Thin-film Gauges Research Articles

Parameter-Free Data Reduction for Short-Time Hypersonic Heat Flux Measurements

High-speed flows associated with hypersonics require significant, diverse, and successful ground-test campaigns before engaging in a flight test program. The present investigation focuses on demonstrating a new data reduction pathway for estimating the source heat flux using an elegant, though fragile, thin-film temperature gauge. The rapid response time of such sensors makes them well-suited for shock tunnel experiments. In such experiments, contaminated flow, composed of diaphragm debris, can often damage the sensing element. For the moment, the existence of an ideal coating (or even a hardened sensing element) is presumed that preserves the sensor’s survivability and accuracy over several test runs. A dynamic, physics-based data reduction methodology is proposed that accounts for the protective coating and that is applicable to millisecond testing times. This paper addresses three critical issues for acquiring the best estimate of the source heat flux. These issues include a) the formation of a baseline data reduction view that accounts for thin coatings; b) the development of a dynamic calibration method that removes the need for specifying thermophysical or geometrical properties; and c) the introduction of a time-scaling that allows for calibration to be performed in alternative and convenient time frames. This last point demonstrates the concept of the dimensionless time map and its novel consequences. The procedure is demonstrated on a reduced formulation, illustrating the merit of the concepts.

Low-cost two-dimensional digital image correlation system

A low-cost digital image correlation (DIC) system for measuring two-dimensional displacement fields is described. Using an off-the-shelf camera, lens, and open-source DIC analysis software, displacement fields in aluminum and steel dog-bone tensile specimens were measured. Correction for out-of-plane motion is used to obtain strains from the displacement fields. Proposed DIC strain measurement system is validated using conventional thin-film strain gauges for strains below 1%. Average strain measurements from the DIC system were found to be within 1% of the measurement obtained using strain gauges. For strains between 1% and 10%, strain histories from the DIC systems displayed excellent correlation with strain measurements obtained using an extensometer.

Directly Deposited Thin-Film Strain Gauges for Force Measurement at Guide Carriages

Directly Deposited Thin-Film Strain Gauges for Force Measurement at Guide Carriages

Understanding Thermal Unsteadiness in Engine Representative Flows and Improved Methodologies for Derived Heat Transfer Calculations Using Thin-Film Gauges

Abstract The Oxford Turbine Research Facility (OTRF) is a high-speed rotating transient test facility, which allows unsteady aerodynamic and heat transfer measurements at engine representative conditions. In addition, a variety of inlet temperature profiles can be simulated in the rig including radial distortion, circumferential distortion, and swirl. However, the engine representative flows cause complications in the processing of heat transfer data. The unsteadiness in temperature data was found to significantly rise as temperature distortions were introduced in the nozzle guide vane (NGV) inlet profile, to model a lean-burn combustor exit. Using the NGV inlet temperature profile survey data, the thermal unsteadiness has been quantified and compared with a uniform inlet. The experiments with a radially varying NGV inlet temperature profile showed up to nine times higher thermal unsteadiness, compared to the uniform inlet. The second part of the paper is a continuation of the work presented in a previous paper by Singh et al. and describes improved methodologies for derived heat transfer calculations using thin-film gauges. In addition, the uncertainty associated with the derived heat transfer parameters, such as the heat transfer coefficient and adiabatic wall temperature has been quantified. The refined processing techniques have been demonstrated on casing heat transfer measurements, acquired in the OTRF with two inlet temperature profiles.

Study on the Fabrication and Characteristics of Tantalum-Nitride (TaN) Thin-Film Strain Gauges on the Silicon Substrate for Silicon-Based Heterogeneous Integration Application

Study on the Fabrication and Characteristics of Tantalum-Nitride (TaN) Thin-Film Strain Gauges on the Silicon Substrate for Silicon-Based Heterogeneous Integration Application

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.

