Foil Strain Gauges Research Articles

LTCC Substrates for High Performance Strain Gauges

Recent advances in the development of high gauge factor thin-films for strain gauges prompt the research on advanced substrate materials. A glass ceramic composite has been developed in consideration of a high coefficient of thermal expansion and a low modulus of elasticity for the application as support material for thin-film sensors. Constantan foil strain gauges were fabricated from this material by tape casting, pressure-assisted sintering and subsequent lamination of the metal foil on the planar ceramic substrates. The sensors were mounted on a strain gauge beam arrangement and load curves and creep behavior were evaluated. The accuracy of the assembled load cells correspond to accuracy class C6. That qualifies the load cells for the use in automatic packaging units and confirms the applicability of the LTCC substrates for fabrication of accurate strain gauges. To facilitate the deposition of thin film sensor structures onto the LTCC substrates, the pressure-assisted sintering technology has been refined. By the use of smooth setters instead of release tapes substrates with minimal surface roughness were fabricated. Metallic thin films deposited on these substrates exhibit low surface resistances comparable to thin films on commercial alumina thin-film substrates. The presented advances in material design and manufacturing technology are important to promote the development of high performance thin-film strain gauges.

Magnetoelastic resonance sensor for remote strain measurements

A low cost passive wireless strain sensor is proposed. The basis of the sensor is formed by two softmagnetic magnetostrictive ribbons. The first magnetostrictive ribbon transforms mechanical stress into a stress dependent magnetic field. The second ribbon senses this field by magnetoacoustic oscillations. The resonance frequency directly depends on the applied mechanical stress. For the proposed sensor, a gauge factor Gf, which is defined as the relative change of the resonance frequency divided by the strain ɛ, of Gf = 380 is obtained. This is significantly higher than the gauge factor of standard metal foil strain gages.

Research on Integrated and Portable Weigh-in-Motion Scale

The integrated dynamic weighing scale with a high accuracy was developed based on analyzing the loads when vehicles passed on the weighing scale. The ANSYS software was applied to determine the sensor’s foil strain gauge position and the dynamic characteristic was verified through the experiment; meanwhile the hardware and measuring software in the system were simply introduced in this article. Finally through the experiments the Weigh-In-Motion (WIM) system can be used in traffic data collection and is assistant tool for overload check.

Carbon nanotubes grown on glass fiber as a strain sensor for real time structural health monitoring

In order to more effectively monitor the health of composite structures, a fuzzy fiber sensor has been developed. The fuzzy fiber is a bundle of glass fibers with carbon nanotubes or nanofibers (CNTs or CNFs) grown on the surface. The nanotube coating makes the fiber bundle conductive while the small conductive path increases sensitivity. The fuzzy fiber sensor can replace conventional metal foil strain gauges in composite applications. The electrical response of the sensor is monitored in real time to measure strain, vibration, cracking and delamination. Continuous monitoring provides instant notification of any problems. Implementation of this sensor network in a composite can increase service life, decrease maintenance costs and greatly reduce inspection downtime.

Strain measurement on stiff structures: experimental evaluation of three integrated measurement principles

This paper presents an experimental evaluation of three different strain measuring principles. Mounted on a steel beam resembling a car engine mount, metal foil strain gauges, piezoresistive silicon strain gauges and piezoelectric patches are investigated to measure structure-borne forces to control an active mounting structure. FEA simulation determines strains to be measured in the range of 10−8 up to 10−5 m × m−1. These low strains cannot be measured with conventional metal foil strain gauges, as shown in the experiment conducted. Both piezoresistive and piezoelectric gauges show good results compared to a conventional piezoelectric force sensor. Depending on bandwidth, overload capacity and primary electronic costs, these principles seem to be worth considering in an adaptronic system design. These parameters are described in detail for the principles investigated.

Design of thin-film polyvinylidene fluoride sensor rosettes for isolation of various strain components

Thin-film polyvinylidene fluoride piezoelectric sensors have long been recognized as a promising alternative to traditional metal foil strain gauges in applications where only dynamic or quasistatic signals are of interest. Compared to metal foil strain gauges, polyvinylidene fluoride sensors feature high sensitivity, high dynamic range, and broad frequency bandwidth. However, transverse sensitivity of the polyvinylidene fluoride sensor is higher than that of a metal foil strain gauge, making it more difficult to isolate a particular strain component or a deformation mode when the host structure is under complex loading. In addition, polyvinylidene fluoride films are sensitive to changes in ambient temperature due to the pyroelectric effect. In this article, three temperature-compensated polyvinylidene fluoride sensor rosette designs are proposed for isolating specific strain component(s) and deformation mode(s) of interest. First-principles based models are derived to relate the polyvinylidene fluoride sensor rosette output to the actual elastic strain component of interest. Experimental validation is conducted to verify the proposed models and to compare the performance of the polyvinylidene fluoride sensor rosettes with their metal foil strain gauge counterparts.

