Bending Strain Research Articles

Comparison of Flexoelectric and Piezoelectric Distributed Sensing Signal of Toroidal Shell

In this study, the flexoelectric and piezoelectric distributed sensing signal of the toroidal shell is discussed. By considering the curvature radii and Lamé parameters of the toroidal shell, dynamic strains are derived based on the double-curvature shell. Flexoelectric and piezoelectric distributed sensing models of the toroidal shell are established. Based on the direct flexoelectric effect and direct piezoelectric effect, the flexoelectric/piezoelectric distributed sensing signal is evaluated respectively. The local neural sensing signal is discussed while the flexoelectric and piezoelectric sensor patches approach to infinitesimal. The neural sensing signal is made of different signal components, and the components effects are discussed to elaborate the difference between the flexoelectric and piezoelectric sensing signal. The results indicate that the membrane-induced signal components and bending-induced signal components both affect the piezoelectric sensing signal, while only the bending-induced signal components affect the flexoelectric sensing signal. To elaborate the significance of the components in different directions, signal induced by different strains in different directions are discussed. The signal induced by the meridional bending strain dominates for the flexoelectric sensing while signal induced by the meridional membrane strain is dominant for piezoelectric sensing.

쌍안경식 로드셀의 실험적 방법과 수치적 방법을 통한 변형 비교

In this paper, the structure and merits of the binocular type load cell are mentioned, and the principle of deformation of the load cell is assumed to be the deformation behavior of Statically indeterminate, and then theoretically analyzed. In addition, finite element analysis was conducted to determine the suitability of the principle and bending strain was measured. In order to compare this theory through actual experiments, an experimental method of measuring strain by attaching a strain gauge was conducted, and an additional optical analysis was performed. Through the shadow moire experiment, which is a technique, it was possible to draw conclusions by conducting comparisons with numerical methods. As a result of this analysis, the theory and finite element analysis showed an error of about 6.75%, and the basis for assuming negative information was given. have derived However, the shadow moire method showed a difference when compared to the numerical method, and these causes were analyzed and concluded.

Aerodynamic Aspect of the Problem Relating to the Reduction of the Vibration Strain in the Axial Compressor Blades of the Gas Turbine Engine

Consideration was given to the design methods available in practice for an increase in the vibration reliability of the blades of axial compressor. The problem was formulated to show the possibility of the reduction of the strain in the blade nib by the control of the exciting aerodynamic forces. When it is impossible to eliminate the resonance completely and the measures taken to increase structural damping fail to give positive effect it is reasonable to make use of the possibility of the strain reduction by the control of the excitation source. Consideration was given to the aerodynamic aspect of the problem relating to an increase of the vibration reliability of the blades of axial compressor. The aerodynamic loads affecting the axial compressor blades ranging from the trace to potential effects of adjacent shrouds were determined numerically. The program package SUnFlow with the realized in it numerical integration of the Reynolds-averaged Naiver-Stocks equations was used as an investigation tool. The high-pressure compressor stage containing 120 blades of the input guide unit, 83 operating blades and 104 blades of the guide system was used as a test object. The computations were done for the initial structure of the compressor stage and for the stage structure with embedded measures in the form of the variable- pitch input guide unit. Nonstationary computations of the options were done by including the three stage rings into the computation domain of total circumferences. Based on the obtained computation data, the integral and distributed loads onto operating blade were analyzed for comparable stage options. For the obtained distributed loads, the bend strains were calculated using the rod theory. Based on the obtained experimental data, the conclusion was made that the strains can be reduced in the blade nib by the control of the exciting aerodynamic forces.

Numerical Investigation and Prediction of Side-By-Side Tunneling Effects on Buried Pipelines

With the fast development of underground space engineering, it is inevitable for buried pipelines to be crossed by twin tunnels. Previous studies mainly focused on the single-tunneling effects on pipelines. To emphasize the twin-tunneling effects on buried pipelines, we first examined the effectiveness of the ground settlement prediction method under twin-tunneling conditions. Then, the estimated ground settlement boundary condition was applied to the beam-on-spring finite element model. The numerical results show that with the decrease in tunnel depth and twin tunnel space, the values and positions of the maximum ground settlement and longitudinal pipe bending behavior both changed significantly. The biased distance of the maximum settlement position and the distance to the inflection point of the final ground settlement curve can be obtained by curve fitting. Based on that, a semi-empirical prediction method for the longitudinal pipe bending strain was proposed. The predicted values matched quite well with the numerical results, which can thus provide a quick and effective structural safety and integrity assessment approach for buried pipelines subjected to twin-tunneling conditions.

