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1
Leski, Andrzej, Wojciech Wronicz, Piotr Kowalczyk, Michał Szmidt, Robert Klewicki, Karol Włodarczyk, and Grzegorz Uliński. "Modular Test Stand for Fatigue Testing of Aeronautical Structures – Verification of Assumptions." Fatigue of Aircraft Structures 2020, no. 12 (December 1, 2020): 78–91. http://dx.doi.org/10.2478/fas-2020-0008.
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Abstract The Modular Test Stand was developed and manufactured to decrease the cost of fatigue testing and reduce the time of its completion as well as to enable testing specimens under more complex load conditions. The stand consists of three connected sections, similar to a wing box, all being loaded in the same way. Thanks to that, several specimens can be tested simultaneously. This configuration requires that stress and strain distribution should be reasonably uniform, as assumed in the design stage. The structure can be loaded with bending or torsion. A whole section, selected structural node or a specimen mounted in the structure as well as a repair or a sensor can be a test object. Two stands, one for bending and one for torsion were prepared. This paper presents the verification of the assumed strain and stress distributions on the skin panels. The measurements were performed with the use of Digital Image Correlation (DIC) as well as strain gauges. DIC measurements were performed on one skin panel of the central section. Five strain gauge rosettes were installed on both panels of the one section. In addition, one rosette was applied to one skin panel in each of two other sections. Measurements were performed on the stand for torsion as well as on the stand for bending. The results of DIC analysis and strain gauge measurement during torsion show uniform shearing strain distributions on the panels. During bending, on the tensioned side, the strains obtained indicate quite uniform strain distributions. On the compressed side, local buckling of the skin panels results in high strain gradients. Strain levels obtained with the use of a DIC analysis and strain gauge measurements were similar. Moreover, horizontal displacements of markers in the spar axis during bending was determined based on a series of photographic. The deflection line obtained in this way has a shape similar to arc, which is characteristic of the constant bending moment. The stand was tested with torsional and bending loads in order to verify the design assumptions. The results of strain distributions on the skin panels with the use of DIC and strain gauges as well as the deflection line of the spar axis indicate that the Modular Test Stand performs as assumed and can be used for tests.
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Ridge, I. M. L., J. Zheng, and C. R. Chaplin. "Measurement of cyclic bending strains in steel wire rope." Journal of Strain Analysis for Engineering Design 35, no. 6 (August 1, 2000): 545–58. http://dx.doi.org/10.1243/0309324001514288.
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This paper reports strain gauge measurements of cyclic bending strain in the wires of a six-strand right-handed Lang's lay steel wire rope running on and off a pulley. The paper describes the measurement procedures and presents the results for the two tests conducted which had different gauge configurations along and around the sample. It was found that the strain waveforms observed had some similarities with those reported elsewhere and the magnitudes of strains matched theoretical predictions. However, in contrast with behaviour reported for fluctuating tension, the initial differences between and along wires rapidly attenuated. This observation helps to explain reported similarities in bending fatigue performance of ropes from different sources which contrasts with the very significant differences in characteristics found in tensile fatigue. The dependence of wire strain amplitude on rope bending deformation further contrasts with tensile fatigue in which wire strain range is dependent on the local sharing of axial load.
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Liu, Shucong, Dezhi Zheng, Tianhao Wang, Mengxi Dai, Rui Li, and Qingshan Feng. "A novel algorithm for pipeline displacement and bending strain of in-line inspection based on inertia measurement technology." Advances in Mechanical Engineering 10, no. 12 (December 2018): 168781401881675. http://dx.doi.org/10.1177/1687814018816755.
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The in-line inspection tool with Inertial Measurement Unit tool is becoming a routine and important practice for many pipeline companies and is effective for whole-line bending strain measurement. However, the measurements of Inertial Measurement Unit tool are always affected by noises and errors, which are caused by inherent inaccuracies and deficiencies of the experimental techniques and measuring devices. For the calculations of the bending strain, the results are very sensitive to the noises and errors. A filtering algorithm based on cubic spline interpolation was proposed for Inertial Measurement Unit data processing to eliminate noises and errors for bending strain, and the effectiveness is validated through the pipeline field test. The results showed that the average pipeline displacement deviation declined 13.82% in the three tests, and the bending strain error reduced from 0.037% to 0.014%. The proposed method effectively improves the inspection accuracy and provides an effective method for pipeline displacement and strain inspection, which ensures the safe operation of the pipeline.
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Socha, Bernard J., Edward T. Bednarz, and Wei-Dong Zhu. "A combined loading transducer for calculating the bending moment and torque in a slender circular beam using the minimum numbers of strain gauges, strain grids, and measurement channels." International Journal of Distributed Sensor Networks 16, no. 6 (June 2020): 155014772092177. http://dx.doi.org/10.1177/1550147720921774.
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The purpose of this work is to develop a new methodology that uses the minimum numbers of strain gauges, strain grids, and measurement channels to calculate the bending moment and torque in a slender circular beam under combined loading from measured strains in it. In general, each independent variable requires a minimum of one independent measurement. Two grids of a single-rosette strain gauge located at 45° and −45° from the longitudinal axis of the beam are used in conjunction with two measurement channels to gather all measurements and form a combined loading transducer. A theoretical set of equations of the new methodology is developed to minimize numbers of strain grids and measurement channels, and an experimental configuration was tested in a variety of scenarios. Calibration factors were independently developed for the bending moment and torque of the beam by separately loading it in their respective directions. These calibration factors were applied to different combined loading scenarios, where errors were found to be on average 1.6% for moment comparison and 6.7% for torque comparison.
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Devivier, C., Daniel Thompson, Fabrice Pierron, and M. R. Wisnom. "Correlation between Full-Field Measurements and Numerical Simulation Results for Multiple Delamination Composite Specimens in Bending." Applied Mechanics and Materials 24-25 (June 2010): 109–14. http://dx.doi.org/10.4028/www.scientific.net/amm.24-25.109.
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This paper studies the effect of delaminations on strain maps for a simple cantilever beam. The aim is to build an experimental set-up which allows detecting very slight modifications in the strain maps. The case studied is a single delamination on the mid-plane. The measurement method is the deflectometry technique which enables direct slope measurements on a reflective specimen. The comparison with finite element models clearly indicated that the surface strains bear the information of the extent of the delamination. The second step is to use these surface strains to identify a stiffness reduction map for real impact damages.
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Yu, Feng, and Michael T. Hendry. "A new strain gauge configuration on the rail web to decouple the wheel–rail lateral contact force from wayside measurement." Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit 233, no. 9 (January 13, 2019): 951–60. http://dx.doi.org/10.1177/0954409718822870.
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The simultaneous presence of bending moments and torques produced by the lateral and vertical contact forces between the wheel and the rail generates a complex strain state on the rail surface, which makes it difficult to identify the strain signals produced purely from the lateral contact force. In this study, a new strain gauge configuration is proposed to decouple strain signals of the wheel–rail lateral contact force from wayside measurements by analyzing the bending strains on the rail web using a full Wheatstone bridge. For this purpose, a finite element modeling of the wheel–rail contact is performed to analyze the bending strains on the rail web and to optimize two instrumented sections for eight electric resistance strain gauges. Laboratory testing is also used to examine the installation scheme of the strain gauges at the two optimal instrumented sections. A good agreement is observed between the experimental data and the simulation results. Strain signals are evenly distributed for about 10 cm in the middle region between the two optimal instrumented sections and only account for the lateral contact force.
