Application Of Strain Gauges Research Articles

The relevance of shock absorber friction on the total friction of a MacPherson suspension system during lateral manoeuvres

The friction potential of the suspension is typically considered to be invariant as the vertical dynamics of a vehicle are analysed. However, the current research on MacPherson suspensions indicates a strong dependence of the suspension friction on the present driving situation, which is primarily characterised by the wheel deflection relative to the chassis, and the tyre forces. Although it is well known that the shock absorber is generally subjected to side loads that can vary and initiate a certain amount of friction, the precise contribution of the shock absorber friction to the total suspension friction has yet to be investigated in detail. It is therefore essential to conduct a quantitative study on the importance of the shock absorber in the context of specific driving situations regarding the development of new, friction optimised shock absorber generations. The present study investigates the relationship between total suspension friction and the friction of the shock absorber, with a particular focus on the case of wheel lateral forces that aim to represent a simplified cornering manoeuvre of the vehicle. This is realised by using a multi-body simulation approach and a strain gauge application in order to estimate the side force at the shock absorber’s top mount. Subsequently, the shock absorber friction is determined using a test setup that considers the realistic load and mounting situation from the perspective of the MacPherson suspension subsystem. The combination of simulation and shock absorber friction measurement is sufficient to fully explain the characteristic friction trend on suspension (subsystem) level. The contribution of the shock absorber friction to the total suspension friction is determined to be a maximum of 80%, emphasising the importance of considering the side force at the shock absorber while aiming for suspension friction minimisation and ride comfort performance enhancement. On the other hand, the shock absorber’s contribution is also observed to be limited depending on the actual wheel force, indicating that the friction of the other components remains a crucial factor in the MacPherson suspension concept.

Fatigue Strength Analysis of a Prototype Francis Turbine in a Multilevel Lifetime Assessment Procedure Part III: Instrumentation and Prototype Site Measurement

Part I of this series of publications addressed the background and fundamentals of the lifetime assessment of prototype Francis turbines. Part II concentrated on the developed methods of numerical calculation and assessment procedures. The present contribution (Part III) deals with the instrumentation and the metrological range of the assessment procedure. The most important sensors, measurement tools, and data acquisition units are presented (background). The instrumentation of the prototype Francis turbine is used, on the one hand, for machine unit monitoring and plant operating and, on the other hand, for generating measurement data to validate and adjust/correct the numerical simulations. Measurement data form the basis for further evaluations at various levels. A wide variety of measured variables are required to carry out the remaining lifetime of a component using fatigue analysis. Those variables include pressure and acceleration signals, vibration monitoring, and strain gauge applications for mechanical stress analysis. The available measurement signals are divided into groups based on the developed method. Thus, already-available data from the control room are compared with machine monitoring and temporarily measured data. The correlation of all available data is essential today to determine an exact idea of the occurring flow phenomena and their effects on the mechanical stresses on the component. This interaction of the different data sources and, subsequently, the use of selected quantities for the numerical calculation are part of the newly developed concept for fatigue strength analysis of mechanical components of a turbine unit (methods). The results of this journal article are divided into the discussion of the necessary instrumentation and mounting of the sensors and into the evaluation, presentation, and interpretation of the measurement data. In addition, a fatigue strength assessment is made at the position of the strain gauges. These results serve as a basis for validating the numerical stress calculation. It is worth mentioning that the validation of the numerical results and the discussion of the deviations and error consideration is carried out in Part IV of this publication series (results). This journal article of the series on condition assessment of prototype Francis turbines ends with a discussion of the results and conclusions for further data processing (conclusion).

