Reverse Bending Research Articles

Fatigue analysis on flax-epoxy composites: insights and implications

This study investigates the performance of flax fiber and epoxy resin composites, focusing on fatigue testing, which is scarcely reported in the literature. Fatigue behavior is evaluated under full reverse bending loading conditions: R = −1. Apart of the definition of the classic S-N curve, the analysis deeply investigated the evolution of the hysteresis leaf generated during each cycle over the entire fatigue life. This approach allows evaluating interesting parameters such as the evolution of the loss factor and the apparent modulus over life, being these informations fundamental for practical application of natural-fiber composites in engineering applications.

Effect of path-dependent plasticity on springback in reverse bending and its application to roll forming

This study investigates springback behavior in martensitic advanced high-strength steels (AHSS) undergoing pure bending and reverse bending sequences. The comparison between a conventional isotropic hardening model and the Homogeneous Anisotropic Hardening (HAH20) model had been made, which accounts for non-isotropic hardening effects. Both models were calibrated using uniaxial tensile, cyclic, and loading–unloading tests. The results show that the HAH20 model predicts a higher initial springback compared to the isotropic model. However, reverse bending significantly reduces the overall springback for both models due to a minimized recovery moment. In scenarios with reverse bending, a specific strain exists where both models predict identical springback due to the secondary Bauschinger effect in tensile stress. This phenomenon is also observed in roll forming, a sequential bending process that incorporates reverse bending steps. Experimental findings from roll forming confirm a decrease in springback after the reverse bending stage. Furthermore, the study explores the impact of non-isotropic hardening on the part crashworthiness with the calibration of cross-loading effects. The Bauschinger effect and cross-loading contraction were found to reduce the maximum crash load by 6.2%.

Programmable multi-stability of curved-crease origami structures with travelling folds

Multi-stable structures capable of rapid switching among different stable states have seen applications in various fields such as energy absorption, mechanical computing, and soft actuators. Curved-crease origami, which naturally involves simultaneous deformation of creases and facets, shows great potential in the development of multi-stable structures. However, upon loading, existing curved-crease origami structures tend to follow the same deformation mode as in the curved surface formation process which involves facets elastic bending, flattening, and reverse bending, thus leading to only two stable states. To achieve multi-stability, here we propose a series of curved-crease origami structures composed of planar facets and curved ones. Through a combination of experiments, numerical simulations, and analytical modelling, we demonstrate that the planar facets forming a Sarrus linkage guide the deformation mode of the curved ones, leading to the initiation and propagation of travelling folds in the curved facets. By transforming the travelling folds at specific positions into actual creases, we can achieve multiple stable states in a single structure. In addition, the number and positions of the stable states, as well as the initial peak force, can be programmed by varying the geometric parameters. Consequently, this work opens a new pathway for the development of generic multi-stable structures with programmable mechanical properties.

Multifunctional Magnetic Muscles for Soft Robotics

Despite recent advancements, artificial muscles have not yet been able to strike the right balance between exceptional mechanical properties and dexterous actuation abilities that are found in biological systems. Here, we present an artificial magnetic muscle that exhibits multiple remarkable mechanical properties and demonstrates comprehensive actuating performance, surpassing those of biological muscles. This artificial muscle utilizes a composite configuration, integrating a phase-change polymer and ferromagnetic particles, enabling active control over mechanical properties and complex actuating motions through remote laser heating and magnetic field manipulation. Consequently, the magnetic composite muscle can dynamically adjust its stiffness as needed, achieving a switching ratio exceeding 2.7 × 10³. This remarkable adaptability facilitates substantial load-bearing capacity, with specific load capacities of up to 1000 and 3690 for tensile and compressive stresses, respectively. Moreover, it demonstrates reversible extension, contraction, bending, and twisting, with stretchability exceeding 800%. We leverage these distinctive attributes to showcase the versatility of this composite muscle as a soft continuum robotic manipulator. It adeptly executes various programmable responses and performs complex tasks while minimizing mechanical vibrations. Furthermore, we demonstrate that this composite muscle excels across multiple mechanical and actuation aspects compared to existing actuators.

