Strain Gauge Measurements Research Articles

A developed hybrid experimental–analytical method for thermal stress analysis of a deep U-notched plate

A general framework of hybridizing experimentally-recorded load-induced thermal information by means of thermoelastic stress analysis (TSA) of a loaded structure with the Michell solution of Airy stress function in isotropic linear elasticity is proposed for in-plane stresses determination. The capability of the proposed hybrid method in separating the TSA signals into individual stresses is demonstrated by stress-analyzing a deep U-notched aluminum plate without neither knowing the entire geometry and distant loading/boundary conditions nor using supplementary experimental information. Even though no experimental data were processed at, and adjacent to, the edges of the U-notched plate, the individual stresses are determined throughout the surface of the plate. Prior processing actual experimental TSA data, the accuracy and the stability of the proposed hybrid method through adding artificial noise scatters in the processed simulated data with the number of retained terms in the generalized Airy stress expressions are firstly investigated. The effects of the superimposed noise scatters as well as the number of employed data in the evaluated stresses are also assessed. Finally, the reliability of the determined hybrid-experimental stresses is supported through a comparison with finite-element predictions and strain gauge measurements. The ease of implementation, the accuracy and the precision of the evaluated stress, and the versatility to the type of employed data make the proposed hybrid method more attractive and superior than other hybrid methods.

Investigation of the Effect of Loading on Fatigue Life by Comparing Strain Gauge Measurements and Finite Element Analysis Under Gradually Increasing Load in An Axle Housing

In this study, the stress values obtained from commercial finite element analysis software ANSYS® and stress values measured by strain gauges applied on an axle housing in test environment were compared. The axle housing is a test sample from heavy duty commercial vehicles. Besides from stress values comparison, fatigue behavior of the housing was observed under gradually increased loading conditions via hydraulic loaded test benches. Load conditions, configuration change steps, test parameters and fatigue life results will be explained in detail. It was observed that the results of FEA and strain gauge are coherent to each other and as the load was increased, the fatigue life decreased. The stress values in specified points of housing increase linearly with the load increment. However, as predicted, the relationship between load change and fatigue life is not linear. For instance, fifty percent increase in load reduces life by about seventy-five percent. The aim of the study is firstly correlate the FEA results by comparing with the test measurements and then try to observe the effect of load increase on the fatigue life which will be a beneficial source for estimation of the life of the axle housing under diverse loadings in the further studies.

Approach for Measuring a Ship to Shore Crane Actual Wheel Load

Knowing the real crane deadweight, center of gravity (COG) and wheel loads instead of nominal ones is crucial for many reasons. One of the reasons relates to the checking the quay strength where the crane is going to be installed and it should be based on the crane maximum real wheel loads. Another example could be the crane transportation by sea on the deck of the vessel (Starykov & Van Hoorn, 2017). In this case predicting the precise value of the crane deadweight and its COG plays a key role in accurate calculation of the vessel stability, acceleration calculation from the ship motions and the vessel’s deck strength. This paper demonstrates a new approach to finding the crane wheel load and in the result the deadweight and COG position. This method does not need special arrangement and uses combination of strain gauge measurements and Finite Element (FE) analysis only. The application of the method is demonstrated on example of the ship loader for which the possibility of capacity increase has been assessed.

"AN AUTOMATIC LIQUID LEVEL CONTROL SYSTEM WITH THE USE OF THE ARDUINO MICROCONTROLLER AND STRAIN GAUGES - ANALYSIS OF APPLICATION POSSIBILITY IN MANUFACTURING PROCESSES "

The aim of the work was to present the possibility of automatic regulation of the liquid level in the tank with the use of the Arduino platform, strain gauge measurements and pump operation regulation by means of a PID controller. The possibility to program the Arduino and implementing the algorithm of the PID controller was presented. To be able to use the PID controller, the controller was tuned using the II Ziegler-Nichols method and the manual method. To check how the applied controller works in automatic liquid level control and how its settings affect the operation of the system, tests were carried out comparing the operation of various configurations of the PID controller in various operating conditions. The work carried out showed the possibility of developing a low-cost automatic liquid level control system, which can be successfully used in manufacturing processes.