Infrared thermography techniques for boundary layer state visualisation

Decarbonising power generation and aviation requires step changes in aerothermal technology. This necessitates working in large design spaces where boundary layer state and resulting loss and heat transfer characteristics are difficult to predict. Standard measurement techniques such as thin-film gauges and oil flow visualisation are intrusive and time consuming, so there is a need for rapid testing methods to diagnose boundary layer state and develop physical understanding. Infrared (IR) thermography has found wide use in aerothermal research and IR measurements of boundary layer state have been demonstrated in many experiments, however there is minimal literature on the best practices for fast and accurate measurements. IR transition measurements rely on temperature differences between laminar and turbulent regimes which are dependent on the thermal characteristics of the system. This paper shows how a 1D heat transfer analysis can be used to maximise the signal-to-noise ratio (SNR) of IR measurements. This can improve measurement quality and minimise complexity. Experimental validation is presented along with a demonstration of the value of IR in rapid testing.

Ultrafast high-temperature sintering of polymer-derived ceramic nanocomposites for high-temperature thin-film sensors

Polymer-derived ceramic nanocomposites (PDC-NCs) are promising materials for high-temperature thin-film sensor (TFS) applications. However, owing to their inherent high-resistance characteristics and the high-temperature furnace sintering process, it is difficult to integrate PDC-NCs with high-conductive and low high-temperature tolerant alloy/metal components. In this study, an ultrafast high-temperature sintering (UHS) method was employed to prepare PDC-NC TFSs in minutes. The TiB2/SiCNO film sintered by the UHS technique shows high-sensitive microstructure and properties to sintering parameters. The UHS technique allows rapid sintering toward the desired phase, controls the grain size and microstructure, promotes the precipitation of free carbon in the SiCNO matrix within minutes, and suppresses high-temperature oxygen pollution. For example, TiB2/SiCNO films show high conductivity (18.1 S cm−1 at room temperature) and high-temperature stability (up to 800 ℃). In comparison, these properties are orders of magnitude better than those of samples sintered in the furnace. High-quality films sintered using ultrafast heating and cooling rates can also withstand thermal shocks of up to 1000 ℃. With the UHS technique, high-quality and high-conductivity films can be prepared using an ultrafast sintering rate to prevent substrate thermal damage. The TiB2/SiCNO thin-film strain gauge with high sensitivity (GF = 8.6) and low thermal noise was fabricated on alloy substrates, and its high-temperature (25–800 ℃) strain sensing performance was verified. This method offers a new route for co-sintering devices with alloy/metal substrates that suffer from low high-temperature tolerance and regulating the microstructure and electrical performance of these devices.

A Bilayer Thin-Film Strain Gauge With Temperature Self-Compensation

A Karma–CuNi bilayer strain gauge with a low-temperature coefficient of resistance (TCR) is designed for temperature self-compensation. The impact of heat treatment and structural parameters on its performance is investigated. The TCR of the bilayer thin-film strain gauge can be adjusted to near 0 ppm/°C by controlling the thickness ratio and the annealing temperature. Besides, the Karma–CuNi thin films had a gauge factor (GF) of 2.2. Finally, the Karma–CuNi bilayer thin-film strain gauge was fabricated on the metal substrates and bone-like metal elastomer. An experimental setup based on bending beam theory was developed to determine the GF of the strain gauges fabricated on metal substrate. It shows promising applications for in situ strain or torque measurement of some metal component when high sensitivity and high spatial resolution is required.