Study on the formulation of green/eco thick film piezo resistive paste for strain gauge application

Thick film piezo resistors, such as strain gauges fabricated using screen printing technology, are widely used for pressure-sensing applications. This paper reports the study of RuO2-based piezoresistive pastes formulation using lead-free glass frits for their potential application for strain gauges. Thermal analysis (TG/DTA) of the prepared glass frit and piezo resistor paste composition was performed to understand the thermal behavior of the paste and the glass transition temperature of the glass frit. The XRD patterns of the films revealed no variation in the conductive phase concentration concerning the firing temperature. SEM analysis of the glass frit powders and the RuO2 powder show submicron-sized agglomerated particles. Electrical measurements showed that the samples fired at 750 ​°C have high gauge factor values (GFL ​= ​18.08, GFT= 12.50), indicating that this is the most suitable firing temperature to achieve the high gauge factor in the present study.

Application of a full-scale strain gauge to study the stress-strain state of structures subjected to the action of a liquid-metal coolant at high temperatures

A technique for studying the stress-strain state of structural elements exposed to an aggressive liquid metal with temperatures up to 500°C was developed. Strain gauges were used to solve the problem installed on the internal and external surfaces of the equipment. The operability of measuring instruments was checked during bench tests under conditions close to operational ones. An algorithm was proposed to determine the stresses at dangerous points of the structure. The developed technique was assessed during tests of a BN-type nuclear reactor.

A Post-Processing Method Based on Radial Basis Functions for the Fast Retrieval of the Strain Field in Digital Image Correlation Methods.

Digital image correlation methods allow the determination of the displacement (and thus the strain) field of a target by picture comparisons, without the application of strain gauges or other invasive devices. Homologous sites are mapped from the undeformed to the deformed configuration, and displacements retrieved at a cloud of points in a scattered fashion. Radial basis functions (RBF) offer a rapid and reliable tool to post-process on-the-fly data from image correlation, in order to compute deformations directly without the need for generating a numerical grid over the measurement points. Displacements and associated strains can be computed only where desired, tracking automatically only the most reliable features for each image. In this work, a post-processing strain evaluation method for large displacement problems, based on RBF and the Green-Lagrange tensor, is presented and demonstrated for several test cases. At first, the proposed method is adopted on a set of artificially generated pictures, demonstrating a faster convergence with respect to FEM even when few points are used. Finally, the approach is applied to cases for which experimental results are available in the literature, exhibiting a good agreement.

Compliant Mechanism-Based Sensor for Large Strain Measurements Employing Fiber Optics.

We propose a sensor design for measurement of large strains where direct application of a fiber optic strain gauge is impossible due to the stiffness mismatch between the optical fiber and the structure under test. The sensor design is based on a rhombus type compliant mechanism, which functions to attenuate input strain and transfer it to the ends of the sensing beam with the mounted optical strain gauge. We developed an analytical model of the sensor, which allows us to relate actuation forces, input displacement/strain, and output strain. The analytical model was verified with the finite element analysis and validated against an experimental prototype. The prototype sensor was able to handle input strains exceeding ±2.5 × 105 µε. Potential application areas of the proposed sensor include compliant elastomeric structures, wearables, and soft robotics.

A constitutive equation for the kinetics of high temperature hydrogen attack and its use for structural life prediction

