Reverse Bending Research Articles

Mechanical Properties of 6061 Aluminum Alloy under Cyclic Tensile Loading

During the service process of an aluminum alloy structure, its complex deformation zone experiences repeated loading problems such as repeated tension, compression, bending and reverse bending. At the same time, the cyclic loading and heat treatment process also have a certain impact on the mechanical properties of aluminum alloy extruded tubes. Therefore, the study of heat treatment process parameters has important engineering and practical value for the mechanical properties of aluminum alloy extrusion tubes under cyclic loading conditions. The experiment takes 6061-T6 aluminum alloy extruded tubes as the research objects. In the study, heat treatment and cyclic tensile tests were carried out on 26 aluminum alloy specimens to study the effects of different heat treatment parameters (such as heating temperature, holding time, and cooling method) on the stress–strain hysteresis curves, stress characteristics, hysteretic energy, skeleton curves and failure characteristics of the alloy under the same loading system. In addition, different cyclic tensile tests were carried out on 20 aluminum alloy samples without secondary heat treatment to discuss the effects of different cyclic loading regimes on the mechanical properties of the alloy. The research results indicate that the effect of heating temperature on the cyclic loading performance of the alloy is greater than that of the holding time, and the effect of the cooling method on the cyclic loading performance of the alloy is not obvious. A cyclic tensile loading regime has a significant impact on the strength, elongation and hysteresis energy of the alloy. The hysteretic behavior of the alloy during cyclic tensile loading depends on the applied stress level and loading history. As the number of cycles increases, the shape of the hysteresis curve tends to be stable, but there is no monotonic relationship between the number of cycles loaded and the hysteresis energy.

MXene‐Based Soft Actuators with Multiresponse and Diverse Applications by a Simple Method

AbstractSmart actuators that can convert external energy stimuli into mechanical energy output have great potential in industrial, biomedical, and military applications. However, the existed disadvantage such as complex fabrication process, single stimulus source, and the requirement of artificial energy restrict their further development. Herein, a MXene/polyethylene (PE)‐based soft actuator with multistimulus response and the ability to be driven by natural sunlight and human humidity is proposed through a simple method. Owing to the excellent electrical conductivity, high photothermal conversion capability, and surface hydrophilicity of MXene, the MXene/PE actuator exhibits rapid and large bending deformation in response to external multistimuli such as light, electricity, heat, and humidity. Owing to the simple preparation, and anisotropic, tailorable and programmable properties of the MXene/PE actuator, a soft robot that can crawl directionally under light conditions is constructed. In addition, based on the high sensitivity response of the actuator to light and humidity, smart clothing that can generate reversible bending deformation under natural sunlight as well as sweat conditions is developed. These results provide a new inspiration for the design of high‐performance soft actuators with multistimulus response, and demonstrate the potential applications of the MXene/PE actuators in smart devices, bionic robots, and wearable clothing.

An elastic luminescent organic single crystal with linear and nonlinear optical waveguide properties

In recent years, organic single crystals combining elastic and photoluminescent (PL) properties have attracted extensive attention due to their promising applications in many fields. However, elastic organic crystals with two-photon luminescence (2 PL) waveguiding properties are still rarely found, which is imperative for various applications, including near-infrared (NIR) bioimaging and nonlinear optical (NLO) photonic devices. This work reports an elastic single crystal with a long needle shape, anthracene-9,10-dicarbaldehyde (An-DC). Its crystal (100) face exhibits highly reversible bending by applying the mechanical force, which is facilitated by the van der Waals (C– H···π), H-bond (C–H⋯O), and π···π interactions among molecules. The crystal emits a strong orange-red fluorescence when excited by blue-violet light. Interestingly, it also exhibits excellent two-photon fluorescence emission when stimulated by near-infrared light. Based on these linear and nonlinear optical characteristics, the waveguide applications of the An-DC crystal were implemented. Notably, in the bending state, the luminescence performance and the crystal structure of the An-DC crystal are maintained well, which can be used as a low-loss material for linear and nonlinear optical waveguide devices, thus expanding the potential use of flexible organic crystals.

Bilayer Hydrogel Composed of Elastin-Mimetic Polypeptides as a Bio-Actuator with Bidirectional and Reversible Bending Behaviors.

