Wireless Strain Measurement Based on a Microstrip Patch Antenna

Wireless interrogation of a rectangular microstrip patch antenna for strain measurement is investigated by simulations.To analyze the antenna performance,a microstrip line-feeding patch antenna at 10 GHz is designed.A patch antenna wirelessly fed by a horn is proposed to measure the strain.The direction information of strain detected by the patch antenna is also considered.The strain can be detected both in the width and length directions.It is shown that the strain can be measured wirelessly using a standard horn antenna.This kind of wireless strain-sensing technique offers significant potential for wireless structural health monitoring(SHM),especially for high-end equipment.

Strain Measurement on the Toroidal Field (TF) Coil Cases

The stress-strain state of the structure is a matter of interest to designer. The strain measurement of superconducting magnets at cryogenic temperature is a specific technique. Based on strain measurement of TF coil case for EAST, this paper presents a measuring technique at cryogenic temperature and on intense magnetic field. The compensation methods for both temperature and magnetic field effects of the gauges, together with the measured results are involved, and the discussions of the measured results are given in the paper.

In-situ strain measurement and error analysis of arc welding with 2D digital image correlation

The deformation and residual stress generated by the welding process can seriously affect the use of components.As a result,it is very important to understand the evolution of stress and strain during the welding process.The strain measurement method based on digital image correlation(DIC)is an excellent method to detect welding strain and residual stress.The out-of-plane translation and out-of-plane rotation introduce errors to the two-dimensional DIC.In this paper,the causes of errors are analyzed theoretically,and the formulas of errors caused by the out-of-plane displacement and the out-of-plane rotation are derived.The out-of-plane translation experiment and the out-of-plane rotation experiment were carried out to verify the theory,and the experimental results are consistent with the theoretical analysis results.The error caused by the out-of-plane translation can be reduced by increasing the object distance;the error caused by the out-of-plane rotation is greatly affected by the rotation angle.

Strain Measurement for Hollow Projectiles During Its Penetration of Concrete Targets

Gives a new technique to measure the dynamic deformation behavior and strain development of a hollow steel projectile during its penetration of concrete targets. Direct strain measurement was performed by applying strain gages attached to the inner walls of the hollow projectile, linked with on-board testing and storage recorder. This on-board test-record system is easy to operate, cost-effective and can provide reasonable, accurate and detailed information. Obverse ballistic experiments were carried out on ogival-nose hollow projectiles normally impacting concrete targets at velocities from 150 m/s to 300 m/s. The deformation process of projectiles was measured, recorded and played back. Profiles of voltage-time relationship were successively obtained and transfered to strain-time relationship with the aid of calibration tables. It was found that projectiles go through a series of compression and tension deformations intermittently. Relationships between strain development and projectile deformation process were discussed.

STRAIN MEASUREMENT IN THE SMART COMPOSITE

The smart composite structure is a new type of structure developed in recent years. It can be used in aircraft or some other important devices. The smart composite structure in which some sensors, actuators and other components are embedded can perform the tasks such damage evaluation, strain measurement, changing stress and suppressing vibration by itself. In the Performance of the tasks above, many parameters must be measured, among which the measurement of strain field is very important. In this paper, some distributed and quasi-distributed embedding optic fiber strain sensors are introduced, and their specialities are discussed.

APPLICATION OF GRATING DIFFRACTION IN STRAIN MEASUREMENT

In this paper a new technique for measuring strain is presented. Using grating as the strain sensor, we can obtain strain and stress components by measuring the deformation of the space position of diffraction spots. The cost of the holographic grating by embossing is much reduced. By using the video and computer techniques the strain and stress values can be obtained automatically.

