High Temperature Strain Gauges Research Articles

High-Temperature PdCr Thin-Film Strain Gauge With High Gauge Factor Based on Cavity Structure

High-Temperature PdCr Thin-Film Strain Gauge With High Gauge Factor Based on Cavity Structure

Structural Uncertainty Analysis of High-Temperature Strain Gauge Based on Monte Carlo Stochastic Finite Element Method.

The high-temperature strain gauge is a sensor for strain measurement in high-temperature environments. The measurement results often have a certain divergence, so the uncertainty of the high-temperature strain gauge system is analyzed theoretically. Firstly, in the conducted research, a deterministic finite element analysis of the temperature field of the strain gauge is carried out using MATLAB software. Then, the primary sub-model method is used to model the system; an equivalent thermal load and force are loaded onto the model. The thermal response of the grid wire is calculated by the finite element method (FEM). Thermal-mechanical coupling analysis is carried out by ANSYS, and the MATLAB program is verified. Finally, the stochastic finite element method (SFEM) combined with the Monte Carlo method (MCM) is used to analyze the effects of the physical parameters, geometric parameters, and load uncertainties on the thermal response of the grid wire. The results show that the difference of temperature and strain calculated by ANSYS and MATLAB is 1.34% and 0.64%, respectively. The calculation program is accurate and effective. The primary sub-model method is suitable for the finite element modeling of strain gauge systems, and the number of elements is reduced effectively. The stochastic uncertainty analysis of the thermal response on the grid wire of a high-temperature strain gauge provides a theoretical basis for the dispersion of the measurement results of the strain gauge.

High-Tolerance Thin-Film Solder Joints for Electrical Interconnection in Harsh Environments

This paper presents a pioneering use of thin-film solder joint in the electrical interconnection of high-temperature thin-film sensors, which aims to improve the low tolerance of traditional soldered balls in extreme environments. The structure of the thin-film solder joint, composed of silver foil, solder joint paste, and metal wire, has a negligible mass compared to traditional soldered balls. As a result, the inertia force on the solder joint/substrate interface during vibration and force impact is greatly reduced, improving the reliability of the solder joint under thermal-mechanical coupling impacts. The thin-film solder joint has been verified using both metal (AgPd paste) and ceramic (TiB2/SiCNO paste) solders, and can withstand extreme environments such as thermal shock and high "g" loading. The designed thin-film solder joint can withstand impact energy of up to 3 J at 1000 °C without failure, which is 6 times higher than that of traditional soldered balls (with a statistical failure rate of up to 67% under 0.5 J impact). The thin-film solder joint was successfully used for electrical interconnection of high-temperature thin-film strain gauges, demonstrating excellent reliability under thermal-mechanical coupling impacts at 1000 °C. Our high-tolerance thin-film solder joints show promising potential for use in electrical interconnection in harsh environments.

Enhanced high-temperature stability of indium tin oxide - Indium oxide thermocouples by two-step annealing

The complex internal structure of the aero-engine and the high-temperature, high-pressure, and high-speed airflow make it difficult to measure the internal temperature. Indium tin oxide (ITO) and In2O3 films have been studied for their application in high-temperature thermocouples and strain gauges. Due to their large Seebeck coefficient and high-temperature stability, ceramic thin-film thermocouples are expected to be used at high-temperature measure. In this paper, ITO-In2O3 thermocouples were fabricated by magnetron sputtering. Besides, the electrical properties of the air-annealed and two-step nitrogen-annealed thermocouples were compared, including the repeatability of thermoelectric response after multiple thermal cycles and the drift rate during the high-temperature duration. The microstructure and electrical conductivity of both the as-deposited and post-annealed ceramic thin films were tested respectively. The result shows that the resitivity and Seebeck coefficient of the thin films annealed in nitrogen is reduced, but the stability at high temperature is greatly improved.