The damage due to high temperature hydrogen attack (HTHA) accumulates over time through the formation, growth, and coalescence of methane-filled cavities, followed by microcrack and macrocrack formation and presenting a threat to structural integrity. Early attempts at the prevention of this damage mechanism from occurring in steels in hydrogen service at high temperatures were based on the first publication of the Nelson Curves in 1949 but have not always been successful. The consequence of HTHA failures have often been disastrous and much work is currently being done with a view to better prediction of the course of the HTHA damage process and assessment of structural integrity in the face of HTHA. Current work coordinated by the WRC is based on the calculation of the dynamic methane pressure in grain boundary cavities, since the methane pressure provides the driving force for cavity growth and damage evolution. The WRC work makes use of a Methane Factor, α, which is material and microstructure specific. It also utilizes a concept of an “additional stress”, Δσ, due to the internal methane pressure.In this paper, high-temperature strain gauging was used on samples exposed to accelerated HTHA conditions in an autoclave. The strain gauges were applied to various zones of a C-0.5Mo welded joint in order to track the damage evolution in the base metal, HAZ and weld metal. Over time, the process of HTHA damage gave rise to steadily increasing strain due to the formation and growth of voids and the subsequent HTHA damage processes, up to a saturation point, beyond which the strain remained static. These curves were subsequently converted to Damage Fraction - Time curves, with the Damage Fraction ranging from 0 to 1, similar to the MPC-Omega creep curves used in API 579. It was found that the kinetics of HTHA damage evolution could be described by a single sigmoidal equation with different constants for the various weld zones and for different steels. The results of published strain-time curves for a carbon steel were similarly analyzed and similar findings were made.Analysis of the HTHA damage evolution rate vs time curves, indicate that the damage rate steadily increases with increasing time up to a maximum value, where after it decreases steadily up to the point where the damage rate is zero, at the end of the HTHA damage evolution process. The time corresponding to maximum damage evolution was generally found to be midway through the HTHA damage process. This behavior was attributed to the depletion of carbides with increasing damage evolution, resulting in declining damage rates at times beyond the time corresponding with the maximum damage rate. It is shown how the HTHA damage curves can be compared to experimentally determined or calculated creep damage curves in order to determine the “additional stress” and Methane Factor terms, used in the WRC HTHA structural integrity assessments. It was furthermore discussed how the kinetic equations formulated can be used in conjunction with the in-situ application of high-temperature strain gauges to various structural elements in HTHA service, can be used as an aid in HTHA life assessment.

Impact of Annealing on Magnetic Properties and Structure of Co40Fe40W20 Thin Films on Si(100) Substrate.

Co40Fe40W20 monolayers of different thicknesses were deposited on Si(100) substrates by DC magnetron sputtering, with Co40Fe40W20 thicknesses from 10 to 50 nm. Co40Fe40W20 thin films were annealed at three conditions (as-deposited, 250 °C, and 350 °C) for 1 h. The structural and magnetic properties were then examined by X-ray diffraction (XRD), low-frequency alternative-current magnetic susceptibility (χac), and an alternating-gradient magnetometer (AGM). The XRD results showed that the CoFe (110) peak was located at 2θ = 44.6°, but the metal oxide peaks appeared at 2θ = 38.3, 47.6, 54.5, and 56.3°, corresponding to Fe2O3 (320), WO3 (002), Co2O3 (422), and Co2O3 (511), respectively. The saturation magnetization (Ms) was calculated from the slope of the magnetization (M) versus the CoFeW thickness. The Ms values calculated in this manner were 648, 876, 874, and 801 emu/cm3 at the as-deposited condition and post-annealing conditions at 250, 350, and 400 °C, respectively. The maximum MS was about 874 emu/cm3 at a thickness of 50 nm following annealing at 350 °C. It indicated that the MS and the χac values rose as the CoFeW thin films’ thickness increased. Owing to the thermal disturbance, the MS and χac values of CoFeW thin films after annealing at 350 °C were comparatively higher than at other annealing temperatures. More importantly, the Co40Fe40W20 films exhibited a good thermal stability. Therefore, replacing the magnetic layer with a CoFeW film improves thermal stability and is beneficial for electrode and strain gauge applications.

β-Ga2O3 Schottky diodes based strain gauges with high resistance, large gauge factor, and high operating temperature

We report observation of the piezoresistive effect of β-Ga2O3 Schottky diodes and investigate its application for strain gauge sensors. The Schottky diode-based strain gauge exhibits resistance on the order of 107 Ω, which allows low power applications. A large gauge factor of −201 ± 43 is measured from a Pt/(2¯01) β-Ga2O3 Schottky diode at room temperature, enabling the strain-induced resistance change to be measurable without a Wheatstone bridge. Mechanical exfoliation in the (100) surface produces β-Ga2O3 single crystal thin films, which are more suitable for strain gauge applications than bulk substrates. Owing to the wide bandgap nature, we demonstrate high-temperature operation of strain sensing based on β-Ga2O3 Schottky diodes up to 800 K. The β-Ga2O3 Schottky diodes simultaneously function as temperature sensors, which may enable temperature compensation of strain gauge output.

