Pairs Of Strain Gauges Research Articles

Strain-based multi-dimensional force sensing system for robotic friction stir welding

Accurately measuring the force in friction stir welding (FSW) is essential for monitoring and controlling the welding process. However, current research primarily focuses on force sensing in gantry FSW equipment, which has limited demand compared to FSW robot. Commercial force sensors are mostly designed for six-axis welding robot and lack for high-force hybrid FSW robot. To address this gap, we developed a wireless multi-dimensional force sensing system for hybrid FSW robot. Our system utilizes elastomer and incorporates 8 pairs of strain gauges to detect tiny deformations. Through calibration, we achieved a wider measurement range than most commercial sensors, ensuring high accuracy with low cross-talk. Extensive testing determined the static and dynamic characteristics of the system. We performed robotic FSW experiments, analysing the force/torque characteristics in each direction and investigating the effects of welding speed and plunge depth on axial force. The results demonstrate the stability and practicality of our system.

Design of the System for Measuring UAV Parameters

This article deals with the design and creation of a tensometric measuring system to measure the parameters of an unmanned aerial vehicle (UAV) of the quadcopter type. The system was designed to measure the total UAV thrust and the thrust of its individual motors. The distribution of forces from the UAV motors and their transmission to the sensors was ensured by a specially designed construction, for which the mechanical stresses were simulated and analysed for different modes of the UAV flight. The thrust measurement was performed by four pairs of strain gauges. A measurement system designed in this way and the measured parameters of the UAV can be used for tuning the flight control algorithms applied in the autopilot.

Experimental and analytical investigation of the shear resistance of a rock joint held by a fully-grouted bolt and subject to large deformations

Failures of rock bolts installed in jointed rock masses due to shear movement along weak joints in bedding rock slopes or underground caverns are common. Existing models to design rock bolts often only consider a rock bolt’s shear behavior in the elastic stage and ignore their larger non-elastic deformations, which significantly underestimates the bolt’s contribution to the joint shear resistance. Therefore, developing an analytical model capable of reflecting the plastic strain‑hardening of rockbolts subjected to large deformation is very necessary for more effective numerical simulation models as well as rock support design. An experimental investigation was conducted on grouted bolts subjected to joint shear movement. The bolt installation angle with respect to the joint was varied in the tests. Pairs of strain gauges attached to the surface of the bolt shank near the joint measured the bolt deformation during the shear testing. The deformation characteristics of the bolt and grout in the elastic and the plastic stages were evaluated. Based on the experimental measurements, a new analytical model to predict the bolt’s ultimate contribution to the shear resistance of a joint was developed. This model considers large deformations. The analytical model includes the influences of the bolt angle, rock mass strength, joint dilation angle, and bolt tensile strain. A comparison of the model predictions with results from large-scale tests and other existing methods shows good agreement with the tests and an improvement over existing methods.

A Laboratory Forced-Oscillation Apparatus for Measurements of Elastic and Anelastic Properties of Rocks at Seismic Frequencies

In presented paper, we describe the technical and physical aspects of the application of a low-frequency (LF) apparatus based on a longitudinal type of forced oscillations. In particular, we investigate the influence of the strain gauge position on a tested sample on measurement results, we also examine the creep effect associated with the mineralogy of rocks, as well as the dispersion and attenuation in a liquid-saturated rock sample caused by the presence of the volume of pore fluid exterior to the sample (dead volume). The effect of the position of the strain gauges is investigated using a cylindrical acrylic sample and two pairs of strain gauges fixed in the middle and at one of the sample ends under a uniaxial pressure of 15 MPa. The obtained results demonstrate that elastic and anelastic parameters of the tested sample are independent from the location of the strain gauges. The impact of the creep phenomenon on elastic moduli was studied using three room-dry samples of Savonnieres limestone, Berea sandstone and Eagle Ford shale. The measurements were conducted for 120 h at a frequency of 2 Hz under a uniaxial pressure of 10 MPa and demonstrated that the LF moduli of all rocks were noticeably reduced with time. The effect of dead volume was investigated at seismic frequencies using limestone saturated with n-decane. It was found that the Young’s and bulk moduli exhibit strong dispersion at frequencies above 10 Hz if the dead volume is close to or greater than the pore volume of the sample. We also found that the characteristic frequency of dispersion corresponding to the attenuation peak is independent of the size of the dead volume and determined only by the physical parameters of the sample and pore fluid. We present also the results of the Young’s modulus and attenuation measurements conducted at seismic frequencies on vertical and horizontal shale samples saturated with water. It was shown that the relationship between the extensional attenuation and the Young’s modulus dispersion observed in the samples saturated at a relative humidity of 97.5% is consistent with the Kramers–Kronig relation.

