Electrical Resistance Strain Gauges Research Articles

Structural monitoring for asset management of railway bridges

This paper demonstrates the advantages of site monitoring to aid modelling of the existing condition of a railway bridge with structural problems and to assess the current structure and future remediation. The authors undertook monitoring and assessment on a major 28-span post-tensioned prestressed concrete box-girder bridge on a strategically important railway line in India. The bridge exhibited significant longitudinal web cracking, which restricted its load-carrying capacity to relatively light urban passenger rolling stock. Monitoring of rail traffic was supplemented by full-scale load tests for both static and dynamic loading. Optical strain sensors and electric resistance strain gauges were used for strain measurement and piezoelectric sensors were used to record accelerations. Sensors were also installed to record crack widths. A programme of numerical modelling was undertaken with finite-element models developed for both cracked and uncracked conditions. Results were compared with field data and the models were then refined to achieve a representative model for use as a predictive tool for future assessment and structural remediation of the bridge.

Evaluation of the stress distribution change at the adjacent facet joints after lumbar fusion surgery: a biomechanical study.

Spinal fusion surgery has been widely applied in clinical treatment, and the spinal fusion rate has improved markedly. However, its postoperative complications, especially adjacent segment degeneration, have increasingly attracted the attention of spinal surgeons. The most common pathological condition at adjacent segments is hypertrophic degenerative arthritis of the facet joint. To study the stress distribution changes at the adjacent facet joint after lumbar fusion with pedicle screw fixation, human cadaver lumbar spines were used in the present study, and electrical resistance strain gauges were attached on L1-L4 articular processes parallel or perpendicular to the articular surface of facet joints. Subsequently, electrical resistance strain gauge data were measured using anYJ-33 static resistance strain indicator with three types of models: the intact model, the laminectomy model, and the fusion model with pedicle screw fixation. The strain changes in the measurement sites indirectly reflect the stress changes. Significant differences in strain were observed between the normal and laminectomy state at all facet joints. Significant differences in strain were observed between the normal and the pedicle screw fixation fusion state at the L1/2 and L3/4 facet joints. The increased stress on the facet joints after lumbar fusion with pedicle screw fixation may be the cause of adjacent segment degeneration.

Development of a Monitoring System for Crack Growth in Bonded Single-Lap Joints Based on the Strain Field and Visualization by Augmented Reality

In this work, a method for monitoring fatigue crack growth in a metal to composite bonded joint based on the strain field is proposed and applied in the framework of a visualization tool based on Augmented Reality (AR). This tool superimposes some virtual objects, which are the data acquired by the sensors and the crack length, directly on top of the specimen under inspection and in real time. By finite element (FE) analyses, a good correlation between the crack tip position and the strain field in a single lap specimen is found and this feature is exploited to monitor the crack length during fatigue tests and to feed the AR system to virtually visualize the crack on the real specimen. An array of electrical resistance strain gauges is bonded to the surface of one adherend. A Matlab function collects values from the strain gauges mounted on the specimen under investigation analyses them on the basis of the FE analysis and finally feeds the AR system. The validation of this process is done by measuring the crack by optical microscope. This procedure is also tested with the use of Fiber Bragg Gratings (FBG) optical strain gauges.