Carrier fringe method of moire interferometry for tiny strain measurements in micro-field

In this paper, we demonstrate a new optical method for tiny strain measurements based on the principle of carrier fringes of moire interferometry. A cross-line grating with frequency of 1200 lp/mm is replicated on the specimen surface, and the strain can be deduced from the changes in carrier fringes before and after the deformation of an object. Four coherent laser beams are used to obtain the carrier fringe patterns of field U and V. Both theoretical analysis and numerical simulation indicate that the ideal accuracy of strain can be controlled within a range of ±1με. Case study of a plane extension experiment shows that the measurement accuracy of strain can be controlled within the range of ±10με. The average strain values of every row of field U and every column of field V can be obtained by using this method, and approximated strain of every pixel in the whole-field can be further acquired, and thus it is possible to measure tiny strains occurred in a micro-field. The technology in this paper can provide comprehensive information for analyzing related mechanical content in the field of MEMS.

Instantaneous Creep in Face-centered Cubic Metals at Ultra- low Strain Rates by a High-resolution Strain Measurement

Instantaneous creep in face-centered cubic metals, 5N Al（99.999%）, 2N Al （99%） and 4N Cu （99.99%） with different grain sizes, was firstly investigated by sudden stress-change experiments at ultra- low strain rates ε ≤10-10 s-1 and temperature T 〈 0.32 Tn. The experimental results indicate that the observed instantaneous creep is strongly dependent on grain size, the concentration of impurity, and stacking fault energy. Creep in high-purity aluminum, 5N Al, with a very large grain size, d 〉 1600μm, shows non-viscous behavior, and is controlled by the recovery of dislocations in the boundary of dislocation cells. On the other hand, for 5N A1 with a small grain size, d=30μm, and low-purity aluminum, 2N A1, with d8= 25μm, creep shows viscous behavior and may be related to ＇low temperature grain boundary sliding＇. For high-purity copper, 4N Cu, with d= 40 grn and lower stacking fault energy, creep shows a non-viscous behavior, and is controlled by the recovery process of dislocations. For all of the samples, creep shows anelastic behavior.

Liquid modified photonic crystal fiber for simultaneous temperature and strain measurement

A liquid modified photonic crystal fiber(PCF)integrated with an embedded directional coupler and multi-mode interferometer is fabricated by infiltrating three adjacent air holes of the innermost layer with standard 1.48 refractive index liquids.The refractive index of the filled liquid is higher than that of background silica,which can not only support the transmitting rod modes but also the"liquid modified core"modes propagating between the PCF core and the liquid rods.Hence,the light propagating in the liquid modified core can be efficiently coupled into the satellite waveguides under the phase-matching conditions,resulting in a dramatic decrease of the resonant wavelength intensity.Furthermore,there is a multi-mode interference produced by modified core modes and rod modes.Such a compact(~0.91 cm)device integrated with an embedded coupler and interferometer is demonstrated for high-sensitivity simultaneous temperature(~14.72 nm∕℃)and strain(~13.01 pm∕με)measurement.

Non-uniform strain measurement along a f iber Bragg grating using optical frequency domain reflectometry

A novel method of measuring non-uniform strain along a fiber Bragg grating(FBG) using optical frequency domain reflectometry(OFDR) is proposed and experimentally demonstrated. This method can overcome the problems of traditional non-uniform strain measurement methods for FBGs, i.e., the likelihood of chirping and multiple peaking in the spectrum when FBG is subjected to inhomogeneous strain fields. Wavelength interrogation is realized by OFDR with a narrow-line-width tunable laser as the optical source. When non-uniform strain distributions along areas adjacent to structural damage are measured by this method, good agreement is obtained between measurements and theoretical simulation results.

Development of highly sensitive mechanoluminescent sensor aiming at small strain measurement

This paper was focused on the elasticoluminescence(ELS)characteristics,especially a response to small strain(below 1000μst),of mechanoluminescence(ML)sensor using strontium aluminate doped with small amount of europium(SrAl_(2)O_(4):Eu)synthesized by different methods.By using nitrate decomposition method as a synthetic method of SrAl_(2)O_(4):Eu,the response to small strain of the ML sensor was enhanced in comparison with using a conventional solid-state reaction method.Based on SEM observation and thermoluminescence(ThL)measurement,we proposed a hypothesis that the sensing characteristic of small strain affect the platelike shape of SrAl_(2)O_(4):Eu grain and/or shallower carrier trap levels formed by nitrate decomposition method.