Development and evaluation of PPP-BOTDA based optical fiber three dimension strain rosette sensor

PPP-Brillouin Optical Time Domain Analysis (BOTDA) system based strain rosette is presented, in which optical fiber sensor rosette is investigated and fabricated as rectangular pattern for the measurement of three dimension strains. Experiments are carried on to evaluate the performance of optical fiber rosette with temperature compensation. Experimental results show that the BOTDA based optical fiber strain rosette exhibit a good strain response comparing with calibration foil strain gauge, which indicates a promising long distance and distributed multi-point combined stress measurement solution.

Measurement of tongue–artificial nipple contact pressure during infant sucking

AbstractTo clarify the motor function of the infant tongue during sucking, we developed an artificial nipple that contained multiple small built‐in force sensors integrated with a PC‐based system which is capable of measuring tongue–artificial nipple contact pressures in real time. The force sensor is a cantilever structure with a small, thin stainless steel beam where an all‐purpose foil strain gauge is attached to the surface of the beam. An artificial nipple made of an elastomer containing these sensors is connected through an amplifier and an A/D converter to a PC via a USB port. Using this system, measurements were taken in three infants whose oral feeding was well established and in one infant of low birth weight. The results from each force sensor showed a pressure waveform of a nearly simple harmonic motion that indicated a peristalsis‐like movement of the tongue; the sucking frequency was found to be about two times per second. In addition, in the low‐birth‐weight infant, the pressure changed as the infant grew. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

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.

Optical Sensor Developments for Measuring the Surface Strains in Prestressed Concrete Members

Abstract: Conventionally, transfer‐length strain measurements are performed using mechanical gauges such as the Whittemore gauge, or demountable mechanical (DEMEC) strain gauges, and others devices using ‘contact’ measuring principles. These methods involve tedious surface preparation, and are also prone to significant human errors and inaccuracies. Furthermore, these mechanical sensors can only detect lateral displacements. This paper presents a new optical sensor of measuring prestress concrete surface strains. It makes use of the laser‐speckle displacement that is detected by cross correlating the associated optical signals from a Charged‐Coupled Device (CCD) sensor. The sensor was designed to be able to measure the surface displacement components without being affected by other surface motions that are generally present during the concrete detensioning process. Experiments were conducted on a compressed concrete beam and a real prestressed concrete member during the manufacturing process. The results from the optical strain sensor showed good consistency with contact measurements made by using both a foil strain gauge and a Whittemore gauge.

IDENTIFICATION OF DAMAGE IN REINFORCED CONCRETE COLUMNS UNDER PROGRESSIVE SEISMIC EXCITATION STAGES

Prompt and accurate detection of realistic damage in constructed facilities is critical for effective condition assessment and structural health monitoring. This paper reports the experimental investigations of eccentric reinforced concrete columns mounted onto a shaking table and subject to progressively increasing seismic excitations. The investigation was aimed at studying the changes in the dynamic parameters in order to assess the structural conditions of the concrete columns after each post-seismic stage. The dynamic response of the structure was measured using accelerometers, traditional foil-strain gauges, and long-gauge fiber Bragg grating (FBG) sensors. The post-seismic conditions of the columns were evaluated via vibration-based damage identification methods. Results from this study demonstrate the applicability of specially packaged surface-mounted long-gauge FBG sensors for detecting the initiation and the progression of cracks due to reverse dynamic loads. The concept of modal macrostrain analysis was also introduced to identify and localize mild damage due to the applied seismic excitations of increasing intensities. The performance of the sensors for structural identification is also discussed.

SUS630 다이아프램을 이용한 반도체식 로드셀

The load cell is a force sensor and a transducer that is used to convert a physical force into a electrical signal for weighing equipment. Most conventional load cells are widely used a metal foil strain gauge for sensing element when force being applied spring element in order to converts the deformation to electrical signals. The sensitivity of a load cell is limited by its low gauge factor, hysteresis and creep. But silicon-based sensors perform with higher reliability. This paper presents the basic design and development of the silicon type load cell with an SUS630 diaphragm. The load cell consists of two parts the silicon strain gauge and the SUS630 structure with diaphragm. Structure analysis of load cell was researched by theory to optimize the load cell diaphragm design and to determine the position of peizoresistors on a silicon strain gauge. The piezo-resistors are integrated in the four points of silicon strain gauge processed by ion implantation. The thickness of the silicon strain gauge was polished by CMP under 100 <TEX>${\mu}M$</TEX>. The 10 mm diameter SUS630 diaphragm was designed for loads up to 10 kg with 300 <TEX>${\mu}M$</TEX> of diaphragm thickness. The load cell was successfully tested, the variation of <TEX>${\Delta}$</TEX>R(%) of four points on the silicon strain gauge is good linearity properties and sensitivity.

