Strain Measurement Technology Research Articles

Research on a novel inclinometer based on distributed optical fiber strain and conjugate beam method

The inclinometer is widely used in the deformation monitoring of civil and hydraulic engineering, but the manual observation required for existing traditional inclinometers is time-consuming, laborious and workload-intensive; an inclinometer with automatic monitoring is expensive, difficult to use for achieving distributed monitoring and shows poor instrument durability. To overcome the shortcomings of traditional inclinometers, a distributed optical fiber inclinometer (DOFI) is developed based on the conjugate beam method and distributed strain measurement technology. Compared to Euler-Benuli beam based converting method, the conjugate beam based method is more flexible and accurate to monitor the deformation of the slope under the heterogeneity geological conditions. Numerical simulation and laboratory tests show that the conjugate beam based inclinometer (DOFI) is effective, feasible and accurate. It can be used to quickly and accurately measure the deformation and direction of rock and soil mass, such as slope, and can realize long-term on-line monitoring.

Strain measurement and determining coefficient of plastic anisotropy using digital image correlation (DIC)

The deformation and strain measurements have always been one of the main issues in structural engineering. Measuring displacements accurately without damaging structures are an important aim in experimental analysis. For an example, the existing structures need to be evaluated whether they are still fit for purposes or not. To assess complex structures, we need an acceptable and enough amount of data Current strain measurement technologies are not capable of evaluating compounded structures. This paper investigates on an alternative method that uses digital images to provide a full displacement and strain field called Digital Image Correlation (DIC); This technique compares the digital images taken from digital cameras, before and after deformation. We also calculated the coefficient of plastic anisotropy. An aluminium 1050 specimen was loaded in tension according to ASTM E8 testing method while the Sony camcorder captured the video of the specimen being loaded. Once the video was captured, the images were snapshot from video strip using a built-in function of the camera. After that, the images were processed using the Matlab software. The results determined by the extensometer and the optical strain measurement method were compared to each other. This comparison shows that if the test’s setup could be configured in a good way, the error will be less than 2%.

Pipeline Bending Strain Measurement and Compensation Technology Based on Wavelet Neural Network

The bending strain of long distance oil and gas pipelines may lead to instability of the pipeline and failure of materials, which seriously deteriorates the transportation security of oil and gas. To locate the position of the bending strain for maintenance, an Inertial Measurement Unit (IMU) is usually adopted in a Pipeline Inspection Gauge (PIG). The attitude data of the IMU is usually acquired to calculate the bending strain in the pipe. However, because of the vibrations in the pipeline and other system noises, the resulting bending strain calculations may be incorrect. To improve the measurement precision, a method, based on wavelet neural network, was proposed. To test the proposed method experimentally, a PIG with the proposed method is used to detect a straight pipeline. It can be obtained that the proposed method has a better repeatability and convergence than the original method. Furthermore, the new method is more accurate than the original method and the accuracy of bending strain is raised by about 23% compared to original method. This paper provides a novel method for precisely inspecting bending strain of long distance oil and gas pipelines and lays a foundation for improving the precision of inspection of bending strain of long distance oil and gas pipelines.

Carbon nanotubes as non-contact optical strain sensors in smart skins

Progress is reported in the development of a novel non-contact strain measurement technology in which the sensors are single-walled carbon nanotubes. This approach exploits the characteristic short-wave infrared fluorescence signatures of semiconducting single-walled carbon nanotubes and the systematic shifts of their fluorescence wavelengths when the nanotubes are axially strained. A strain-sensing smart skin is prepared by coating the surface to be monitored with a thin film of a composite containing well-dispersed single-walled carbon nanotubes embedded in a urethane varnish host. Strain in the surface transfers through the host polymer to the embedded nanotubes. The nanotube strains are then quantitatively monitored by exciting the region of interest with a visible laser beam and capturing and analyzing the resulting single-walled carbon nanotube fluorescence spectrum. High-quality spectra are shown for strain-sensing smart skin films in which the nanotubes were pre-processed by selective extraction with the organic polymer poly(9,9-dioctylfluorenyl-2,7-diyl) and purification by centrifugation. The design of a compact, field-portable optical system for exciting, collecting, and interpreting strain-sensing smart skin spectral data is also described. This system is used to validate the linear dependence of peak shifts with strain in test specimens subjected to multiple tension cycles inducing strains from 0 to 5000 µε. Adequate linearity is found up to 1500 µε; however, minor hysteresis is observed above this level. The gage length for these measurements can be as small as several micrometers, and the strain resolution is currently between 10 and 100 µε (depending on strain magnitude). Cyclic reversible strain measurements are demonstrated, with minor hysteresis being attributed to imperfect adhesion between nanotube sidewalls and the surrounding polymer host.

