Bending Strain Research Articles

Microstructure and mechanical property of Y2O3-based ODS-Cu alloy fabricated by MA-HIP with novel elemental addition process

The oxide dispersion strengthened (ODS)-Cu alloys produced by the combined process of mechanical alloying and hot isothermal pressing (MA-HIP) process have high strength properties, although they have low ductility. In this study, the MA-HIP process was modified based on the yttrium addition and oxygen addition methods to improve the ductility by controlling the microstructure of the ODS-Cu alloys. Namely, we replaced pure Y and Cu2O powders with a Cu-Y intermetallic compound and pre-heated Cu powders as the starting materials. The final product showed considerable microstructural differences: on the macro-scale, the frequency of interconnection of large/small Cu grain colonies, which was a main factor in brittle fracture, was reduced; while on the nanoscale, yttrium remained as yttria (Y2O3) particles within the large size Cu grains. These multiscale microstructural changes resulted in the improved mechanical property: the newly-developed ODS-Cu bulk did not fracture at bending strains of 18% or greater, which can be compared with the previous value of 5% or less in a three-point bending test. Furthermore, the conductivities of our ODS-Cu alloys are 94–96% of pure Cu. This improvement in properties, therefore sheds light to the future application of the ODS-Cu alloys in high-temperature environments.

Wearable Strain Sensor With a Graphene Localized Warping Structure for Ultra-Wide Range Strain Detection and Bending Direction Recognition

The practical need for the accurate detection of human activities requires wearable flexible strain sensors that can detect subtle and large strains and recognize the bending direction of joints. However, it remains challenging to integrate these detection capabilities into a single strain sensor. Herein, we prepared flexible strain sensors with firmly attached locally warped graphene on the surface of anhydride-grafted styrene-butadiene-styrene triblock copolymer films using a swelling-self-assembly method. The unique localized warpage structure of graphene sheets gives the sensor excellent strain response performance and the ability to recognize the bending direction. The detection limit of the sensor to strain is independent of the sensitivity to strain, which allows it to detect ultralow (0.01%) and large strains (500%). Moreover, the sensor has a large linear response range (0~94%) and good test stability (3000 cycles of strain). The sensor can be used to recognize the bending direction by generating opposite response signals to different bending directions. The excellent response behavior allows the sensor to accurately monitor the joint bending angle, direction of the human body, and subtle tremors of the human skin, which makes it a potential application for wearable devices and smart prosthetics.

Flexible and sustainable printed sensor strips for on-site, fast decentralized self-testing of urinary biomarkers integrated with a portable wireless analyzer

Flexible and sustainable electronic devices may fulfill the requirements of Sustainable Development Goals (SDGs) contained in Agenda 2030 from United Nations, however, the use of degradable and eco-friendly devices for rapid, selective and on-site decentralized monitoring of patient health status with portable systems toward diagnosis, fast decision and medical interventions is relatively new. Herein, we introduce flexible and sustainable substrates/support of degradable bio-based PLA films from renewable resources produced by casting method as a sustainable alternative to conventional petroleum-based plastics toward portable electronic devices and sensing applications. The flexible devices containing full electrochemical sensing system were built with screen-printing process on PLA sustainable substrates for on-site, rapid decentralized monitoring of molecular biomarkers in non-invasive sample. Reliable urinary dopamine and uric acid analysis with limit of detections of 0.138 µM and 0.595 µM could be performed with low-cost sustainable devices (<US$ 0.08 per unit) in undiluted human urine using a flexible sensor strip coupled with a Sensit BT portable analyzer connected via Bluetooth to a smartphone, laptop or tablet. The flexible eco-friendly sensor was highly robust against severe bending strains, reproducible and selective without interference from other compounds in human urine. The sustainable sensor response was fast within 3 min with an analytical performance comparable to the gold standard method.