Dispersion and Attenuation of Elastic Wave Velocities: Impact of Microstructure Heterogeneity and Local Measurements

AbstractThe variation of the seismic properties with frequency of a brine‐saturated sandstone sample with a porosity of 22% was measured using a forced oscillation apparatus. Two pairs of orthogonal biaxial strain gauges were pasted at different locations at the length center of the sample. In the frequency range of 1–300 Hz, using these two pairs of strain gauges, we observed experimentally the same global flow but different local flows (squirt flow). Therefore, the observation of the local flow is influenced by the position of the strain gauges in contrast to the global flow. Indeed, local flow is strongly influenced by the microstructure (structure of the grain contacts and microcracks). In particular, we show that although the sample is homogeneous in terms of porosity and crack density, it is not the case in terms of crack aspect ratio, which may slightly vary along the sample. A 3D diffusion model coupled with a simple squirt model was built to further interpret the data. These results show that the wave‐induced fluid flows occur at different scales and controls the dispersion and attenuation of saturated rocks.

Dynamic characterisation of interlaminar fracture toughness in carbon fibre epoxy composite laminates

In this work, the rate dependence of mode I interlaminar fracture toughness for two different materials systems, IM7/8552 and IM7/M91, both unidirectional UD carbon-fibre epoxy composite laminates have been examined over a wide range of loading rates from 0.5 mm/min up to 2000 mm/s at room temperature. Quasi-static fracture tests were performed using a DCB (double-cantilever beam) method with a screw-driven testing machine, while the dynamic tests were carried out using a WIF (wedge-insert fracture) specimen loaded dynamically in a hydraulic system. For performing the tests at high displacement rates, a special setup was designed and manufactured which allowed the insertion of the wedge within the DCB specimens at different cross-head displacement rates. The experimental technique used a pair of strain gauges attached to the bending surface of one of the arms of the cantilever beams and far from the initial crack tip. The peak values of the recorded strain were used to determine the fracture toughness under dynamic conditions through use of the compliance calibration method. A finite element model was developed to check the consistency of the measurements and validate the data reduction method used. The results exhibited rate insensitive behaviour in the case of the IM7/8552 laminates while IM7/M91 showed the contrary behaviour with maximum peak at 500 mm/s of displacement rate, with a toughness increase of ≈95% with respect to the quasi-static conditions.

Nonlinear topology optimization of parallel-grasping microgripper

This paper presents a piezo-driven microgripper which can realize parallel grasping in a large displacement range (more than 140μm). The proposed microgripper is derived by a two-step nonlinear topology optimization method. A conventional linear topology optimization problem with loose boundary condition is solved first, and its solution is used as the initial design domain of the following nonlinear topology optimization. The comparison of the convergence results shows that this method can find a better structure of microgripper and save computation time simultaneously. Both the finite element analysis and experiment are used to verify the performance of the proposed microgripper. The experimental results show that the parasitic movement of the jaw is only 0.299% of the grasping movement and the average inclination angle of the jaw is 0.055mrad/μm. A pair of strain gages is integrated as a displacement sensor, and its performance is presented and verified by experiments.

Strain gauges position based on machine vision positioning

In this article, in order to meet the requirement of automatic positioning before strain gauge grinding, we proposed a new machine vision algorithm based on connected region extraction and minimum circumferential rotation rectangle delineation. At first, based on the location information of the strain gauge, we used algorithms for image binaryzation, and extracted the strain gauge block by using the connected component extraction method, next roughly positioned strain gauges. And then we dispersed the part which connected to the strain gauge, moreover, found the minimum external rotating rectangle of each strain gauge in the pair of strain gauges so as to located the center of the strain gauge and realize the strain gauge positioning in the end. Then the position of other strain gauge was inferred according to the position of strain gauge in the corner. Experimental verification showed that the error of the algorithm in this article is under 0.05mm, and the algorithm met the requirements of project positioning that the error has to below 0.1mm.