Liquid Core Detection and Strand Condition Monitoring in a Continuous Caster Using Optical Fiber

Real-time monitoring of the liquid core position during the continuous casting of steel has been demonstrated using low-cost distributed optical-fiber-based strain sensors. These sensors were installed on the containment roll support structures in the segments of a production continuous caster to detect the position of the solid-liquid interface and monitor the strand condition during the continuous casting. Distributed Fiber Bragg Grating sensors (FBGs) were used in this work to monitor strain at six roll positions in the caster. The sensor performance was first validated by comparing optical strain measurements with conventional strain gauge measurements in the lab. Next, optical strain measurements were performed on an isolated caster segment in a segment maintenance facility using hydraulic jacks to simulate the presence of a liquid core under the roll. Finally, the sensors were evaluated during caster operation. The sensors successfully detected the load increase associated with the presence of a liquid core under each instrumented roll location. Incidents of bulging and roll eccentricity were also detected using frequency analysis of the optical strain signal. The liquid core position measurements were compared using predictions from computer models (digital twins) in use at the production site. The measurements were in good agreement with the model predictions, with a few exceptions. Under certain transient caster operating conditions, such as spraying practice changes and SEN exchanges, the model predictions deviated slightly from the liquid core position determined from strain measurements.

Experimental and numerical verification of stress distribution in additive manufactured cylindrical pressure vessel — A continuation of the dished end optimization study

The presented paper refers to the recent study of shape optimization of dished ends with the aim of reducing the maximum von Mises stress. An adequate method is sought to manufacture pressure vessel models with optimized dished end. Following the results of the static tensile test, Multi Jet Fusion technology is selected to manufacture the models. After evaluating the mechanical properties of PA12 material, the dished end shape is reoptimized. Manufactured models are pressurized and strain gauge measurements are taken. Finally, the optimized stress distribution is compared with the numerical and experimental results, indicating a good agreement between them.

Buckling and Post-buckling Characteristics of Stiffened Panels Under Compression-Shear Load

Experiments have been conducted to investigate the buckling and post-buckling behavior of a T-the stiffened composite panel in size of 2412 by 1420mm under a compression-shear load. DIC was used to monitor the local buckling and post-buckling, and the results were compared with that of strain gauges. The results show that DIC can accurately capture the displacement field and the whole progress of the buckling mode transition, and the buckling modes at different times are clearly and intuitively, the error of the initial buckling load is less than 5% compared with the load measured by the strain gauge. Four different buckling determination methods based on strain gauge measurement and DIC measurement are presented, and a more accurate and convenient method for judging buckling load is obtained. The initial principal strain angle is related to the ratio of shear stress to compressive stress and changes greatly after the buckling, and the fracture angle approaches 45 degrees. The experimental results show that the hole with 6mm in the weighted middle of the web has a slight effect on the buckling load but has an obvious effect on the load capacity.

Very high cycle fatigue under tension/torsion loading of mold low alloy steel

AbstractUltrasonic fatigue testing (UFT) is a recent fatigue methodology that applies resonance to achieve very high cyclic load frequencies. Its primary purpose is to study fatigue in the very high cycle fatigue regime. In this study, an UFT machine was used to conduct multiaxial tension/torsion fatigue tests at a 20‐kHz frequency. The objective was to reach a reliable multiaxial fatigue test and methodology by modifying the geometry of the specimen, enabling also different shear to axial stress ratios. The study conducted numerical and experimental modal behavior analysis of the ultrasonic setup and specimens focused on achieving a consistent modal deformed shape and associating the measured displacement to the induced stresses thermographic imaging, laser and rosette strain gauges measurements were carried out to validate the results. A good numerical to experimental agreement was achieved. Tension/torsion fatigue test series were conducted to three combining dimension specimens with different shear/axial stress ratios. The crack initiation angles and fracture surfaces were analyzed and compared among each other and with tension–compression and pure torsion ultrasonic tested specimens. The results prove a clear trend in crack propagation details with the increase of the induced stress ratio.

Improving the fatigue life of large offshore foundations

Offshore foundations are subject to fatigue due to wind and wave loads during their lifetime. Post-weld treatment is a group of techniques well known to improve the fatigue life. This study investigates how this is applicable for large structures, i.e. a 2.4 meter jacket T-node. A large scale empirical study was performed and results were obtained from a SN-diagram based on three repetitions and supported by a theoretical background. The as welded samples performed as expected and on the safe side of the category 56 line. Unexpectedly, the burr grinded samples showed no improvement and had an evidently larger variance. Both ultrasonic impact treatment and especially pneumatic impact treatment showed improvements, but did not reach the expected category 125 line. The results were substantiated with strain-gauge measurements for hot spot analysis. The obtained results on fatigue life improvements give rise to apply post weld treatment in an industrial scale for offshore construction. However, it also brings up the discussion of the necessity to redesign structures in order to automate the treatment in a cost efficient manner.