AgPd Thin-Film Strain Gauges Fabricated by Direct Writing for High-Temperature Application

In-situ strain detection of complex structures at high temperatures remains a challenging task. In this article, the feasibility and performance of silver-palladium (AgPd) high-temperature thin-film strain gauge (TFSG) fabricated by direct ink writing (DIW) based on the Weissenberg effect is investigated, providing an in-situ strain detection method for structures working at high temperatures. The micrometer-thick AgPd film was directly written on a planar alumina substrate, and its surface topography and electrical were characterized. The four-wire resistance measurement method was adopted to eliminate the wire resistance and the contact resistance at the solder joint, thereby improving the accuracy of detection. The strain test at room temperature showed that the gauge factor (GF) of AgPd TFSGs under both tension and compression was about 1.25. They also possessed excellent linearity ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}$ </tex-math></inline-formula> 2 = 0.998), good static and dynamic responses, and extremely low mechanical hysteresis. To verify the high-temperature performance of the AgPd TFSG, the strain dynamic test was carried out at 600 °C. And there was no severe attenuation of the GF. AgPd TFSG fabricated by DIW provides an efficient method for in-situ static and dynamic strain detection of complex structures at high temperatures.

Influence of girth welding material on thermal and residual stress fields in welded lined pipes

An experimental and numerical investigation on the thermal and mechanical response of a lined pipe (compound pipe) under welding is presented. The welding process consists of a single-pass overlay welding (inner lap-weld) and a two-pass girth welding (outer butt-weld). The influence of the filler material of the girth welding has been examined thermally and mechanically as it is a key factor that can affect the quality of lined pipe welding. To this end, a three-dimensional non-linear finite element model based on the ABAQUS code has been developed and successfully validated against small-scale experimental results. This study was conducted on two specimens of lined pipe joined together by a girth welding deposited either by mild steel or by austenitic stainless steel. Furthermore, in this study, a pre-heat treatment required to produce lined pipe specimens has been taken into account. Strains and residual stresses have been measured by means of high temperature strain gauges, residual stress gauges and the X-ray diffraction technique along the inner and outer surfaces of the welded lined pipe whereas the thermal history has been recorded by thermocouples. The findings point out that replacing the girth welding mild steel by austenitic stainless steel has a significant effect on the residual stress results but no influence on the thermal history results.

TiB₂/SiCN Thin-Film Strain Gauges Fabricated by Direct Writing for High-Temperature Application

The in situ strain/stress monitoring of hot components in harsh environments remains a challenging task. In this study, TiB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /SiCN thin-film strain gauges were fabricated on nickel base alloy substrates via direct writing. The static and dynamic strain responses were investigated from 25 °C up to 800 °C. The results show that this thin-film strain gauge fabricated by ceramic-based materials exhibits excellent thermal stability and strain response. Without any anti-oxidative protective layer deposited, its operating temperature is as high as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$700^{\circ }\text{C}$ </tex-math></inline-formula> , which is 200 °C higher than that of the high-temperature piezoresistive thin-film strain gauges that have been developed and comparable to thin-film strain gauges with protective layers. The gauge factor of theTiB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /SiCN high-temperature thin-film strain gauge is 7.12, which is higher than that of most high-temperature thin-film strain gauges. In addition, the strain gauge exhibits excellent resistance stability with a mechanical hysteresis of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3~\mu \varepsilon $ </tex-math></inline-formula> and a resistance drift of 0.0008/h at room temperature. Therefore, TiB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /SiCN thin-film strain gauges provide an effective approach for the measurement of in-situ static and dynamic strain of hot components in harsh environments.