Accuracy of strain measurement systems on a non-isotropic material and its uncertainty on finite element analysis

The application of strain gauges as recommended by the ASTM standards provides accurate strain measurements in isotropic materials. However, their use in composite materials becomes more challenging due to their anisotropic nature. In this study, we hypothesized that the use of the distributed sensing system and the three-dimensional digital image correlation, which can average strain along a line and surface, respectively, may account for strain variability in composite materials. This study shows an investigation on the mechanical properties of unidirectional, cross-ply, and angle-ply carbon-epoxy specimens using strain gauges, distributed sensing system, and digital image correlation. The Bhattacharyya distance method was used to provide a preliminary evaluation of the closeness of the three different measurement techniques while the B-basis statistical method was used to analyze the experimental data in order to obtain a more conservative and reliable material parameter compared to the conventional averaged value, recommended by ASTM standards. Finally, a finite element model was created in Ansys Workbench™ as a means of evaluating the implication of a single point strain gauges measurement, versus a line or a surface strain measurement. The finite element analysis investigation was performed at a laminae level using the measured experimental elastic modulus and at a lamina–lamina level in which the elastic modulus of the unidirectional case was used as input in all the laminate configurations. The former analysis showed good agreement between the finite element analysis and all the strain measurement systems with an averaged percentage difference below 5%. The latter analysis showed a higher discrepancy in the measured percentage difference. A comparison between the finite element analysis and the strain gauges measurements showed an overall percentage difference between the range of 10% and 26%. Distributed sensing system and three-dimensional digital image correlation measurements provided an overall percentage difference below 10% for all the specimen configurations with a maximum percentage difference recorded for the longitudinal angle-ply case of approximately 9%.

Measurement of Strain Induced on a Deep Placement Fertilizer Applicator by Static load and Finite Element Simulation

This paper briefly reveals study results performed on a deep placement fertilizer applicator (DPFA) in order to measure strain gage resistances and calibrate a strain gage piece of equipment in laboratory conditions. The finite element method (FEM) simulation was performed in order to identify stress concentrated areas by strain gage attachments, and to determine optimum material properties for a DPFA prototype fabrication. New laboratory arrangements and theories of resistance force determination of a DPFA were developed in order to simulate different soil depths (0.15, 0.20, 0.25m) and apply a static load (5000N) in laboratory conditions. Unique practical knowledge was obtained in terms of different strain gage applications on the DPFA in its rigid form to obtain strain gage resistances. It was found that the strain sensitivity of the strain gages depended on the work dimensions of strain gage characteristics.

Simultaneous static and dynamic bulk modulus measurements under hydrostatic stress conditions and without applying strain gauge

The static properties of subsurface rocks are needed for geomechanical applications, but the dynamic properties are usually more extensively available and can be acquired with much less effort. Therefore, it is important to know the relationships between the static and dynamic properties. Studying these relationships based on traditional triaxial testing yields confusing results, partly due to intrinsic deficiencies of the experimental setup and testing procedures. We have developed a new approach to study the relationship under hydrostatic stress conditions. The traditional ultrasonic velocity measurement system is sufficient for all of the testing, and it requires no application of the traditional strain gauge. During the pressure-dependent ultrasonic velocity measurements, the rock sample experiences static deformation when the pressure changes are in the order of megapascals. If the pore pressure is kept constant, the pore volume will vary with the confining pressure. The pore volume change can be monitored accurately by the pore pressure controlling pump, and it can be related to the volume strain of the rock for estimating the static bulk modulus of the rock sample. Based on the laboratory ultrasonic measurements available in the literature, we analyzed the effects of the differential pressure, clay content, crack density, and pore fluid on the relationship between the static and dynamic bulk moduli. From the analyses, we inferred that most of the laboratory-observed differences between the static and dynamic property may not exist for the reservoir rock under in situ conditions.