Multilayer co-sintered Pt thin-film strain gauge for high-temperature applications

Typical high-temperature thin-film sensors are fabricated by layer-by-layer deposition and layer-by-layer sintering, which are time and energy consuming. In this study, thin-film strain gauges (TFSGs) were fabricated on superalloy substrate by co-sintering process for the first time. The co-sintering behavior of glassy insulating layer and Pt thin-film resistance grid was studied. Compared with layer-by-layer sintering, the weak interface constraint between the top and sub layers of co-sintered TFSG allows the free in-plane shrinkage of the Pt resistance grid. In the co-sintering process, the glassy SiO2 in the insulating layer fills the pores in the Pt resistance grid, significantly improving the compactness. Further, no Pt element diffuses into the insulating layer. Owing to the remarkable advantages of the co-sintering process, the co-sintered Pt TFSG not only inherits the high-temperature insulation (2.8 MΩ at 800 °C) of the layer-by-layer sintered insulating layer, but also significantly increases the high-temperature stability of the Pt grid resistance; the resistance change rate of layer-by-layer sintered samples at 800 °C is 7.3 % h−1, while that of co-sintered samples at 800 °C is only 0.9 % h−1. Finally, the high-temperature strain response of co-sintered Pt TFSG up to 800 °C was tested.

Temperature-insensitive conductive composites for noninterference strain sensing

Very few thin-film strain gauges (TFSGs) that exhibit temperature self-compensation have been developed. Their temperature insensitivity range is typically < 100 °C, and they cannot be used for static strain sensing in variable-temperature environments. In this study, environmental interference owing to temperature fluctuations was successfully eliminated by controlling electron scattering and thermally assisted hopping transport in conductive composites. A new temperature-insensitive material was developed. The proposed strategy enables noninterference dynamic strain monitoring over an ultrawide temperature range of 30–300 °C, which is approximately 200 °C higher than that of noninterference TFSGs that have been reported. In particular, we propose the smallest feature unit of electron transport in conducting composites, that is, the pathway of an electron through a conductive particle and adjacent junction. This unit retains all the features of the entire conductive network, such as the temperature-resistivity effect, and is the smallest unit that can fully reflect the electron transport behavior. We manipulated the microstructure such that the static strain affects only the arrangement and number of temperature-insensitive feature units without destroying its internal structure, enabling temperature independence under static strain. The first noninterference TFSG was designed with a gauge factor of > 2300 for static strain sensing. The thermal output strain error at 30–200 °C was < 0.0016%.

Graphene/SiCN Thin-Film Strain Gauges Fabricated by Direct Writing

The in situ strain/stress detection of hot components in harsh environments remains a challenging task. In this study, graphene/SiCN (G-SiCN) thin-film strain gauges (TFSGs) were fabricated on alumina substrates by direct ink writing (DIW). The percolation model and the piezoresistive effect of G-SiCN composites were systematically studied. On this basis, a TFSG with high conductivity (0.1 S/cm) and high sensitivity (gauge factor (GF) 9.9) of ceramic matrix conductive composites was fabricated. The graphene/SiCN TFSG has excellent static and dynamic strain response at room temperature. Subsequently, the strain dynamic test was conducted at 400 °C, and there was no attenuation of the GF, so as to verify the high-temperature performance of the G-SiCN TFSG. Therefore, G-SiCN TFSGs provide an effective approach for the measurement of the in situ static and dynamic strain of hot components in high-temperature environments.

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.

Abnormal Graphitization Behavior in Near-Surface/Interface Region of Polymer-Derived Ceramics.

The in situ free carbon generated in polymer-derived ceramics (PDCs) plays a crucial role in their unique microstructure and resultant properties. This study advances a new phenomenon of graphitization of PDCs. Specifically, whether in micro-/nanoscale films or millimeter-scale bulks, the surface/interface radically changes the fate of carbon and the evolution of PDC nanodomains, promotes the graphitization of carbon, and evolves a free carbon enriched layer in the near-surface/interface region. Affected by the enrichment behavior of free carbon in the near-surface/interface region, PDCs exhibit highly abnormal properties such as the skin behavior and edge effect of the current. The current intensity in the near-surface/interface region of PDCs is orders of magnitude higher than that in its interior. Ultrahigh conductivity of up to 14.47Scm-1 is obtained under the action of the interface and surface, which is 5-8 orders of magnitude higher than that of the bulk prepared under the same conditions. Such surface/interface interactions are of interest for the regulation of free carbon and its resultant properties, which are the core of PDC applications. Finally, the first PDC thin-film strain gauge that can survive a butane flame with a high temperature of up to ≈1300°C is fabricated.