Modulating saturation magnetization and topological Hall resistivity of flexible ferrimagnetic Mn4N films by bending strains

The ferrimagnetic rare-earth-free Mn4N films are considered as a good candidate in spintronics due to its low saturation magnetization (MS) and high Néel temperature. Here, Mn4N films are directly deposited on flexible mica to investigate strain-related magnetic and electronic transport properties. The MS variation of 11.0 nm Mn4N film reaches 453% at tensile strain of radius of curvature (ROC) = 2 mm. Bending strains cannot affect anomalous Hall resistivity and magnetoresistance. However, the topological Hall resistivity of 147.0 nm Mn4N film increases by 58% at tensile strain of ROC = 5 mm due to frustrated exchange interactions. The flexible Mn4N films have great potential applications in flexible magnetic sensor and strain gauge due to strain modulated MS, resistance, and stable magnetoresistance.

Development of Basalt Fiber Reinforced Fine-Grained Cementitious Composites for Textile Reinforcements

Cementitious composites have been the prevalent field of research in recent eras due to their excellent bending and high strains. However, textile reinforcement requires materials with fine grain size to make proper binding between the yarns in the textile reinforcement and improve the strength characteristics. This concern has led to the development of fine-grained cementitious composites by dispersing chopped basalt fiber to improve strain-hardening capabilities with reduced voids. The basalt fiber content is varied by 0, 0.2, 0.4, 0.5 and 1% to the volume of the cementitious matrix. Various testing methods have evaluated the mechanical and microstructural properties of fine-grained cementitious composites with basalt fiber. Adding basalt fiber up to 0.4% to the volume of the matrix improves the compressive, split tensile, flexural strength and dynamic modulus of elasticity compared to the controlled cementitious matrix. Also, higher fiber content escalated the impact resistance and degree of carbonation. From the results, obtained basalt fiber reinforced fine-grained cementitious composites have higher mechanical characteristics, and the particles are densely packed compared to cementitious composites. Thus it provides good bonding between the textile reinforcement and helps to construct thin structural elements.

Rebound control in multipass roll forming of cap-shaped parts based on segmental boundary optimization function

Bending angle is an important parameter in multi-pass roll forming. However, in actual manufacturing, there is still a lack of theoretical guidance; hence, rebound defects are commonly observed. In this paper, a bending angle distribution function with an optimized segmented boundary combination is proposed to improve the forming quality and reduce the rebound defects in multi-pass roll forming. For cap-shaped sheets, COPRA, a roll-bending simulation software, is used to investigate the bending angle distribution to optimize the process of cap-shaped roll-bending. Furthermore, the stress and strain distributions in the sheets after each forming pass is analyzed using finite element simulation. The influence law of different bending angle parameters on the quality of sheets is obtained. The finite element simulation is verified by comparing the experimental results of the change law of rebound defects of cap-shaped parts under different bending angle distribution conditions. Based on the segmented boundary combination of bending angle optimization functions, the stress and strain distributions in the sheets during roll-bending forming of the cap-shaped parts are improved, the rebound defects in the bending area are smaller, and the forming quality is better than the other bending angle distribution methods.

Study on the Low Temperature Cracking Mechanism of Steel Slag Asphalt Mixture by Macroscale and Microscale Tests

Steel slag’s physical and mechanical properties are close to natural gravel, which can replace natural aggregate with paving asphalt mixture pavement. Based on macro- and microscales, it is necessary to study the low-temperature cracking characteristics of steel slag asphalt mixture (SAM). This paper aims to study the low-temperature cracking characteristics and influence mechanism of steel slag asphalt mixture by macro- and microscale tests. This article analyzes the strain field distribution and cracks propagation law of SAM at low temperatures by the three-point bending test combined with digital image correlation (DIC). The microscopic pore characteristics of SAM were studied by nuclear magnetic resonance (NMR). Based on fracture mechanics and weight function theory, the variation law of the stress intensity factor at the crack tip of the asphalt mixture with crack propagation is derived. The correlation between microscopic pores and low-temperature cracking characteristics of asphalt mixture was analyzed based on the grey correlation theory. The results show that SAM has more small and less large pores, and its total porosity is lesser than that of the basalt asphalt mixture (BAM). The initial elastic stage of SAM resisting bending deformation is longer than that of BAM, the bending strain energy density (dW/dV) is larger, and the crack penetration is slower. The horizontal strain energy density (DE) of SAM is greater than BAM, and the crack tip stress is greater. The porosity correlates well with the low-temperature crack resistance of the asphalt mixture.