Mechanical damage characteristics of CR/PPA composite modified asphalt pavement under multi-factor coupling effect in the seasonally frozen region

Asphalt pavements are inevitably affected by coupled effects of dry-wet/freeze-thaw cycles, UV radiation, temperature, and loading during service, resulting in degradation of their road performance and reduced service life. Therefore, this study used crumb rubber (CR) and polyphosphoric acid (PPA) as modifiers to prepare CR/PPA composite modified asphalt mixtures for testing. To investigate the mechanical properties of the composite modified asphalt mixtures under the action of multi-factor coupling. Meanwhile, the performance analysis of matrix asphalt and SBS modified asphalt mixtures were carried out as a comparison. Density and water penetration tests, splitting tests, beam bending tests, and four-point bending fatigue tests reveal the evolution of asphalt mixture road performance. Finally, regression fitting was performed on the test data to establish the mechanical damage model of each type of asphalt mixture. The results show that with the increase of wet-dry/freeze-thaw cycles and the increase of UV radiation time, the void ratio and water permeability coefficient increase and the splitting strength, bending and tensile strain, and fatigue life decrease for all types of asphalt mixtures. When the number of wet-dry/freeze-thaw cycles reached 8, the mechanical properties of the asphalt mixture decreased significantly, while the changes leveled off after the number of cycles reached 15. When the UV radiation time is less than 4 months, the mechanical properties of the asphalt mixture decay more slowly. However, with a further increase in radiation time, the mechanical properties decay rapidly. The water-saturated specimens have a more significant effect on the mechanical damage of each type of asphalt mixture. Compared with the other two mixtures, the composite modified asphalt mixtures have superior mechanical properties and fatigue life. The mixture performance damage model based on the least squares Levenberg-Marquardt method (L-M method) was able to simulate the experimental data well, with a minimum correlation coefficient R2 of 0.9285. In summary, the road performance of all types of asphalt mixtures under the coupling of multiple factors has deteriorated, while the composite modified asphalt mixtures have better anti-damage characteristics, with good prospects for promotion.

A non-local approach for Reissner–Mindlin shell elements in dynamic simulations: Application with a Gurson model

Numerical prediction of ductile tearing during a car crash is necessary to ensure the structural integrity of the vehicle. Recently, encouraging results were obtained by Davaze et al., (2021) with a non-local damage approach, compatible with dynamic explicit simulations and preserving parallel computation: an implicit gradient model enabled to reproduce experimental results with DP450 steel sheets with 3D solid elements. However, in the automotive industry, thin sheets of metals are mostly modeled with shell elements for computation time efficiency. Shell elements have a more complex formulation: their kinematic description is enriched accounting for displacements but also rotations, leading to two different strain contributions: membrane strain and bending strain. The transverse strain is computed independently in a post-processing step from local internal variables with a zero normal stress assumption. This formulation is known to lead to strain localization after the onset of necking, while this is not the case with 3D solid elements. The problem is even more challenging when considering shells in association with a softening material accounting for damage as this also leads to strong mesh dependency, as with 3D solid elements. This complex problem is solved using non-local formulations for the material behavior. The proposed solution accounts for both in-plane and in-thickness damage gradients. It consists of a two-step regularization procedure introducing nested wire elements in the shell thickness. Using non-local variables to evaluate the transverse strain enables to obtain a continuous spatial distribution for strains, in agreement with the 3D solid case. An updated Lagrangian formulation is used to account for large strains. The performance of the strategy is demonstrated in three test cases, with a comparison with an experimental result for one of them. The results obtained following the proposed strategy lead are equivalent to the ones obtained with the non-local method proposed by Davaze et al., (2021) and are thus consistent with the experimental data.

Corrections to the Theory of Elastic Bending of Thin Plates for 2D Models in the Reissner Approximation

Elastic bending stresses and strains in the lithosphere are typically calculated based on the Kirchhoff–Love (thin) plate theory. The criterion for its applicability is the smallness of plate thickness to length ratio. In oceanic plates, due to the buoyant force of the mantle, the main deformations are not uniformly distributed along the plate but are concentrated in the vicinity of the subduction zone. Therefore, the effective length of the bending part of the plate is a few fractions of the actual length, and the criterion of a thin plate is partially violated. In this paper, we analyze the possibility of applying thick plate bending equations. The existing variational theories of 3D bending of thick plates are much more complicated than the Kirchhoff–Love theory, as they involve solving three differential equations instead of one, and have limited application due to their complexity. Since geophysical applications frequently use 2D models, in this paper we analyze in detail the potential and accuracy of the thick plate bending theory for 2D models. After the conversion to the 2D plane strain and plane stress approximation, the original 3D Reissner thick plate bending equations are written out in the form similar to the Kirchhoff equations with additive corrections and are supplemented with the explicit formulas for longitudinal displacement. The comparison of the analytical solutions of the 2D Reissner equations with the exact solutions shows that the 2D approximation only provides a correction for the plate bending function. However, this correction refines the Kirchhoff–Love theory by almost an order of magnitude. At the same time, the solution of the equations in this case turns out to be almost as simple as the solution of the thin plate equations.