Investigation of a High-Pressure Turbine Stage in a High-Speed Rotating Transient Test Facility for Rotor Tip Study and a Parametric Study for Improved Heat Transfer Calculation

Abstract The first part of the paper presents commissioning of a single-stage high-pressure (HP) turbine employed in a series of extensive experiments to study the aerodynamics and heat transfer on the rotor surface and casing liner. The Oxford Turbine Research Facility (OTRF), a high-speed rotating transient test facility has the capability to take unsteady aerodynamic and heat transfer measurements at engine representative conditions with a variety of inlet temperature profiles including radial distortion and swirl. A temperature profile survey was conducted at the inlet of the HP nozzle guide vane (NGV). Static and total pressure and temperature measurements have been taken at various locations on the rig including NGV surface, inlet and exit, and rotor exit to establish rig operating conditions. Detailed description of mass flow rate measurements along with calculation of heat loss factor in the rig is presented. The second part of the paper presents a parametric study performed to improve heat transfer measurement calculations from high-frequency response thin-film gauges. The effect of parameters like material properties and thickness of substrate on heat flux has been studied. A detailed uncertainty analysis for heat flux is also presented. A thermal model calibrated with analytical solutions has been developed to optimize thin-film gauge configurations and to study side-conduction effects.

Development of High-Temperature Wire-Grid Thin Film Strain Gauges.

Aero-engine turbine stator blades are often used in harsh environments with high temperatures and high pressure and are prone to fatigue fractures. Real-time and accurate monitoring of blade surface stress and strain is critical to ensure safe operation. In this study, thin-film strain gauges (TFSGs) that can be used in high-temperature environments above 1000 °C were designed and fabricated using a PtRh6 thin film as the sensitive material. The hysteresis effect of the stress transfer upon establishing a thermo-mechanical coupling finite element model of the Inconel718 high-temperature nickel-based alloy equal-strength beam PtRh6 TFSGs was analyzed and the optimal combination of thin-film thickness and longitudinal grid length of wire-grid TFSGs was determined. In order to solve the problem of high-temperature insulation, the insulating properties of a single-layer Al2O3 insulating film, a single-layer ZrO2 insulating film, a double-layer Al2O3/ZrO2 composite insulating film, and a four-layer Al2O3/ZrO2/Al2O3/ZrO2 composite insulating film at high temperature were compared and studied using scanning electron microscopy to analyze the microscopic morphology and composition of the four insulating film structures. The results showed that the four-layer Al2O3/ZrO2/Al2O3/ZrO2 composite insulating film had the best insulating properties at high temperatures. On this basis, an Al2O3/ZrO2/Al2O3/ZrO2 composite insulating film, PtRh6 sensitive layer, and Al2O3 protective film were sequentially deposited on a high-temperature nickel-based alloy equal-strength beam using DC pulsed magnetron sputtering technology to obtain an Inconel718 high-temperature nickel-based alloy equal-strength beam PtRh6 TFSG. Its gauge factor (GF) and temperature coefficient of resistance (TCR) were calibrated, and the results showed that the sensor could be used in harsh environments of 1000 °C. The above results provide new ideas for measuring stress and strain in aerospace under high-temperature and high-pressure environments.