Biologically derived hydrogels have attracted attention as promising polymers for use in biomedical applications because of their high biocompatibility, biodegradability, and low toxicity. Elastin-mimetic polypeptides (EMPs), which contain a repeated amino acid sequence derived from the hydrophobic domain of tropoelastin, exhibit reversible phase transition behavior, and thus, represent an interesting starting point for the development of biologically derived hydrogels. In this study, we succeeded in developing functional EMP-conjugated hydrogels that displayed temperature-responsive swelling/shrinking properties. The EMP-conjugated hydrogels were prepared through the polymerization of acrylated EMP with acrylamide. The EMP hydrogel swelled and shrank in response to temperature changes, and the swelling/shrinking capacity of the EMP hydrogels could be controlled by altering either the amount of EMP or the salt concentration in the buffer. The EMP hydrogels were able to select a uniform component of EMPs with a desired and specific repeat number of the EMP sequence, which could control the swelling/shrinking property of the EMP hydrogel. Moreover, we developed a smart hydrogel actuator based on EMP crosslinked hydrogels and non-crosslinked hydrogels that exhibited bidirectional curvature behavior in response to changes in temperature. These thermally responsive EMP hydrogels have potential use as bio-actuators for a number of biomedical applications.

Dried bonito flakes-inspired moisture-responsive actuator with a gradient structure for smart devices

Exploring high-performance soft actuators from biomass resources is significant for developing eco-friendly smart devices. Dried bonito (DB) flake is a common food as well as a biomass material, and it can produce irregular motion in changed moisture, just like dancing. Inspired by this intriguing phenomenon, a cost-effective, biocompatible, and biodegradable moisture-responsive DB film actuator with a gradient structure is developed. The DB film actuator exhibits rapid and reversible bending deformation triggered by a humidity gradient with a high bending speed (40° s–1) and a maximum bending angle (180°). Moreover, the DB film actuator shows large bending deformation (–71° to +51°) with a high actuation force (214.7 Pa) in response to changes in relative humidity. Furthermore, the actuation performance can be also tuned by adjusting the thickness of the film. Potential applications of this actuator, including smart grippers, crawling robots, and biomimetic flowers for visible humidity sensing, are demonstrated. More importantly, smart sweat-responsive wearables that automatically deform to promote sweat evaporation and convection during exercise are constructed based on the actuator, making it promising for adaptive personal thermal management. This work offers an easily processable, cost-effective, and environmentally benign strategy to construct moisture-responsive actuators for future eco-friendly smart devices.

High Performance and Multifunction Moisture-Driven Yin-Yang-Interface Actuators Derived from Polyacrylamide Hydrogel.

High actuation performance of a moisture actuator highly depends on the presence of a large property difference between the two layers, which may cause interfacial delamination. Improving interfacial adhesion strength while increasing the difference between the layers is a challenge. In this study, a moisture-driven tri-layer actuator with a Yin-Yang-interface (YYI) design is investigated in which a moisture-responsive polyacrylamide (PAM) hydrogel layer (Yang) is combined with a moisture-inert polyethylene terephthalate (PET) layer (Yin) using an interfacial poly(2-ethylhexyl acrylate) (PEA) adhesion layer. Fast and large reversible bending, oscillation, and programmable morphing motions in response to moisture are realized. The response time, bending curvature, and response speed normalized by thickness are among the best compared with those of previously reported moisture-driven actuators. The excellent actuation performance of the actuator has potential multifunctional applications in moisture-controlled switches, mechanical grippers, and crawling and jumping motions. The Yin-Yang-interface design proposed in this work provides a new design strategy for high-performance intelligent materials and devices.