Stress State Evaluation in Complete Denture by Electrical Resistance Strain Gage

Total dentures are made of acrylic resins and artificial teeth. Among the prevalent fracture types of the dentures, 29% was a mid-line fracture, in which 68% were observed in maxillary complete dentures and 28% in mandibular complete dentures. Due to the large number of failures recorded on the maxillary dentures, several studies were conducted to establish the causes that produce these failures but also to find solutions for their prevention. One source of information about the strength of a maxillary denture under the applied load, is represented by the establishment of the stress and strain state during the loading. Different methods have been used for investigating the strain or stress distribution during deformation of dentures. The purpose of this paper is to evaluate the stress and strain state of a maxillary denture loaded in compression until the final fracture. For this study, electrical resistance strain gage were used for evaluation the strain and stress distribution in the maxillary denture made of different acrylic resins. Based on observations from practice, the strain gages were applied on the middle line of the denture at the base of the incisors and respectively on the sides of the denture, under molars. The dentures were loaded until failure and were registered the strains in the located strain gages. Also, for each type of acrylic resin were determined separately the mechanical properties of elasticity and strength. Based on the tests conducted were determined the critical stress and strain in the areas of interest. In all the tests carried out the fracture occurred in the median area of the denture and the crack was initiated between the incisor teeth. The stress and strain field associated with the crack initiation mode showed a strong influence of geometry on the fracture strength of denture. Also the type of acrylic resin has a significant effect on the fracture strength of complete denture either by strength capacity but especially by their ability to elasticity. Based on this analysis have been established new criteria for selection of acrylic resins, not only for aesthetic reasons but also for elasticity and strength reasons.

A preliminary study on the treatment of bruxism by biofeedback therapy

Objective: To evaluate the effect of wireless biofeedback therapy on bruxism. Methods: Fifteen bruxiers participated to be treated by this therapy. The abnormal movements of teeth during sleep were monitored by a maxillary splint with an electric resistance strain gauge. Meanwhile, the receiver device recorded these details and analyzed the data, including the value of the biting force, occurring time and duration. If the value of biting force or duration exceeds the threshold, a vibrating device like a watch style will alert the patient to relax the masticatory muscles and nervous system to stop the abnormal grinding or clenching. Data were recorded during 8 hours’ sleep and analyzed after the 12 weeks’ treatment and 24 weeks’ treatment. Results: The average episodes of bruxism have declined from (10.60 ± 1.23) to (6.60 ± 0.75) after 12 weeks’ treatment (p p treatment, and the average duration of bruxism events was reduced to (3.37 ± 0.34) s (p

전기저항식 변형률 게이지를 이용한 콘크리트의 열팽창계수 측정법

PURPOSES : The purpose of this study is to provide the method of how to measure the coefficient of thermal expansion of concrete using temperature compensation principle of electrical resistance strain gauge. METHODS : The gauge factor compensation method and thermal output(temperature-induced apparent strain) correction method of self-temperature compensation gauge were investigated. From the literature review, coefficient of thermal expansion measurement method based on the thermal output differential comparison between reference material(invar) and unknown material(concrete) was suggested. RESULTS : Thermal output is caused by two reasons; first the electrical resistivity of the grid conductor is changed by temperature variation and the second contribution is due to the differential thermal expansion between gauge and the test material. Invar was selected as a reference material and it's coefficient of thermal expansion was measured as <TEX>$2.12{\times}10^{-6}m/m/^{\circ}C$</TEX>. by KS M ISO 11359-2. The reliability of the suggested measurement method was evaluated by the thermal output measurement of invar and mild steel. Finally coefficient of thermal expansion of concrete material for pavement was successfully measured as <TEX>$15.45{\times}10^{-6}m/m/^{\circ}C$</TEX>. CONCLUSIONS : The coefficient of thermal expansion measurement method using thermal output differential between invar and unknown concrete material was evaluated by theoretical and experimental aspects. Based on the test results, the proposed method is considered to be reasonable to apply for coefficient of thermal expansion measurement.

An Experimental Investigation of Edge Strain and Bow in Roll Forming a V-Section

V-sections were roll formed from two grades of steel, and the strain on the top and bottom of the strip near the edge was measured using electrical resistance strain gauges. The channels were bent to a radius of 2 and 15 mm along the centerline. The steel strips were of mild and dual phase steel of yield strength 367 MPa and 597 MPa respectively. The longitudinal bow was measured using a 3-dimensional scanning system. The strain measurements were analysed to determine bending and mid-surface strains at the edge during forming. The peak longitudinal edge strain increased with material yield strength for both profile radii. For the 15 mm radius, the bow was larger in the dual phase steel than in the mild steel. For the 2 mm profile radius, the bow was smaller compared with the 15 mm profile radius and it was similar for both steels. It was observed that the difference between the peak longitudinal edge strain and yield strength to Youngs modulus ratio of the material is an important factor in determining longitudinal bow.

