Strain Gauges Research Articles

Model Updating and Assessment using Axial Strains for a Statically Determinate Truss Bridge

The safety of aging structures over the course of their service life is given by structural reliability. Additionally, there is a lack of techniques available for processing raw structural health monitoring (SHM) data in a way that makes it possible to validate and/or update structural reliability. Along with the diagnosis of structural anomaly using SHM techniques, the prognosis of structural condition is also an important aspect. Field-measured strain responses can be used as an indication of structural safety and provide information regarding the load-carrying capacity of the structure. Reliability assessment can be conducted only if a more accurate digital analogue is obtained for the actual bridge and when the structural responses can be predicted accurately. This paper validates a digital model of a real-life railway truss bridge. Pamban bridge is a century-old railway bridge having one track and four internally statically determinate truss leaves. Electrical strain gauges are instrumented to measure the axial strain responses in 84 out of 92 members of the bridge. Strain responses of 1072 train movements that traversed the bridge from 1st January 2021 to 14th July 2021 are recorded, and root mean square error (RMSE) between these field-measured strain responses and analytically computed strain responses from the digital model are estimated. The stationary trend of the time history of RMSE values depicts constant structural reliability. A technique is also proposed to forecast structural strain responses, which is validated with field-measured strain responses.

Simulation-based Optimal Sensor Placement in Tunnel Structures considering Uncertain in-situ Conditions and Multiple Loading Scenarios

The expansion of the underground infrastructure and the necessity to maintain the full functionality of the existing tunnels highlights the role of structural health monitoring in keeping track of the behaviour of the structure over time. In the study, the focus is on segmental tunnel lining for deep and long tunnels. The aim of this research is to investigate the best position for sensor placement based on the potential loading scenarios that might insist on the tunnel structure. Since for the evaluation of the lining safety we are interested in the maximum stresses reached in the structure, which might lead to durability critical cracking or crushing of concrete, a method is presented to suggest optimal positions for strain gauges. Due to uncertain geological conditions, multiple loading configurations acting on the tunnel structure are simulated using a finite element model. The results are employed to better identify the sensor locations, on the basis of where damage is prone to occur and where maximum information about the stress state in the structure can be inferred. The results obtained by the framework are discussed in light of a practical engineering perspective and the advantages as well as the limitations of the proposed approach are expounded.

Electrically Controlled High Sensitivity Strain Modulation in MoS2 Field-Effect Transistors via a Piezoelectric Thin Film on Silicon Substrates.

Strain can modulate bandgap and carrier mobilities in two-dimensional (2D) materials. Conventional strain-application methodologies relying on flexible/patterned/nanoindented substrates are limited by low thermal tolerance, poor tunability, and/or scalability. Here, we leverage the converse piezoelectric effect to electrically generate and control strain transfer from a piezoelectric thin film to electromechanically coupled 2D MoS2. Electrical bias polarity change across the piezo film tunes the nature of strain transferred to MoS2 from compressive (∼0.23%) to tensile (∼0.14%) as verified through Raman and photoluminescence spectroscopies and substantiated by density functional theory calculations. The device architecture, on silicon substrate, integrates an MoS2 field-effect transistor on a metal-piezoelectric-metal stack enabling strain modulation of transistor drain current (130×), on/off ratio (150×), and mobility (1.19×) with high precision, reversibility, and resolution. Large, tunable tensile (1056) and compressive (-1498) strain gauge factors, electrical strain modulation, and high thermal tolerance promise facile integration with silicon-based CMOS and micro-electromechanical systems.

Loss of pre-stress in impregnated superconducting magnets, experimental results and numerical analysis