Influence of Uneven Subgrade Frost Heave on Deformation and Damage of CRTSIII Slab Track

The problem of uneven frost heave deformation of high-speed railway subgrade in seasonal freezing areas seriously affects the service state and service life of slab track structures and threatens the safe operation of high-speed vehicles. Based on the damage plasticity theory of concrete, in this study, an analytical model is established for CRTSIII slab track with damage plasticity and reinforcement. The influences of various frost heaving parameters on track structure deformation, interlayer seam, as well as the stress and damage behaviors were analyzed in detail. The results show that, as compared with a linear elastic model, the damage plastic model better reflects the softening behavior and stress attenuation of track structure concrete after reaching its tensile strength. The deformation and the interlayer seam reach their maximum values when the frost heaving wave peak acts at the position that is one-sixth of the base length from the edge of the concrete base. When the frost heaving wave peak acts on grooves at the base center, initially, the track structure is seriously damaged. The interlayer seam and damage decrease with an increase in frost heaving wavelength and increase with an increase in frost heaving wave amplitude. The interlayer seam of the track structure is more sensitive to frost heave deformation having a wavelength of less than 10 m. The extent of damage to the concrete base gradually increases with a decrease in the wave/amplitude ratio. It undergoes three stages of damage evolution: (i) no damage, (ii) upper surface bending damage, (iii) reverse bending damage. In order to improve efficiency, it is recommended, during track maintenance, to focus on the position of the central groove of the base and the position that is one-sixth of the base length from the edge of the concrete base.

Two-Way Shape Memory Effect of a Shape Memory Composite Strip

In this work, a NiTi shape memory alloy (SMA) wire was embedded into a rubber/shape memory polymer (SMP) soft matrix to form a composite strip with a two-way reversible bending behavior. First, the elastic moduli of SMA wire were characterized as increasing about 3 times (18.6 GPa at martensite phase and 50.1 GPa at austenite phase) from 25 °C to 90 °C. Then, an SMA composite strip using SMP to replace the rubber matrix was fabricated to significantly improve the load-bearing ability (16-fold) at 28 °C. After that, the good two-way bending behaviors of the rubber/SMP-based SMA strip with high shape deploying ratio above 80% were demonstrated. Finally, the application of rubber/SMP-based composite strips in a space-deployable antenna model with two-way reversible bending behavior was developed and demonstrated through a heating and cooling temperature cycle.

Characterization of the dissipative large deformation bending response of dry fabric composites as occurs during forming

Bending rigidity is known to play a significant role in the formability of composite fabrics, as it can affect wrinkles formation and reduce the mechanical properties of the final part. However, measuring the highly nonlinear dissipative bending behaviour of unconsolidated fabrics undergoing large deformation, is an ongoing challenge. In this article, a customized setup is employed to capture the bending as well as reverse bending responses of unconsolidated fabrics under large deformation (up to ±90o bent angle). As a test case, a typical fiberglass fabric that is thick and has high areal density, as well as a carbon fiber fabric with lesser thickness and lower areal density are considered and compared. In addition, the response of the fabrics was compared to that of individual yarns, suggesting that the interlaced architecture and the dissipative behavior of yarns affect the effective bending rigidity, along with the ensuing hysteresis effects during loading/unloading. Furthermore, when the unconsolidated fabrics were oriented off-axis relative to the bending axis, the bending rigidity interacted with the in-plane trellising (reach to maximum of 3.3o shear at full bent angle), suggesting that the classical laminate theory would not apply to capture shear-bending coupling in dry fabrics.

Investigation of the block toppling evolution of a layered model slope by centrifuge test and discrete element modeling

Primary toppling usually occurs in layered rock slopes with large anti-dip angles. In this paper, the block toppling evolution was explored using a large-scale centrifuge system. Each block column in the layered model slope was made of cement mortar. Some artificial cracks perpendicular to the block column were prefabricated. Strain gages, displacement gages, and high-speed camera measurements were employed to monitor the deformation and failure processes of the model slope. The centrifuge test results show that the block toppling evolution can be divided into seven stages, i.e. layer compression, formation of major tensile crack, reverse bending of the block column, closure of major tensile crack, strong bending of the block column, formation of failure zone, and complete failure. Block toppling is characterized by sudden large deformation and occurs in stages. The wedge-shaped cracks in the model incline towards the slope. Experimental observations show that block toppling is mainly caused by bending failure rather than by shear failure. The tensile strength also plays a key factor in the evolution of block toppling. The simulation results from discrete element method (DEM) is in line with the testing results. Tensile stress exists at the backside of rock column during toppling deformation. Stress concentration results in the fragmented rock column and its degree is the most significant at the slope toe.