Multi-Functional Measurement Using a Single FBG Sensor

This paper describes the measurement of average strain, strain distribution and vibration of a cantilever beam made of Carbon Fiber Reinforced Plastics (CFRP), using a single Fibre Bragg Grating (FBG) sensor mounted on the beam surface. Average strain is determined from the displacement of the peak wavelength of reflected spectrum from the FBG sensor. Two unstrained reference FBG sensors were used to compensate for temperature drift. Measured strains agree with those measured by a resistance foil strain gauge attached to the sample. Stress distributions are measured by monitoring the variation in the full width at half maximum (FWHM) values of the reflected spectrum, using a proposed optical analytical model, described in the paper. FWHM values were measured for both the cantilever test beam and for a reference beam, loaded using a four-point bending rig. The trend of the stress distribution for the test beam matches with our analytical model, however with a relatively large noise present in the experimentally determined data. The vibration of a cantilever beam was measured by temporal analysis of the peak reflection wavelength. This technique is very stable as measurements are not affected by variations in the signal amplitude. Finally an application of FBG sensors for damage detection of CFRP plates, by measuring the natural frequency, is demonstrated. With small defects of different sizes applied to the CFRP plate, the natural frequency decreased with damage size.

A simple four-point-bending setup for measurement of mechanical stress on silicon field-effect transistors

A simple four-point-bending setup integrated with a foil strain gauge is presented for the direct measurement of mechanical stress (MS) on metal–oxide–semiconductor field-effect transistors (MOSFETs). The magnitude of the external MS applied to MOSFETs can be directly obtained through the resistance change due to strain in the strain gauge mounted on the wafer strip. Then the resistance change in the strain gauge is detected in a Wheatstone quarter-bridge circuit. In addition, the validity of the direct stress measurement is confirmed by using the finite element analysis. Finally, through the direct stress measurement on MOSFETs, the longitudinal piezoresistance coefficients appear to be fairly comparable with the reported values in earlier literatures. The stress measurement is also expected to be applicable to the evaluation of uniaxial-process-induced strained MOSFETs.

Geosynthetic strain gage installation procedures and alternative strain measurement methods for roadway applications

ABSTRACT: The measurement of geosynthetic strain is important to the development of numerical models that can predict the behavior of geosynthetic-reinforced flexible pavements. This paper outlines the key issues regarding foil strain gage selection, installation, and calibration on geosynthetics for dynamic strain measurement in roadway applications. The flexible nature of geosynthetics and the interaction of these materials with the adjacent layers of the pavement structure in a dynamic loading application limit the ability to use all types of strain gages and adhesives. While this paper does not cover every type of geosynthetic, it provides sufficient procedural details and illustrations of foil strain gage installations on a variety of geosynthetics (woven geotextiles and geogrids, nonwoven geotextiles and punch/drawn geogrids) and then outlines several alternative methods (wire extensometers, inductance coils and fiber optics) of dynamic strain measurement. While foil strain gages and closely spaced wire extensometers provide a localized value of displacement on a geosynthetic, wire extensometers and inductance coils provide a measure of global displacement (which includes slack in the geosynthetic) and redundancy in total strain measurements. Fiber optics is an emerging and very promising method of accurately measuring strain in geosynthetics, and at least one delivery system has been developed.

A new device for fretting fatigue testing

Fretting fatigue damage occurs in contacting parts when they are subjected to fluctuating loads and sliding movements at the same time. Fretting fatigue can reduce the fatigue life of materials by half or even more. Fretting fatigue tests are usually performed using universal hydraulic testing devices. The contact pressure is produced by a fixture, typically designed and manufactured by researchers. In this investigation, a new device is introduced in which the fluctuating loading is supplied by a variable crank system (VCSD). The device called VCSD for abbreviation is basically a position control machine in which displacements can be imposed with an accuracy of 0.01 mm. The axial and contact loads are measured by load cells. The friction load is also measured by using foil strain gauges using a Wheatstone bridge configuration. The functionality of the device is examined by making a comparison between fretting fatigue lives of a number of Al7075-T6 specimens tested on a universal testing machine and VCSD. The results show a very close agreement between the functionality of the two testing rigs. The main advantages of VCSD are its higher frequency with respect to universal devices, simplicity, and cheapness. It can be developed further for high and low temperature tests in future.