(Invited) Progress Towards a Novel Technology for Non-Contact Strain Measurements Based on SWCNT Fluorescence Spectroscopy

One of the most distinctive properties of semiconducting single-walled carbon nanotubes (SWCNT) is their emission of structure-specific fluorescence (band gap photoluminescence) in the short-wave infrared (SWIR) spectral region. The fluorescence peak from each (n,m) structural species shifts in wavelength as the nanotube’s band gap is altered by axial strain. These shifts are known from theory and experiment to depend on the nanotube’s chiral angle and on its mod (n-m,3) value, and they are linear with strain for realistic axial deformations. We have previously shown that this effect may lead to a new strain measurement technology (called S4, for strain-sensing smart skin) in which individualized SWCNTs embedded in a polymeric film serve as strain sensors and readout is achieved by non-contact optical methods.1 Recent research progress aimed at enabling such an implementation will be described. Focus areas include processing and dispersing SWCNTs for effective use in S4; comparing suitability of different polymer formulations as S4 hosts; applying and stabilizing the S4 films; understanding factors that influence interfacial adhesion between SWCNTs and host molecules; miniaturizing the optical hardware to allow excitation and capture of SWCNT fluorescence spectra with hand-held devices; refinement of data analysis methods for deducing strains from spectral data; tests of sensitivity and reproducibility for S4 measurements with plastic, aluminum, and steel substrates; and construction of two-dimensional strain maps from sets of single-point measurements. 1 P. A. Withey, V. S. M. Vemuru, S. M. Bachilo, S. Nagarajaiah, and R. B. Weisman, Nano Lett. 12, 3497 (2012).

Distributed Strain Behavior of a Reinforced Concrete Bridge: Case Study

To effectively assess and manage aging infrastructure, sensing technologies that produce accurate and useful quantitative data are required. Distributed fiber optic strain measurement systems are one potential technology that could fulfill this requirement. This case study investigates the performance of a distributed fiber optic strain measurement technology with high accuracy and spatial resolution during a load test on a RC bridge. The measurements from the fiber optic system are compared with conventional strain gauges and linear transducers, and good agreement between the sensors was found. The fiber optic measurements are also used to examine the bridge support conditions as well as the load distribution between beams. The results show that assumptions made about the support conditions during design do not match the actual bridge behavior, although the load distribution between beams is as expected.

Study on Bending and Twisting Mechanical Properties of High Voltage Porcelain Post Insulator

To study the mechanical properties of porcelain post insulators, the finite element model was established by ANSYS to calculate stress and strain distribution under bending or torsion moments. Mechanical tests based on resistance strain measurement technology were carried out on the actual porcelain post insulators to measure their strain distribution. The results show that sheds will cause strain concentration at the roots of porcelain column whether the post insulator is bearing bending or torsion load. The stress and strain of shed roots gradually increase from top to bottom along the post insulator when bearing bending moment, while they are relatively uniform under torsion moment. It should be taken full account of the stress concentration caused by sheds during the selection or maintenance of porcelain post insulators.

Damage Identification in Reinforced Concrete Beams Using Spatially Distributed Strain Measurements

AbstractBrillouin optical time domain reflectometry or analysis (BOTDR/A) is one of the strain measurement technologies that is suitable for smart monitoring of civil engineering infrastructures. Although the technology has the advantage of supplying spatially distributed data, it is currently limited to a spatial resolution of approximately 1 m. This infers that the technology may lack the ability to identify the exact type and source of damage; that is, different geometrical configurations of cracking within a concrete beam may lead to similar BOTDR/A readings, and hence, the exact nature of cracking might not be resolved. This study suggests different crack indicators and analytically and experimentally examines their correlations with BOTDR/A readings of damaged RC beams. The analytical part entails a finite-element based statistical analysis of hundreds of cracking cases in fractured RC beams and their effects on the simulated BOTDR/A readings. It is found from the analysis that the increase of curva...

The Development of Surface Acoustic Wave Sensors (SAWs) for Process Monitoring

Wirelessly interrogated surface acoustic wave (SAW) sensors can operate passively and in harsh conditions. Development of SAW sensors allows investigation of their potential to quantify measurands such as strain in aggressive environments. In this paper, a one port SAW resonator strain sensor is presented fully packaged and is shown to exhibit highly sensitive and linear responses to applied strain. The sensor detailed is fabricated on AT-X quartz, packaged using an off the shelf Kovar package, and instrumented with commercially available strain gauge adhesives. The sensor is initially presented on a characterised strain calibration platform developed in TCD with a foil strain gauge as reference technology for performance validation and comparison. The sensor is then shown instrumented with a Sandvik CNC tool holder for direct process monitoring of machining operations. The tool holder coupled with the integrated SAW strain measurement technology is calibrated using a Kistler Dynamometer in an Instron loading machine. The fully calibrated sensor is a platform for dynamic tool condition monitoring in a commercial CNC machine is then described. The work presented is to provide a basis for SAW technology in tool condition monitoring and process monitoring systems in the future.