Rectification of Gas Pipeline Bridging with the Support of Experimental Stress Analysis and Means of Regression and Correlation Analysis

The paper deals with the connection between the issue of rectification of the structural system and the corresponding experimental and related statistical analysis of stresses. The solution was demonstrated in the example of replacing the aboveground gas pipeline with an underground solution. During the implementation of landscaping for the underground solution, there was a risk of damage to the existing structure. Due to the specific problems in stress analysis based on strain gauge measurements, especially with regard to the narrow range of gas pressure as the primary input quantity, the obtained data had to be subjected to complex statistical procedures. Several linear and non-linear regression models were compiled and subjected to normality, homoscedasticity, and autocorrelation tests. The data obtained in this manner ruled out the possibility of limited state occurrence on the existing structure and, in conjunction with other information, enabled the successful completion of the rectification process to its current form. The scientific added value of the contribution should be the demonstration of procedure methodology and relatively unconventional use of regression and correlation analysis methods and means in the technical field for stress analysis in solving engineering practice problems.

In situ simultaneous measurement system combining photoelastic, strain gauge measurement, and DIC methods for studying dynamic fracture

The photoelastic, digital image correlation (DIC), and strain gauge measurement methods are extensively used for studying dynamic fracture mechanics. However, few studies on dynamic fracture focus on combining these methods. In this study, a simultaneous measurement system for in situ investigation on dynamic fractures using the photoelastic, DIC, and strain gauge measurement methods was established for the first time. To reveal the performance of the system, impact experiments were conducted on three-point bending beam specimens fabricated using epoxy resin; consistent results were obtained from the three methods. The developed system provides rich experimental data, including full-field information of the stress, displacement, and strain fields.

An engineering approach for the prediction of fatigue damage in the part load regime

Due to the volatile electricity received from solar and wind power plants, the energy market requires highly variable hydropower machines which are able to cope with fast changes of their operating regimes. With the need for flexible operation, Francis runners are exposed to various operating conditions outside the traditional operating range. Hence, the runners must be specifically designed for long time part load operation to meet hydraulic and structural requirements. Therefore, it is inevitable to have a reliable but also practical engineering approach in the design phase of the projects in order to ensure sufficient fatigue life of the Francis runners. Deep part load operation mainly consists of stochastic loads acting on the runner blades. Previous publications show that it is reasonable to normalize the Rainflow matrix of stress amplitudes to represent the characteristic behaviour at deep part load operation. Hence, it is feasible to utilize the normalized Rainflow matrix to predict the fatigue damage of Francis runner designs without prototype measurements. Within this paper, a scaling method to derive project specific fatigue results for deep part load is introduced and subsequently validated through an intercomparison of available strain gauge measurement data and prediction. Based on the results, the accuracy of the proposed engineering approach and possible impacts of different boundary conditions are discussed.

Experimental Evaluation of Eccentric Mechanism Power Loading of Movable Pressure Plate in Die-Cutting Press

Abstract The paper reports experimental research on torques during cardboard cutting in the die-cutting press with eccentrics in the drive of the movable pressure plate. To conduct the research, an experimental bench with eccentrics in the drive of the die-cutting press is designed and manufactured. The manufactured experimental device for the research on cardboard blanks provides the possibility of getting dependencies of loadings at different parameters of the die-cutting process. The experimental approach envisages the use of the strain gauge measurement method and the wireless module for data collecting, as well as the software for its processing, for getting trustworthy results with minimum faults. The method gives an opportunity to study the torque values during the cardboard-cutting efforts on the drive shaft. The paper shows changes in the torque value on the drive shaft during the kinematic cycle with and without the use of cardboard blank. The angle of the drive shaft rotation during the cutting process was evaluated at selected values of the cardboard thickness. The relationship between the linear cutting efforts and the cardboard thickness, its fibre direction, cutting rule type and rotational speed of the drive shaft is elaborated. This kind of data is approximated by a logarithmic function (logarithmic curve), at R 2 from 0.90 to 0.98. The thickness of the cardboard significantly influences the value of the linear cutting effort at all the studied parameters.