The SMC (Short Model Coil) R&D program was started at CERN around 2007 to develop the Nb3Sn technology. The small magnet structure allowed relatively cheap and fast testing of various superconducting coils. One of the key questions to be answered, was related to the relation between the pre-stress and the magnet’s performance. To measure this dozens of strain gauges were installed on the coils, the axial tie-rods and the external shell. The experimental results of the strain measurements during all stages of the load: room temperature (RT) pre-stress, cool-down, powering, warm-up were analyzed in an extensive report [56]. A repeatable pattern of a decreasing strain after the warm-up, compared to the value before the cool-down, was observed on the external cylinder for all the tested coils. Values from 2 % to 50 % were reported.In this work a viscoelastic model was used to explain this effect. The Nb3Sn coil was treated as a composite material with decreasing stiffness due to mechanical damage. The Generalized Maxwell Solid model (Prony series model) was employed, including one spring and one damper, leading to a relatively simple model characterized by only two parameters. The two constants of the viscoelastic model were found: 1st – the relative relaxation moduli α based on a calibration curve derived from the experimental results of the SMC program and the 2nd one – relaxation time τ – based on minimizing the computational cost, by finding the asymptotic solution in one integration step. The model showed the capability of explaining the strain drop (loss of pre-stress) of more than 80 %. In addition to the viscoelastic effects, the role of friction coefficient was studied revealing the possibility of explaining up to 14 % of the strain drop. Yet, to fit with the experimentally measures strains on the SMC cylinder, especially during the RT pre-load, the most-probable value of the friction coefficient should be μ<0.4. The strong impact of the stiffness of the G-10/G-11 laminate used to spread the load on the coil was found, indicating the need of knowing the elastic properties of this material very precisely. In addition, the experimentally measured strain values showed strong asymmetric, both in plane and along the magnet’s axis, revealing the potential sensitivity to the geometric imperfections and the need for 360° magnet models.

Quantitative digital image correlation approach for the monitoring of fatigue damage development in 10CrMo9-10 steel in the as-received state and after extended service

In this paper, the quantitative Digital Image Correlation (DIC) approach was used to study the long-time degradation of two different states of 10CrMo9-10 (10H2M) power engineering steel. The specimens subjected to cyclic loading (R = 0) were monitored by using the DIC technique. The data obtained from DIC measurements were presented in form of strain distributions for specified, independent points within the strain gauge of specimens. Furthermore, the strain profiles were extracted for the particular stages of fatigue damage development (FDD). The presented methodology provides a different approach of DIC application, in which, the data could be treated more quantitative than qualitative.

Deciphering the sensory landscape: a comparative analysis of fiber Bragg grating and strain gauge systems in structural health monitoring

Deciphering the sensory landscape: a comparative analysis of fiber Bragg grating and strain gauge systems in structural health monitoring

Increased Microvascular Filtration and Vascular Endothelial Growth Factor-D associated with Changed Lymphatic Vessel Morphology in Breast Cancer Treated Patients.

Vascular endothelial growth factors (VEGF) and inflammatory cytokines are indicated to be implicated in lymphedema development. We aimed to describe changes in microvascular filtration and VEGFs in a patient cohort vulnerable to breast cancer-related lymphedema development correlated with data on lymphatic morphology and function. Consecutive node-positive breast cancer patients operated in the axilla and evaluated approximately 12 months after adjuvant locoregional radiotherapy were studied. Capillary filtration rate (CFR) and isovolumetric pressure of the arms were measured by strain gauge plethysmography, and 13 blood proteins were quantified by Luminex and Elisa technology in 28 patients and 18 healthy controls. The CFR was reduced in both arms from baseline to 1-year follow-up (ipsilateral: P = 0.016 and contralateral: P = 0.001). When stratifying lymphatic complications (morphologic abnormalities and/or breast cancer-related lymphedema), CFR reached a lower steady-state in the arms with normal morphology (I:P = 0.013 and C:P = 0.013) whereas the ipsilateral arm with lymphatic complications remained unchanged (P = 0.457). In patients with lymphatic abnormal vessels, the levels of VEGF-D were 86% higher than in patients with normal lymphatic vessels (P = 0.042), whereas levels of VEGFR-3 were 64% higher (P = 0.016). Through one year of follow-up, CFR did not decrease in the lymphatic complicated treated arms as observed in noncomplicated treated arms. The patients had increased levels of VEGF-D and VEGFR-3. This correlation suggests that VEGF plays a role in the appearance of subcutaneous abnormal lymphatic vessels in the treated arms, which also maintain a fluid filtration/drainage mismatch up to one year after breast cancer treatment.