Real-time detection of damage evolution and failure of EB-PVD thermal barrier coatings using an environmental simulator with high-temperature and high-speed rotation

Thermal barrier coatings (TBCs) are key to improving aero-engine performance. The lifetime assessment of TBCs in a simulation environment is an essential consideration for successful application. Environmental simulators for rotor blade TBCs are still scarce, largely owing to the difficulty in obtaining real-time TBC failure data in extreme environments. In this work, an environmental simulator with high-speed rotation and gas thermal shock characteristics was developed and tested. High-temperature resistant strain gauges and thermocouples were fixed onto the surface of turbine blades by a flame-sprayed Al2O3 layer. The damage evolution and failure mechanism of TBCs were analysed by the real-time detection of strain damage and temperature field. The results reveal only a little fluctuation in the temperature distribution of the TBC surface (122 °C) under the synergistic effect of high-speed rotation and thermal shock, and the strain at each measuring point is tensile. During thermal cycling tests of the TBCs, the strain at a specific point varied from 0.21% to 0.79%. The final thermal shock life was determined to be 156 cycles, thus proving that the coating enables good thermal shock resistance. The spalled area was mainly distributed from the suction surface to the leading edge, and TBC failure could be attributed to crack initiation and propagation caused by the impact of the high-temperature flame and accumulation of fatigue load. The present work paves the way for coating preparation process optimisation and real service performance evaluation.

Contact High Temperature Strain Automatic Calibration and Precision Compensation Technology

In order to solve the problem of contact high temperature strain precision measure-ment, this paper established an automatic calibration device for high temperature strain gauges. The temperature of the high temperature furnace was automatically con-trolled by the temperature control device. The electric cylinder was driven by the servo motor to apply the load to the calibration beam. The output signal of the high temperature strain gauge, the thermocouple signal and the displacement signal of the grat-ing ruler were collected at the same time. The deformation measurement results obtained after temperature correction were used to calculate the theoretical mechanical strain, which were fed back to control the loading action to complete the automatic calibration process. Based on the above calibration device, the high temperature strain measurement accuracy correction software was developed to calibrate the high temperature strain gauge with multi-parameters, and the curves of sensitivity coefficient, thermal output, zero drift and creep characteristics with temperature were obtained, and a strain measurement accuracy compensation model was established. The high temperature strain measurement experiment was carried out to verify that the modified model can meet the requirements in each temperature range.

Microstructural influences on the damage evolution and kinetics of high temperature hydrogen attack in a C-0.5 Mo welded joint

In the refining industry, steels can be susceptible to a damage mechanism known as high temperature hydrogen attack (HTHA). The detection of damage in such structures through non destructive testing (NDT) requires insight into the damage development in various parts of welded joints. Once damage is detected, the tracking of the damage progression and estimation of remaining life is problematic. The performance of C-0.5 Mo steels in such environments is also variable, and the current tendency is to regard the HTHA resistance of C-0.5 Mo as similar to that of carbon steels. The current investigation explores the possibility of using high-temperature capsule strain-gauges for the in-situ evaluation of swelling – which generally accompanies HTHA in susceptible steels – and, thereby, evaluate the development and kinetics of HTHA damage for a C-0.5 Mo steel welded joint. Specimens were prepared representing the base metal (BM), the HAZ region, both fine-grained and coarse-grained, and the weld-metal (WM). The specimens were exposed to hydrogen at 200 bar at a temperature of 500 °C in an autoclave, with certain specimens fitted with high-temperature strain gauges; i.e. instrumented test labelled as IWM, IHAZ and IBM. Metallographic evaluation of the specimens – regarding the three locations mentioned – were performed; with exposure times reflecting both incipient and advanced damage. In the case of the base metal and the fine grained HAZ, and after pronounced damage, macrocracks were observed. The orientation and location of these cracks were aligned with the rolling direction, and the cracks were evident in the through-thickness plane of the plate. It was found that the reason for this observation was due to preferential damage accumulation within banded regions, where high concentrations of carbides were observed. A sigmoidal equation was developed that described the swelling kinetics of the HAZ. The expression of swelling-induced strain rate (SISR) versus time showed a low initial SISR until incipient damage is formed, followed by accelerated attack. The peak SISR was observed midway through the damage evolution, where after the SISRs decreased as the presense of carbides – that feed the methane reaction – diminishes. It is proposed that the attachment of the encapsulated strain gauges to structures or components where HTHA damage is suspected, will assist in the tracking of damage and the estimation of remaining life; if used in conjunction with the developed sigmoidal equation.