Validation of deep part load dynamic stresses for axial runners

To accommodate renewable energy production and load demand variability, hydropower plant owners need to increase their operating range regardless of their units’ original design load envelop. When this increased operating range is an issue for the fatigue life of the old runners, solutions need to be found with the design of a new runner to sustain those new challenging loads of the increased operating range. In recent years, many papers have been published to show the challenging loads on Francis runners at speed-no-load and deep part load conditions. Andritz demonstrated a good numerical prediction capability for stress levels at deep part load conditions for Francis runners. However, for axial units, very little has been published. Very recently, some papers showed good predictability by CFD of the flow behavior at deep part load including the vortices present at those conditions. This paper demonstrates the prediction capability of the numerical tools by comparing strain gage measurements on an axial runner to CFD-FEA stress predictions. The measurement campaign was conducted conjointly by the unit owner and the manufacturer for research purposes. In the deep part load operating zone under the effect of columnar vortices, frequency analysis of the measured vibrations and strain gage signals confirmed the flow behavior predicted by CFD, and the measured dynamic strain amplitudes were well predicted. Numerical prediction of dynamic stress in the complete range from 0-100% power of the measured unit as well as detection of high vibration zones was successful.

Experimental study on the relationship between local deformation and macro-crack evolution of granite under conventional triaxial compression

Brittle failure of rock is characterized by the initiation, propagation and coalescence of micro- and macro-cracks. To study the macro-crack evolution of rocks, a parallel long strain gauge measurement apparatus was developed, which was composed of multiple long axial strain gauges and linear variable differential transformers (LVDTs). Using the developed strain measurement apparatus, conventional triaxial compression (CTC) tests were carried out on Linghai granite specimens. The results showed that a) using the radial strain of rock specimens monitored by LVDT as the servo feedback signal, the strain gauges can obtain the local complete stress–strain curves of the specimen. b) Macro-cracks often formed in the areas with large pre-peak axial strain (ε 1) values, but not in the areas with small pre-peak ε 1 values. c) There were three typical cracking patterns in Linghai granite: rapid tensile cracking, slow tensile cracking, and rapid shear cracking, among which rapid tensile cracking was the most common. d) The macro-crack evolution process can be deduced through the fracture sequence of the strain gauges and the failure pattern of the specimen. In addition, the typical crack propagation velocity of Linghai granite under a confining pressure of 80 MPa was approximately 667 m/s.

Full-scale experimental and numerical analyses of a flexible riser under combined tension-bending loading

The flexible riser top connection with floating production units presents additional tensile armour integrity assessment uncertainties associated to the bend stiffener contact interaction that leads to a non-uniform curvature and contact pressure distribution in a region of large dynamic forces and moments. In this paper, a full-scale 6″ flexible riser and bend stiffener bending-tension experimental campaign is carried out in a horizontal rig. The external tensile armour wires are instrumented with strain gauges for axial strain measurement in several riser cross-sections inside and outside the bend stiffener region. The rig assembly allows the riser rotation in order to measure strains at different circumferential angular positions. The bend stiffener polyurethane hyperelastic mechanical response is obtained by uniaxial tensile tests performed at room temperature. A nonlinear finite element model (FEM), including the riser/bend stiffener contact interaction and interlayer friction mechanisms, is employed to numerically investigate the mechanical behaviour of the flexible riser subjected to the experimental loading conditions. The FEM axial strains on the tensile armour wires are compared with the measured results for pure tension and tension-bending loads. Under axisymmetric loading a relevant experimental axial strain dispersion is observed when compared to the average values. Under tension-bending loading, the interlayer friction coefficient influences on the contact pressure and curvature distribution are initially assessed with the numerical model. The strain gauges located in the cross-sections with highest values of contact pressure and curvature are selected for a detailed numerical-experimental strains comparison. In addition, a parametric study is conducted to calibrate the friction coefficient that yields the minimum mean squared error for all measured data. Generally, good correlations are found between the experimental and numerical results.