Validation of a model-based dual-band modal decomposition and expansion approach for fatigue monitoring of offshore wind turbine foundations

The fatigue limit state strongly drives the lifetime of offshore wind turbine support structures. Despite steady advancements in their design, the accumulation of fatigue damage over the lifetime of the structure remains uncertain; one way to improve certainty is to directly monitor structural loads at fatigue-critical locations, e.g., near or below the mudline. However, directly monitoring the loads at these locations is often not possible, since these locations do not allow for easy installation or retrofitting of sensors. To this end, model-based virtual sensing techniques can be employed to estimate the structural response at unmeasured locations based on vibration response data and a finite element model which can accurately describe the modal and operational deflection shapes of a specific turbine [1,2,3]. For this contribution, a modal decomposition and expansion (MDE) algorithm [4] will be used to predict strain time series at fatigue-critical locations, based on acceleration and strain data obtained from the tower of an operational OWT. Emphasis will be put on sparse data situations in which a realistic amount of sensor data is used as input. Fibre-optical strain gauges close to and below the mudline level (Fig 1) will be used for direct validation of the extrapolation capabilities. The required finite element model is built using an in-house developed and verified integrated FE model class [5,6], in combination with a unique database which contains all available geotechnical and structural data of offshore wind turbines (owimetadatabase) [7,8]. This combination allows us to generate fleet-wide, turbine-specific, finite elements models for several wind farms. The results will be presented in terms of time series (e.g., Fig. 2) and fatigue damage-related metrics. Preliminary results show that strain time series estimated with the MDE method show good agreement with the validation data.

Impact energy in Heat-Treated aluminium alloy 6061 and 7075

Instrumented Charpy impact is one of the promising methods to assess the impact energy; toughness and resilience of a material. The test consists of the Charpy machine and instrumentation equipment which is the strain gauge and the data acquisition system. Impact energy evaluations are important to understand the material behaviour subjected to sudden impact loading. Aluminium 7075 has good strength strength-to-weight ratio than aluminium 6061 and hence the AL 7075 is usually used in the aerospace industry, whilst the AL 6061 is commonly used in the automotive industry. The objective of the study is to observe and analyse the impact response of the Aluminium 6061 and 7075 at different heat- treated conditions; O-anneal and T6 temper. In addition to the impact energy absorbed value, the impact strain signal is recorded too. Theoretical impact energy is calculated as well based on the information given by the Charpy machine software. Aluminium 7075 exhibits a lower value of impact energy absorbed and a smaller area under the curve compared to Aluminium 6061. The energy absorption capacity for each material grade and heat-treated condition are different from one another. O-anneal aluminium has a lesser energy absorbed value and a smaller area under the curve than the T6 temper aluminium. The outcome reveals that the heat treatment process alters the material microstructure and mechanical properties, whereas in this study the impact energy responses are influenced by these circumstances. Moreover, the chemical composition of the aluminium alloy distinguishes these two grades from one another, thus resulting in different impact responses.

Analysis of Reinforced Concrete Pipe Strain Due to Jacking Force Case Study: Sudetan Ciliwung River Project to the East Flood Canal

Pipe Jacking is an innovation in trenchless technology that has been utilized in various sectors including municipal wastewater systems, oil and gas transportation, and hydraulic engineering. One of the critical aspects to ensure the success and safety of the pipe jacking process is strain monitoring. This study discussed the strain characteristics of reinforced concrete pipe structures during pipe jacking. The analysis was conducted using a numerical approach, which compared to field monitoring. Field strain monitoring was performed by strategically placing strain gauges along the pipe during the jacking operation, resulting in real-time data on deformation and pressure values. When the strain was monitored, the numerical test was conducted simultaneously using finite element analysis of Rocscience 3D. Those activities were done to consider the interaction between the reinforced concrete pipe and the surrounding soil. The strain analysis results indicated that the pipe responded during the pipe jacking process. The values of strain were various, depending on jacking force, condition of excavated soil layers, and distance between twin tunnels. The maximum stress occurred at the beginning of jacking process, when the pipe infiltrated into the soil with stress value of 512 kPa.

Design and Research of a Strain Elastic Element with a Double-Layer Cross Floating Beam for Strain Gauge Wireless Rotating Dynamometers.