Easy Processable Photomechanical Thin Film Involving a Photochromic Diarylethene and a Thermoplastic Elastomer in Supramolecular Interaction.

A novel supramolecular photoactuator in the form of a thin film of centimetric size has been developed as an alternative to traditional liquid crystal elastomers (LCE) involving azobenzene (AZO) units or photochromic microcrystals. This thin film is produced through spin coating without the need for alignment or crosslinking. The photoactuator combines a photochromic dithienylethene (DTE) functionalized with ureidopyrimidinone (UPy) units, and a telechelic thermoplastic elastomer, also functionalized with UPy, allowing quadruple hydrogen bonding between the two components. Upon alternating ultraviolet (UV) and visible light exposure, the film exhibits reversible bending and color changes, studied using displacement and absorption tracking setups. For the first time, the photomechanical effect (PME) is quantitatively correlated with photochromism, showing that DTE units drive the movement under both UV (photocyclization) and visible (photoreversion) light. In situ illumination techniques reveal that the PME arises from photoinduced strain within 160 nm UPy-bonded DTE domains, which expand and contract by approximately 50% under UV and visible light, respectively. The semicrystalline nature of the elastomer and a robust supramolecular network connecting both components are critical in converting microscopic photostrain into macroscopic actuation.

High energy density picoliter-scale zinc-air microbatteries for colloidal robotics.

The recent interest in microscopic autonomous systems, including microrobots, colloidal state machines, and smart dust, has created a need for microscale energy storage and harvesting. However, macroscopic materials for energy storage have noted incompatibilities with microfabrication techniques, creating substantial challenges to realizing microscale energy systems. Here, we photolithographically patterned a microscale zinc/platinum/SU-8 system to generate the highest energy density microbattery at the picoliter (10-12 liter) scale. The device scavenges ambient or solution-dissolved oxygen for a zinc oxidation reaction, achieving an energy density ranging from 760 to 1070 watt-hours per liter at scales below 100 micrometers lateral and 2 micrometers thickness in size. The parallel nature of photolithography processes allows 10,000 devices per wafer to be released into solution as colloids with energy stored on board. Within a volume of only 2 picoliters each, these primary microbatteries can deliver open circuit voltages of 1.05 ± 0.12 volts, with total energies ranging from 5.5 ± 0.3 to 7.7 ± 1.0 microjoules and a maximum power near 2.7 nanowatts. We demonstrated that such systems can reliably power a micrometer-sized memristor circuit, providing access to nonvolatile memory. We also cycled power to drive the reversible bending of microscale bimorph actuators at 0.05 hertz for mechanical functions of colloidal robots. Additional capabilities, such as powering two distinct nanosensor types and a clock circuit, were also demonstrated. The high energy density, low volume, and simple configuration promise the mass fabrication and adoption of such picoliter zinc-air batteries for micrometer-scale, colloidal robotics with autonomous functions.

Study on failure of a tie rod for two-wheeler automotive gear mechanism

ABSTRACT Failure studies of gear shifter tie rod assemblies are crucial for enhancing automotive system reliability and safety. The origin of a tie rod assembly failure is analysed through chemical, mechanical, microstructural, and fractographic analysis in this paper. Optical imaging reveals the microstructure of heat-treated steel, while fractography shows fatigue striations, indicating a progressive fracture. According to the analysis, the penultimate thread likely had a fracture due to the minimal radial space between the external thread and the head. The macroscopic and microscopic characteristics indicate failure from reverse bending under cyclic loading. A crack propagation and ultimate fracture mechanism has been proposed to provide a better understanding of tie rod thread part failures. The importance of factors like fatigue, reverse bending, corrosion, misalignment, and material properties in tie rod failures is highlighted in this study.