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Arola, Anna Maija, Antti J. Kaijalainen, and Vili Kesti. "Evaluation of Bendability of Hot-Rolled S960 Grade Steel Using Optical Strain Measurements and FE-Modelling." Key Engineering Materials 651-653 (July 2015): 610–16. http://dx.doi.org/10.4028/www.scientific.net/kem.651-653.610.
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Bending is an important forming process for ultra-high strength steel (UHSS) because it is cost-effective, fast and in many cases it can be used to replace welding in a part manufacturing processes. One major challenge in air bending of UHSS is to predict the limits for bendability since the traditional methods for failure prediction, such as forming limit diagram (FLD), cannot generally be applied to bending process. In this paper, 3D FE-modelling coupled with a CDM-damage model is used to simulate the air bending process and to determine the bendability limits for a hot-rolled 960MPa grade. Damage parameters for the CDM-model are determined by using optical strain measurements and inverse modelling of the tensile test. Three point bending tests with optical strain measuring were carried out to determine the deformation field of the outer bend in different bending angles and the results of the bending simulation are compared with the strain measurements of the bending tests. The damage model is then calibrated using the experimental results of the bending tests to adjust the crack occurrence in the simulation. A good agreement was found between simulations and experimental measurements.
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Weisbrich, Martin, and Klaus Holschemacher. "Comparison between different fiber coatings and adhesives on steel surfaces for distributed optical strain measurements based on Rayleigh backscattering." Journal of Sensors and Sensor Systems 7, no. 2 (November 21, 2018): 601–8. http://dx.doi.org/10.5194/jsss-7-601-2018.
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Abstract. Optical fiber measurement systems have recently gained popularity following a multitude of intensive investigations. A new technique has been developed for these measurement systems that uses Rayleigh backscatter to determine the distributed strain measurement over the total length of a fiber. These measurement systems have great potential in civil engineering and structural health monitoring. This paper addresses some preliminary comparisons between three different fiber coatings and six different adhesives on steel structures. The results are based on a bending test with specimens made of precision flat steel; optical fiber strain measurements were compared with photogrammetric strain measurements. Analysis of the test data showed a strong correlation between the optical measurement system's results and the theoretical results up to the yielding point of the steel. Furthermore, the results indicate that fibers with the Ormocer® and polyimide coatings have almost the same strain values as the reference measurement method. The main results of this investigation are a guideline describing how to attach optical fibers to steel surfaces for distributed fiber optical strain measurements and recommendations for coatings to obtain realistic strain values. Additionally, the advantages of distributed strain measurements were revealed, which illustrates the potential of Rayleigh backscattering applications.
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Song, Xu, Solène Chardonnet, Giancarlo Savini, Shu Yan Zhang, Willem J. J. Vorster, and Alexander M. Korsunsky. "Experimental/Modelling Study of Residual Stress in Al/SiCp Bent Bars by Synchrotron XRD and Slitting Eigenstrain Methods." Materials Science Forum 571-572 (March 2008): 277–82. http://dx.doi.org/10.4028/www.scientific.net/msf.571-572.277.
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The aim of the study presented here was to evaluate the residual stresses present in a bar of aluminium alloy 2124-T1 matrix composite (MMC) reinforced with 25vol% particulate silicon carbide (SiCp) using X-ray diffraction and 3D profilometry (curvature measurement using Mitutoyo/Renishaw coordinate measurement machine) and comparing these results with numerical models of residual strain and stress profiles obtained by a simple inelastic bending model and Finite Element Analysis (FEA). The residual strain distribution was introduced into the test piece by plastic deformation in the 4-point bending configuration. At the first stage of this study the elasticplastic behaviour of the MMC was characterized under static and cyclic loading to obtain the material parameters, hardening proprieties and cyclic hysteresis loops. Subsequently, synchrotron Xray diffraction and CMM curvature measurements were performed to deduce the residual stress profile in the central section of the bar. The experimental data obtained from these measurements were used in the inelastic bending and FEA simulations. The specimens were then subjected to incremental slitting using EDM (electric discharge machining) with continuous back and front face strain gauge monitoring. The X-ray diffraction and incremental slitting results were then analysed using direct and inverse eigenstrain methods. Residual stresses plots obtained by different methods show good agreement with each other.
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Xu, Y., and R. N. Miles. "Experimental determination of bending strain power spectra from vibration measurements." Experimental Mechanics 36, no. 2 (June 1996): 166–72. http://dx.doi.org/10.1007/bf02328714.
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Hack, E., and A. Schumacher. "ESPI Measurements of Strain on a CFRP-Reinforced Bending Beam." Strain 43, no. 3 (August 2007): 235–39. http://dx.doi.org/10.1111/j.1475-1305.2007.00339.x.
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Arola, Anna Maija, Vili Kesti, and Raimo Ruoppa. "The Effect of Punch Radius on the Deformation of Ultra-High Strength Steel in Bending." Key Engineering Materials 639 (March 2015): 139–46. http://dx.doi.org/10.4028/www.scientific.net/kem.639.139.
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Bendability is an important material property for ultra-high strength steel. The bendability of a certain material is expressed as the minimum bending radius Rmin of the inner surface of the bend and expressed in multiples of the sheet thickness. Bendability is limited by either cracking on the surface or the edges of the bend or by surface waviness that usually precedes cracking on the outer surface. Surface waviness is a form of strain localization in bending and the intensity of the phenomenon is dependent on e.g. the punch radius, the lower tool width and the sheet thickness. In this study the bendability of a 960MPa grade steel was investigated using optical strain measurements of three-point bending tests to determine the strain level and the bending angle when localization starts with different punch radii. The unbent samples were marked with a grid using laser marking and the deformation was measured with the GOM ARGUS strain analysis system after bending. The quality of the bend was also evaluated visually. In addition, tensile tests were performed and evaluated with the GOM ARAMIS deformation analysis system to investigate the local mechanical properties of the studied steel. The results of strain measurements and visual evaluation were then compared. It was found that beyond a certain angle the maximum strain across the bend did not significantly change with further increases in the bending angle when the punch radius was at least three times the sheet thickness. But with smaller punch radii the maximum strain increased almost linearly with increasing bending angle until fracture appeared. With the smaller punch radii deformation localizes and surface waviness begins to form in smaller bending angles because the deformation is concentrated in a narrow zone.
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Shetty, S., V. Lehtinen, A. Dasgupta, V. Halkola, and T. Reinikainen. "Fatigue of Chip Scale Package Interconnects Due to Cyclic Bending." Journal of Electronic Packaging 123, no. 3 (March 25, 2000): 302–8. http://dx.doi.org/10.1115/1.1362673.
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This study investigates the effect of quasi-static bending loads (strain rate=0.05/s) on the durability of 0.5 mm pitch Chip Scale Package (CSP) interconnects when assembled on FR4 substrates. The substrates have rows of CSPs and are subjected to three-point bending loads. Overstress curvature limits are experimentally determined and used to identify limits for zero-to-max cyclic bending loads. The test configuration is simulated using finite element modeling (FEM) and the total strain accumulated in the solder joints is estimated. Using the FEM model, a calibration curve is constructed to relate the cyclic curvature range in the substrate to the cyclic strain range in the critical solder joint. Bending moments along the substrate are estimated from the forces applied at the center of the board during the fatigue test. Strains measured on the substrate surface and the bending displacements measured at the center are used to estimate curvatures at different locations along the substrate. Using the calibration curve, the total strains in the solder joint are obtained for the applied loading. A strain-range fatigue damage model proposed by Coffin and Manson, is used to predict the cycles to failure for the applied loading. Predicted durability is compared to experimental measurements. Concave substrate curvature is found to be more damaging than convex curvature, for interconnect fatigue. Finite element simulations are repeated for life-cycle loading to predict acceleration factors. Using the acceleration factors, the product durability is estimated for life-cycle environments.