DISTRIBUTED MICROBEND FIBER-OPTIC STRAIN SENSOR

The distributed strain sensor has significant application in real time measurement of strain status for large and important engineering structures such as aircraft, bridge and dam. In this paper, a quasi distributed optical fiber strain sensor system is set up using optical time domain reflect technique. The local strain sensors based on a novel microbend configuration are designed and applied to measure local strains along the optical fiber. As the result of the experimental research, the microbend sensors show high sensitivity, good linearity and repeatability in certain operation range.

Review of Electronic Speckle Pattern Interferometry(ESPI) for Three Dimensional Displacement Measurement

Three dimensional（3D） displacements, which can be translated further into 3D strain, are key parameters tor design, manufacturing and quality control. Using different optical setups, phase-shift methods, and algorithms, several different 3D electronic speckle pattern interferometry（ESPl） systems for displacement and strain measurements have been achieved and commercialized. This paper provides a review of the recent developments in ESPI systems for 3D displacement and strain measurement. After an overview of the fundamentals of ESP! theory, temporal phase-shift, and spatial phase-shift techniques, 3D deformation measurements by the temporal phase-shift ESPI system, which is suited well for static measurement, and by the spatial phase-shift ESPI system, which is particularly useful for dynamic measurement, are discussed. For each method, the basic theory, a brief derivation and different optical layouts are presented. The state of art application, potential and limitation of the ESPI systems are shown and demonstrated.

Hydraulic bulging process with axial feedings and strain field of U-shaped metal bellows

Based on the traditional hydraulic bulging process,an improved hydraulic bulging process with axial feeding in the bulging process was proposed.The finite element simulation and experiment of bellows formed by the traditional and improved hydraulic bulging processes were conducted.The grid strain measurement system analysis results of strain and wall thickness distribution of the metal bellows,obtained from simulation and experiment,show that the maximum thinning rates of the wall thickness under the traditional and improved processes were 15%and 10%,respectively.And the wall thickness distribution of the metal bellows formed with improved process was more uniform.The strain values from the root to crown of the waveform increased gradually.However,the strain values were smaller than those of traditional process due to the axial feeding of the improved process in bulging process.

Strain data recorded in Xinjiang and their bearing on Tianshan’s uplift/shortening and Tarim basin’s rotation

Based on the continuous strain data recorded in Xinjiang since 1985, we discuss the mechanisms of Tianshan＇ s uplift and Tarim basin＇ s clockwise rotation. The results indicate ： 1 ） The principal - compression directions in Tianshan are nearly NS, and their intersection angles with regional structures and mountains are nearly perpendicular, which is in accordance with Tianshan＇ s uplift and crustal shortening. 2）The principal compressions around Tarim basin tend to facilitate the regional faults＇ left-lateral strike-slip movements and the basin＇ s clockwise rotation. These phenomena of uplift/shortening and rotation are fundamentally the re- suits of India plate＇ s northward push on Euro-Asia plate, and the associated Pamir arc ＇ s rapid northward movement and regional blocks＇ interaction.

Digital Image Correlation Using Specific Shape Function for Stress Intensity Factor Measurement

The stress intensity factor (SIF) is a critical parameter associated with the fracture behaviour of materials. In this paper, we select the displacement function around a crack tip as the shape function of the digital image correlation (DIC), which makes it possible to directly calculate the SIF by the correlation scheme. Moreover, we use a non-rectangular subset, which can reduce the influence of plastic deformation and crack width on the DIC measurement accuracy. We measured the SIF of a mode I crack in a super-hard aluminium alloy specimen to verify the performance of the proposed method. Our experimental results show that a DIC with a specific shape function can be used to accurately and efficiently calculate the SIF. Furthermore, we also present a practical application of our proposed method for determining the SIF, crack propagation angle and crack tip displacement. © 2017, Tianjin University and Springer-Verlag Berlin Heidelberg.