Study and fabrication of a flexible Zr-based metallic glass thin film strain gauge

Metallic glass is an amorphous structure and has excellent mechanical properties such as high strength, hardness and elastic strain limitation. In this study, a Zr-based metallic glass thin film was deposited on a polymer substrate using the sputter technique for strain gauge applications. A copper thin film strain gauge was fabricated to compare with the properties of the Zr-based strain gauge. Different thicknesses of the thin films were fabricated for comparison. The gauge factor of the Zr-based strain gauge is 2.4 times higher than that of the copper strain gauge. The temperature coefficient of resistance of the Zr-based metallic glass thin film is extremely low, 8 × 10−6 °C−1, which is essential to reduce thermal drift for strain gauge applications.

Ultrasonic fatigue testing under multiaxial loading on a railway steel

Ultrasonic fatigue testing is a relative recent fatigue study methodology that applies resonant principles for the induction of stress cycles in a specific designed material specimen. Such experimental method can apply fatigue damage at high frequencies, most commonly at 20 kHz. It was created with the main purpose of studying material fatigue life in the Very High Cycle Fatigue regime between 10E07 and 10E09 cycles with a higher performance of time and energy wise in comparison to conventional servo-hydraulic machines.In this study an ultrasonic fatigue testing machine was used in order carry out multiaxial tension/torsion fatigue tests at a frequency of 20 kHz. The main objective was to reach a reliable multiaxial fatigue testing method, by modifying only the specimen, with the ability to choose the shear-axial stress ratio.The improved design of the testing method was focused in innovative design specimen by conducting both numerical and experimental analysis. Thermographic imaging, laser displacement measurements, and the application of rosette strain gauges to the main stress region of the specimen were carried out in order to validate the new improved design concepts. These strain and displacement results were compared with the ones obtained by finite element and a good agreement was achieved.A first series of fatigue tests were carried out intension/torsion multiaxial fatigue and the results are discussed in order to understand the feasibility of multiaxial fatigue tests at ultrasonic frequencies.

Real-Time Wood Behaviour: The Use of Strain Gauges for Preventive Conservation Applications.

Within the heritage field, the application of strain gauges on wood surfaces is a little-explored but inexpensive and effective method to analyse the environmental appropriateness of rooms for the wooden heritage collections they contain. This contribution proposes a wood sensor connected to a data logger to identify short moments with an elevated risk of harm. Two experiments were performed to obtain insights pertaining to the applicability of wood sensors to evaluate preservation conditions. (1) The representativeness of strain gauges on dummies was tested for their use in evaluating the preservation conditions of a range of wooden objects exposed to the same environment. For this, three situations were mimicked: a bare wood surface, a wood surface covered with a preparation layer, and a wood surface covered with a preparation and varnish layer. (2) The usability of strain gauges to monitor the wood behaviour in real-time measurements was tested with a monitoring campaign of almost two years in a church where a new heating system was installed. The results of both experiments are promising, and the authors encourage a broader application of strain gauges in the heritage field.

Piezoresistive effect and strain gauge application of β-Ga2O3

We report observation of the piezoresistive effect of β-Ga2O3 and investigate its application for strain gauge sensors. Ti/Au ohmic contacts are fabricated on commercially procured β-Ga2O3 materials. We employ the transfer length measurement pattern to remove the influence of contact resistance on the resistance measurement of β-Ga2O3 samples, especially when measuring the relatively small piezoresistance change due to strain. A gauge factor of −5.8 ± 0.1 is measured from a Ti/Au-β-Ga2O3-Ti/Au structure under tensile uniaxial stress in the [010] direction at room temperature.