Calaxin is required for asymmetric bend initiation and propagation in sperm flagella.

Regulation of waveform asymmetry in flagella is critical for changes in direction when sperm are swimming, as seen during the chemotaxis of sperm towards eggs. Ca2+ is an important regulator of asymmetry in flagellar waveforms. A calcium sensor protein, calaxin, is associated with the outer arm dynein and plays a key role in the regulation of flagellar motility in a Ca2+-dependent manner. However, the underlying mechanism of regulating asymmetric waves by means of Ca2+ and calaxin remains unclear. To clarify the calaxin-dependent mechanism for generating Ca2+-dependent asymmetric flagellar waveforms, we analyzed the initial step of flagellar bend formation and propagation in the sperm of the ascidian Ciona intestinalis. Our experiment used demembranated sperm cells, which were then reactivated by UV flash photolysis of caged ATP under both high and low Ca2+ concentrations. Here, we show that initial bends in the flagella are formed at the base of the sperm and propagate towards the tip during waveform generation. However, the direction of the initial bend differed between asymmetric and symmetric waves. When a calaxin inhibitor (repaglinide) was applied, it resulted in the failure of asymmetric wave formation and propagation. This was because repaglinide had no effect on initial bend formation, but it significantly inhibited the generation of the subsequent bend in the reverse direction. Switching of dynein sliding activity by mechanical feedback is crucial for flagellar oscillation. Our results suggest that the Ca2+/calaxin mechanism plays an important role in the switching of dynein activity from microtubule sliding in the principal bend into the suppressed sliding in the reverse bend, thereby allowing the sperm to successfully change direction.

Effect of different roll-forming flower patterns on coiled tubing ovality and pressure performance

The pressure applied by the drilling fluid circulation pumps into Coiled Tubing (CT) compensates for the effects of fluid friction and force applied to the downhole motors. The higher the pressure, the greater the power of the well operation. The critical point of the cross-section of CT is on the earth's surface, where the highest internal and lowest external pressure are applied to it. In this paper, the compressive tolerance value of CT is investigated in relation to its ovality. This ovality can be inherent and created during the construction of the tube. 4 different flower patterns can be used for making CT. This paper aims to roll forming CT without a sizing step so that it preserves its mechanical performance against incoming forces. The geometry-based form definition method calculations have been used to determine the forming path of the strip, and this is the basis for the design of the forming rollers in each stage, finally, according to the similarities in the forming stages, 45 rollers have been designed for simulation. Therefore, assuming that the sizing step is not used in tube roll forming, the effect of roll forming flower patterns on the ovality of the final product of 1 ½ inch CT-70 and its effect on the internal and external pressure tolerance of the tube is investigated and Results of dimensional analysis, a tensile test of a new QT-70, 1 ½ inch tube as a sample and the geometry-based form definition method results are considered as input for the simulation of all four methods and the finite element method was used to simulate tube construction with different flower pattern methods, and its results were used in the geometry of the final product, in CT pressure tolerance analysis. The results show that the behavior of the tube made by the reverse bending flower pattern method shows better tolerance against internal and external pressure so this behavior is related to the ratio of internal to external pressure tolerance in the tube. With the flower pattern method, the reverse bending is approximately 1.08–1.85 times compared to the double-radii pattern and 1.13 to 2.27 times, and 1.18 to 3.21 times compared to the edge flower pattern and circular flower patterns, respectively.

Unexpected pectus carinatum: Reverse bending of xiphisternal joint after modified Nuss procedure

Unexpected pectus carinatum: Reverse bending of xiphisternal joint after modified Nuss procedure

Measuring DNA folding by the SARS-CoV-2 nucleocapsid protein.

The SARS-CoV-2 virus is a deadly virus responsible for COVID-19. Here we are interested in the mechanics of how the nucleocapsid protein (N-protein) in SARS-CoV-2 folds the viral RNA into the capsid. This process could be a target for antiviral research which looks to prevent further proliferation of the virus. Our goal is to understand the role that electrostatic interactions play in the folding of the negatively charged RNA by the positively charged N-protein. To isolate these interactions from specific interactions with the RNA bases or conformation, we measure N-protein folding single molecules of double-stranded DNA. We take structural images of the folding using an atomic force microscope (AFM) or look at real-time folding using tethered particle motion (TPM) assays. We hypothesize that N-proteins might fold double-stranded DNA using a method similar to positively charged protamine proteins which act to package the DNA in sperm cells. These protamine proteins “bind and bend” the DNA in multiple locations using discrete, long-lived (∼100 s), reversible bending steps. We observe similar folding characteristics for N-protein, but also see some important differences. We will report on progress toward this goal.