Towards determination of power loss at a rowing blade: Validation of a new method to estimate blade force characteristics.

To analyze on-water rowing performance, a valid determination of the power loss due to the generation of propulsion is required. This power los can be calculated as the dot product of the net water force vector () and the time derivative of the position vector of the point at the blade where is applied (). In this article we presented a method that allows for accurate determination of both parameters using a closed system of three rotational equations of motion for three different locations at the oar. Additionally, the output of the method has been validated. An oar was instrumented with three pairs of strain gauges measuring local strain. Force was applied at different locations of the blade, while the oar was fixed at the oarlock and the end of the handle. Using a force transducer and kinematic registration, the force vector at the blade and the deflection of the oar were measured. These data were considered to be accurate and used to calibrate the measured strain for bending moments, the deflection of the oar and the angle of the blade relative to its unloaded position. Additionally, those data were used to validate the output values of the presented method plus the associated instantaneous power output. Good correspondence was found between the estimated perpendicular blade force and its reference (ICC = .999), while the parallel blade force could not be obtained (ICC = .000). The position of the PoA relative to the blade could be accurately obtained when the perpendicular force was ≥ 5.3 N (ICC = .927). Instantaneous power output values associated with the perpendicular force could be obtained with reasonable accuracy (ICC = .747). These results suggest that the power loss due to the perpendicular water force component can be accurately obtained, while an additional method is required to obtain the power losses due to the parallel force.

Active Flow Control of a Low Reynolds Number S809 Wind Turbine Blade Model under Dynamic Pitching Maneuvers

A low Reynolds number wind turbine blade model based on the S809 airfoil was tested in a subsonic wind tunnel to study the structural vibration of the blade under dynamic pitching maneuvers. Piezoelectric-based synthetic jet actuators were embedded inside the blade and activated with a synthetic jet momentum coefficient, Cμ of 2.30 × 10-3. Structural vibration was quantified for a range of unsteady angles undergoing “pitch up and down” and “sinusoidal pitch” maneuvers at a Reynolds number of 5.28 × 104. The blade tip deflection amplitude and frequency were acquired utilizing a pair of strain gauges mounted at the root of the model. Using active flow control vibration reduction was more effective during the pitch up portion of the blade motion cycle compared to the pitch down portion. This effect is due to dynamic stall, where a leading edge vortex is shed during the pitch up motion and contributes to higher lift compared to static angles of attack and lower lift when the blade is pitched down. Dynamic stall was measured with phase-locked stereoscopic particle image velocimetry (SPIV), where global mean flow measurements reveal a shift in location and reduction in the size of a recirculating flow structure near the suction surface of the blade during the pitch up motion compared to the pitch down.

Dynamic Fracture of Layered Plates Subjected to In-Plane Bending

Layered structures typically used in applications such as windshields, thermal protection systems, heavy armor, etc., have property jumps at the layer interfaces. Present study focuses on understanding crack initiation and propagation in such systems under dynamic loading particularly when the property jumps are across the crack front. Layered plates were fabricated by joining polymethylmethacrylate (PMMA) and epoxy sheets using an epoxy-based adhesive (Araldite). Single-edge notched (SEN) specimens were subjected to dynamic loading using a modified Hopkinson bar setup. High-speed imaging coupled with dynamic photoelasticity was used to record the crack-tip isochromatic fringes from which the stress intensity factor (SIF) history was obtained. In selected experiments, a pair of strain gages installed on surfaces of specimen was used to record the strain history in the layers, from which the SIF in each layer was obtained. The results indicated that, prior to crack extension, the strain in both layers was identical. The crack tips in the layers start extending at different time instants with the one in the relatively brittle epoxy layer extending first followed by the one in the PMMA layer. At low impact velocity, the delay obtained was significantly higher than that at high impact velocity. The speed of epoxy crack was lower initially due to the bridging of the crack by the uncracked portion of the PMMA layer till initiation of the crack in the PMMA layer. This effect reduced at higher impact velocity for which the delay was much lower and the cracks propagated at a higher-speed.