Influence of Heat Treatments on the Microstructure and Mechanical Properties of Two Fine Mg–Li–Y Alloy Wires for Bioresorbable Applications

Two Mg–4Li–xY (x = 0.5 and 2.0 wt%) alloy wires are investigated for application in bioresorbable medical devices that experience high levels of plastic deformation. The two wires are supplied cold drawn to a diameter of 125 μm, and a series of thermal treatments are applied to maximize ductility. The ductility of the alloys is maximized soon after complete recrystallization. Prolonged annealing causes grain coarsening in the Mg–4Li–0.5Y alloy and precipitation of a Mg24Y5 phase in both alloys. Both wires are shown to achieve ≈20% elongation to failure in tension and survive high idealized bending strains (>40%). When heat treated for optimum mechanical properties for the intended application, the Mg–4Li–0.5Y alloy develops an intense transverse basal texture; however, this is shown to weaken with increased Y content in the Mg–4Li–2Y alloy wire. The increased Y content also prevents grain coarsening, indicating that the increased Y content restricts grain boundary mobility during annealing. Both alloys have relatively high ductility, meaning both are identified as promising new materials for application in bioresorbable medical devices that require to achieve and support high levels of plastic deformation during their life cycle.

Wearable potentiometric biosensor for analysis of urea in sweat

Herein, we introduce wearable potentiometric biosensors on screen-printed carbon electrodes (SPCEs) for on-body and on-site monitoring of urea in sweat. The biosensor architecture was judiciously designed to detect urea at different pHs and incorporate a pH sensor, thus containing polyaniline ink, urease bioink and a polyvinylchloride membrane. Urea detection could be performed in the wide range from 5 to 200 mM at pH 7.0, encompassing urea levels in human sweat. The biosensor response was fast (incubation time 5 min), with no interference from other substances in sweat. Reliable urea detection could be done in undiluted human sweat with a skin-worn flexible device using the pH correction strategy afforded by the pH sensor. The performance of the epidermal biosensor was not affected by severe bending strains. The feasibility of mass production was demonstrated by fabricating epidermal flexible biosensors using slot-die coating with a roll-to-roll technique.

Preparation of Conductive Screen-Printing Ink for High-Performance Bendable and Wearable ECG Electrodes on Fabric Substrates

Monitoring of vital signs is a necessary tool to diagnose the symptoms of illness. This work developed screen-printing inks for conductive nanomaterials to fabricate electrocardiogram (ECG)-compatible fabric electrodes. The contents of the polymer matrix, calcium carbonate additive filler, and conductive nanomaterials (silver nanoparticles and copper nanowires) on the resistivity of the composite inks were optimized. A facile process of screen printing was applied to fabricate the electrodes on fabric to create an efficient conductor with high stability in conduction. The fabricated electrodes exhibited flexible and bendable behavior over 0.7% bending strain for wearable components. The results showed that the fabricated electrode based on copper nanowires resistivity was 40.01 ± 1.94 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{k}\Omega $ </tex-math></inline-formula> /cm, and the proposed signal-to-noise ratio (SNR) was approximately 27.16 ± 9.37 dB. Therefore, these fabricated electrodes can be applied in wearable vital biosignal detection devices that perform with high sensitivity during movement, thereby providing health monitoring opportunities. Moreover, the fabricated electrodes can be used without excessive pressure or an electrolyte gel layer, thus overcoming the challenges of developing a portable device.