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Wakeling, J. M., and I. A. Johnston. "White muscle strain in the common carp and red to white muscle gearing ratios in fish." Journal of Experimental Biology 202, no. 5 (March 1, 1999): 521–28. http://dx.doi.org/10.1242/jeb.202.5.521.
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White muscle strains were recorded using sonomicrometry techniques for 70 fast-starts in the common carp Cyprinus carpio L. High-speed cine images were recorded simultaneously for 54 of these starts, and muscle strain was calculated independently from the digitized outlines of the fish. Sonomicrometry measurements of superficial muscle strain were not significantly different from the strain as calculated from the theory of simple bending of a homogeneous material: superficial muscle strain thus varied with chordwise distance from the spine. However, white muscle strain across a transverse section of the myotome shows less variation with chordwise position than would be expected from simple bending theory. Muscle strains measured using sonomicrometry thus do not necessarily represent the more uniform strain predicted for the whole section of the fish. White muscle strain can be accurately predicted from the spine curvatures as measured from the cine images if the gearing ratio between the red and white muscle fibres is known. A model for calculating the gearing ratio from the helical muscle fibre geometry was re-evaluated using current data for the kinematics of fast-starting C. carpio. This model predicted a mean gearing ratio of 2.8 for these fast-starts. A quicker, alternative approach to estimating gearing ratio from the position of the centroid of white fibre area is proposed and results in ratios similar to those calculated from the model of helical geometry. White muscle strains in fish can thus be estimated from measurements of spine curvature and muscle distribution alone.
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He, X., J. Ma, and T. Welo. "Strain distribution at the transition from bent to unbent regions in tube rotary draw bending: an in-situ, real-time measurement study." IOP Conference Series: Materials Science and Engineering 1270, no. 1 (December 1, 2022): 012059. http://dx.doi.org/10.1088/1757-899x/1270/1/012059.
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In tube bending processes, accurate control of springback is of crucial importance as this affects the dimensional accuracy of the final product and overall equipment efficiency. The distribution of stress and strain during bending is one of the most fundamental issues determining the springback magnitude of the product. In conventional analyses of rotary draw bending, the deformation behaviour along the bending direction is normally assumed to be uniform for constant-radius bends, following the contour of the die configuration. In practice, however, the stress-strain distribution is non-uniform, particularly at the transition between the bent and unbent regions of the formed component. The distribution makes a significant contribution to springback and its variations, especially for low bend-angle components. This research focuses on exploring the strain distribution at the end transition of the bend of aluminium tubes in rotary draw bending. An experimental test setup for strain measurements with a strain gauge glued to the unbent area has been designed and conducted to measure the strain distribution during bending. The characteristics of non-uniform strain distribution during tube bending, including the evolving transition behaviour at the transition between bent and unbent areas, are studied. The results enhance the understanding of deformation characteristics of bent tubes, and contribute to improved physically-based models and springback control routines in industrial practice.
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Maekawa, Akira, Toru Oumaya, Michiyasu Noda, Shigeru Takahashi, and Toru Saito. "Residual Stress Distribution in Austenitic Stainless Steel Pipe Butt-Welded Joint Measured by Neutron Diffraction Technique." Materials Science Forum 652 (May 2010): 116–22. http://dx.doi.org/10.4028/www.scientific.net/msf.652.116.
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This paper describes residual stress measurements and analysis of austenitic stainless steel pipe with a butt-welded joint. The measurements were done with neutron diffraction and strain gauge techniques. The measured results had typical characteristics of butt-welded pipe regarding both the decline of stress along the axial direction and the bending distribution of axial stress along the radial direction. The measured residual stress distribution by neutron diffraction was shifted more to the tensile side than that by the finite element method simulation. However, the measured radial and axial strains, except for the hoop strain determined by neutron diffraction, coincided well with analysis strains. The hoop strain was actually equivalent strain converted by a correction method because a different lattice plane had to be used to measure hoop strain. This might be one reason why the difference occurred. Therefore, future study of the correction method would be desirable.
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Brachman, R. WI, I. D. Moore, and R. K. Rowe. "Local strain on a leachate collection pipe." Canadian Journal of Civil Engineering 27, no. 6 (December 1, 2000): 1273–85. http://dx.doi.org/10.1139/l00-074.
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Local strain measurements opposite gravel contacts and around a single isolated perforation are reported for a high-density-polyethylene pipe (320 mm outside diameter, 32 mm thick) typical of that commonly used as part of the leachate collection system in municipal solid waste landfills. Emphasis is given to examining the localized effect of coarse gravel contacts on pipe strain and the strain distribution around the perforation. The laboratory testing featured a cylindrical volume of soil with the pipe located in the middle with radially compressive stresses applied along the outer perimeter of the backfill. Two different backfill materials were used. When tested with medium sand backfill the pipe response was essentially uniform, indicative of the near-continuous support and loading provided by the sand. Large variations in local pipe strains were measured with coarse gravel backfill, such as that used in landfill leachate collection systems. Local bending induced by the discontinuous support and loading from the coarse gravel resulted in variations in circumferential and axial strains of over 40%. The local bending effects were not sufficiently large to produce circumferential tension in the pipe tested. A multiplication factor of 1.5 is suggested to account for increases in compressive strain from the coarse gravel. Measurements of surface strain around an isolated 32 mm diameter perforation revealed that a complex three-dimensional response is induced by the presence of the hole. Maximum strains near the hole were found to be 2.7 times larger than those distant from the perforation.Key words: leachate collection pipes, HDPE pipes, leachate collection systems, landfill design.
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Valentini, Emilio, Alessio Benincasa, and Ciro Santus. "Bending Test Rig for Validating the Hole Drilling Method Residual Stress Measurement." Materials Science Forum 768-769 (September 2013): 150–57. http://dx.doi.org/10.4028/www.scientific.net/msf.768-769.150.
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This paper shows a large validation activity of the strain gage Hole Drilling Method. The residual stress measurements can not be validated easily, unless with Round Robin activity and/or comparison with other residual stress measurements such as X-ray diffraction. An accurate validation procedure is reported in the present paper, using abending test rig. The bending stress experimentally simulated a residual stress (known with uncertainty lower than 1%) that was considered as the reference stress distribution. The results showed very accurate measurement in terms of relaxed strain distributions, that were compared with the prediction obtained with the Influence Function technique. The differences were in the order of 0.5 microepsilon as standard deviation on a large number of tests. The bending stress prediction was consequently very accurate and the stress differences were as small as 1 MPa showing the accuracy potentiality of the method.
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Černý, Ivo. "Monitoring of Internal Damage of Glass Fibre Reinforced Composite Components Using Strain Measurements with Strain Gauges and Fibre Optic Sensors." Applied Mechanics and Materials 486 (December 2013): 58–61. http://dx.doi.org/10.4028/www.scientific.net/amm.486.58.