Piezo-gated flexible transistors: A path to energy-efficient multi-functional piezotronic devices

Developing smart sensors and advanced electronics for the need of the internet of things prevails yet under the constraint of energy efficiency. Therefore, the development of multi-functional devices toward low power is the research spotlight. Due to the low energy consumption, semiconductor-based piezo-gated devices hold great promises. Herein, a flexible multi-dimensional strain sensor by growing two ZnO thin film-based terminals on both sides of a mica substrate is developed. This Multidimensional Piezo-Gated Flexible Transistor (M-PGFT) device successfully detects the positive (upward) bending, negative (downward) bending, and compressive load. Where the gauge factor (GF) of the Top/Bottom terminals under positive and negative bending strains are −3.44/+9.78 and +5.44/−4.03, respectively, and +94.93/+74.70 for compressive load is obtained. Notably, the GF of both ZnO terminals is asymmetric under two bending types of loads, whereas symmetric under compressive load. This unique behavior made this smart multi-dimensional strain sensor to distinguish between different types of strains. Furthermore, the same device can be implemented as a piezo-gated three-valued logic device, demonstrating standard ternary inversion and standard ternary NAND operations. This study presents a unique and simple design to fabricate flexible multi-functional piezo-gated devices for multi-dimensional strain sensing and three-valued logic operation at low power.

Experimental and numerical investigation of ratcheting behavior of SS316L seamless straight pipe under cyclic internal pressure and in-plane cyclic bending

In this paper, the ratcheting behavior of SS316L seamless straight pipes under cyclic internal pressure and in-plane cyclic bending is investigated experimentally and numerically. In order to applying the simultaneous cyclic bending and cyclic internal pressure, a special fixture was designed that can be mounted on the gripers of fatigue machine and so ability to apply cyclic pressure to inside pipe specimen and apply in-plane cyclic bending on pipe specimen simultaneously. According to experimental fatigue data, increasing the cyclic bending load and cyclic pressure, increases the accumulation of ratcheting strain in hoop and axial directions. So axial ratcheting strain creates due to cyclic bending and hoop ratcheting strain creates due to cyclic pressure inside pipe specimen. Finally, the finite element analysis was performed by ABAQUS software base on the nonlinear kinematic/isotropic hardening model and the experimental fatigue data were compared with the numerical results and it was found that the numerical results are in good agreement with experimental data.

Predictions for Bending Strain at the Tower Bottom of Offshore Wind Turbine Based on the LSTM Model

In recent years, the demand and requirement for renewable energy have significantly increased due to concerns regarding energy security and the climate crisis. This has led to a significant focus on wind power generation. As the deployment of wind turbines continues to rise, there is a growing need to assess their lifespan and improve their stability. Access to accurate load data is crucial for enhancing safety and conducting remaining life assessments of wind turbines. However, maintaining and ensuring the reliability of measurement systems for long-term load data accumulation, stability assessments, and residual life evaluations can be challenging. As a result, numerous studies have been conducted on load prediction for wind turbines. However, existing load prediction models based on 10 min statistical data cannot adequately capture the short-term load variations experienced by wind turbines. Therefore, it is essential to develop models capable of predicting load with a high temporal resolution to enhance reliability, especially with the increasing scale and development of floating wind turbines. In this paper, we developed prediction models with a 50 Hz resolution for the bending strain at the tower bottom of offshore wind turbines by combining SCADA data and acceleration data using machine learning techniques and analyzed the results. The load prediction models demonstrated high accuracy, with a mean absolute percentage error below 4%.