Cutting force is one of the most basic signals that can reflect the information of the cutting process, so it is very necessary to study the strain elastic element of strain gauge wireless rotating dynamometers. This paper proposes a strain elastic element with a double-layer cross floating beam that can be applied to the strain gauge wireless rotating dynamometer, which can simultaneously obtain the four-component cutting force/torque information of FX, FY, FZ, and MZ. Based on the proposed strain elastic element, a compact strain gauge wireless rotating dynamometer is designed, which is composed of a tool holder, upper connection flange, strain elastic element, lower connection flange, tool base, and data acquisition and wireless transmission system. The static model of the double-layer cross floating beam on the strain elastic element is established by the segmented rigid body method, and the relationships between the material, force, structural parameters, and the strain and deformation of the floating beam are obtained. The static model is consistent with the finite element solution, which proves the rationality of the static model. Based on the established static model, the sequential quadratic programming algorithm is used to optimize the structural parameters of the double-layer cross floating beam to maximize the sensitivity of the floating beam. The overall structure of the strain elastic element is analyzed by finite element software, and the strain of the structure under simulation conditions is obtained, which provides a reference for subsequent calibration tests and circuit design. The calibration matrix and dynamic performance of the strain elastic element are obtained by the static calibration test, dynamic calibration test, and cutting test. The results show that the proposed strain elastic element has high sensitivity and low cross-sensitivity error, and can be applied to the strain gauge wireless rotating dynamometer to measure medium- and low-speed cutting forces.

Experimental determination of mode I notch stress intensity factors using valid strain gage locations

Accurate experimental determination of mode I notch stress intensity factors (NSIFs) of various sharp V-notched configurations using strain gages plays an important role in notch fracture mechanics. However, practically feasible, economical, and efficient strain gage techniques are hardly available for the sharp V-notched problems. Considering problems associated with the sharp V-notched bodies, the authors recently proposed a strong theoretical basis for an efficient single strain gage technique with valid gage locations for the accurate measurement of mode I NSIFs of sharp V-notched configurations. The main thrust of the present investigation is the experimental substantiation of the above strain gage technique using different V-notched configurations. It has been shown that these valid locations are governed by two parameters rmin and rmax of a sharp V-notched configuration. The results of the present investigation clearly demonstrate that very accurate NSIFs can be obtained from a single strain gage located at the suggested valid locations, which need not necessarily be in the vicinity of a notch tip. Further, the results also show that highly erroneous NSIFs can result if the gages are located at invalid radial locations. The results explicitly indicate that adopting the valid gage locations is beneficial rather than pasting the gages based on guesswork or other speculations.

A monitoring method for wind loads exerted on offshore gravity wind turbine through optimised mathematical model

The actual load borne by a structure throughout its entire lifecycle, such as the wind load on fixed offshore wind turbines, is unknown. This leads to significant differences between the actual life of a structure and the fatigue analysis results during the design phase. Wind-load identification can effectively obtain the wind load borne by a fixed fan throughout its lifecycle. However, measurement noise and an ill-posed mathematical model affect the identification accuracy and stability. In this study, the optimal orientation of the sensor was determined to improve the signal-to-noise ratio according to the stress analysis of the tower structure. A successive addition method (SAM) was proposed to reduce the ill-posedness and dimensions of the mathematical model used for wind-load identification in the frequency domain by removing inefficient strain gauge locations and directions. A distributed successive addition method (DSAM) was developed to improve computational efficiency. The SAM and DSAM were described in detail using a specific case study of an offshore gravity wind turbine; a mathematical model was established through structural harmonic-response analysis. The spectrum superposition method and Dirlik distribution were used to analyse the fatigue damage of the wind-power tower. Several numerical examples were used to demonstrate the effectiveness of the SAM and DSAM. The simulation results demonstrated that the SAM and DSAM can completely eliminate the ill-posedness of mathematical models. In addition, the results of the structural fatigue analysis using the identified wind loads were extremely similar to the fatigue analysis results using the original wind loads, with an error of less than 3%.

Technologies for measuring the dynamic parameters of rowing based on strain gauge systems

Technologies for measuring the dynamic parameters of rowing based on strain gauge systems

Methods and means of ensuring the accuracy of bending deformation measurements of connecting pipe between the VVER reactor and the steam generator in the conditions of a fuel campaign