Research on the 2A11 Aluminum Alloy Sheet Cyclic Tension–Compression Test and Its Application in a Mixed Hardening Model

The increasing application of aluminum alloy, in combination with the growth in the complexity of components, provides new challenges for the numerical modeling of sheet materials. The material elastic–plasticity constitutive model is the most important factor affecting the accuracy of finite element simulation. The mixed hardening constitutive model can more accurately represent the real hardening characteristics of the material plastic deformation process, and the accuracy of the material property-related parameters in the constitutive model directly affects the accuracy of finite element simulation. Based on the Hill48 anisotropic yield criterion, combined with the Voce isotropic hardening model and the Armstrong–Frederic nonlinear kinematic hardening model, a mixed hardening constitutive model that considers material anisotropy and the Bauschinger effect was established. Analysis of the tension–compression experiment on the sheet using finite element method. Using the finite element model, the optimum geometry of the tension–compression experiment sample was determined. The cyclic deformation stress–strain curve of the 2A11 aluminum alloy sheet was obtained by a cyclic tensile–compression test, and the material characteristic parameters in the mixed hardening model were accurately determined. The reliability and accuracy of the established constitutive model of anisotropic mixed hardening materials were verified by the finite element simulation and by testing the cyclic tensile–compression problem, the springback problem, and the sheet in bending, unloading, and reverse bending problems. The tensile–compression experiment is an effective method to directly and accurately obtain the characteristic parameters of constitutive model materials.

Multi-stimuli responsive bilayer film based on clay and graphene derivative for flexible and smart devices

Designing a smart actuator with multi-response behaviors is highly demanded for the development of intelligent systems by using low-cost materials and facile fabricating method. Herein, the bilayer actuators with controlled and large deformation, were prepared with montmorillonite (Mt), graphene oxide (GO) and their derivatives (organic montmorillonite (OMt) and reduced graphene oxide (rGO)) by simple casting method. The prepared bilayer films with periodic microchannel patterns consist of hydrophilic GO-Mt layer and hydrophobic rGO-OMt layer, exhibiting good actuating performance under the external stimuli of humidity, organic solvent and infrared (IR) light. With the increase of rGO/OMt ratio, the humidity-triggered bending angle of the bilayer films increases, but the humidity-triggered deformation changes from reversible bending to irreversible state. Remarkably, different from the bending direction toward rGO-OMt side in humid environment, the bending in opposite directions toward GO-Mt side is observed in response to organic solvent and IR light. The bilayer films show reversibly bidirectional bending under the alternating stimuli of humidity/organic solvent or humidity/IR light. These bilayer films were tailored to fabricate the programmable actuators, which were successfully applied as smart switches, smart windmills, bioinspired blooming flowers, flapping wings of paper cranes and predatory tongue of frogs. This work provides a potential pathway for the development of low-cost multi-responsive materials for more versatile applications in various smart devices.