In situ observation of the pseudoelasticity of twin boundary

Twin boundary (TB) is a special and fundamental internal interface that plays a key role in altering the mechanical and physical properties of materials. However, the atomistic deformation mechanism of TB remains under debate, of which the most concerned aspect is how TB would affect the mechanical strength and plasticity of a material. Herein, we introduce our new discovery that the pseudoelastic strain of a TB can recover with decomposition and escape of pile-up dislocations, demonstrated by imposing a spontaneous pseudoelastic deformation with recoverable plastic bending strain up to 5.1% on a TB. We found that the steps on the curved TB gradually annihilated during the migration of the TB, which was induced by the slip of decomposition dislocations on the TB. The TB not only provides local strain hardening through interaction with dislocations during the loading stage but also acts as a channel for the fast movement of decomposition dislocations during the recovery stage. Beside, the TB can maintain excellent pseudoelasticity under a multicycle bending test, which may play an important role in improving the fatigue resistance of materials. These findings could open up a new avenue for optimizing the mechanical properties of materials by manipulating their twin boundaries at the nanoscale.

Wearable Piezoelectric Films Based on MWCNT-BaTiO3/PVDF Composites for Energy Harvesting, Sensing, and Localization

Polymer-based lead-free piezoelectric composites provide environmentally friendly and scalable space for energy conversion and structural health monitoring. In this paper, multi-walled carbon nanotubes (MWCNT)-BaTiO3/polyvinylidene fluoride (PVDF) piezoelectric composite films for energy harvesting, sensing, and localization were prepared. The highest β-phase content of 90.21% in PVDF composite nanofibers was achieved owing to the synergistic effect of MWCNT and BaTiO3 nanoparticles. The open-circuit voltage of the flexible piezoelectric nanogenerator based on interdigital electrodes reached 11.4 V at 2 Hz and a bending strain of 4 mm with an optimal power and power density of 8.67 μW and 1.16 μW/cm2, respectively, and can light up to 8 LED lights simultaneously. The output voltage did not decay during 1800 cycles, which met the power and stability requirements of a commercial capacitor. In addition, the prepared piezoelectric sensors exhibited anisotropy and high sensitivity. They had a maximum amplitude sensitivity of 93 dB, which was superior to the reported PVDF-TrFE sensors and suitable for low-frequency signal monitoring in the range of 20–40 kHz. Localization accuracy was greater than 90% in linear and planar localization tests, demonstrating the potential of preparing acoustic emission sensors. These properties facilitate the reduction of the quantity of sensors required to identify the source of damage.

Stokes wave traveling along a thin elastic plate floating at water surface

This paper addresses nonlinear deflection waves traveling along a thin elastic plate floating at the water surface. The investigations are based on both the analytical and experimental aspects. A finite amplitude wave theory for the waves traveling on the plate developed by the present authors, in which, the nonlinear wave is formulated by a perturbation with respect to the wave height/wavelength ratio, is used. The behavior of the nonlinear wave traveling on the plate is like what the Stokes wave theory predicts for the free surface. However, for the waves traveling on the plate, there is an instability frequency at which the second order wave component grows considerably. The sign of the second order wave component is inverted at the instability frequency when the incident wave frequency is changed from low to high regions. These predictions are verified in a tank test in the two-dimensional flume using a long flexural plate that was newly designed. The spatio-temporal distribution of the deflection and bending strain on the plate was measured directly using the stereo Digital Image Correlation (DIC) technique with two high-speed CCD cameras. The measured results are compared with the predictions by analytical theory. The instability frequency is found in the tank test and the nonlinear wave properties are discussed.

Effect of Carbon Nanofibers on the Strain Rate and Interlaminar Shear Strength of Carbon/Epoxy Composites.

The static bending properties, different strain rates and interlaminar shear strength (ILSS) of carbon-fiber-reinforced polymers (CFRP) with two epoxy resins nano-enhanced with carbon nanofibers (CNFs) are studied. The effect on ILSS behavior from aggressive environments, such as hydrochloric acid (HCl), sodium hydroxide (NaOH), water and temperature, are also analyzed. The laminates with Sicomin resin and 0.75 wt.% CNFs and with Ebalta resin with 0.5 wt.% CNFs show significant improvements in terms of bending stress and bending stiffness, up to 10%. The values of ILLS increase for higher values of strain rate, and in both resins, the nano-enhanced laminates with CNFs show better results to strain-rate sensitivity. A linear relationship between the logarithm of the strain rate was determined to predict the bending stress, bending stiffness, bending strain and ILSS for all laminates. The aggressive solutions significantly affect the ILSS, and their effects are strongly dependent on the concentration. Nevertheless, the alkaline solution promotes higher decreases in ILSS and the addition of CNFs is not beneficial. Regardless of the immersion in water or exposure to high temperatures a decrease in ILSS is observed, but, in this case, CNF content reduces the degradation of the laminates.