Over-pressure test on BARCOM pre-stressed concrete containment

Bhabha Atomic Research Centre (BARC), Trombay has organized an International Round Robin Analysis program to carry out the ultimate load capacity assessment of BARC Containment (BARCOM) test model. The test model located in BARC facilities Tarapur; is a 1:4 scale representation of 540MWe Pressurized Heavy Water Reactor (PHWR) pre-stressed concrete inner containment structure of Tarapur Atomic Power Station (TAPS) unit 3&4. There are a large number of sensors installed in BARCOM that include vibratory wire strain gauges of embedded and spot-welded type, surface mounted electrical resistance strain gauges, dial gauges, earth pressure cells, tilt meters and high resolution digital camera systems for structural response, crack monitoring and fracture parameter measurement to evaluate the local and global behavior of the containment test model.The model has been tested pneumatically during the low pressure tests (LPTs) followed by proof test (PT) and integrated leakage rate test (ILRT) during commissioning. Further the over pressure test (OPT) has been carried out to establish the failure mode of BARCOM Test-Model. The over-pressure test will be completed shortly to reach the functional failure of the test model. Pre-test evaluation of BARCOM was carried out with the results obtained from the registered international round robin participants in January 2009 followed by the post-test assessment in February 2011. The test results along with the various failure modes related to the structural members – concrete, rebars and tendons identified in terms of prescribed milestones are presented in this paper along with the comparison of the pre-test predictions submitted by the registered participants of the Round Robin Analysis for BARCOM test model.

Tension in a flat belt transmission: Experimental investigation

In this paper we report the results of an experimental investigation aimed at determining the tension variation in a flat belt transmission. The belt tension was obtained by measuring its deformation with electrical resistance strain gauges. The investigation results are preceded by a reference to the belt transmission theory, in particular to Grashof's and Firbank's models. With regards to the Firbank model, in order to better interpret the experimental results, some original calculations were carried out starting from Firbank's paper.The test results showed the efficiency of the Grashof model, as regards the presence of both an adhesion arc and a sliding one, which respectively decrease and increase with the growth of the force transmitted into the device and, at the same time, showed the Firbank model's validity in relation to the presence both of a shear strain and different sliding angles on the driving and driven pulleys.

The Reinforcement Effect of Strain Gauges Embedded in Low Modulus Materials

ABSTRACTThe reinforcement effect of electrical resistance strain gauges is well‐described in the literature, especially for strain gauges installed on surface. This paper considers the local reinforcement effect of strain gauges embedded within low Young modulus materials. In particular, by using a simple theoretical model, already used for strain gauges installed on the surface, it proposes a simple formula that allows the user to evaluate the local reinforcement effect of a generic strain gauge embedded on plastics, polymer composites, etc. The theoretical analysis has been integrated by numerical and experimental analyses, which confirmed the reliability of the proposed model.

The behaviour of weldable strain gauges under nuclear reactor core conditions

Electrical resistance strain gauges are a very useful tool to measure mechanical parameters such as deformation, stress, dynamic strain, vibration, etc. This paper presents our experience with strain gauges in nuclear reactor environments.The nature of nuclear applications and the desirable characteristics of nuclear strain gauges are discussed. Several in-reactor experiments featuring the use of strain gauges are described. The behaviour of weldable strain gauges under intense nuclear radiation is discussed. Experimental results and techniques for the successful applications of strain gauges in nuclear environments are presented.It is concluded that weldable stain gauges can be used successfully under the very hostile conditions of nuclear reactor cores if appropriate procedures are followed.