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Glass fibre reinforced polymer (GRP) composites are perspective materials for manufacture of components in different machinery applications. Favourable characteristics of these materials include very high specific strength, ratio of static and dynamic stiffness, particularly beneficial in dynamically loaded structures, and potentially excellent fatigue strength provided that there are no latent internal imperfections, occurring usually in the manufacture process. Defects like insufficient wet-out of glass fibres by resin result in significant reduction of static and fatigue strength in shear. If the component thickness is high and it is loaded by bending, considerable shear stresses occur in the neutral plane, which can cause premature shear failure of the component. Results of static and fatigue tests in bending of full-scale models of longitudinal frames of railway freight vehicle bogies, manufactured from GRP polyester composites, are shown and analysed in the paper. Surface strains measured using strain gauges were monitored during the component loading, its continuous damage and were analysed. The results are in a good agreement with the subsurface strains evaluated using fibre optic sensors embedded in the component during the manufacture process. Asymmetry of strains, both internal and surface, was connected with internal defects and consequently reduced strength. On the contrary, very good fatigue resistance was characteristic for components, where strain values were symmetrical.
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Pascual, Javier, Francis Chalvet, Tanja Lube, and Goffredo de Portu. "Strain Mismatch in Ceramic Multilayers: Determination by Strength Measurements." Key Engineering Materials 333 (March 2007): 239–42. http://dx.doi.org/10.4028/www.scientific.net/kem.333.239.
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In asymmetrical 3-layer laminates with constant overall and inner layer thickness, the residual compressive stresses in the two outer layers are not longer the same: compression is higher in the thinner layer.Therefore, it can be expected that the strength also depends on the outer layer thickness. Experimental evidence of this behavior was found by measuring the bending strength of asymmetrical tri-layers. A value of the thermal expansion mismatch was determined by fitting the theoretical expression to the experimental data.
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Arola, Anna Maija, Kari Mäntyjärvi, and Jussi A. Karjalainen. "FEM - Modeling of Bendability of Ultra-High Strength Steel." Key Engineering Materials 549 (April 2013): 333–39. http://dx.doi.org/10.4028/www.scientific.net/kem.549.333.
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Ultra-high strength steels have been widely used in different industrial applications. It is necessary to understand the behavior of these materials in common forming processes such as air bending. It is known that the bendability of ultra-high strength steels is lower than other high-strength steels but what are yet to be discovered are the parameters that define the limits of bendability of these steels. The aim of this study was to investigate the factors affecting the bendability of ultra-high strength steel using optical strain measurements and FEM-modeling of the bending process. By using the true stress-strain relation measured by optical strain measuring system the bendability of ultra-high-strength steel was modeled fairly accurately. As a result, it was noted that the strain distribution at the bend of a steel possessing better uniform strain was more widely distributed and there were no highly localized strains. On the other hand as the failure occurred the strains were considerably smaller than the true failure strain of the material in uniaxial tension. As a conclusion it was stated that the ability to withstand the localization of deformation might describe the bendability of ultra-high-strength steel better than the values of the uniform or true failure strain in uniaxial tension test.
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Vervloet, Jolien, Tine Tysmans, Michael El Kadi, Matthias De Munck, Panagiotis Kapsalis, Petra Van Itterbeeck, Jan Wastiels, and Danny Van Hemelrijck. "Validation of a Numerical Bending Model for Sandwich Beams with Textile-Reinforced Cement Faces by Means of Digital Image Correlation." Applied Sciences 9, no. 6 (March 25, 2019): 1253. http://dx.doi.org/10.3390/app9061253.
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Sandwich panels with textile-reinforced cement (TRC) faces merge both structural and insulating performance into one lightweight construction element. To design with sandwich panels, predictive numerical models need to be thoroughly validated, in order to use them with high confidence and reliability. Numerical bending models established in literature have been validated by means of local displacement measurements, but are missing a full surface strain validation. Therefore, four-point bending tests monitored by a digital image correlation system were compared with a numerical bending model, leading to a thorough validation of that numerical model. Monitoring with a digital image correlation (DIC) system gave a highly detailed image of behaviour during bending and the strains in the different materials of the sandwich panel. The measured strains validated the numerical model predictions of, amongst others, the multiple cracking of the TRC tensile face and the shear deformation of the core.
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Patel, Jay, Adarsh Ayyar, and Pedro Peralta. "Kink band evolution in polymer matrix composites under bending: A digital image correlation study." Journal of Reinforced Plastics and Composites 39, no. 21-22 (June 19, 2020): 852–66. http://dx.doi.org/10.1177/0731684420933951.
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Polymer matrix composites are attractive structural materials in automotive, defense, and aerospace industries due to their high strength to low weight ratios. However, due to their low shear strength, compression dominated failure mechanisms such as plastic microbuckling lead to the development of kink bands, which are a key strength-limiting factor in modern polymer matrix composites. This phenomenon has been studied extensively, particularly for uniaxial compression; however, experimental measurements of the strain fields leading to and developing inside these bands under bending are not well explored. In this study, digital image correlation is used to measure strains inside kink bands developing during three-point bending of cross-plied [0/90] laminated composite Dyneema™ HB80. Measurements indicated large normal and shear strains developed inside the band in a way that suggested systematic increases in ply rotation angle as the band evolved with increased bending deflection. Results also suggested intermittent buckling events involving fiber bundles that correlate with oscillations observed in the load–displacement curve. Optical microscopy of failed samples showed failure resulted from a combination of plastic microbuckling and axial splitting.
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Liu, Han, Simon Laflamme, Jian Li, Caroline Bennett, William N. Collins, Austin Downey, Paul Ziehl, and Hongki Jo. "Soft Elastomeric Capacitor for Angular Rotation Sensing in Steel Components." Sensors 21, no. 21 (October 23, 2021): 7017. http://dx.doi.org/10.3390/s21217017.
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The authors have previously proposed corrugated soft elastomeric capacitors (cSEC) to create ultra compliant scalable strain gauges. The cSEC technology has been successfully demonstrated in engineering and biomechanical applications for in-plane strain measurements. This study extends work on the cSEC to evaluate its performance at measuring angular rotation when installed folded at the junction of two plates. The objective is to characterize the sensor’s electromechanical behavior anticipating applications to the monitoring of welded connections in steel components. To do so, an electromechanical model that maps the cSEC signal to bending strain induced by angular rotation is derived and adjusted using a validated finite element model. Given the difficulty in mapping strain measurements to rotation, an algorithm termed angular rotation index (ARI) is formulated to link measurements to angular rotation directly. Experimental work is conducted on a hollow structural section (HSS) steel specimen equipped with cSECs subjected to compression to generate angular rotations at the corners within the cross-section. Results confirm that the cSEC is capable of tracking angular rotation-induced bending strain linearly, however with accuracy levels significantly lower than found over flat configurations. Nevertheless, measurements were mapped to angular rotations using the ARI, and it was found that the ARI mapped linearly to the angle of rotation, with an accuracy of 0.416∘.
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Corning, WR, and AA Biewener. "In vivo strains in pigeon flight feather shafts: implications for structural design." Journal of Experimental Biology 201, no. 22 (November 1, 1998): 3057–65. http://dx.doi.org/10.1242/jeb.201.22.3057.