Influence of a heterolayered Al2O3–ZrO2/Al2O3 ceramic protective overcoat on the high temperature performance of PdCr thin film strain gauges

The application of PdCr thin film strain gauges on gas turbine engines requires protective overcoats to prevent the oxidation of the PdCr sensitive element. In this work, a heterolayered Al2O3–ZrO2/Al2O3 ceramic film, which was fabricated by electron beam evaporation, is utilized as a protective overcoat over the PdCr sensitive thin film. The morphology and microstructure of the prepared films indicate that the composite Al2O3–ZrO2 film is smooth and compact, and the interface between the composite Al2O3–ZrO2 film and Al2O3 film is crack-free, which contributes to improving the protective performance of the heterolayered Al2O3–ZrO2/Al2O3 ceramic protective overcoat at high temperature. Moreover, the PdCr thin film strain gauge with heterolayered Al2O3–ZrO2/Al2O3 ceramic film as protective overcoat displays a minimum drift rate of less than 0.09%/h at 800 °C, and excellent cyclic repeatability such that the eight cyclic curves of the relative grid resistance are almost overlapped from room temperature to 800 °C, indicating the excellent protecting performance of the heterolayered Al2O3–ZrO2/Al2O3 ceramic overcoat. It also reveals the smallest temperature coefficient of resistance of 155.3 ppm/°C compared to the monolayer Al2O3 overcoat and composite Al2O3–ZrO2 overcoat.

Przegląd metod badania napięcia taśm gumowych w przenośnikach taśmowych wykorzystywanych w transporcie bliskim

The review of existing solution and the proposal of the test equipment for belts tension detection on the conveyor in the real time is presented. Application of strain gauges made it possible to obtain the data, which would enable to make proper work condition diagnosis and to adapt the process to requirements of the Industry 4.0.

Ultrasonic fatigue testing under multiaxial loading conditions on a railway wheel

Ultrasonic fatigue testing is a relative recent fatigue methodology that uses resonant principles for the induction of stress cycles in a specific designed material specimen. This experimental method can apply very high cycle frequency, the most common frequency being 20 kHz, and was created with the main purpose of studying material fatigue life in the Very High Cycle Fatigue regime between 107 and 109 cycles with a higher performance of time and energy wise in comparison to conventional servo-hydraulic machines. In this study an improvement of an already built multiaxial ultrasonic fatigue machine in the Instituto Superior Técnico laboratories was carried out to specific designed specimens and afterwards a fatigue study was made for a material of a worn-out railway wheel. The particular design of the specimen was achieved by numerical and experimental analysis based on previous experiments and components. Thermographic imaging and the application of rosette strain gauges to the main throat of the specimens were conducted in order to validate the improved specimen design and to understand the real induced stresses on the specimen. Afterwards fatigue tests were conducted for several specimens for a wide range of stresses with a stress ratio R=-1 and an axial vs shear stress ratio of around 0.58. Results were analysed and fracture analysis was also carried out.

Efficient Generation of Engine Representative Tip Timing Data Based on a Reduced Order Model for Bladed Rotors

In modern compressors, the assessment of blade vibration levels as well as health monitoring of the components are fundamental tasks. Traditionally, this assessment is done by the application of strain gauges (SG) to some blades of the assembly. In contrast to SGs, blade tip timing (BTT) offers a contactless monitoring of all blades of a rotor and there is no need of a telemetry system. A major issue in the interpretation of BTT data is the heavily undersampled nature of the signal. Usually, newly developed BTT algorithms are tested with sample data created by simplified structural models neglecting many of the uncertainties and disturbing influences of real applications. This work focuses on the creation of simulated BTT datasets as close as possible to real case measurements. For this purpose, a subset of nominal system modes (SNM) representation of a compressor rotor is utilized. This model is able to include a large number of features present in real measurements, such as mistuning, static blade deflections due to centrifugal loads, aerodynamic damping, and multiple mode resonances. Additionally, manufacturing deviations of the blade geometry, probe positioning errors (PPEs) in the BTT system, and noise in the time of arrivals (TOAs) are captured by the BTT simulation environment. The main advantage of the created data is the possibility to steadily increase the signal complexity. Starting with a “perfect” signal the simulation environment is able to add different uncertainties one after the other. This allows the assessment of the influence of different features occurring in real measurements on the performance and accuracy of the analysis algorithms. Finally, a comparison of simulated BTT data and real data acquired from a rig test is shown to validate the presented approach of BTT data generation.