Strain Sensitive Element Research Articles

A preliminary study on multi-material fused filament fabrication of an embedded strain gauge for low-cost real-time monitoring of part strain

Unlike other manufacturing techniques, additive manufacturing enables part consolidation through the production of multi-material parts with enhanced functionality. With reference to the functionality of monitoring the structural integrity of a product during its use, conductive filaments can be used in additive manufacturing. This work aims to investigate the applications of multi-material fused filament fabrication to produce embedded strain gauges for real-time monitoring of part deformations. In layer-by-layer fabrication, conductive filaments can be used to produce strain-sensitive elements inside products at a low cost. This preliminary study demonstrated the feasibility of the proposed approach using tensile samples fabricated through additive manufacturing. The samples were produced using a polyethylene terephthalate glycol filament and an acrylonitrile styrene acrylate filament, while electrically conductive polylactic acid was used for the strain gauge. The characterization and testing activities were conducted by comparing the results of the tensile testing with data acquired through an experimental system set up with an Arduino board, aligning with the resistance-based strain gauge theory. The findings show that the co-fabricated strain gauge successfully traces part deformation, enabling real-time monitoring of strain in the elastic field. Nevertheless, further optimization of the proposed approach is imperative to enhance the reliability and accuracy of the methodology.

INSTRUMENT FOR MEASURING PULSATION CHARACTERISTICS IN TURBULENT FLOWS

The paper considers the design of a two-component strain gauge construction for measuring pulsation characteristics in turbulent flows.
 The analysis is carried out and the shortcomings of the existing sensor models and their influence on the reliability and accuracy of the experimental results are shown. The limited frequency range of such sensors is also emphasized.
 The design of the previous types of sensors is based on a plate on which wire or film strain gauges are glued. In such models, the main part of the perceiving hydrodynamic pressure goes to the formation of stresses in the elastic plate, and only a small part (up to 4%) - to create stresses in the strain-sensitive elements. Such sensors require an increase in the size of sensitive elements, this causes an additional disturbance in the flow, which in turn also reduces the accuracy of the measurement.
 The use of glue in the design of the sensor is associated with adverse effects such as creep and aging of the glue.
 The proposed sensor used strain gauges in the form of constantan wires stretched parallel to each other, which helped to get rid of elastic plates and glue, and also reduced the size of the sensing element.
 A construction of the sensor is shown and its design is described.
 The sensor has a free vibration frequency in water of more than 300 Hz, which is more than an order of magnitude higher than the frequency of water flow oscillations. This allows a more accurate measurement of pulsation characteristics.
 The principle of operation of the strain gauge is considered.
 The presence in the construction of four correspondingly located tensile strands made it possible to measure the longitudinal and transverse components of the pulsation velocities in turbulent flows.

Comprehensive detection device and physical testing for mechanical properties of seabed sediments and shallow gas

In this paper, a comprehensive detection device for the mechanical properties of seabed sediments and shallow gas is designed, which is mainly composed of the seabed sediment mechanical properties detection part, the shallow gas detection part and the ultrasonic wireless transmission part. The mud water gas separation structure of the shallow gas detection part separates the shallow gas from the mud water, and then the methane concentration in the shallow gas is measured by the non-dispersive infrared methane sensor, which realizes the collection of the submarine shallow gas and the automatic real-time monitoring of the concentration. The measurement of the mechanical properties of seabed sediments realizes the real-time measurement of the three parameters of cone resistance, sidewall friction and pore water pressure, which characterize the mechanical properties of seabed sediments, through strain-sensitive elements. The ultrasonic wireless data transmission part is mainly for the data detected by the mechanical properties of the seabed sediments to be wirelessly transmitted to the sensor placement room through the ultrasonic transducer across the mud-water-gas separation structure. Finally, the data measured by the two parts are transmitted to the mother ship through the cable located in the sensor placement room. The experimental results show that it has the ability to comprehensively detect the mechanical properties of seabed sediments and shallow gas, and has strong operability.