The welded joint zone (WJ) No. 111 is a welding unit for the "hot" collector of the primary coolant to the DN1200 steam generator nozzle. The experience of operation of steam generators PGV-1000M of NPP power units with VVER-1000 shows that the WJ zone No. 111 is prone to the formation and development of operational defects. According to the results of periodic non-destructive testing of the WJ No. 111 zone performed at the PG of various power units of the VVER-1000 NPP, cases of detection of extended planar-type discontinuities, including through ones, were repeatedly recorded. Thus, this zone is one of the most critical zones of the reactor plant (RU) with VVER -1000. The root cause of the formation and development of operational defects has not yet been identified. Solving the problem of cracking of WJ No. 111 steam generators of nuclear power plants with VVER-1000 is one of the priority areas for improving the safety of operation of the power unit during the over-design service life. This problem is determined by a complex combination of temperature conditions, mechanical and corrosive effects, is relevant and has not yet been definitively solved. Therefore, it is very important to ensure the collection of reliable data on the actual stress-strain state of the WJ No. 111 zone in various operating modes (pressure loading of steam generators, heating/cooling of the power unit, hydraulic testing of the 1st and 2nd circuits). The article reveals the approaches and stages of creating and applying a strain gauge installation to ensure metrological suitability in the conditions of a campaign fuel company at an NPP power unit by using an adequate physical model to obtain additive and multiplicative correction coefficients.

A strain field reconstruction method based on digital twin considering real-time loading deviations from intended test

For the static loading test, digital twin (DT) constructed by multi-type data fusion can combine the advantages of these data, which has potential application in test monitoring. Affected by assembly and manufacturing defects of test system, the loading deviations are difficult to avoid and quantify, and it has an important effect on the strain state of structures. However, the current DT is built by data fusion of strain gauges data and strain field of finite element analysis (FEA) only, and how to build DT considering real-time loading deviations by fusing multi-type sensor data remains a challenging task. Therefore, a strain field reconstruction method based on DT considering the real-time loading deviations (DT-SFRM-LD) is proposed to improve the accuracy of DT. In the test, the loading deviations calculated by displacement sensors data are used as FEA database input to obtain FEA strain field considering real-time loading deviations. The FEA strain field is combined with strain gauges data to construct DT in real time, which combines all the multi-type data advantages of displacement gauges, FEA strain field and strain gauges. A cylindrical shell test is performed to validate the high accuracy of DT-SFRM-LD. Results indicate that the AvgErr (5.0%) and MaxErr (13.6%) of DT-SFRM-LD are 4.3% and 10.0% lower than those of conventional DT method, and the AvgErr of DT-SFRM-LD is less affected by the eccentricity distance. In general, under different test conditions, the accuracy of DT-SFRM-LD is always higher than that of conventional DT method, indicating that considering the real-time loading deviations by displacement gauges is helpful to provide accurate FEA strain field distribution and to improve the accuracy of DT-SFRM-LD.

Improved calculations of joints in anisotropic structural materials

Introduction. Contemporary methods for the design and calculation of building structures are often limited to the elastic stage of the material work. In order to analyze the stress-strain state of joints, it is necessary to take into account the properties of the material, as well as its operation under the load, including both elastic and non-linear stages. In this case, anisotropic materials, e.g. wood, represent a particular interest. Therefore, the paper presents a theoretical and practical study of the work, performed by wooden samples.Aim. To perform tests and numerical simulations for analyzing the stress-strain state and improve the calculations of anisotropic structural materials.Materials and methods. Compression tests of wooden samples, made of second-grade pine, were carried out along the fibers with fixed vertical compression stresses and strains. The tests were performed using a hydraulic press with a maximum load of 50 t. Strain gauge equipment was used to record strains and stresses. Based on the data of compression tests, the numerical simulation of the samples in the LIRA-SAPR and ANSYS software packages was performed.Results. According to the test results, the elastic stage of the compressed wood ranges up to 90 kN, followed by a transition to the plastic deformation. The performed numerical simulation of the samples in the LIRA-SAPR and ANSYS software packages demonstrated the convergence of the results. However, the ANSYS software package allows for a more detailed simulation and calculation of joints and structures. The comparison of distributions of vertical compression stresses σy, obtained in tests and ANSYS software package numerical simulation, proved the convergence of the results (discrepancy of less than 5 %). This confirms the effectiveness of using this software package for simulating the joints of anisotropic materials.Conclusions. The results of tests and numerical simulation showed the effectiveness of using the ANSYS software package to calculate complex joints of anisotropic structural materials. The convergence of the results is established for the elastic stage. An additional study is required to simulate the plastic stage.