Study of Strain and Temperature Simultaneous Measurement Technology Based on Sampled Grating

Choice appropriate parameters of the sampled fiber Bragg grating base on the influence of the sampled fiber Bragg grating length, sampling rate, refractive index modulation depth and sampling period to the reflective spectrum of sampled fiber Bragg grating. Get the reflective spectrum of sampled fiber Bragg grating by using transmission matrix method, form the sampled fiber Bragg grating suitable for sensing. Get the strains of the sampled fiber Bragg grating and the data from Temperature-sensor through simulation experiment, then determine the sensing-parameters A, B, C, D by using SPSS13.0 statistics software in regression analysis. Strain measurement ranged from 0με to 1800με，temperature measurement ranged from 0°C to 180°C.

Malrotation in total knee arthroplasty: Effect on tibial cortex strain captured by laser-based strain acquisition

Malrotation of the tibial and femoral components has been recognized to be a clinical complication affecting the performance and durability of total knee arthroplasty. This study used a novel strain acquisition technique to determine the effect of tibio-femoral component malrotation on tibial torque and strain distribution of the proximal tibial cortex with a cemented fixed-bearing posterior-stabilized knee. Using electronic speckle pattern interferometry, strain on the proximal tibia of human cadaveric knees was obtained in response to 1500N axial loading for neutrally aligned tibial and femoral components, and for 10 degrees internal and external malrotation between the tibial and femoral components. Local strain gage measurements were combined with full-field optical strain measurements to quantify effects on tibial cortex strain and strain distributions caused by the 10 degrees malrotations. In addition, tibial torque was measured for incremental degrees of tibio-femoral malrotation. Tibio-femoral malrotations as small as 2 degrees caused tibial torque in excess of 4 Nm. At 10 degrees malrotation, tibial torque significantly increased to over 8 Nm (P<0.001) as compared to neutrally aligned components. Local strain gage results significantly increased from 500 muepsilon to 632 muepsilon compressive strain in response to 10 degrees external malrotation, and to 1000 muepsilon compressive strain in response to 10 degrees internal malrotation. Full-field optical strain reports yielded the highest strain of 2153 muepsilon for 10 degrees internal malrotation 30 mm below the joint line. Laser-based strain measurement technology provides novel capabilities to capture cortex strain fields. The sensitivity of cortex strain and torsion to small amounts of tibio-femoral malrotation may explain factors contributing to aseptic implant loosening of the tibial component.

광섬유센서를 이용한 Beam-column 조인트의 하중에 따른 변위 계측

For monitoring of the civil and building structure, optical fiber sensors are very convenient. The fiber sensors are very small and do not disturb the structural properties. They also have several merits such as electro-magnetic immunity, long signal transmission, good accuracy and multiplexibility in one sensor line. Strain measurement technologies with fiber optic sensors have been investigated as a part of smart structure. In this paper, we investigated the possibilities of fiber optic sensor application to the monitoring of beam-column joints of structures. We expect that the fiber optic sensors replace electrical strain gauges. The commercial electric strain gauges show good stability and dominate the strain measurement market. However, they lack durability and long term stability for continuous monitoring of the structures. In order to apply the strain gauges, we only have to attach them to the surfaces of the structures. In this paper, we investigate the possibility of using fiber optic Bragg grating sensors to joint structure. The sensors show nice response to the structural behavior of the joint.

A Feasibility Study on the Application of Fiber-Optic Distributed Sensors for Strain Measurement in the Taiwan Strait Tunnel Project

Taiwan Strait Tunnel (TST) will be an extra-long tunnel or tunnel-bridge complex, running over 150 km of seafloor geologic body with complicated topographic and geologic units. It is therefore necessary to measure and monitor the strain distribution along the TST. In this article, the Brillouin optical time-domain reflectometer (BOTDR), a newly developed strain measurement and monitoring technology, is introduced, and the feasibility of its application in the strain monitoring for TST is analyzed through the monitoring achievement with BOTDR of a tunnel located in Nanjing City, China. The results indicate that the BOTDR has many unique merits such as distributed measurement, long-distance, real-time, and resistibility for strain monitoring application in a tunnel such as TST. Finally, apreliminary scheme for BOTDR application in TST monitoring is proposed.

The role of strain measurement technology in structural evaluation

AbstractThis paper describes the importance of structural evaluation to the process of design assessment and outlines the significant role played by strain measurement technology in extending the scope of strain history data collection and facilitating strain monitoring of full‐scale structures in the laboratory. After some general discussion of the various models of structural behaviour, it then proceeds to give a brief historical account and outlines the principles of thermoelastic stress analysis (TSA). A general desciption is provided of a specific TSA technique namely Stress Pattern Analysis by Thermal Emission (SPATE).Despite the level of innovation and development in strain measurement technology, the use of bonded strain gauge elements is still by far the most commonly used strain measurement and monitoring technique in structural evaluation work at NEL. The paper highlights several recent test programmes carried out at NEL in the form of case studies which demonstrate different aspects of measuring, monitoring and validation of this and other strain measurement techniques; and verification of analytical models.