Commissioning and Evaluation of a Fiber-Optic Sensor System for Bridge Monitoring

This paper describes the design, commissioning, and evaluation of a fiber-optic strain sensor system for the structural health monitoring of a prestressed concrete posttensioned box girder railway bridge in Mumbai, India, which shows a number of well-documented structural problems. Preliminary laboratory trials to design the most appropriate sensor system that could be readily transported and used on site are described, followed by a description of load tests on the actual bridge undertaken in collaboration with Indian Railways and using locomotives of known weight. Results from the load tests using the optical system are compared with similar results obtained using electrical resistance strain gages. Conclusions are summarized concerning the integrity of the structure and for the future use of the sensor system for monitoring bridges of this type. Crack width measurements obtained during the load tests are also described.

Preliminary study of wireless biofeedback therapy for treatment of bruxism

To access the effect of wireless biofeedback therapy on bruxism. Ten voluntary bruxers (seven female and three male, mean age 26.1 years) were invited to participate in this clinical research. An electric resistance strain gauge was embedded in the position of canine of a maxillary splint for monitoring the abnormal clenching or grinding movement of teeth during sleep. The relevant details of bruxism events, including value of relative force, occurring time and duration were recorded and analyzed by the receiver device and monitoring program respectively. Meanwhile, for the purpose of nerve system and muscle relaxation, a watch-style device around the patient's wrist will vibrate to alert the patient of teeth grinding or clenching if the value of biting force and duration exceed the threshold. Total average episodes of bruxism and duration was observed during eight hours sleep, and was analyzed with one-way analysis of variance in SPSS 19.0 by the end of 6th week and three months following biofeedback therapy. The average episodes of bruxism has declined dramatically from (9.8 ± 2.2) times to (3.0 ± 1.2) times during one night (P < 0.05), and the average duration of bruxism events was reduced from (20.7 ± 12.2) s to (10.0 ± 3.4) s (P < 0.05) after six weeks biofeedback therapy. By the end of three months, the average episodes declined to (2.9 ± 1.2) times (P < 0.05), and the average duration decline to (9.2 ± 2.9) s (P < 0.05) with contrast to preliminary night. The pressure-based wireless biofeedback device is able to monitoring clenching and grinding of bruxism. The results suggest that biofeedback therapy may be an effective, novel and convenient measure for treatment of bruxism according to several months therapy.

Accelerated Fatigue Crack Growth in 6082 T651 Aluminium Alloy Subjected to Periodic Underloads

This paper presents a review of available evidence of higher than expected crack growth rates obtained under variable amplitude loading, and explanations for such behaviour. New findings based on fatigue tests performed using 6082 T651 aluminium alloy under a simple loading sequence that was expected to cause crack growth acceleration are presented. Crack propagation was monitored using both optical and the direct current potential drop (DCPD) method. In addition, electrical resistance strain gauges were used to detect the presence of crack closure. Scanning electron microscopy was also performed to correlate observed striations on the fracture surfaces with applied load sequences.

Fluctuation of bond stress–slip behaviour of deformed bar under displacement control

The fluctuation of the bond stress as a function of the slip of deformed bar was determined experimentally, under displacement control, using 200 mm concrete cubes with centrally embedded 16 mm deformed bar designed to be in a confined condition. The observed global fluctuation in the bond stress, measured by linear variable differential transformers, was verified by independent measurement of the local strains along the length of the embedded bar using bonded electrical resistance (ER) strain gauges. In the pull-out tests, the failure mode was by shear. The ER strain gauges were installed inside grooves carefully machined in the steel bar to prevent direct friction from the concrete damaging the strain gauges. This approach also prevented damage to the wires and wire/gauge connection during the process of bar slip. The global fluctuation of the bond stress–slip behaviour was determined graphically and analysed using a number of statistical methods and independently verified from the local strain variation along the bar obtained from the strain gauge readings. Based on these observations, the fluctuation in bond stress with slip under displacement control has been shown to be mainly dependent on the transverse rib pattern of the bar.

Research on the Residual Stresses in Cold-Formed Hat-Shaped Section

In the paper,the electrical discharge machining(EDM) technique was used to cut strips for cold-formed residual stress measurement of hat-shaped section.After adjusting the electrolyte ratio,designing specific the cutting tool and improving the methodof antiseptic treatment,the test results improved significantly. Electrical resistance strain gauges with EDM cutting technique were used to establish the magnitude and distribution of the residual stresses in cold-formed hat-shaped section.Based on the experimental findings, an idealized distribution pattern of the residual stress in cold-formed hat-shaped section is presented.