Using Resistance-Band Tests to Evaluate Trunk Muscle Strength in Chronic Low Back Pain: A Test-Retest Reliability Study.

Exercise is a front-line intervention to increase functional capacity and reduce pain and disability in people with low strength levels or disorders. However, there is a lack of validated field-based tests to check the initial status and, more importantly, to control the process and make tailored adjustments in load, intensity, and recovery. We aimed to determine the test-retest reliability of a submaximal, resistance-band test to evaluate the strength of the trunk stability muscles using a portable force sensor in middle-aged adults (48 ± 13 years) with medically diagnosed chronic low back pain and healthy peers (n = 35). Participants completed two submaximal progressive tests of two resistance-band exercises (unilateral row and Pallof press), consisting of 5 s maintained contraction, progressively increasing the load. The test stopped when deviation from the initial position by compensation movements occurred. Trunk muscle strength (CORE muscles) was monitored in real time using a portable force sensor (strain gauge). Results revealed that both tests were highly reliable (intra-class correlation [ICC] > 0.901) and presented low errors and coefficients of variation (CV) in both groups. In particular, people with low back pain had errors of 14-19 N (CV = 9-12%) in the unilateral row test and 13-19 N (CV = 8-12%) in the Pallof press. No discomfort or pain was reported during or after the tests. These two easy-to-use and technology-based tests result in a reliable and objective screening tool to evaluate the strength and trunk stability in middle-aged adults with chronic low back pain, considering an error of measurement < 20 N. This contribution may have an impact on improving the individualization and control of rehabilitation or physical training in people with lumbar injuries or disorders.

A new anal manometry technique for assessing the functional state of the rectal sphincter apparatus

Objective. To develop a new modern precession strain gauge sphincterometer for assessing the functional state of the sphincteric apparatus of the rectum in the normal state with an increase in the accuracy of the results of recording the absolute pressure values generated in it. Materials and methods. The results of anal manometry (sphincterometry) of 90 patients (45 men and 45 women) aged 18 to 72 years without anorectal pathology and manifestations of anal incontinence were analysed to establish normal indicators of the state of the sphincteric apparatus of the rectum using a newly developed modern precession strain gauge sphincterometer. Results. The conducted sphincterometric study allowed to establish the following indicators of the functional state of the sphincteric apparatus of the rectum in the norm for men: sphincter tone (26.7 ± 2.2) mm Hg, maximum contraction (35.6 ± 5.1) mm Hg, gradient of voluntary contraction (9 ± 4.9) mm Hg, cough test (36.5 ± 4.9) mm Hg, test with straining (38.2 ± 3.5) mm Hg; for women: sphincter tone (23.3 ± 2.5) mm Hg, maximum contraction (31.3 ± 4.3) mm Hg, voluntary contraction gradient (8.0 ± 3.6) mmHg, cough test (31.6 ± 3.0) mmHg, and expiratory test (32.4 ± 3.0) mmHg. Conclusions. The proposed method of anal manometry allows for a detailed study and objective assessment of the functional state of the sphincteric apparatus of the rectum in men and women in the normal state according to such indicators as sphincter tone and maximum contraction, gradient of voluntary contraction, as well as cough and straining tests.

Healing Function for Abraded Fingerprint Ridges in Tactile Texture Sensors.

Tactile texture sensors are designed to evaluate the sensations felt when a human touches an object. Prior studies have demonstrated the necessity for these sensors to have compliant ridges on their surfaces that mimic human fingerprints. These features enable the simulation of contact phenomena, especially friction and vibration, between human fingertips and objects, enhancing the tactile sensation evaluation. However, the ridges on tactile sensors are susceptible to abrasion damage from repeated use. To date, the healing function of abraded ridges has not been proposed, and its effectiveness needs to be demonstrated. In this study, we investigated whether the signal detection capabilities of a sensor with abraded epidermal ridges could be restored by healing the ridges using polyvinyl chloride plastisol as the sensor material. We developed a prototype tactile sensor with an embedded strain gauge, which was used to repeatedly scan roughness specimens. After more than 1000 measurements, we observed significant deterioration in the sensor's output signal level. The ridges were then reshaped using a mold with a heating function, allowing the sensor to partially regain its original signal levels. This method shows potential for extending the operational lifespan of tactile texture sensors with compliant ridges.