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To evaluate the safety factor for flight feather shafts, in vivo strains were recorded during free flight from the dorsal surface of a variety of flight feathers of captive pigeons (Columba livia) using metal foil strain gauges. Strains recorded while the birds flew at a slow speed (approximately 5-6 m s-1) were used to calculate functional stresses on the basis of published values for the elastic modulus of feather keratin. These stresses were then compared with measurements of the failure stress obtained from four-point bending tests of whole sections of the rachis at a similar location. Recorded strains followed an oscillatory pattern, changing from tensile strain during the upstroke to compressive strain during the downstroke. Peak compressive strains were 2.2+/-0. 9 times (mean +/- s.d.) greater than peak tensile strains. Tensile strain peaks were generally not as large in more proximal flight feathers. Maximal compressive strains averaged -0.0033+/-0.0012 and occurred late in the downstroke. Bending tests demonstrated that feather shafts are most likely to fail through local buckling of their compact keratin cortex. A comparison of the mean (8.3 MPa) and maximum (15.7 MPa) peak stresses calculated from the in vivo strain recordings with the mean failure stress measured in four-point bending (137 MPa) yields a safety factor of between 9 and 17. Under more strenuous flight conditions, feather stresses are estimated to be 1.4-fold higher, reducing their safety factor to the range 6-12. These values seem high, considering that the safety factor of the humerus of pigeons has been estimated to be between 1.9 and 3.5. Several hypotheses explaining this difference in safety factor are considered, but the most reasonable explanation appears to be that flexural stiffness is more critical than strength to feather shaft performance.
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Gawedzki, Waclaw, and Jerzy Tarnowski. "Design and Testing of the Strain Transducer for Measuring Deformations of Pipelines Operating in the Mining-deformable Ground Environment." Measurement Science Review 15, no. 5 (October 1, 2015): 256–62. http://dx.doi.org/10.1515/msr-2015-0035.
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Abstract Design and laboratory test results of the strain transducer intended for monitoring and assessing stress states of pipelines sited in mining areas are presented in this paper. This transducer allows measuring strains of pipelines subjected to external forces - being the mining operations effect. Pipeline strains can have a direct influence on a tightness loss and penetration of the transported fluid into the environment. The original strain gauge transducer was proposed for performing measurements of strains. It allows measuring circumferential strains and determining the value and direction of the main longitudinal strain. This strain is determined on the basis of measuring component longitudinal strains originating from axial forces and the resultant bending moment. The main purpose of investigations was the experimental verification of the possibility of applying the strain transducer for measuring strains of polyethylene pipelines. The obtained results of the transducer subjected to influences of tensile and compression forces are presented and tests of relaxation properties of polyethylene are performed.
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Araújo, F. M., L. A. Ferreira, J. L. Santos, and F. Farahi. "Temperature and strain insensitive bending measurements with D-type fibre Bragg gratings." Measurement Science and Technology 12, no. 7 (June 8, 2001): 829–33. http://dx.doi.org/10.1088/0957-0233/12/7/314.
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Carl, Matthew, Baozhuo Zhang, and Marcus L. Young. "Texture and Strain Measurements from Bending of NiTi Shape Memory Alloy Wires." Shape Memory and Superelasticity 2, no. 3 (July 19, 2016): 254–63. http://dx.doi.org/10.1007/s40830-016-0073-0.
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Miles, R. N., W. Bao, and Y. Xu. "Estimation of Random Bending Strain in a Beam from Discrete Vibration Measurements." Journal of Sound and Vibration 174, no. 2 (July 1994): 191–99. http://dx.doi.org/10.1006/jsvi.1994.1271.
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Schöberl, Erich, MN Mavrogordato, I. Sinclair, and SM Spearing. "Fibre direction strain measurement in a composite ply under pure bending using Digital Volume Correlation and Micro-focus Computed Tomography." Journal of Composite Materials 54, no. 14 (April 22, 2020): 1889–912. http://dx.doi.org/10.1177/0021998320918648.
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This paper presents an experimental demonstration and validation of high-resolution three-dimensional experimental strain measurement using Digital Volume Correlation (DVC) on Carbon Fibre-Reinforced Polymers, via through-thickness strain analysis under a state of pure bending. To permit the application of DVC to displacements and/or strain measurements parallel to the fibre direction in well-aligned unidirectional materials at high volume fractions, a methodology was developed for the insertion of sparse populations of 400 nm BaTiO3 particles within the matrix to act as displacement trackers (i.e. fiducial markers). For this novel material system, measurement sensitivity and noise are considered, along with the spatial filtering intrinsic to established DVC data processing. In conjunction with Micro-focus Computed Tomography, the technique was applied to a simple standard specimen subjected to a four-point flexural test, which resulted in a linear strain distribution through the beam thickness. The high-resolution, fibre-level strain distributions (imaged at a voxel resolution of ∼0.64 µm) were compared against the classical beam theory (Euler–Bernoulli) in incrementally decreasing averaging schemes and different sub-set sizes. Different sampling and averaging strategies are reported, showing that DVC outputs can be obtained that are in very good agreement with the analytical solution. A practical lower limit for the spatial resolution of strain is discerned for the present materials and methods. This study demonstrates the effectiveness of DVC in measuring local strains parallel to the fibre direction, with corresponding potential for calibration and validation of micromechanical models predicting various fibre-dominated damage mechanisms.
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Dhanasekar, M., and W. Bayissa. "Performance of square and inclined insulated rail joints based on field strain measurements." Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit 226, no. 2 (August 15, 2011): 140–54. http://dx.doi.org/10.1177/0954409711415898.
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Insulated rail joints (IRJs) possess lower bending stiffness across the gap containing insulating endpost and hence are subjected to wheel impact. IRJs are either square cut or inclined cut to the longitudinal axis of the rails in a vertical plane. It is generally claimed that the inclined cut IRJs outperform the square cut IRJs; however, there is a paucity of literature with regard to the relative structural merits of these two designs. This article presents comparative studies of the structural response of these two IRJs to the passage of wheels based on continuously acquired field data from joints strain-gauged closer to the source of impact. Strain signatures are presented in time, frequency, and wavelet domains and the peak vertical and shear strains are systematically employed to examine the relative structural merits of the two IRJs subjected to similar real-life loading. It is shown that the inclined IRJs resist the wheel load with higher peak shear strains and lower peak vertical strains than that of the square IRJs.
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Mäkinen, Jari, Keijo Fränti, Matti Korhonen, Joshua Fillion, and Markku Heinisuo. "End-Plate Connections in Bi-Axial Bending - Measurements." Key Engineering Materials 710 (September 2016): 275–80. http://dx.doi.org/10.4028/www.scientific.net/kem.710.275.
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In this paper we consider the measurements of bolted end-plate connections of tubular beams with cold-formed hollow rectangular aluminium sections. The motivation for these measurements originates from the fact that the aluminium standard (EN 1999-1-1) [1] does not cover the design of this very frequently used type of connection, where the bolts are located outside the edge-lines of the cross-section, i.e. corner bolts. Many tests and studies regarding this area have been conducted, but this paper brings value to the case where bi-axial bending is applied. The measurements have been carried out and the detailed results shall be shown. In this paper, we will focus on the six measurements where the tubular beams were bent uniaxially and biaxially to these limit points. The tests were stopped when the ultimate limit state was reached. In this case the connection never actually broke, but effectively the joint had lost its load bearing capacity. Some residual capacity still remained, but the displacements were too great resulting in a totally different behavior of the connection. The behavior of this connection is highly non-linear, since aluminium (AW 5754) as a material is strain hardening and the mechanism in the connection changes as the displacements increase.
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Entwistle, Kenneth M. "The mechanosorptive effect in Pinus radiata D. Don." Holzforschung 59, no. 5 (September 1, 2005): 552–58. http://dx.doi.org/10.1515/hf.2005.091.