Variability in the Material Properties of Polymer Matrix Composites for Marine Structures

Abstract The test results from a composite material round robin manufacturing study are presented. The objective of the study was to investigate material property variability when different manufacturers were used to fabricate identical composite parts. The study was part of an ongoing Office of Naval Research project to determine the causes of material property variability of E-glass/vinyl-ester structural composites fabricated with a vacuum-assisted resin transfer molding process. The manufacturers that participated in the study consisted of five industrial composite fabricators that either had experience with U.S. naval fabrication projects or possessed commercial marine fabrication experience. The materials specified for the study were a 24 oz woven roving E-glass fabric and a rubber-toughened vinyl-ester resin system. The tests performed included constituent volume, tension, compression, in-plane shear, and flexure. The material coupon tests were performed on 5.1 mm (0.20 in.) thick cross-ply laminates in a warps parallel lay-up. A three-dimensional digital image correlation system was used to measure strain during testing to reduce the variability often experienced when using conventional foil strain gauges on heavy woven fabrics. The results of the testing indicated that compression had the most variability in both strength and modulus, which was attributed to the waviness of the fabric, while the flexural strength and tensile modulus had the least amount of variability.

Final report on supplementary comparison APMP.M.P-S8 in hydraulic gauge pressure from 100 MPa to 1000 MPa

This report describes the results of a supplementary comparison of hydraulic high-pressure standards at two national metrology institutes (NMIs) – National Metrology Institute of Japan, AIST (NMIJ/AIST) and Physikalisch-Technische Bundesanstalt (PTB), Germany – which was carried out during the period January 2007 to March 2007 within the framework of the Asia-Pacific Metrology Programme (APMP) and the European Association of National Metrology Institutes (EURAMET) in order to determine their degrees of equivalence at pressures in the range 100 MPa to 1000 MPa for gauge mode.The pilot institute was NMIJ/AIST. NMIJ/AIST used a hydraulic pressure balance and a pressure multiplier, and PTB used a controlled-clearance pressure balance as their pressure standards. High-precision pressure transducers were used as a transfer standard. The sensing element of the transducers was a foil strain gauge. To ensure the reliability of the transfer standard, two pressure transducers were used on the transfer standard unit. At the beginning and the end of this comparison, the transfer standard was calibrated at the pilot institute.From the calibration results, the behaviour of the transfer standard during the comparison period was characterized and it was found that the capability of the transfer standard for the purpose of this supplementary comparison was sufficient. The degrees of equivalence of the national measurement standards were expressed in terms of deviations from the supplementary comparison reference values and from each other, considered in combination with associated uncertainties of these deviations. The hydraulic pressure standards in the range 100 MPa to 1000 MPa for gauge mode of the two participating NMIs were found to be equivalent within their claimed uncertainties.Main text.To reach the main text of this paper, click on Final Report.Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by APMP, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Laboratory Evaluation of Geogrid Base Reinforcement and Corresponding Instrumentation Program

Abstract The performance of geogrid base reinforcement in pavement on weak subgrade under cyclic plate load testing was studied. The performance of instrumentation sensors was also evaluated to improve future instrumentation programs. The tests were conducted inside a test box of dimensions of 2.0×2.0×1.7 m3 using a servo-hydraulic actuator. A 40-kN load at a frequency of 0.77 Hz was applied through a 305-mm-diameter steel plate. The sensors used included linear variable displacement transducers, pressure cells, bondable foil strain gages, and piezometers. The test results showed that the inclusion of geogrid at the subgrade/base course layer interface can significantly improve the performance of flexible pavement on weak subgrade (California bearing ratio=0.5 %) and that the traffic benefit ratio can be increased up to 3.5 for a rutting depth of 25 mm. The test results also showed that the reinforcement can redistribute the applied load to a wider area, thus achieving an improved stress distribution on the subgrade, which will eventually reduce the permanent deformation of subgrade. The bondable foil strain gages are unsuitable for long-time continuous monitoring of strain development within geogrid under high number of cyclic loading.

フォトリソグラフィを用いたインテリジェントタイヤ用ゴムベース電気容量型ひずみセンサの作製

From a traffic safety point-of-view, there is an urgent need for intelligent tires equipped with strain sensors as a warning system for road conditions and for optimized braking control on poor road surfaces. However, since a conventional foil strain gage has high stiffness, it causes the analyzed region to behave unnaturally. The present study proposes a novel rubber-based strain sensor fabricated using photolithography. The rubber base has the same mechanical properties as the tire surface; thereby the sensor does not interfere with the tire deformation and can accurately monitor the behavior of the tire. This investigation details the design and manufacture of the rubber-based sensor. For verification, the sensor was attached to a beam specimen and found to have a fatigue life of over 10^6 and a measurable strain range up to 14%. The sensor was applied to a commercially available automobile tire and found to successfully measure the strain of the tire.