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.

Reliability of strain gauge measurements to clarify the strength of structures at high temperatures

The paper considers the problem of ensuring the reliability of experimental data obtained by tensometric studies of existing power plants. A technique that allows taking into account the change in the metrological characteristics of high-temperature strain gauges has been proposed. The design of the installation for determining the sensitivity of strain gages at temperatures up to 700°C has been considered.

Turbine Blade Mechanics Research Based on Strain Gauge Bonding Position

Aiming at the high-temperature strain gauge on the turbine blade of aero-engine, which needs to bear the high-temperature effect and reliably carry out the strain test, the turbine blades and adhesive strength of rubber layer of adhesive strain gauge were studied by the theoretical analysis, software simulation and experimental verification method. Three-dimensional model of turbine blade was built firstly. And then, the CFD of the blade fluid domain was analyzed. The bonding position of the strain gauge was determined under the actual working condition by the coupling analysis of hydrodynamics, centrifugal force, thermal stress and aerodynamic force. The reliability of strain position simulation of turbine blade was verified by dynamic strain contact measurement experiment. The effect of high temperature and CFD analysis of turbine blades with rubber layer was carried out. The effects of different rotational speeds on the adhesive strength of the adhesive were studied. It was shown that the strain and stress distribution of the blade’s pressure surface was more uniform than the suction surface.

Remaining Life Evaluation Based on Strain Deformation Monitoring

The operating conditions of a power plant affect its structural integrity due to many degradation mechanisms, among which is creep. Strain measurements constitute a relatively simple and reliable method of obtaining accurate data regarding the capability of engineering materials to withstand loads and of determining stress distribution in all manner of structural components. This work carried out a critical evaluation of the application of a high-temperature strain gage on a strain and stress analysis. The sensor was undergoing a group of long-term creep tests whose results were compared with the creep machine’s acquisition system. The same strain gage was part of a monitoring system and its out some used on the remaining life evaluation a power plant’s pipeline. The methodology consists of online strain monitoring of those components or regions more susceptible to creep failure, which were identified by finite element analysis. The long-term creep tests using high-temperature strain gages showed that the relative position between sensor and the sample necking region exercises great influence on the measured results. Linear relationship between minimum creep rate obtained by strain gages and rupture time values was observed. The power plant pipeline analysis showed that thermomechanical fatigue is the predominant degradation mechanism.

Experimental and numerical thermo-mechanical analysis of welding in a lined pipe

Experimental tests of multi-pass lined pipe welding are reported and a computational procedure for the determination of the history of temperature, strains and residual stresses is presented in this paper and validated against the experimental test results. The effect of the manufacturing process of the lined pipe on the thermo-mechanical analysis has been investigated. A 3-D FE model using ABAQUS has been developed to simulate a circumferential single-pass weld overlay (lap-weld) and two-pass girth welding (butt-weld). Thermal history and strain fields have been recorded during welding using thermocouples and high temperature strain gauges, respectively. Residual stresses have been measured using residual stress gauges, deep-hole drilling technique and the X-ray diffraction technique along the outer and inner surfaces of the lined pipe. The welding test has been repeated twice to assess the accuracy of thermal and mechanical measurements. Overall, very good correlation has been observed between the experimental and numerical results.

Influence of the sputter gas composition on the electromechanical properties and on the stability of TiAlNxO1-x thin films

Sputter deposited TiAlNxO1-x thin films are investigated as potential candidates for high temperature strain gauge applications. In this study the influence of the reactive gas atmosphere during deposition on the electromechanical properties is investigated up to 500°C with a custom-built measurement setup enabling gauge factor determination. It is shown, that TiAlNxO1-x thin films with no oxygen admixture during the deposition process show the most promising electromechanical properties. The gauge factor decreases from 3.3 to 2.4 between room temperature and 500°C, while in this temperature range the linear temperature coefficient of the electrical resistance has a value of −3.8·10−4K−1. Time-of-flight secondary mass ion spectrometry measurements are evaluated against the results of electrical resistance measurements to estimate the growth of an oxide layer on the surface of the TiAlNxO1-x thin films when operated at 500°C in air.