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Abstract Measurements are reported of the mechanosorptive strain in Pinus radiata specimens stressed either in torsion or in bending. It is demonstrated that, to secure valid data, correction must be made for the moisture-induced distortion at zero load. A series of measurements can be made on a single specimen if two successive mechano-sorptive loading cycles are used and the sense of the stress is reversed for the second cycle. At the end of this procedure the specimen has reverted to its original dimensions. The mechanosorptive strain is shown to vary linearly with the applied stress; the ratio of the mechanosorptive strain to the initial elastic strain is therefore an appropriate way of quantifying the mechanosorptive effect. Analysis of torsion and bending data reveals that there is a strong correlation between the magnitude of the mechanosorptive strain and the shear stress component of the applied stress along the cellulose microfibril direction. It is suggested that the mechanosorptive effect arises from the effect of stress on the distribution of hydrogen bonds in hemicelluloses. A detailed model must await more information about the molecular structure of hemicelluloses in the cell walls.
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Shawki, G. S. A., and S. A. R. Naga. "On the Mechanics of Grey Cast Iron Under Pure Bending." Journal of Engineering Materials and Technology 108, no. 2 (April 1, 1986): 141–46. http://dx.doi.org/10.1115/1.3225851.
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This paper presents the results of experiments conducted on lamellar graphite grey cast iron of rectangular section subjected to pure bending. Strain measurements confirm the traditional speculation that plane sections remain plane under strain. Owing to the nonlinear relationship between stress and strain, however, the neutral axis of a loaded specimen is shown to shift away from the centroidal axis. This shift is evidently amplified with increased loading. A computer program is herein specially devised for calculating the shift in neutral axis through satisfaction of the conditions of equilibrium together with checking for possible crack initiation at the extension side. While the simple flexural formula holds very nearly true for the compression side, it fails, however, to predict stresses on the extension side, the situation being further aggravated by higher bending moments. The apparent high bending strength of grey cast iron is fully accounted for.
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Lee, Sung Hyuk, and Nak Sam Choi. "Bending Performance Evaluation of Reinforced Aluminum Square Tube Beams Considering Local Buckling Behavior." Key Engineering Materials 297-300 (November 2005): 2290–96. http://dx.doi.org/10.4028/www.scientific.net/kem.297-300.2290.
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Bending performances of aluminum square tube beams reinforced by aluminum plates under three point bending loads have been evaluated using experimental tests combined with theoretical and finite element analyses. Basic properties of aluminum materials used for initial input data of the finite element simulation were obtained from the true stress-true strain curves of specimens which had bean extracted from the Al tube beams. True stresses were determined from applied loads and cross-sectional area records of a tensile specimen with a rectangular cross-section by real-time photographing. True strains were obtained from in-situ local elongation measurements of the specimen gage portion by the multi-point scanning laser extensometer. Four kinds of aluminum tube beam specimens adhered by aluminum plates were employed. The bending deformation behaviors up to the maximum load described by the numerical simulation were in good agreement with experimental ones. An aluminum tube beam strengthened by aluminum plate on the upper web showed an excellent bending capability.
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Wu, Yan-Kuei, Sheng-Chih Shen, Chun-Yen Lee, and Yen-Ju Chen. "A Self-Powered Strain Sensor Applied to Real-Time Monitoring for Movable Structures." Sensors 22, no. 16 (August 15, 2022): 6084. http://dx.doi.org/10.3390/s22166084.
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This study uses near-field electrospinning (NFES) technology to make a novel self-powered strain sensor and applies it to the real-time monitoring of a bending structure, so that the measurement equipment can be reduced in volume. A self-powered strain sensor consists of polyvinylidene difluoride (PVDF) fibers, a PDMS fixed substrate, and an aluminum electrode. PVDF fibers are spun with DMSO and acetone using NFES technology, with a diameter of about 8 μm, Young’s modulus of 1.1 GPa, and piezoelectric effect of up to 230 mV. The fixed substrate is a film made of PDMS by thermal curing, then adhered to the PDMS film surface of the sheet Al metal as an Al electrode, and then combined with PVDF fiber film, to become a self-powered strain sensor. As a result, the XRD β value of the self-powered strain sensor reaches 2112 and the sensitivity is increased by 20% over a traditional strain sensor. The cumulative angle algorithm can be applied to measure the angular change of the object over a unit of time or the cumulative displacement of the object over the entire period of motion. The experimental results demonstrate that the self-powered strain sensor combined with the angle accumulation algorithm may be applied to monitor the bending structure, thereby achieving continuous measurements of bending structure changes, and improving on traditional piezoelectric sensors, which can only be sensed once. In the future, self-powered strain sensors will have the ability to continuously measure in real-time, enabling the use of piezoelectric sensors for long-term monitoring of structural techniques.
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Riehemann, Werner, and Zuzanka Trojanová. "Fatigue Behavior of Magnesium Alloy AJ91 Studied by Amplitude Dependent Damping Measurements." Solid State Phenomena 184 (January 2012): 185–90. http://dx.doi.org/10.4028/www.scientific.net/ssp.184.185.
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The amplitude dependent damping of two bending beam samples of magnesium alloy AJ91 (9 wt.% Al, 1 wt.% Sr) was measured at room temperature in as cast condition, after quenching from high temperatures into water of room temperature and after various bending cycles to fatigue. Some measurements were performed successively with about 33 Hz and 100 Hz resonant frequency. The measurements show typical dislocation damping in as cast condition, after heat treatment at temperatures lower than 420°C, and cycle numbers lower then 50.000. For higher quenching temperatures the damping increases over the whole measured strain range with increasing quenching temperature and number of cycles to fatigue. After quenching from temperatures higher than 478°C the crack damping becomes dominant. The effects of damping seem to increase with increasing frequency. In one sample damping of individual cracks could be identified in the amplitude dependent damping curves by their characteristic course very similar to the ones postulated in an earlier publication by a simple rheological model [4]. The extending of crack length leads to a shift of the damping to lower strains.
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Rudnev, I., A. Mareeva, N. Mineev, S. Pokrovskiy, and A. Sotnikova. "Contactless measurements of local transport characteristics of coated conductors under the bending strain." Journal of Physics: Conference Series 507, no. 2 (May 12, 2014): 022029. http://dx.doi.org/10.1088/1742-6596/507/2/022029.
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Perbawa, A., E. Gramajo, T. Finkbeiner, and J. C. Santamarina. "Rock Triaxial Tests: Global Deformation vs Local Strain Measurements—Implications." Rock Mechanics and Rock Engineering 54, no. 7 (April 5, 2021): 3527–40. http://dx.doi.org/10.1007/s00603-021-02389-z.
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AbstractAccurate stress–strain measurements in triaxial tests are critical to compute reliable mechanical parameters. We focus on compliance at the interfaces between the specimen and endcaps, and test specimens under various triaxial conditions using different instrumentation protocols. The tested materials include aluminum, Eagle Ford shale, Berea sandstone, and Jubaila carbonate. Results obtained following common practice reveal that surface roughness at the specimen-endcap interfaces leads to marked seating effects, affects all cap-to-cap based measurements and hinders ultrasonic energy transmission. In particular, cap-to-cap deformation measurements accentuate hysteretic behavior, magnify biases caused by bending and tilting (triggered by uneven surfaces and misalignment), and affect the estimation of all rock parameters, from stiffness to Biot’s α-parameter. Higher confining pressure diminishes seating effects. Local measurements using specimen-bonded strain gauges are preferred (Note: mounting strain gauges on sleeves is ill-advised). We confirm that elastic moduli derived from wave propagation measurements are higher than quasi-static moduli determined from local strain measurements using specimen-bonded strain gauges, probably due to the lower strain level in wave propagation and preferential high-velocity travel path for first arrivals.