High temperature static and dynamic strain response of PdCr thin film strain gauge prepared on Ni-based superalloy

Thin film resistance strain gauges are being developed to monitor the in-situ static and dynamic strain of engine blades in aerospace propulsion and power generation system. In this work, the palladium chromium thin film strain gauge, which consists of four layers: graded buffer layer, insulating layer, strain sensitive element and protective layer, is prepared on Ni-based superalloy by vacuum sputtering deposition technique. The static and dynamic strain responses are investigated from room temperature up to 800 °C. The results of static testing demonstrate that the resistance of the gauge exhibits a linear change dependent on strain and displays excellent repeatability. The gauge factor shows temperature dependence, which is calibrated to be 1.78, 1.94, 2.03 and 2.13 at 25, 400, 600 and 800 °C, respectively. For dynamic strain response, the resistance of palladium chromium thin film strain gauge varies periodically, which keeps the same frequency with the K465 test bar vibrates driven by the shaker system at the resonance frequency. The results indicate that PdCr thin film strain gauge has a fast response enough to monitor the dynamic strain change. Then, the dynamic strain can be derived from the dynamic variation of resistance of the thin film strain gauge up to 800 °C. Therefore, palladium chromium thin film strain gauge provides an effective approach for the measurement of in-situ static and dynamic strain of engine blades in aerospace propulsion.

Design of SAW sensor for longitudinal strain measurement with improved sensitivity

This paper presents the design of a highly sensitive surface acoustic wave (SAW)-based sensor with novel structure for the longitudinal strain measurement. The sensor utilizes thin lithium niobate (LiNbO3) diaphragm as the sensing element rather than the bulk substrate. The application of the diaphragm effectively decreases the cross-sectional area of the strain sensitive element, and meanwhile reduces the resistance between the sensor and the specimen. The newly designed strain sensor is to operate around a frequency of 50 MHz. The insertion loss of − 12 dB and quality factor of 63 are obtained analytically from impulse-response model. The sensor performance with tensile testing of the steel beam is predicted by the finite element method. The prestressed eigenfrequency analysis is conducted with the COMSOL commercial software. The simulation shows the resonance frequency of the sensor shifts linearly with the strain induced in the testing beam. For the SAW sensor with traditional configuration applying 1 mm thick substrate, the strain sensitivity is obtained as 0.41 ppm/μe. For the sensor with the novel design employing thin diaphragm with the thickness of 200 μm, the strain sensitivity is increased to 0.83 ppm/μe. With the availability of the bulk micromachining of LiNbO3, the application of the piezoelectric diaphragm as sensing element in SAW strain sensor can be an alternative way to enhance the sensor sensitivity.

Fully integrated carbon nanotube composite thin film strain sensors on flexible substrates for structural health monitoring

Multifunctional thin film materials have opened many opportunities for novel sensing strategies for structural health monitoring. While past work has established methods of optimizing multifunctional materials to exhibit sensing properties, comparatively less work has focused on their integration into fully functional sensing systems capable of being deployed in the field. This study focuses on the advancement of a scalable fabrication process for the integration of multifunctional thin films into a fully integrated sensing system. This is achieved through the development of an optimized fabrication process that can create a broad range of sensing systems using multifunctional materials. A layer-by-layer deposited multifunctional composite consisting of single walled carbon nanotubes (SWNT) in a polyvinyl alcohol and polysodium-4-styrene sulfonate matrix are incorporated with a lithography process to produce a fully integrated sensing system deposited on a flexible substrate. To illustrate the process, a strain sensing platform consisting of a patterned SWNT-composite thin film as a strain-sensitive element within an amplified Wheatstone bridge sensing circuit is presented. Strain sensing is selected because it presents many of the design and processing challenges that are core to patterning multifunctional thin film materials into sensing systems. Strain sensors fabricated on a flexible polyimide substrate are experimentally tested under cyclic loading using standard four-point bending coupons and a partial-scale steel frame assembly under lateral loading. The study reveals the material process is highly repeatable to produce fully integrated strain sensors with linearity and sensitivity exceeding 0.99 and respectively. The thin film strain sensors are robust and are capable of high strain measurements beyond

Glass based IDC sensor element for flex loads on MLCCs in PCB manufacturing chain

This paper presents a new in situ monitoring method of mechanical flex loads, which are acting on MLCC (multi-layer ceramic capacitors) devices in a PCB (printed circuit board) manufacturing chain. This method allows also considering solder joint properties as well. For this purpose a S3MD (stress sensitive surface mounted device) was designed as glass based package equivalent with strain sensitive pattern for a 0805 SMD chip device. Here, an interdigital capacitor was used as strain sensitive element. A solderable termination was created to enable the solder mounting. To obtain the load limits for different MLCC termination types, several bending tests were done in accordance to AEC Q200 Board Flex standard. In this case a suitable active measurement circuit was used with an overall accuracy of 4 fF and a noise level of 15 aF. Finally the characteristics of the sensor response, related to the AEC Q200 standard bending experiment, were determined. The use of such a S3MD instead of MLCC allows to record loads at several device locations during specific processes. This sensor can further be used as assessment criteria for process validation in the PCB manufacturing chain.

