•Full-field strain and strain-rate fields of rock was obtained by high-speed 3D-DIC.•The 256 × 256 pixels and 200,000 fps are suggested in dynamic measurement of rock.•Wave propagation, dispersion ...and radial inertial effect on the specimen were found.•The comparison was conducted between 2D- and 3D-DIC in strain measurement.•The failure of sandstone is a shear mode in the test of split Hopkinson pressure bar.
Full-field strain and strain-rate fields of rock materials under dynamic compression were studied by the high-speed three-dimensional digital image correlation (3D-DIC) method. A series of dynamic tests was conducted on Hawkesbury sandstones using a split Hopkinson pressure bar (SHPB) at three different strain rates. The real-time images of the loaded specimen were captured by two high-speed cameras at a frame rate of 200,000 frames per second (fps) with a resolution of 256 × 256 pixels. Wave propagation, dispersion and radial inertial effect on the specimen were found by DIC results. The strain rate vibration pattern on the specimen, which was visualised by DIC, found to be dependent on the input waveform. A recovery of strain in the post-peak stage was detected on the specimen by DIC, which is unrevealed in the traditional one-dimensional theory method (i.e., strain gauge signals). The results showed that strain localisation initiated from the interface of the bar and specimen with the order of tensile, shear and vertical. The initiation of crack from strain localisation is found rate-independent. Comparison between 2D- and 3D-DIC in strain measurement of the same experiment showed that the error in the strain obtained by 2D-DIC could be up to 32%.
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•Full-field Experimental Modal Identification on high-speed videos.•LSCF eigenvalue stabilization from accelerometer data and LSFD modal constant from high-speed video.•High frequency ...(close to 10kHz) mode shapes.•Identification below the noise level.
Vibration measurements using optical full-field systems based on high-speed footage are typically heavily burdened by noise, as the displacement amplitudes of the vibrating structures are often very small (in the range of micrometers, depending on the structure). The modal information is troublesome to measure as the structure’s response is close to, or below, the noise level of the camera-based measurement system. This paper demonstrates modal parameter identification for such noisy measurements. It is shown that by using the Least-Squares Complex-Frequency method combined with the Least-Squares Frequency-Domain method, identification at high-frequencies is still possible. By additionally incorporating a more precise sensor to identify the eigenvalues, a hybrid accelerometer/high-speed camera mode shape identification is possible even below the noise floor. An accelerometer measurement is used to identify the eigenvalues, while the camera measurement is used to produce the full-field mode shapes close to 10kHz. The identified modal parameters improve the quality of the measured modal data and serve as a reduced model of the structure’s dynamics.
Owing to recent developments in CMOS technology, it is now possible to exploit tomographic microscopy at third‐generation synchrotron facilities with unprecedented speeds. Despite this rapid ...technical progress, one crucial limitation for the investigation of realistic dynamic systems has remained: a generally short total acquisition time at high frame rates due to the limited internal memory of available detectors. To address and solve this shortcoming, a new detection and readout system, coined GigaFRoST, has been developed based on a commercial CMOS sensor, acquiring and streaming data continuously at 7.7 GB s−1 directly to a dedicated backend server. This architecture allows for dynamic data pre‐processing as well as data reduction, an increasingly indispensable step considering the vast amounts of data acquired in typical fast tomographic experiments at synchrotron beamlines (up to several tens of TByte per day of raw data).
The GigaFRoST detector enables high acquisition rates and long scanning times for dynamic experiments.
•Hydrate particle formation and flow experiments in a visual cell.•High speed camera was used to capture the micromorphologies and micro flow behaviors of hydrate particles.•Complete process of ...hydrate agglomeration under flow conditions was captured.•A physical model for the complete process of hydrate particle “agglomeration” was established.