Structural analysis of REBCO coated conductors and quasi-isotropic strands under bending using continuum shell element

The electro-mechanical properties of Rare-Earth Barium Copper Oxide (REBCO) coated conductors (CCs) are crucial for practical structures such as power cables, magnet coils and so on. Many tests including tension and bending tests were conducted to estimate the critical current of REBCO CCs under different loadings. However, standard test method for the electro-mechanical properties of REBCO CCs has not been established, especially for bending tests. Therefore, finite element simulations of bending tests of REBCO CCs are still needed to further analyze the electro-mechanical behavior under loading. Structural responses of REBCO CCs and quasi-isotropic (Q-IS) strands under bending are analyzed using continuum shell element in this study. The numerical results indicate that bending strains obtained from finite element simulations match well with the analytical calculations in pure bending state. Furthermore, the influences of former shapes are also discussed to evaluate the bending tolerance of REBCO CCs in different cases. In addition, the mechanical properties and critical current degradation of Q-IS strands under bending are analyzed.

Effect of Interlayer Bonding Temperature on the Bending Properties of Asphalt Concrete Core Wall.

In the construction process of an asphalt concrete impermeable core wall, the interlayer bonding of the core wall is the weak link of the core wall structure and also the focus of construction, so it is important to carry out research on the influence of interlayer bonding temperature on the bending performance of an asphalt concrete core wall. In this paper, we study whether asphalt concrete core walls could be treated with cold-bonding by fabricating small beam bending specimens with different interlayer bond temperatures and conducting bending tests on them at 2 °C. The effect of temperature variation on the bending performance of the bond surface under the asphalt concrete core wall is studied through experimental data analysis. The test results show that the maximum value of porosity of bituminous concrete specimens is 2.10% at lower bond surface temperature of -25 °C, which does not meet the specification requirement of less than 2%. The bending stress, strain, and deflection of bituminous concrete core wall increase with the increase of bond surface temperature, especially when the bond surface temperature is less than -10 °C. If the lower bonding surface temperature is less than 10 °C, the upper layer of asphalt mixture with large grain size aggregate cannot be effectively buried in the low bond surface, resulting in flat fracture and brittle damage to the specimen, which is detrimental to construction quality; therefore, the bonding surface should be heated so that the temperature of the bottom bonding surface is 30 °C. If the lower bonding surface temperature is 10 °C or above, no heating is required.

81‐3: Design of Narrow Border Flexible OLED Display Based on Simulation Analysis and Optimization

This paper analyzes the design of the down border of the flexible OLED display, and studies the influence of the neutral layer and the sensitivity of SD strain of different stacks of Pad Bending in the narrow border area based on the finite element simulation. The neutral layer is located in the PI2 layer, and the order of the strain sensitivity of SD at Bending edge is MCL&gt;Organic layer&gt;PI1&gt;PI2, MCL thickness has the greatest influence on SD strain. Through the stacking optimization design based on the sensitivity analysis results, the SD strain is reduced from 11.1% to 6.6%. Finally realize the industry's smallest R0.1mm Pad Bending design. Based on bending strain gauge and 25N static push test, SD strain is at a safe level and pass more than 50 times push tests. Narrow border products with R0.1mm Pad Bending can pass various environmental reliability tests to meet the environmental requirements of terminal products.

High stretch-ability and high linearity for elastic strain sensor constructed by multiple micro-cracks and complex wrinkles

Flexible sensors have been widely studied in smart wear, human health monitoring, biomedical and other applications because of its high bio-compatibility. However, it is still a challenge to achieve high sensitivity, wide sensing range, and high stability at the same time, which limits the application of flexible sensors in many directions. In order to solve the above problems, we construct a micro-crack composite wrinkle structure enhanced fiber strain sensor using SEBS rubber elastomer as the substrate and carbon nanotube film functional materials. The micro-cracks composite wrinkle structure for carbon nanotubes ([email protected]) ensures that the sensor has an ultra-wide sensing range of 0–600 %, and the impact factor reaches 1.0676 under the tension state. The wrinkle structure ensures the sensor can maintains good sensing performance after >10,000 tests, and has high linearity. The response time is 153 ms, the recovery time is 169 ms, and the hysteresis of the sensor can be ignored. At the same time, it also has the sensing performance of bending strain, which broadens the application of the sensor. Our strain sensor has promising applications in wearable electronic devices for detecting human motion.