Reflective crack initiation of asphalt overlays on jointed concrete pavement using finite element model

ABSTRACT In this study, a three-dimensional (3D) finite element model (FEM) consisting of an asphalt concrete (AC) overlay on top of jointed plain Portland cement concrete (PCC) slabs was developed to investigate the mechanism of the crack initiation of traffic-induced reflective cracking. Strain values at the bottom of AC overlay were the primary response obtained from the simulation results to represent the damage induced in the AC layer. Different bonding situations between the two layers, traffic load locations, material properties and thicknesses of the AC layer were taken into consideration. The analysis results show that the dominating strain for damage is dependent on the bonding condition between the AC and PCC layers. When the AC layer is completely bonded with the PCC layer, the damage will initiate firstly at the top of the joint corner between the PCC slabs to deteriorate the bonding, then the AC bottom will be susceptible to bending strain. It was observed that the most critical load location for modeling the case of fully bonded overlays is related to the AC thickness while in the case of partially bonded overlays, the most critical load location is always located on the top of one side of the PCC joint.

A Study on Stress Measurement of Weld Part using Double Exposure Mehtod

This paper describes a stress measurement from a welded part of an austenitic stainless steel using synchrotron X-rays. Observing the diffractions from a single crystal, coarse grained material and the welded part, the diffraction pattern of the welded part shows the feature of textured materials with large grains. Difficulty measuring the X-ray stress of the welded part is caused by the broadening of the diffraction spot in the radial and circumferential directions. The bending strains of the rectangular bar made of the welded part were measured using synchrotron white X-rays and the double exposure method. However, the results were not enough accuracy to obtain the strains. To improve the energy resolution, monochromatic synchrotron X-ray of 70 keV was used. The diffraction pattern showed the sharp arc like a pattern from texture material. The diffraction profile was obtained from the integral of the diffraction intensity in the direction of the circumference. The diffraction angle was determined using the double exposure method. As a result, the distribution of the residual stresses of the welded part could be measured.

Printable Graphene-Sustainable Elastomer-Based Cross Talk Free Sensor for Point of Care Diagnostics

Developing sensors for monitoring physiological parameters such as temperature and strain for point of care (POC) diagnostics is critical for better care of the patients. Various commercial sensors are available to get the job done; however, challenges like the structural rigidity of such sensors confine their usage. As an alternative, flexible sensors have been looked upon recently. In most cases, flexible sensors cannot discriminate the signals from different stimuli. While there have been reports on the printable sensors providing cross-talk-free solutions, research related to developing sensors from a sustainable source providing discriminability between signals is not well-explored. Herein, we report the development of a stencil printable composition made of graphene and epoxidized natural rubber. The stencil printability index was vetted using rheological studies. Post usage, the developed sensor was dissolved in an organic solvent at room temperature. This, along with the choice of a sustainable elastomer, warrants the minimization of electronic waste and carbon footprint. The developed material demonstrated good conformability with the skin and could perceive and decouple the signals from temperature and strain without inducing any crosstalks. Using a representative volume element model, a comparison between experimental findings and computation studies was made. The developed sensors demonstrated gauge factors of -506 and 407 in the bending strain regimes of 0-0.04% and 0.04%-0.09%, respectively, while the temperature sensitivity was noted to be -0.96%/°C. The printed sensors demonstrated a multifunctional sensing behavior for monitoring various active physiological parameters ranging from temperature, strain, pulse, and breathing to auditory responses. Using a Bluetooth module, various parameters like temperature and strain could be monitored seamlessly in a smart-phone. The current development would be crucial to open new avenues to fabricate crosstalk-free sensors from sustainable sources for POC diagnostics.

Fatigue Life Calculation of Tubing for In Situ Drilling Rig

The severe bending strain that the tubing of the in-situ drilling rig is subjected to during the operation under pressure, which exceeds the elastic limit, will cause periodic plastic deformation of the tubing of the in-situ drilling rig, so that fatigue cracks will occur on the internal and external surfaces of the tubing of the in-situ drilling rig and expand rapidly, leading to the greatly shortened service life of the tubing of the in-situ drilling rig. Based on the stress analysis of the dangerous points of the tubing of the in-situ drilling rig, the relationship between the predicted and the standard measured tubing life of the in-situ drilling rig is obtained in this paper. The number of tubing cycles of in-situ drilling rig decreases sharply with the increase of internal pressure. The greater the internal pressure is, the greater the circumferential stress and uniaxial alternating stress are, which causes the number of tubing cycles of in-situ drilling rig to decrease when tubing fails. It shows that the fatigue life of tubing of in-situ drilling rig is significantly affected by internal pressure.