Compensation of Bending Waves in an Optically Instrumented Miniature Kolsky Bar

Kolsky (split-Hopkinson) bars are susceptible to bending which may introduce flexural wave components to the expected longitudinal loading waves. The traditional method of removing these components by using a pair of strain gages is not practical for bars with very small diameters (<3 mm). For such bars strain gages are replaced with optical interferometers: a normal displacement interferometer located on the free end of the output bar and transverse displacement interferometer (TDI) together with a diffraction grating on the surface of the input bar. In this work we propose a method to remove bending wave components from the compressive loading pulse through modifications of the existing optical measurement system to include a pair of TDIs that are positioned on opposite sides of the input bar. Short, square longitudinal loading pulses with sub-microsecond rise times, free of bending wave components, were successfully measured using this system.

수평재하에 따른 복합말뚝의 거동분석

A composite pile consisted of a concrete lower part with a steel tubular pile at upper part was installed by pre-drilling method. Seven pairs of strain gauges and inclinometer were attached on the pile in order to measure stresses and displacement along the pile during the lateral loading test. The results of instrumentation were analyzed using various theoretical approaches. The back analysis showed that the measured stresses were smaller than those of the calculated. The maximum stress is measured at the steel upper part and decreased rapidly with depth of the pile. The calculated lateral displacement along the pile provide very good agreement with the measured values if the coefficient of subgrade reaction is selected properly. The design concept of a composite pile is verified by the measured stresses and displacement which is within the tolerable limits of the pile.

Using cross-correlations of ambient vibrations for passive structural health monitoring of a high-speed naval ship

Previous studies have used the cross-correlation of ambient vibrations (CAVs) technique to estimate the impulse response (or Green's function) between passive sensors for passive imaging purposes in various engineering applications. The technique (CAV) relies on extracting deterministic coherent time signatures from the noise cross-correlation function computed between passive sensors, without the use of controlled active sources. Provided that the ambient structure-borne noise field remains stable, these resulting coherent waveforms obtained from CAV can then be used for structural monitoring even if they differ from the actual impulse response between the passive sensors. This article presents experimental CAV results using low-frequency random vibration data (>50 Hz) collected on an all-aluminum naval vessel (the HSV-2 Swift) operating at high speed (up to 40 kn) during high sea states. The primary excitation sources were strong wave impact loadings and rotating machinery vibrations. The consistency of the CAV results is established by extracting similar coherent arrivals from ambient vibrations between the pairs of strain gages, symmetrically located across the ship's centerline. The influence of the ship's operating conditions on the stability of the peak coherent arrival time, during the 7 days trial, is also discussed. [Sponsored by ONR, N00014-09-1-0440.]

Passive structural health monitoring of a high-speed naval ship from ambient vibrations

Previous studies have used the cross-correlation of ambient vibrations (CAV) technique to estimate the impulse response (or Green's function) between passive sensors for passive imaging purposes in various engineering applications. The technique (CAV) relies on extracting deterministic coherent time signatures from the noise cross-correlation function computed between passive sensors, without the use of controlled active sources. Provided that the ambient structure-borne noise field remains stable, these resulting coherent waveforms obtained from CAV can then be used for structural monitoring even if they differ from the actual impulse response between the passive sensors. This article presents experimental CAV results using low-frequency random vibration data (<50 Hz) collected on an all-aluminum naval vessel (the HSV-2 Swift) operating at high speed (up to 40 knots) during high sea states. The primary excitation sources were strong wave impact loadings and rotating machinery vibrations. The consistency of the CAV results is established by extracting similar coherent arrivals from ambient vibrations between the pairs of strain gages, symmetrically located across the ship's centerline. The influence of the ship's operating conditions on the stability of the peak coherent arrival time, during the 7 days trial, is also discussed.

Validation of boundary PIV measurements of soil–pipe interaction

It is a well-established argument that side-wall interface friction can influence the behaviour of soil located at the boundary of physical model test chambers. This effect has a potentially significant influence on measurement techniques such as particle image velocimetry that often rely on images captured at vertical transparent boundaries. However, it is hypothesised that under kinematically controlled boundary conditions, particle image velocimetry can yield not only qualitative but highly accurate quantitative measurements of deformation. In this paper, this hypothesis is tested for the specific soil–structure interaction problem of pipelines being subject to vertical faulting. In the middle of the model, a circular model pipeline was heavily instrumented with 32 pairs of strain gauges. At the same elevation but at the window of the test chamber, an identical model pipeline was split in half axially along its centreline to give a semi-circular cross-section, and placed against the visible window. Three digital cameras were used to record deformations of the pipe and the surrounding soil during the test. After image processing and filtering, measurements of peak curvature obtained from digital image analysis on the half pipeline section are shown to be within 5% of the results obtained from strain gauges.