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SENG, KOK-YONG, and PIN-MIN LAM. "RELIABILITY OF AN ADVANCED METHOD FOR ISOMETRIC NECK MUSCLE STRENGTH MEASUREMENT." Journal of Mechanics in Medicine and Biology 02, no. 02 (June 2002): 117–29. http://dx.doi.org/10.1142/s0219519402000290.
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This paper is a descriptive study involving repeated within and between studies of maximal isometric strength measurements to determine the reproducibility of an advanced mechanical device in assessing maximal isometric strength of the cervical musculature. Measurements of neck muscular strength and endurance present unique challenges, due to the complexity of neck motion and absence of appropriate reference bony landmarks. Assessment of cervical musculature characteristics is further complicated by a lack of affordable and reliable measurement equipment. Previous methods commonly employed strain gauge measurement and customized helmet dynamometry, but no device, engaging a computer-controled dynamometer, has been presented so far. A new device incorporating anthropometry measurements of the local population was constructed for neck strength evaluation on the Biodex isokinetic dynamometer (Biodex, Corp., Shirley, NY). Intratester repeatability testing of the device was conducted in four principal directions: flexion, extension and left and right lateral bending. The result for intraday and day-to-day studies was good for all measured parameters. This new device can be used to measure isometric flexion, extension and lateral bending torque. By permitting the neck's 'natural' motions, it may also quantify maximal isokinetic strength and endurance ratios. Hence, the device can serve as a useful and practical tool for neck strength measurement, training and rehabilitation purposes.
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Soltani Dehkharqani, Arash, Fredrik Engström, Jan-Olov Aidanpää, and Michel J. Cervantes. "Experimental Investigation of a 10 MW Prototype Kaplan Turbine during Start-Up Operation." Energies 12, no. 23 (December 2, 2019): 4582. http://dx.doi.org/10.3390/en12234582.
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An increase in the start/stop cycles of hydraulic turbines due to the penetration of intermittent renewable energy sources is important. Hydraulic instabilities that occur in hydraulic turbines during start/stops may cause structural issues in the turbine components. High-stress fluctuations on the runner blades are expected during start-ups due to the unsteady pressure loading on the runner blades. This paper presents experiments performed on a 10 MW prototype Kaplan turbine at the Porjus Hydropower Center during a start-up cycle. Synchronized unsteady pressure and strain measurements on a runner blade and axial, bending (in two directions) and torsion strain measurements on the shaft were performed. In addition, the general parameters of the turbine (e.g., rotational speed, guide vane opening and runner blade angle) were acquired. Low-frequency fluctuations (0–15 Hz) were observed in the pressure data on the runner blade after opening the guide vanes from the completely closed position. A higher strain value was observed on the strain gauges installed on the runner blade near the hub (200–500 μ m / m ) compared to the ones near the shroud at the leading and trailing edge. The strain fluctuation level on the shaft decreased after loading the generator by further opening the guide vanes. Higher fluctuations were observed in the torsion strain compared to axial and bending strain. In addition, the torsion strain peak-to-peak value reached 12 times its corresponding value at 61% guide vane opening.
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Barkey, M. E., D. F. Socie, and K. J. Hsia. "A Yield Surface Approach to the Estimation of Notch Strains for Proportional and Nonproportional Cyclic Loading." Journal of Engineering Materials and Technology 116, no. 2 (April 1, 1994): 173–80. http://dx.doi.org/10.1115/1.2904269.
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An analytical method is developed to estimate notch root strains in a notched bar of elastic-plastic, isotropic material subjected to proportional and nonproportional multiaxial nominal loading. The method uses anisotropic plasticity theory to define a structural yield surface in nominal stress space that incorporates both the isotropic material properties and the anisotropic geometry factors of the notch. Notch root plastic strain increments and anisotropic work-hardening effects are then related to this yield surface using standard methods of plasticity. Comparisons of the proposed method with previously published strain estimates using the finite element method for a notched shaft under proportional nominal bending and torsion, and with strain gage measurements of a circumferentially notched solid steel shaft subjected to a series of box-shaped nonproportional loading paths in tension-torsion nominal stress space are presented. The strain calculations agree well both qualitatively and quantitatively using an appropriate nominal load-notch plastic strain relationship, and are suitable for strain-life fatigue calculations.
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Thomas, Peter R., Ángela Carmen Blázquez Calzada, and Kevin Gilmour. "Modeling of macro fiber composite actuated laminate plates and aerofoils." Journal of Intelligent Material Systems and Structures 31, no. 4 (December 16, 2019): 525–49. http://dx.doi.org/10.1177/1045389x19888728.
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This article investigates the modeling of macro fiber composite-actuated laminate plates with distributed actuator patches. The investigation details an analytical and finite element modeling, with experimental validation of the bending strain and deflection of an epoxy E-glass fiber composite laminate. An analytical approach is also developed to estimate the plate deflection from the experimental strain measurements. The analytical method uses direct integration of single dimensional plate bending moments obtained by strain-induced shear moments from the macro fiber composite actuators. Finite element analysis software was used with the composite laminate modeled in ANSYS ACP. The results from both analytical and numerical models show good agreement with the experimental results, with strain values agreeing within 20 ppm and the maximum difference in deflection not exceeding 0.1 mm between models. Finally, an application of the analytical model for developing morphing aerofoil designs is demonstrated.
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Meya, Rickmer, Carl Kusche, Christian Löbbe, Talal Al-Samman, Sandra Korte-Kerzel, and A. Tekkaya. "Global and High-Resolution Damage Quantification in Dual-Phase Steel Bending Samples with Varying Stress States." Metals 9, no. 3 (March 12, 2019): 319. http://dx.doi.org/10.3390/met9030319.
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In a variety of modern, multi-phase steels, damage evolves during plastic deformation in the form of the nucleation, growth and coalescence of voids in the microstructure. These microscopic sites play a vital role in the evolution of the materials’ mechanical properties, and therefore the later performance of bent products, even without having yet led to macroscopic cracking. However, the characterization and quantification of these diminutive sites is complex and time-consuming, especially when areas large enough to be statistically relevant for a complete bent product are considered. Here, we propose two possible solutions to this problem: an advanced, SEM-based method for high-resolution, large-area imaging, and an integral approach for calculating the overall void volume fraction by means of density measurement. These are applied for two bending processes, conventional air bending and radial stress superposed bending (RSS bending), to investigate and compare the strain- and stress-state dependent void evolution. RSS bending reduces the stress triaxiality during forming, which is found to diminish the overall formation of damage sites and their growth by the complimentary characterization approaches of high-resolution SEM and global density measurements.
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Ren, Jianying, Bing Zhang, Xinqun Zhu, and Shaohua Li. "Damaged cable identification in cable-stayed bridge from bridge deck strain measurements using support vector machine." Advances in Structural Engineering 25, no. 4 (January 10, 2022): 754–71. http://dx.doi.org/10.1177/13694332211049996.