Silicon based in-situ measurement system for flex loads on MLCCs in PCB manufacturing chain

A new in-situ monitoring method of mechanical loads acting on MLCC (multi layer ceramic capacitors) devices during the PCB manufacturing chain is presented in this paper. A S3MD (stress sensitive surface mounted device) is designed as a silicon based package equivalent with strain sensitive pattern for an 0805 SMD chip device. Metal thin film resistors of Cu55Ni45 and Ni65Cr35 are used as resistive strain sensitive elements. A solderable termination is created to get the solder mounting option. Bending tests like descripted in AEC Q200 “Board Flex” were done to obtain the load limits for different MLCC termination types. Therefore a suitable PCB is designed with 4-terminal-sensing. Different bending speeds are performed to characterize the possibility to analyze creeping behavior of the solder or adhesive joint with the S3MD sensor elements. Finally a depaneling process with rotary blade is performed with an in-situ measurement of the load intensity acting on the devices during the process depending on the cutting edge distance.

Preliminary development, simulation and validation of a weigh in motion system for railway vehicles

The development of efficient Weigh In Motion (WIM) systems with the aim of estimating the axle loads of railway vehicles in motion is quite interesting both from an industrial and an academic point of view. This kind of systems is very important for safety and maintenance purposes in order to verify the loading conditions of a wide population of vehicles using a limited number of WIM devices distributed on the railway network. The evaluation of the axle load conditions is fundamental especially for freight wagons, more subjected to the risk of unbalanced loads which may be extremely dangerous both for the vehicle safety and the infrastructure maintenance. In this work the authors present the development, the simulation and the validation of an innovative WIM algorithm with the aim of estimating the axle loads $\widehat{N}$ of railway vehicles (the axle loads include the wheelset weights). The new estimation algorithm is a general purpose one; theoretically it could be applied by considering as input different kinds of track measurements (rail shear, rail bending, sleepers with sensors, etc.) and could be easily customized for different kinds of signals. In the paper a benchmark case based on rail bending measurements is proposed in which the longitudinal deformations e xx measured on the rail foot through strain sensitive elements are used as input. The considered input is affected by noise and bandwidth limitations and, consequently, is a good benchmark to test the robustness of the new algorithm. To estimate the axle loads, the algorithm approximates the measured physical input through a set of elementary functions calculated by means of a single fictitious load moving on the track. Starting from the set of elementary functions, the measured signal is then reproduced through Least Square Optimization (LSO) techniques: in more detail, the measured signal is considered as a linear combination of the elementary functions, the coefficients of which are the axle loads to be estimated. Authors have also developed a physical model of the railway track. The model consists of the planar FEM (finite elements method) model of the infrastructure and of the two-dimensional (2D) multibody model of the vehicle (the effects of lateral dynamics are treated as disturbances) and takes into account both the coupling between adjacent loads moving on the track and the vehicle dynamics. The physical model of the track and the innovative WIM algorithm (both considering possible measurement errors) have been validated by means of the experimental data kindly provided by Ansaldo STS and have been implemented in the Matlab and Comsol Multiphysics environments. In particular the model of the railway track has been developed expressly to test the WIM algorithm with a suitable simulation campaign when experimental data are not available; in other words it provides simulated inputs to test the WIM algorithm when there are no experimental inputs.

Development of a Miniature Strain Gauge

The cervical facet joint capsule is the major origin of neck pain. To in vivo test the cervical facet capsule strain, a flexible, miniature strain gauge was developed. A special liquid metal served as the strain sensitive element, and a tubular structure was selected as the configuration of this miniature strain gauge. Calibration tests and rear-end crash simulation experiments were performed to analyses the behavior of this new gauge. A physical head-neck model or living goat model was used as a human surrogate. Experiment results indicated the good linearity and stability of this miniature strain gauge. With the improvement of structural designs and manufacturing techniques, the miniature strain gauge stated in this paper has the potential to in vivo test the cervical facet capsule strain.

A simple strain sensor using a thin film as a low-finesse fiber-optic Fabry–Perot interferometer

A simple extrinsic optical-fiber strain sensor that uses a thin transparent elastic polymer film acting as a low-finesse Fabry–Perot interferometer has been developed and tested. The polymer is mounted at the end of a multi-mode optical fiber as a strain sensitive element. The strain resolution of the sensor is 2×10 −6, the accuracy is 5×10 −6 over dynamic range 0–5000×10 −6.