Generalised proportional integral torque control for single-link flexible manipulators

In this study, a generalised proportional integral (GPI) output feedback control scheme is proposed to control the torque of a single-link flexible arm for free and constrained motion. The control is based on the properties of differential flat systems. The control is also found to be robust with respect to the motor static friction. The only variable to measure is the torque in the hub by means of only one sensor, which in this case, is constituted by a pair of strain gauges. An hybrid control law is presented to control the manipulator in collision with an object (constrained motion) and when it can freely move (free motion) commanded by an on-line impact detection algorithm. Experiments are presented to verify the goodness of the proposed control law.

Dynamic lumbar pedicle screw-rod stabilization: in vitro biomechanical comparison with standard rigid pedicle screw-rod stabilization

It is unclear how the biomechanics of dynamic posterior lumbar stabilization systems and traditional rigid pedicle screw-rod systems differ. This study examined the biomechanical response of a hinged-dynamic pedicle screw compared with a standard rigid screw used in a 1-level pedicle screw-rod construct. Unembalmed human cadaveric L3-S1 segments were tested intact, after L4-5 discectomy, after rigid pedicle screw-rod fixation, and after dynamic pedicle screw-rod fixation. Specimens were loaded using pure moments to induce flexion, extension, lateral bending, and axial rotation while recording motion optoelectronically. Specimens were then loaded in physiological flexion-extension while applying 400 N of compression. Moment and force across instrumentation were recorded from pairs of strain gauges mounted on the interconnecting rods. The hinged-dynamic screws allowed an average of 160% greater range of motion during flexion, extension, lateral bending, and axial rotation than standard rigid screws (p < 0.03) but 30% less motion than normal. When using standard screws, bending moments and axial loads on the rods were greater than the bending moments and axial loads on the rods when using dynamic screws during most loading modes (p < 0.05). The axis of rotation shifted significantly posteriorly more than 10 mm from its normal position with both devices. In a 1-level pedicle screw-rod construct, hinged-dynamic screws allowed a quantity of motion that was substantially closer to normal motion than that allowed by rigid pedicle screws. Both systems altered kinematics similarly. Less load was borne by the hinged screw construct, indicating that the hinged-dynamic screws allow less stress shielding than standard rigid screws.

Active Vibration Control of a Wind Turbine Blade Using Synthetic Jets

Active vibration control via an array of synthetic jet actuators was investigated experimentally in a wind tunnel. Using synthetic jets the flow over a small scale S809 finite wind turbine blade was controlled, resulting in reduction of the blade's structural vibrations. The effectiveness of the synthetic jets was explored for a range of post-stall angles of attack at Reynolds numbers between 7.1 × 104 and 2.38 × 105. The blade vibrations were measured and quantified using a pair of strain gauges mounted at the root of the model. Using flow control, significant vibration reduction was observed for some post-stall angles of attack. A correlation between vibration reduction and the degree of flow reattachment, measured using Particle Image Velocimetry, was found.

A-19 キックロボット用センサ・フットの開発研究 : キック力計測用センサ部構造の提案(サッカー)

An instrumented device equipped with strain gauges was designed to measure exerting forces upon the ball kicked by the impact type ball ejection unit. The device consists of L-shape aluminum alloy beam, contact plate and a connector with the ejection unit Seven pairs of strain gages were attached on the beam connected to the ejection units. The output of the sensors was converted into the values of forces by resolving the static equilibrium equations. The results from the calibration procedure shows good agreement between actual forces measured with load cell and calculated forces with strain gauge signals exerted on the device. The results obtained from the measurement in kick motion with use of the instrumented device shows : (1) The normal component of the force with respect to the contact plate were large relative to those of other axial components, and (2) the tangential component of the force was oscillating during contact.