Cyclic bending of steel tubes with Lüders bands

Preceding experiments and analyses revealed that bending of tubes whose material exhibits Lüders banding leads to the progressive nucleation of inclined bands of higher strain organized into periodic diamond clusters. The diamonds cover both the tensioned and compressed sides of the tube with the affected length developing a higher curvature than the unaffected section. Between the diamond patterns are elastic zones required for each periodic domain to conform to the curvature of the tube (Hallai and Kyriakides, 2011a,b). The present work examines how this inhomogeneously deformed structure behaves on unloading, reverse bending, and curvature symmetric cycling. The inelastic behavior of the material is modeled through a combined isotropic/kinematic hardening constitutive model. The model incorporates partial softening over the extent of the Lüders strain and uses nonlinear kinematic hardening for reverse loading. A tube of virgin material is bent until the whole length is Lüders deformed and is in uniform curvature. The curvature remains uniform during unloading with the strain in the diamonds gradually being erased, but simultaneously a secondary set of local higher strain patterns emerge in the hitherto elastic zones between the original diamonds. During reverse bending to the symmetric negative curvature, the secondary patterns continue to grow in intensity. The tube is unloaded again and bent back to positive curvature completing the cycle. In the course of the second half cycle, localized strain patterns evolve in the reverse order to that of the first half cycle. The secondary patterns are gradually erased, and the diamond patterns reappear now concurrently reaching the same intensity as that acquired progressively during the bending of the virgin material. The same appearance, erasure, and reappearance of localized deformation take place in subsequent cycles. Once past the initial bending, the structure bends uniformly.

Role of supramolecular polymers in photo-actuation of spiropyran hydrogels.

Supramolecular-covalent hybrid polymers have been shown to be interesting systems to generate robotic functions in soft materials in response to external stimuli. In recent work supramolecular components were found to enhance the speed of reversible bending deformations and locomotion when exposed to light. The role of morphology in the supramolecular phases integrated into these hybrid materials remains unclear. We report here on supramolecular-covalent hybrid materials that incorporate either high-aspect-ratio peptide amphiphile (PA) ribbons and fibers, or low-aspect-ratio spherical peptide amphiphile micelles into photo-active spiropyran polymeric matrices. We found that the high-aspect-ratio morphologies not only play a significant role in providing mechanical reinforcement to the matrix but also enhance photo-actuation for both light driven volumetric contraction and expansion of spiropyran hydrogels. Molecular dynamics simulations indicate that water within the high-aspect-ratio supramolecular polymers exhibits a faster draining rate as compared to those in spherical micelles, which suggests that the high-aspect-ratio supramolecular polymers effectively facilitate the transport of trapped water molecules by functioning as channels and therefore enhancing actuation of the hybrid system. Our simulations provide a useful strategy for the design of new functional hybrid architectures and materials with the aim of accelerating response and enhancing actuation by facilitating water diffusion at the nanoscopic level.

Reverse bend option for a 6 GeV storage ring lattice

Several high-energy synchrotron facilities adopted the Hybrid Multi-Bend Achromat scheme (HMBA) developed for the ESRF-EBS [1]. The considered lattice has been developed for a generic 6 GeV storage ring (SR) of 1100 m circumference [2]. It includes a short bending (SB) magnet at the center of the cell, and achieves a ~70 pm rad equilibrium horizontal emittance. The optics of such SR are modified introducing reverse bending magnets [3, 4] to further reduce the natural horizontal emittance to 53 pm rad. The impact of such modification on dynamic aperture and lifetime is assessed and optimized.

Moisture-Responsive Actuators Based on Hyaluronic Acid with Biocompatibility and Fast Response as Smart Breather Valves

Moisture-responsive actuators with biocompatibility, fast response, and tough interfacial bonding are developed as smart breather valves for humidity management. The proposed actuators are featured with a bilayer structure consisting of a moisture-sensitive methacrylated hyaluronic acid (HAMA) layer and a moisture-inert porous poly(vinylidene fluoride) (PVDF) layer. The HAMA/PVDF bilayer films are fabricated by casting HAMA precursor solutions on the ethanol-treated porous PVDF films first and then converting the precursor solutions into crosslinked HAMA hydrogels via UV-initiated crosslinking. The fabricated HAMA/PVDF bilayer films exhibit rapid, reversible, and repeatable moisture-responsive bending performances upon the change of environmental relative humidity. The molecular weight and mass concentration of HAMA in a precursor solution affect the moisture-responsive actuating speed of the HAMA/PVDF bilayer films, and the fastest response time needed for completing 70% of the moisture-responsive deformation of a HAMA/PVDF bilayer film can be as short as 0.5 s. Due to the fast moisture-responsive bending property and biocompatibility, the HAMA/PVDF bilayer films are successfully developed into smart breather valves by designing and patterning them into fence-like structures and then equipped on the outdoor masks for efficient management of humidity inside the masks. The proposed moisture-responsive actuators show great potential in various applications, especially those related to environmental humidity management.