Experimental characterization of dynamic micromechanical transducers

This paper starts with a short review on interferometric methods for optical analysis of resonant structures. Three important types of resonant sensor elements are then discussed: a piezoelectrically driven beam as the strain sensitive element of a bulk micromachined force-sensor, electrothermally driven/piezoresistively detected single and triple beams as the sensing elements of a bulk micromachined resonant accelerometer, and an electrostatically driven capacitively detected torsional resonator in surface micromachining technology, the key element of a (pseudo-) vibrating gyroscope. We present optical and electrical measurements and discuss the importance of crosstalk in the electric pickup signal. The dynamic behaviour of the resonant accelerometer in closed-loop undamping circuitry is analyzed by external excitation on a shaker table.

Characteristics of polysilicon resonant microbeams

Polysilicon resonant microbeams can be used as strain-sensitive elements to replace conventional silicon piezoresistors in precision sensor applications, such as pressure sensors and accelerometers. These elements are combined with conventional silicon diaphragms or flexures with a proof mass to convert pressure or acceleration directly into a frequency output. Vacuum-enclosed resonant microbeam elements 200 or 400 μm long, 45 μm wide and 1.8 μm thick have been fabricated using LPCVD mechanical-grade polysilicon at the University of Wisconsin. Q-values determined using gain/phase analysis are typically over 25 000. Lower Q-values are primarily the result of residual gas in the cavity. Closed-loop operation from −60 to 180°C using piezoresistive sensor and electrostatic drive has been achieved with automatic gain control (AGC) to prevent overdrive. The characteristic resonance frequencies of the beams have been measured, with 550 kHz, 1.2, 2.2 and 5.2 MHz being typical of the frequencies of the one-dimensional bending modes for the 200 μm length. These measurements of the multiple resonance frequencies of a single beam provide a means of testing mathematical models of the dynamic behavior as well as determining the residual beam stress. The one-dimensional (1D) differential equation of motion of a doubly clamped single-span beam with an axial load can be solved analytically for lateral natural frequencies and mode shapes. These 1D solutions have been verified by 3D finite-element methods. In addition, the finite-element models are used to identify both lateral and torsional modes. The closed-form solutions agree closely with the numerical results and the experimental data.

Free-end beam-type force sensor with thick film resistor as strain-sensitive element: Towards an optimum construction

An analytical method useful for the optimization of force sensors based on the deflection of a free-end beam with a thick-film resistor on its surface is presented. Formulae describing the dependence of sensor sensitivity, resolution and peak force value (the sensor is capable of converting) on its construction parameters have been obtained. In many cases the method leads to a considerable saving of resistive paste and a reduction of sensor size, with simultaneous sensor-parameter preservation. The sensitiveness of the sensor sensitivity to changes of its parameters has been calculated and a tolerance analysis of the sensor sensitivity using a Monte Carlo method has been done. The measured parameters of test sensors based on Dupont 1451 and 8049 resistive pastes and alumina substrates are in good agreement with theoretical predictions.

Influence of reactor irradiation upon the electrophysical characteristics of heteroepitaxial p-silicon-on-sapphire layers

This paper reports on the results of an investigation of the influence of neutron and gamma reactor radiation upon the electrophysical properties and the coefficients of elasto-resistivity of highly alloyed p-silicon-on-sapphire structures with concentrations of 5.3 X 10/sup 18/-1.8 X 10/sup 20/ cm/sup -3/ of the alloying admixture. These elements were used as strain transducers of mechanical quantities. The samples were irradiated in a VVR-2000 reactor under normal conditions. The results of the investigations show that highly alloyed silicon-on-sapphire structures with a degree of doping about 6 X 10/sup 19/ cm/sup -3/ can be used to build strainsensitive elements capable of working under the conditions of reactor irradiation without changing their sensitivity by more than 2-4%.

Integrated Strain-Sensitive Element of Mechanical Transducer with Low Temperature Instability

Integrated Strain-Sensitive Element of Mechanical Transducer with Low Temperature Instability

Possibility of designing a force transducer with one-piece strain-sensitive elements

Possibility of designing a force transducer with one-piece strain-sensitive elements

Piezoelectric Gauge for Measurement of Pin and Socket Connector Contact Forces

The need for a convenient means of measurement of the actual contact force for a pin and socket connector is outlined and the design of a piezoelectric strain gauge suitable for use with in-line connectors is described. PZT is used for the strain sensitive element of the gauge, and the relatively large electric charges produced by small strains permit the use of a very simple electrical circuit. With sufficient experimental care, variations in contact force for different sockets of a given type may be correlated with variations in contact resistance.