Experimental Investigation of a Self-Sensing Hybrid GFRP-Concrete Bridge Superstructure with Embedded FBG Sensors

A self-sensing hybrid GFRP-concrete bridge superstructure, which consists of two bridge decks and each bridge deck is comprised of four GFRP box sections combined with a thin layer of concrete in the compression zone, was developed by using eight embedded FBG sensors in the top and bottom flanges of the four GFRP box sections at midspan section of one bridge deck along longitudinal direction, respectively. The proposed self-sensing hybrid bridge superstructure was tested in 4-point loading to investigate its flexural behavior and verify the operation of the embedded FBG sensors. The longitudinal strains of the hybrid bridge superstructure were recorded using the embedded FBG sensors as well as the surface-bonded electric resistance strain gauges. The experimental results indicate that the embedded FBG sensors can faithfully record the longitudinal strains of the hybrid bridge superstructure in tension at bottom flanges and in compression at top flanges of the four GFRP box sections over the entire loading range, as compared with the surface-bonded strain gauges. So, the proposed self-sensing hybrid GFRP-concrete bridge superstructure can reveal its internal strains in serviceability limit state as well as in strength limit state, and it will have wide applications for long-term monitoring in civil engineering.

Toward an ideal electrical resistance strain gauge using a bare and single straight strand metallic glassy fiber

Electrical resistance strain gauges (SGs) are useful tools for experimental stress analysis and the strain sensing elements in many electromechanical transducers including load cells, pressure transducers, torque meters, accelerometers, force cells, displacement transducers and so forth. The commonly used commercial crystalline strain sensing materials of SGs are in the form of wire or foil of which performance and reliability is not good enough due to their low electrical resistivity and incapacity to get thin thickness. Smaller SGs with single straight strand strain sensing materials, which are called ideal SG, are highly desirable for more than seven decades since the first SG was invented. Here, we show the development of a type of minuscule length scale strain gauge by using a bare and single straight strand metallic glassy fiber (MGF) with high resistivity, much smaller lengthscale, high elastic limits (2.16%) and especially the super piezoresistance effect. We anticipate that our metallic glassy fiber strain gauge (MGFSG), which moves toward the ideal SGs, would have wide applications for electromechanical transducers and stress analysis and catalyze development of more micro-and nanoscale metallic glass applications.

Investigation of Static Failure for Cemented Carbide Cylindrical End Mill

Investigation of the cutting tool failure is one of the important factors in order to optimize the cutting parameters. This paper studies the cutting tool stresses (maximum principal, maximum shear and von Mises) at the shank and at the tip using three failure theories. These stresses are analyzed by means of the finite element method using MSC patran/nastran software and the experimental method using electrical-resistance strain gages. The comparison of the stresses obtained from these two methods for different feed rates and different rotation speeds are depicted in figures.

Optics-Based Strain Sensing System

An optics-based strain sensing system is being developed for quazi-distributed strain sensing in locations and environments that are not accessible to conventional strain sensors. The system comprises an Optical Interrogator that has been designed and constructed by Southern Photonics [1], and optical fibre coupled Bragg grating strain sensors. It has been tested using commercial fibre Bragg gratings [2] that were attached to 2 samples of 316 grade stainless steel and cycled in strain and temperature using an Instron mechanical testing machine and temperature controlled cabinet. The results have been compared to the performance of conventional electrical resistance strain gauges. Pairs of fibre Bragg gratings were simultaneously interrogated at 1540 and 1550 nm centre wavelengths to demonstrate the ability of the system to use multiple sensors for quazi-distributed sensing and temperature compensation. The Optical Interrogator resolution is approximately 4 microstrains, accounting for longer term temperature drift, and it is capable of resolving dynamic strains at rates of up to 90 Hz.