase of focal length. At the same time, the results indicate that using a longer known length in calibration can also reduce the measurement uncertainty. (2) u(C) is greatly influenced by the known length used in the calibration procedure. It can be reduced when u(L) is reduced. (3) Under the laboratory circumstances, reducing u(C) can greatly reduce the total measurement uncertainty. (4) The displacement measurement uncertainty is more sensitive to the measurement uncertainty of the known length used in calibration than the projection of the known length in the image. (5) As the working distance grows, the sensitivity to the known length is getting weaker and the sensitivity to the projection of the known length in the image is getting stronger. (6) When a longer focal length lens is used, the influence of the working distance to the sensitivity gets weaker. The reported results can help people better understand the characteristics of this system and better use the system for their own purposes.

Mechanical and magnetocaloric properties of Gd-based amorphous microwires fabricated by melt-extraction

We report a systematic study of a new class of melt-extracted Gd53Al24Co20Zr3 amorphous microwires in terms of fabrication, structural characterization and evaluation of mechanical and magnetic properties. The tensile properties of the wires are characterized by a precision video gauge method and analyzed using the Weibull and lognormal methods. The three-parameter Weibull model and lognormal model based on the median rank value show consistent results and prove to be superior to the two-parameter Weibull model for the studied microwire with a smaller variation. The statistical mean tensile strength and fracture strain are calculated to be ∼1200MPa and ∼2.0%, respectively, which are comparable with those of other metallic glasses. Remarkably, the microwires exhibit a large and reversible magnetocaloric effect (MCE), with the isothermal magnetic entropy change (−ΔSm) and refrigerant capacity (RC) reaching the large values of 5.32Jkg−1K−1 and 467Jkg−1 for a field change of 3T. Albeit with a low Curie temperature, these values are superior to those reported for pure Gd and other Gd-based bulk or ribbon-shaped glasses. The mean field model-based and Langevin function analyses reveal that the second-order magnetic transition behavior of the studied wire originates from the local anisotropy associated with the fine size of the wire and derogation and fluctuation of the exchange integral. These results demonstrate the adaptability and overall excellence of the newly developed Gd-based microwires, making them multifunctional elements for MCE-based cooling applications, especially for liquid nitrogen liquefaction.

BREAKING CRITERIA FOR LABORATORY EXPERIMENTS BASED ON THE PHASE-TIME-METHOD (PTM)

Breaking waves generated by focusing of transient wave packets have been analyzed. By a comparison of video data and gauge measurements the threshold frequency for the use of the PTM as a breaking criterion is derived. The present result is slightly higher than the original value of Zimmermann & Seymour (2002) for spilling breakers, but confirms the results of Irschik & Oumeraci (2006). Additionally the use of the zero down-cross period Tz instead of the peak period TP is investigated. Both definitions lead for the present conditions with plunging breakers to almost identical results.

The ideal flip-through impact: experimental and numerical investigation

Results from a physical experiment and a numerical computation are compared for a flip-through type wave impact on a vertical face, typical of a seawall or breakwater. The physical wave was generated by application of the focused-wave group technique to the amplitudes of a JONSWAP spectrum, with the focus location adjusted to produce a near-breaking wave impact with no discernible air entrainment or entrapment. Details of the resultant impact are presented in the form of high-speed video, pressure transducer and wave gauge records. Numerical reproduction of the wave transformation and impact is achieved by application of a linear wave-analysis model and a fully nonlinear potential-flow solver. Although more advanced models exist, use of the latter model type is interesting as (1) it was applied by Cooker and Peregrine (Proceedings of the 22nd International Conference on Coastal Engineering, 164–176, 1990) in their original numerical discovery of the flip-through impact and (2) the assumptions behind the potential-flow model remain reasonably valid, until the flip-through jet begins to break into droplets. In the present study, the potential-flow model has been extended with the Schwarz–Christoffel conformal mapping, to allow a piece-wise linearly shaped mound geometry. Further, an ad-hoc wave-generation technique has been added, to facilitate an adequate numerical reproduction of long second-order waves in the flume. Free-surface elevations from the potential-flow computations show good agreement with wave gauge data for the wave that produces the flip-through impact. Experimental video frames with the corresponding numerical free-surface profiles overlaid show an excellent match for the flow contraction prior to impact. The deviations between the experiment and numerical solution that occur at the stage of jet formation are discussed and a computation of a slightly weaker impact illustrate the strong sensitivity of impact pressures to the shape of the impacting wave. Ways of improving the numerical description by use of more advanced models are outlined.