Nanowires-Based Stretchable Strain Sensor for Wearable Applications

Flexible, stretchable strain sensors are needed to measure physiological parameters or joint angles in wearable systems and robotics, respectively. This letter presents the stretchable strain sensor that is directly fabricated on environment-friendly Ecoflux substrate. The sensor uses stretchable serpentine-shaped Au interconnects and Ag nanowires (NWs) as the strain-sensitive active channel. The sensor structure has been evaluated under stretching conditions that provided insights about the material integrity during device operation. The device characteristics show good linearity under low strain range (<40%), average gauge factor of 5.8, cyclic stability for more than 5000 cycles, and response time of 200 ms. Finally, the sensor was placed on human finger, as a proof of concept, and measurements were taken to understand the bending strain during finger movements and potential application in smart glove and robotics.

Interfacial Strain Analysis of Bending Bilayer Silicone Elastomer Films Using a Cholesteric Liquid Crystal Sensor

The analysis of the bending strain at the interface of layered polymer films is significant in the design of flexible electronic devices because conductive materials placed on the interface are degraded by strain. Although theoretical calculations and numerical simulations of the interfacial bending strain of polymer films have been conducted, few experimental analyses have been reported because of the difficulty in measuring the interface strain. In our previous study, the internal strain in a bending polymer film was successfully measured using a cholesteric liquid crystal elastomer (CLCE) sensor. Herein, we report the interfacial strain analysis of a bending bilayer film composed of poly(dimethylsiloxane) (PDMS) films with different Young’s moduli using a CLCE sensor. The experimental strain analysis revealed that the bending strain at the interface depends on the distance between the interface and the neutral mechanical plane (NMP), which experiences no strain. Notably, as the bilayer films bend significantly, the NMP shifts toward the inner bending surface because of the change in the balance between the tensile and compressive stresses in the film. This study enables us to understand the interface bending strain in polymer films, which will aid in the design of flexible electronic devices with conductive materials placed on the interface whose strain is minimized.

The MoS2-Graphene-Sapphire Heterostructure: Influence of Substrate Properties on the MoS2 Band Structure

Van der Waals MoS2/graphene heterostructures are promising candidates for advanced electronics and optoelectronics beyond graphene. Herein, scanning probe methods and Raman spectroscopy were applied for analysis of the electronic and structural properties of monolayer (ML) and bilayer 2H-MoS2 deposited on single-layer graphene (SLG)-coated sapphire (S) substrates by means of an industrially scalable metal organic chemical vapor deposition process. The SLG/S substrate shows two regions with distinctly different morphology and varied interfacial coupling between SLG and S. ML MoS2 nanosheets grown on the almost free-standing graphene show no detectable interface coupling to the substrate, and a value of 2.23 eV for the MoS2 quasiparticle bandgap is determined. However, if the graphene is involved in hydrogen bonds to the hydroxylated sapphire surface, an increased MoS2/graphene interlayer coupling results, marked by a shift of the conduction band edge toward Fermi energy and a reduction of the ML MoS2 quasiparticle bandgap to 1.98 eV. The surface topography reveals a buckle structure of ML MoS2 in conformity with SLG that is used to determine the dependence of the ML MoS2 bandgap on the interfacial spacing of this heterostructure. In addition, an in-gap acceptor state about 0.9 eV above the valence band minimum of MoS2 has been observed on locally elevated positions on both SLG/S regions, which is attributed to local bending strain in the grown MoS2 nanosheets. These fundamental insights reveal the impact of the underlying substrate on the topography and the band alignment of the ML MoS2/SLG heterostructure and provide the possibility for engineering the quasiparticle bandgap of ML MoS2/SLG grown on controlled substrates that may impact the performance of electronic and optoelectronic devices therewith.