Extension of AASHTO Load-Spreading Method to Include the Full Benefits of Pavements for Reliable Load Rating of Buried Culverts

This paper develops a two-step procedure to extend the AASHTO Ad Hoc Method (AAM) for live-load spreading through soil to include the full benefits of pavement overlays. The two-step procedure is called AAMP-θ* (“P” for pavements), which combines the Fox two-layer elasticity solution for peak stress at the pavement–soil interface with the improved AAM-θ* theory for load spreading through soil. The AAMP-θ* procedure is applicable to all culvert analysis tools commonly used for Load and Resistance Factor Rating (LRFR) analysis ranging from simple frame models to sophisticated two-dimensional finite element model (2D-FEM) soil structure models. The AAMP-θ* procedure is rigorously and completely developed wherein all approximations are shown to be conservative so that the predicted benefits of pavements are trustworthy and not overstated. This is why the more accurate AAM-θ* load-spreading method is used instead of the simpler but unconservative AAM-30° method. Application of AAMP-θ* for LRFR load rating of buried culverts is described for simple frame models as well as 2D-FEM pavement–soil structure models. Lastly, the AAMP-θ* procedure is validated by comparing structural response predictions from 2D-FEM solutions with strain-gage measurements in a buried corrugated steel culvert loaded by a three-axle truck. One set of strain-gage measurements was made before, and another set of measurements was made after, asphalt pavement was installed. The correlation between field data and 2D-FEM/AAMP-θ* predictions is remarkable and underscores the bottom-line message that AAMP-θ* should be used when performing LRFR analysis on buried culverts to determine realistic rating factor values and avoid predicting false unsafe values.

Bolt loading effects on the structural integrity assessment of defects in industrial components

Applied loads in bolted geometries of safety critical components can vary with time and operating conditions. Structural integrity and remaining life assessments of such components in aging industrial plants must consider the resultant changes in damage accumulation rates and acceptable defect sizes. Two case studies are presented that demonstrate the effect of bolt pre-load on creep and fatigue lives as well as on the acceptability assessments of defects. In the first case the sensitivity of creep damage accumulation and crack propagation rates to bolt pre-load in high temperature flanged connections are considered. Predicted results were found to compare well with actual damage quantified on a high pressure turbine loop pipe flange connection. It was shown that decreased pre-loads, in this case, leads to an increase the allowable safe defect size during assembly at room temperature. In contrast to this the second case study of corrosion fatigue cracking in a boiler water circulating pump illustrates that an increase in bolt pre-load leads to an increase in fatigue initiation life, a decrease in fatigue crack propagation rate and an increase in the acceptable defect size. Strain gauge measurements of bolt and casing strain, which correlated well with finite element calculations, indicated the necessity for close control of bolt pre-load during assembly to ensure specified levels are attained. In both cases metallurgical analysis and structural integrity assessments of cracked and excavated geometries were conducted which enabled limited continued operation of the components after which repairs and/or replacements will be implemented.

Tension lap splices in UHPC beams: Influence of rebar size, steel fibers, splice length, and coarse aggregate

Ultra-high performance concrete (UHPC) is a special type of fiber-reinforced cementitious composites and has been considered an effective solution to reduce the required development length for steel reinforcing bars due to its high bond strength. This study thoroughly investigated the bond strength of deformed steel bars in UHPC using four-point loading tests on sixteen large-scale lap splice UHPC beams. The experimental variables included the bar diameter, macro-steel fibers, splice length, and coarse aggregate. The splice strength of reinforcing bars was estimated using the proposed analytical model and strain gauge measurements. The results showed that the effects of spacing and sizes of reinforcing bars on the splice strength were obvious. The inclusion of coarse aggregate considerably enhanced the splice strength of reinforcing bars in UHPC. The fracture toughening effects by fibers and coarse aggregate can enhance the strain field uniformity in the lap spice zone and increase the bond strength. In addition to the experimental study, the applicability of several prevailing bond strength models for examining the splice strength of reinforcing bars in UHPC was evaluated. Based on the evaluation results, a suitable model that was able to predict the splice strengths of the tested beams with reasonable accuracy was suggested.

Assessment of Strains Produced by Thermal Expansion in Printed Circuit Boards.

The paper proposed an alternative optical metrology to classical methods (strain gauge measurements and numerical simulation) for strain determination on printed circuit board (PCBs) due to thermal loads. The digital image correlation (DIC) technique was employed to record the strain distribution in some particular areas of the PCB. A thermal load was applied using a heating chamber, and the measurements were performed at four different temperature steps (25 °C, 50 °C, 85 °C and 120 °C). An increase in the principal strains with temperature was observed. For validation, the principal strains on the PCB obtained with DIC were compared with the values from gauge strain measurements and numerical simulation. The conclusions highlighted that DIC represents a technique with potential for strain measurement caused by thermal deformation, with the advantages of full field measurement, less preparation of the surface and good accuracy.