DETERMINATION OF INTERNAL STRAIN IN 3-D BRAIDED COMPOSITES USING OPTIC FIBER STRAIN SENSORS

A reliable understanding of the properties of 3-D braided composites is of primary importance for proper utilization of these materials. A new method is introduced to study the mechanical performance of braided composite materials using embedded optic fiber sensors. Experimental research is performed to devise a method of incorporating optic fibers into a 3-D braided composite structure. The efficacy of this new testing method is evaluated on two counts. First, the optical performance of optic fibers is studied before and after incorporated into 3-D braided composites, as well as after completion of the manufacturing process for 3-D braided composites, to validate the ability of the optic fiber to survive the manufacturing process. On the other hand, the influence of incorporated optic fiber on the original braided composite is also researched by tension and compression experiments. Second, two kinds of optic fiber sensors are co-embedded into 3-D braided composites to evaluate their respective ability to measure the internal strain. Experimental results show that multiple optic fiber sensors can be co-braided into 3-D braided composites to determine their internal strain which is difficult to be fulfilled by other current existing methods.

LASER SPECTRAL ANALYSIS OF STRAIN MEASUREMNT

Modern opticai theory has shown that the far field or Fraunbofer diffraction equipment is identical to the Fourier spectral analyzer. In the Fourier speetral analyzer the Fourier spectra or the Fraunhofer diffaction pattern of a graph is formed on the back focal plane when a laser beam is directed on the graph lying on the front foeal plane ; the Fourier spectra of the graph is also subjected to change during the deformation of the graph. Through analyzing the change of Fourier spectra the deformation of the graph can be obtained. A few years ago,based on the above principles the authors proposed a new technique of strain measurement by laser spectral analysis. Demonstration and discussion will be made in detail in this paper.

Stress and strain analysis on the anastomosis site sutured with either epineurial or perineurial sutures after simulation of sciatic nerve injury

The magnitude of tensile stress and tensile strain at an anastomosis site under physiological stress is an important factor for the success of anastomosis following suturing in peripheral nerve injury treatment. Sciatic nerves from fresh adult cadavers were used to create models of sciatic nerve injury. The denervated specimens underwent epineurial and perineurial suturing. The elastic modulus （40.96 ＋ 2.59 MPa） and Poisson ratio （0.37 ＋ 0.02） of the normal sciatic nerve were measured by strain electrical measurement. A resistance strain gauge was pasted on the front, back left, and right of the edge of the anastomosis site after suturing. Strain electrical measurement results showed that the stress and strain values of the sciatic nerve following perineurial suturing were lower than those following epineurial suturing. Scanning electron microscopy revealed that the sciatic nerve fibers were disordered following epineurial compared with perineurial suturing. These results indicate that the effect of perineurial suturing in sciatic nerve injury repair is better than that of epineurial suturing.

Fiber optic sensing and performance evaluation of a water conveyance tunnel with composite linings under super-high internal pressures

For long-distance water conveyance shield tunnels in operation,the high internal water pressure may cause excessive deformation of composite linings,affecting their structural integrity and serviceability.However,the deformation and failure characteristics of lining structures under internal water pressure are not well investigated in the literature,particularly for three-layer composite linings.This study presents an in situ experimental investigation on the response of two types of composite linings(i.e.separated and combined lining structures)subjected to internal pressures,in which a fiber optic nerve system(FONS)equipped with distributed strain and displacement sensing nerves was employed to monitor the performance of the two composite linings during testing.The experimental results clearly show that the damage of the tunnel lining under different internal pressures was mainly located in the self-compaction concrete layer.The separated lining structure responded more aggressively to the variations in internal pressures than the combined one.Moreover,two evaluation indices,i.e.radial displacement and effective stiffness coefficient,are proposed for describing the changes in the structural bearing performance.The effective stiffness coefficients of the two types of lining structures were reduced by 39.4%and 29.5%,respectively.Considering the convenience of field monitoring,it is suggested that the average strains at different layers can be used as characteristic parameters for estimating the health conditions of lining structures in service.The analysis results provide a practical reference for the design and health evaluation of water conveyance shield tunnels with composite linings.