To investigate the microprocess of hydrate particle agglomeration, a high-pressure visual cell was used for repeated experiments of hydrate particle formation and flow from methane + water systems at an experimental temperature of 275.15 K, an initial pressure of 6 MPa and a rotation rate of 200 rpm. During the experiments, a high-speed camera was used to capture the micromorphologies and micro flow behavior of hydrate particles. Based on the experimental data obtained by the high-speed camera, three types of micromorphologies were identified for hydrate particles. Then, the variation in the average diameter of hydrate particles and the characteristics of hydrate particle size distribution were investigated by calculating the equivalent projection area diameter of hydrate particles. During the experiments, particle collision, particle agglomeration and particle breakage were the three main micro flow behaviors of hydrate particles captured by the high-speed camera. The whole process of hydrate agglomeration under flow conditions was also captured by the high-speed camera. Finally, according to the variation in the average diameter of hydrate particles and the micro flow behavior of hydrate particles, a physical model for the whole process of hydrate particle “agglomeration” was established.
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•Improved experimental estimation of full-field FRFs from noisy high-speed camera data.•Hybrid model is formed by mixing two equivalent models using a substructuring ...approach.•Full-field data from a high-speed camera is mixed with accurate accelerometer data to create a single model.•Experiment demonstrates increased consistency of the hybrid model over the whole frequency range.
The use of a high-speed camera for dynamic measurements is becoming a compelling alternative to accelerometers and laser vibrometers. However, the estimated displacements from a high-speed camera generally exhibit relatively high levels of noise. This noise has proven to be problematic in the high-frequency range, where the amplitudes of the displacements are typically very small. Nevertheless, the mode shapes of the structure can be identified even in the frequency range where the noise is dominant, by using eigenvalues from a Least-Squares Complex Frequency identification on accelerometer measurements. The identified mode shapes from the Least-Squares Frequency-Domain method can then be used to estimate the full-field FRFs. However, the reconstruction of the FRFs from the identified modeshapes is not consistent in the high-frequency range. In this paper a novel methodology is proposed for an improved experimental estimation of full-field FRFs using a dynamic substructuring approach. The recently introduced System Equivalent Model Mixing is used to form a hybrid model from two different experimental models of the same system. The first model is the reconstructed full-field FRFs that contribute the full-field DoF set and the second model is the accelerometer measurements that provide accurate dynamic characteristics. Therefore, no numerical or analytical model is required for the expansion. The experimental case study demonstrates the increased accuracy of the estimated FRFs of the hybrid model, especially in the high-frequency range, when compared to existing methods.
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Considering that the direct visualization and real-time control of the laser derusting is challenging mainly in virtue of traditional microscopic procedures, it is very difficult for ...operators to judge the complicated derusting conditions accurately. Acoustic emission (AE) monitoring could be a promising technique to assess the termination of rust removal process, avoid thermal damage of carbon steel substrate efficiently. The AE monitoring and high-speed camera were successfully integrated for reliable investigation of laser derusting mechanism. Dynamic removal characteristics and microscopic changes of rust layer observed and analyzed using AE signals and high-speed images are utilized for further improvement of the mechanism of rust removal by pulsed laser. Based on the spectrum analysis of Fast Fourier Transform (FFT), three characteristic frequency contents including 15˜35 kHz, 65˜85 kHz and 140˜160 kHz of the filtered root mean square (RMS) signals closely associated to laser source impacting on steel substrate or rust layer were determined respectively, which provides the observable AE features relating to the thermal damage of substrate surface. Direct correction between RMS signals and specific laser derusting parameters was established to realize the monitoring of the process of complete rust removal using two representative laser fluences. The FFT was carried out during the same period within 0.3 s in order to validate any changes in the frequency content of 15˜35 kHz relating to the rust removal effect.
•An experimental set-up (a ball between two plates) was designed to study vibro-impact phenomenon.•Motion reconstruction is performed using Digital Image Correlation Technique.•Coefficients of ...Restitution and friction forces are identified reliably.•Results are confronted to simulations using a Hertz-damped model or a Coefficient of Restitution.