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A new two-step approach is developed for damaged cable identification in a cable-stayed bridge from deck bending strain responses using Support Vector Machine. A Damaged Cable Identification Machine (DCIM) based on support vector classification is constructed to determine the damaged cable and a Damage Severity Identification Machine (DSIM) based on support vector regression is built to estimate the damage severity. A field cable-stayed bridge with a long-term monitoring system is used to verify the proposed method. The three-dimensional Finite Element Model (FEM) of the cable-stayed bridge is established using ANSYS, and the model is validated using the field testing results, such as the mode shape, natural frequencies and its bending strain responses of the bridge under a moving vehicle. Then the validated FEM is used to simulate the bending strain responses of the longitude deck near the cable anchors when the vehicle is passing over the bridge. Different damage scenarios are simulated for each cable with various severities. Based on damage indexes vector, the training datasets and testing datasets are acquired, including single damaged cable scenarios and double damaged cable scenarios. Eventually, DCIM is trained using Support Vector Classification Machine and DSIM is trained using Support Vector Regression Machine. The testing datasets are input in DCIM and DSIM to check their accuracy and generalization capability. Different noise levels including 5%, 10%, and 20% are considered to study their anti-noise capability. The results show that DCIM and DSIM both have good generalization capability and anti-noise capability.
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Amin Rashidifar, Mohammad. "Analysis of Elastic Flexural Waves in Non-Uniform Beams Based on Measurement of Strains and Accelerations." Asian Journal of Electrical Sciences 5, no. 1 (May 5, 2016): 13–25. http://dx.doi.org/10.51983/ajes-2016.5.1.1969.
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Elastic flexural waves in an unloaded and unsupported segment of a non-uniform beam were considered. A method based on Timoshenko’s model was established for evaluation of shear force, transverse velocity, bending moment and angular velocity at an arbitrary section from four independent measurements of such quantities at one to four sections. From the evaluated quantities, shear stress, power transmission, etc. can be obtained. Experimental tests were carried out with an aluminium beam which had an abrupt change in height from 15 to 20 mm and was equipped with strain gauges and accelerometers at four uniformly distributed measurement sections and at three evaluation sections. The distance between the two outermost measurement sections was 600 mm, corresponding to 1.12 wave lengths at the upper end of the frequency interval 2500 Hz considered. Bending moments and transverse velocities evaluated from four measurements of any one of these quantities agreed well with those measured at evaluation sections located (i) centrally among the measurement sections and (ii) at a distance of 100 mm, or 0.17 wave lengths, outside. When it was located (iii) at a distance of 500 mm, or 0.83 wave lengths, outside, there was relatively large disagreement as expected from error analysis.
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Nikanorov, S. P., B. K. Kardashev, B. N. Korchunov, and V. N. Osipov. "Elasticity, Anelasticity and Yield Strength of Al-Si Alloys Obtained by Directional Crystallization." Solid State Phenomena 184 (January 2012): 161–66. http://dx.doi.org/10.4028/www.scientific.net/ssp.184.161.
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Acoustic measurements of Young’s modulus and internal friction at frequencies of longitudinal vibrations of about 100 kHz were made in the (5×10-7 to 2×10-4) vibration strain amplitude range for Al-Si alloys. Quasi-static bending stress-strain diagrams were studied as well. The samples of the alloy were prepared using a directional crystallization by Stepanov’s method. The compositions varied from 8 to 25 wt.%Si. The micro-plastic deformation of the materials (acoustic experiments) is explained by dislocation motion in grains of α solid solution. The micro-plastic yield stress has a minimum near the eutectic composition; the flow stress of plastic bending increases smoothly when the Si content increases.
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Iyama, J., O. Chih-Chun, and K. Araki. "Bending moment distribution estimation of an actual steel building structure by microstrain measurement under small earthquakes." Journal of Civil Structural Health Monitoring 11, no. 3 (April 16, 2021): 791–807. http://dx.doi.org/10.1007/s13349-021-00482-z.
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AbstractMost structural health monitoring systems estimate the overall behavior by measuring the acceleration response, which cannot directly measure the stress or damage state of individual structural members. An alternative approach is to use strain measurements; however, methods for analyzing and utilizing strain data for actual steel buildings have not been established. In this study, highly precise semiconductor strain gauges were applied to an actual building. The accelerations and strains measured during earthquake loading were used to calculate the ratio of the bending moment at the beam or column sections to the displacement at the top of the building, which was defined as the “local stiffness.” This physical index represents the stiffness of structural elements near the measurement location and can be easily predicted through simple static frame analysis. The measured local stiffness was comparable to the analytical local stiffness values for the beams but was larger than that for the columns. This indicates that nonstructural members may exhibit a certain degree of restoring force and that the measured local stiffness may be strongly affected by nonstructural elements that are not considered during the structural design stage. Conversely, the measured local stiffness can be used to estimate the behavior of nonstructural components. The measured dominant frequency and local stiffness of the beams and columns showed a dependency on amplitude, but opposite trends were observed for the beams and columns. This indicates that the amplitude dependency of the dominant frequency is not due to the behavior of the beams and columns but to other reasons such as nonstructural components or changes in mass.
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Antoš, Jakub, Václav Nežerka, and Pavel Tesárek. "Use of Digital Image Correlation to Track Strain Evolution in Compressed Masonry Piers." Applied Mechanics and Materials 732 (February 2015): 337–40. http://dx.doi.org/10.4028/www.scientific.net/amm.732.337.
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In order to develop a constitutive material model and to verify its consistency when implemented in a computational code, it is necessary to understand the material and to carry out a comprehensive experimental analysis. This can be a challenging task in the case of composite materials and structures, such as masonry, when using conventional measurements. Strain gauges and allow recording strains at a limited number of discrete points and do not provide sufficient amount of data, thus increasing the cost of the analysis. From that reason a full-field non-contact measurements, such as Digital Image Correlation (DIC), became very popular and valuable for analysis of structures subjected to mechanical loading and precise detection of the onset of strain localization. The presented study deals with tracking the strain localization using DIC in the case of masonry piers loaded by the combination of bending and compression. In such case the strain localizes into more compliant mortar joints while the complete collapse occurs when the masonry blocks fail to transfer tensile stress due to transversal expansion. The obtained data will be used for the validation of a finite element model to predict the behavior of masonry structures.
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Chiarelli, Mario. "Local Strain Distribution Produced by Warping: The Case of a Tail Rotor Blade of a Helicopter." Applied Mechanics and Materials 1-2 (September 2004): 261–0. http://dx.doi.org/10.4028/www.scientific.net/amm.1-2.261.
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Aircraft engineers in the design phase often use practical solutions and results of the elementary theory of structures under the classical hypotheses assumed for shear, torsion and bending behaviour of structural elements that can be studied as "beams". This assumption, very powerful in general, under particular situations (for example: the modification of loading conditions in the development of new aircraft versions) can be inadequate to represent real distributions of stress and strain. This is particularly true when local behaviour of structures depends on secondary phenomena such as warping produced by non-uniform bending and torsion acting on structural elements with variable stiffness along their flexural axis. In this paper the results of analytical and experimental studies carried out for a metallic tail rotor blade of a helicopter are summarised; this research activity was born during a collaboration between the Department of Aerospace Engineering of Pisa and an aeronautical industry. Local strain distributions under real loading conditions have been obtained by means of finite element analyses and by means of strain gauge measurements. To describe warping mechanisms accurately, also caused by the presence of a reinforcing plate of the blade structure, sub-modelling technique has been used and during a fatigue test, the blade was instrumented with an appropriate number of rosettes. Numerical and experimental results show, with a good agreement, that local geometry of the blade and the severe loading condition produce a considerable increase of strains that elementary theory can not predict; moreover, numerical results and above all strain measurements have proved that local yielding of the material can occur during the service life with detrimental effects on the fatigue endurance of the tail rotor blade.