Comparison of Various Means of Attachment of High Temperature Strain Gauge

The article deals with problems of high temperature strain gauge measurements. A preliminary experimental work for purpose of mastery of this technique after a longer break has been kicked off in VZLÚ. Initially, possibilities of usage of commercial products and two means of strain gauge attachment were verified.

Experimental Investigation on Thermal Buckling Behavior of Truss-Core Sandwich Panels

This paper presents an experimental study on the thermal buckling behavior of sandwich panels with truss cores. The ultimate goal is to find the critical buckling temperature and examine postbuckling behavior of this newly developed sandwich panel experimentally. A specifically designed fixture, which can introduce in-plane loads to the sandwich panel through thermal expansion mismatch between the specimen and the load frame, is applied in the experiment. High-temperature strain gauges are attached at the center of the sandwich panel face sheets to measure the local in-plane response, and the critical buckling temperature of panels deformed in symmetric mode is determined by using the Southwell method. To obtain the full-field postbuckling mode as well as critical buckling temperature of the sandwich panel deformed in asymmetric mode in high-temperature environments, a noncontact measurement system based on the three-dimensional digital image correlation technique is also developed. The accuracy of the present noncontact measurement technique is validated by the coordinate measurement machine technique, a conventional contact measurement method. It is found that the critical buckling temperature obtained from experiments is lower than that predicted by theoretical and numerical models, due to defects and imperfections of the truss core and sandwich panel during fabrication. Full-field measurement also indicates that local yielding together with overall buckling is the typical deformation mode in the tested specimen.

Investigation of Bulging Behavior of Coke Drum—A Practical Analysis of Bulging Under Complex Quench Conditions

Coke drums undergo cyclic operations typically in the temperature range from room temperature to about 500 °C (930 °F). During quenching, the coke drum is inevitably subjected to a rapid drop in temperature because cooling water is injected directly into the coke drum through the bottom inlet nozzle. The temperature profile on the shell surface is uneven during quenching, and can vary in each cycle of the quenching operation. Such a complicated thermal profile induces large strains in the shell portion of the coke drum, and eventually causes damage like bulging and/or cracking. The authors have investigated the bulging behavior of the coke drum by the thermal elastic-plastic finite element (FE)-analysis, considering the existence of the overmatch welds and uneven temperature field during quenching (Ohata et al., 2011, “Investigation of Bulging Behavior of Coke Drum—Feasible Study on Causes of Bulging,” ASME PVP2011-57276, Baltimore). In this paper, a practical FE-analysis is developed to estimate the complex strain that leads to bulging under uneven temperature fields during quenching. The actual temperature and strain data during operation are collected by thermocouples and high temperature strain gauges. A thermal analysis model, including an evaluation of boiling heat transfer on the shell's inner surface, is established to simulate the measured shell behavior of the coke drum. By utilizing this FE-analysis model, several parameters thought of as causal factors in bulging can be examined under the uneven temperature profile that is likely to occur during actual operation. This analytical approach can also provide effective technique for improvements in shell durability.

TiAlN Thin Films as High Temperature Strain Gauges

A custom built measurement setup is used for the evaluation of the gauge factor and the temperature coefficient of resistance (TCR) of TiAlN thin films up to 350°C. The films are sputter-deposited on a sapphire beam from a TiAl target in a nitrogen atmosphere. The gauge factor at room temperature is about 2.5, decreasing only moderately at 350°C. In this temperature range, the TCR is about -1.75·10-4 K-1 being significantly lower than that observed at platinum which is taken as reference. The excellent mechanical stability of TiAlN and the low temperature dependency of both the gauge factor and the electrical resistance make this material a promising candidate for a new generation of strain gauges which can be operated reliable even at temperatures above 350°C.