Vibro-impact (VI) based control strategies exploit non-linear phenomena occurring during impacts between oscillating masses and vibrating structures to mitigate vibrations. They are known to be effective on a wide frequency range, in harsh environnement, and they are eco-friendly in comparison to some visco-elastic polymers used for the same application. Different assumptions emerge to explain energy dissipation such as material and contact effects, or dynamic energy transfers between the structure and the oscillating masses acting as non-linear absorbers. As classical vibratory measurement tools do not allow to accurately and easily measure what happens in the contact area and the motion of the absorber, it is difficult to validate and quantify the phenomenon. The purpose of the study is to take advantage of full field measurements of the vibro-impact phenomenon to characterise a vibro-impact absorber and to better understand the interactions occurring during impact. To reach this objective, a dedicated experimental set-up has been designed and a method involving Digital Image Correlation (DIC) and a high-speed camera is used to capture and reconstruct the motion of the oscillating mass. The characterisation allows to estimate the Coefficient Of Restitution (COR) and friction forces, and provides data that are used in two different contact modelling strategies based on the COR and on the Hertz contact theory. The quantities identified in this paper enable to better understand the physical phenomena at stakes in a VI absorber.
Orthogonal planing experiments are conducted with high-speed camera recordings and simultaneous cutting force measurements in order to analyze chip formation during machine tool vibrations. By means ...of carefully designed periodic forcing of the cutting tool, non-stationary cutting experiments are performed including wave generation, wave removal and wave-on-wave cutting, which are then compared to stationary cutting tests. The experiments are performed to address how the cutting force is affected by the chip thickness variation, the surface waviness and the fluctuation of the cutting direction. The results are used to assess some theoretical models that involve shear angle variation and chip segmentation.
•Non-stationary cutting experiments are performed by orthogonal planing.•Wave generation, wave removal and wave-on-wave cutting are investigated.•High-speed camera recordings and simultaneous cutting force measurements are evaluated.•The effects of chip thickness variation, surface waviness and cutting direction fluctuation are analyzed.
•The postharvest kiwifruit was modeled as a multiscale body of flesh and skin.•A finite element model was developed to simulate the drop case process.•The stress, force, energy, and bruise behavior ...of kiwifruit were described by FEM.•The compared results showed the low-level errors between simulation and experiment.
Bruising is one of the most common mechanical damages of fruit, but it is difficult to detect quantitatively. In this study, the finite element method (FEM) was utilized to predict the bruise susceptibility of harvested kiwifruit. The elastic-plastic material properties of fruit flesh at different ripening times, including Young’s modulus, bio-yield stress and tangent modulus, were measured using the compression test. Then the fruit were modeled as a multiscale body of flesh and skin, and a finite element model was developed for dropped fruit. The drop scenarios were successfully simulated by FEM, and the results showed simultaneous activities of the simulation and high speed camera recordings. Results of FEM-based simulation showed that the bruise susceptibility increased with ripening time, but that different drop heights resulted in similar levels of bruise susceptibility. In addition, the horizontal orientation would cause higher bruise susceptibility than the vertical orientation. Results of accuracy analysis showed that the hourglass energy in any of the simulation scenarios kept in a very low level (<5%). The maximum errors between simulation and high speed camera recordings were 5.0%, 19.0% and 11.9% for initial velocity, maximum deformed length and contact time, respectively. Compared with experimental measurement, the maximum errors of simulation were 17.1% for bruise volume and 18.3% for bruise susceptibility. The results confirmed the FEM was reliable for prediction of bruise susceptibility of the fruit, and would be an effective approach to further investigate the bruise damage.
Increased interest has been witnessed for full-field techniques measuring vibrations. 3D vision methods coupled to two high-speed cameras have proven to be a valid solution to measure 3D ...displacements, notably with the Stereo Digital Image Correlation (SDIC) tools. The now conventional pseudo-stereo system with a single high-speed camera and a four-mirror adapter, generating two virtual cameras, may also be used, even if it is rather complex to operate and remains limited to small objects. In a logic of simplification of the protocol, the authors present here a set-up requiring a single high-speed camera and no mirrors, with the associated full-field single-axis vision method. The latter is logically designed to measure the vibrations of items whose displacements are locally along a single axis (usually normal to the surface). This paper reports firstly the results of the full-field measurement of the vibrations of a plate, validated by a comparison with those obtained with the four-mirror adapter set-up, and secondly the application to the full-field measurement of the vibrations of a tambourine. Thirdly, the conventional pseudo-stereo technique and the proposed vision method are compared and assessed, in order to establish their respective limits and potential complementarity. Finally, once the application of the method to plane objects is validated, measurements have been carried out on a non-planar object: a bent plate; the results obtained highlight the possibility of using the proposed approach for non-planar surfaces.
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