Axisymmetric buckling analysis of submerged hemi-elliptic toroidal shells

Toroidal shells have been widely used in various industrial applications for over a decade. Most studies on buckling behavior have focused on circular toroidal shells with uniform loads. In contrast, the existing literature on the shell buckling of a toroid with elliptical cross-sections has received limited attention. This study aims to present numerical solutions for axisymmetric buckling of hemi-elliptic toroidal shells under linearly hydrostatic pressure to append available data and results in this field. The thickness of the hemi-elliptic toroidal shells is assumed to be constant before and after the buckling state. Solution procedures for solving critical buckling loads dealt with eigenvalue problems and were formulated by an energy approach. All relevant parameters such as membrane and bending strain components and in-plane stress resultants were derived based on differential geometry. An in-house FEM program solved the weak formulation derived from a variational method. The buckling results for elliptic toroidal shells with various b/a ratios were established as the critical seawater depth and compared to the previously published results. Additionally, parametric studies on the effect of the variable b/a ratios and the major radius R of elliptic toroidal shells on the axisymmetric buckling loads and mode shapes were examined thoroughly and addressed in more detail herein.

Evaluating Strain Limits of Embedded FBG Sensors in Pultruded Hybrid Composite Rods

This paper demonstrates that relatively inexpensive acrylate coated FBGs can survive short exposure times to high temperatures in a pultrusion process and monitor relatively low magnitude bending and axial tension strains in a composite material. However, under higher sustained axial loads, the observed interfacial failure of the optical fiber and the host material resulted in a significant reduction of the indicated strains during constant elongation. These findings are analyzed by experimental measurements supported by finite element simulations. The optimal placement of embedded optical fibers in the rods is discussed based on the limitations of the rods and the mechanical strength of the commercially available optical fibers.

BENDING FATIGUE BEHAVIOR OF AG NANOWIRE/CU THIN-FILM HYBRID INTERCONNECTS FOR WEARABLE ELECTRONICS

Enhancing the mechanical reliability of metal interconnects is important for achieving highly reliable flexible/wearable electronic devices. In this study, Ag nanowire and Cu thin-film hybrid interconnects were explored as a novel concept to enhance mechanical reliability under bending fatigue. Bending fatigue tests were conducted on the Cu thin films and Cu/Ag nanowire/polyimide (CAP) interconnects. The increase in resistance was larger for the Cu thin films than for the CAP. The single-component Cu electrodes showed multiple crack initiation and propagation due to bending strain, which degraded the electrical conductivity. In CAP, however, no long-range cracks were observed, even after 300,000 cycles of bending, although a wavy structure was observed, probably due to the delamination of the Ag nanowires under repeated bending. Our study confirms that flexible Ag nanowire and metal thin-film hybrids can enhance the mechanical reliability of metal thin-film interconnects under bending fatigue.

Nanoscale Electric Field Probing in a Single Nanowire with Raman Spectroscopy and Elastic Strain.

In this work we investigate the Raman response of extremely strained gallium phosphide nanowires. We analyze new strain-induced spectral phenomena such as 2-fold and 3-fold phonon peak splitting which arise due to nontrivial internal electric field distribution coupled with inhomogeneous strain. We show that high bending strain acts as a probe allowing us to define the electric field distribution with deep subwavelength resolution using the corresponding changes of the Raman spectra. We investigate the nature of the localization with respect to nanowire diameter, excitation spot position, and light polarization, supporting the experiment with 3D numerical modeling. Based on our findings we propose a research tool allowing to precisely localize the electric field in a certain subwavelength region of the nanophotonic resonator.

STATIC BENDING ANALYSIS OF NANOPLATES ON DISCONTINUOUS ELASTIC FOUNDATION WITH FLEXOELECTRIC EFFECT

In this study, rectangular plates subjected to static loads and supported on a discontinuous two-parameter elastic foundation are analyzed. The formulae for the computations are developed from improved shear deformation theory, where the displacement w is divided into bending and shear strain components. The results obtained from this article and other publications are evaluated to prove the accuracy of the proposed theory and the calculation program. Then, a parameter study is carried out to capture the effect of some material and geometrical parameters on the static response of structures. Especially the influence of the flexoelectric effect and discontinuous foundation is investigated. As two elastic foundation parameters and flexoelectric coefficient are increased, the non-dimensional maximum deflection of the plate decreases, indicating that these factors improve the plate's stiffness.