Degeneration Effects of Thin-Film Sensors after Critical Load Conditions of Machine Components

In the context of intelligent components in industrial applications in the automotive, energy or construction sector, sensor monitoring is crucial for security issues and to avoid long and costly downtimes. This article discusses component-inherent thin-film sensors for this purpose, which, in contrast to conventional sensor technology, can be applied inseparably onto the component’s surface via sputtering, so that a maximum of information about the component’s condition can be generated, especially regarding deformation. This article examines whether the sensors can continue to generate reliable measurement data even after critical component loads have been applied. This extends their field of use concerning plastic deformation behavior. Therefore, any change in sensor properties is necessary for ongoing elastic strain measurements. These novel fundamentals are established for thin-film constantan strain gauges and platinum temperature sensors on steel substrates. In general, a k-factor decrease and an increase in the temperature coefficient of resistance with increasing plastic deformation could be observed until a sensor failure above 0.5% plastic deformation (constantan) occurred (1.3% for platinum). Knowing these values makes it possible to continue measuring elastic strains after critical load conditions on a machine component in terms of plastic deformation. Additionally, a method of sensor-data fusion for the clear determination of plastic deformation and temperature change is presented.

Additive-Manufactured Platinum Thin-Film Strain Gauges for Structural Microstrain Testing at Elevated Temperatures

This paper investigates the feasibility and performance of the fabrication of platinum high-temperature thin-film strain sensors on nickel-based alloy substrates by additive manufacturing. The insulating layer was made of a dielectric paste by screen printing process. A 1.8-micron-thick platinum film was deposited directly on the insulating layer. The four-wire resistance measurement method was used to eliminate the contact resistance of the solder joints. Comprehensive morphological and electrical characterization of the platinum thin-film strain gauge was carried out, and good static and dynamic strain responses were obtained, which confirmed that the strain gauge was suitable for in situ strain monitoring of high-temperature complex components.

ZrB2/SiCN Thin-Film Strain Gauges for In-Situ Strain Detection of Hot Components.

The in-situ strain/stress detection of hot components in harsh environments remains a challenging task. In this study, ZrB2/SiCN thin-film strain gauges were fabricated on alumina substrates by direct writing. The effects of ZrB2 content on the electrical conductivity and strain sensitivity of ZrB2/SiCN composites were investigated, and based on these, thin film strain gauges with high electrical conductivity (1.71 S/cm) and a gauge factor of 4.8 were prepared. ZrB2/SiCN thin-film strain gauges exhibit excellent static, cyclic strain responses and resistance stability at room temperature. In order to verify the high temperature performance of the ZrB2/SiCN thin-film strain gauges, the temperature-resistance characteristic curves test, high temperature resistance stability test and cyclic strain test were conducted from 25 °C to 600 °C. ZrB2/SiCN thin-film strain gauges exhibit good resistance repeatability and stability, and highly sensitive strain response, from 25 °C to 600 °C. Therefore, ZrB2/SiCN thin-film strain gauges provide an effective approach for the measurement of in-situ strain of hot components in harsh environments.

1D analytic and numerical analysis of multilayer laminates and thin film heat transfer gauges

The impulse response method is widely used for heat transfer analysis in turbomachinery applications. Traditionally, the 1D method assumes a linear time invariant, isotropic, semi-infinite block and does not accurately model the behaviour of laminated materials. This paper evaluates the error introduced by the single layer assumption and outlines the required modifications for multilayer analysis. The analytic solution for an N layer, semi-infinite laminate is presented. Adapted multilayer basis functions are derived for the impulse response method and used to evaluate the impact of uniform, isotropic assumptions. A numerical solution to the laminate problem is also presented. A penta-diagonal inversion algorithm, for a modified Crank-Nicolson scheme, is evaluated for fast stable implementation of multilayer simulation. The scheme shows comparable performance to the impulse response, whilst removing the requirement for linear time invariance. The methods are demonstrated in the case of analysing a thin film gauge, used in laboratory analysis of heat transfer in a turbine nozzle guide vane. Thin film gauge manufacturing techniques have advanced significantly in recent years. Advanced multilayer constructions are now used however, post-processing commonly relies on outdated single layer methods. This paper provides a universal methodology, required to analyse modern-day multilayer heat transfer measurements.