Effects of thickness and defect on ultrahigh electro strain of piezoelectric ceramics

Piezoelectric ceramics with high electro strain are widely used in actuators, sensors, and so on. Here, this work investigates the electro strain of representative piezoelectric materials, and analyzes the influence of electrode type on the electro strain of PZT41 with significant strain anomalies. It is found that the occurrence of abnormally significant strain is not affected by the electrode but caused by intrinsic defects. Therefore, the ceramic samples with and without defects tailoring in Na0.5Bi0.5TiO3 (NBT) based and PbZr0.52Ti0.48O3 (PZT) based systems were prepared by the solid-state reaction method, and the results show that abnormally ultrahigh electro strains occur in excessively thin samples with diploes due to defects tailoring. Through displacement configuration experiments and comprehensive analysis of polarization switching processes, it is found that the occurrence of asymmetric abnormal significant strains is caused by reversible bending deformation in excessively thin samples. This work provides new support for the emergence of ultrahigh electro strain in piezoelectric ceramics.

The influence of the rolling method on cold forming ability of explosive welded Ti/steel sheets

Products made of clad sheets are a cost-effective alternative to products made entirely of cladding material. The cladding process aims to enhance functional properties, such as corrosion resistance and tribological properties, or modify mechanical properties and conductivity. This publication analyzes the influence of the rolling method on the cold forming ability of explosive welded Ti/steel sheets. Special attention was paid to the quality of the connection between the sheets, as it significantly impacts clad sheet formability. The drawability of these clad sheets was assessed based on the mechanical and technological properties, as well as through microstructural analyses. Experimental analyses revealed that hot rolling of the clad leads to the disappearance of the wave character of the interface and formation in its area of the Frenkel plane and interface layer, which significantly affect the mechanical and technological properties of the analyzed clad. Better cold forming ability, especially in reverse bend test, were obtained for asymmetrically rolled clad, which exhibits greater uniformity of structure.

Influence of a novel leading-edge winglet on the aerodynamic characteristics of a highly loaded turbine

In order to decrease the flow loss of the region close to the endwall, a novel leading-edge modification strategy is proposed in this paper. Specifically, the winglet is installed at the leading edge of the first-stage blade of the highly loaded PW-E3 (Energy Efficient Engine designed by Pratt & Whitney Aircraft Group) turbine. The numerical methods used in this study are validated with the experimental data of the original blade profile of PW-E3. The SST (Shear Stress Transport model) γ-θ turbulence model is employed to calculate the flow field. The schemes of the forward bending winglet and reverse bending winglet are compared with the base case to prove the superiority of this modification strategy. The numerical results indicate a significant increase in stage efficiency by reducing the total pressure loss coefficient. Reverse bending winglets perform better than forward bending ones in terms of efficiency promotion. The effects of the normalized winglet height and bending angle are further explored. For reverse bending winglets, increasing the normalized winglet height and bending angle leads to improved flow control. Conversely, for forward bending winglets, reducing the normalized winglet height and bending angle is more favorable for loss reduction.

Local Mechanical Modulation-Driven Evagination in Invaginated Epithelia.

Local cells can actively create reverse bending (evagination) in invaginated epithelia, which plays a crucial role in the formation of elaborate organisms. However, the precise physical mechanism driving the evagination remains elusive. Here, we present a three-dimensional vertex model, incorporating the intrinsic cell polarity, to explore the complex morphogenesis induced by local mechanical modulations. We find that invaginated tissues can spontaneously generate local reverse bending due to the shift of the apicobasal polarity. Their exact shapes can be analytically determined by the local apicobasal differential tension and the internal stress. Our continuum theory exhibits three regions in a phase diagram controlled by these two parameters, showing curvature transitions from ordered to disordered states. Additionally, we delve into epithelial curvature transition induced by the nucleus repositioning, revealing its active contribution to the apicobasal force generation. The uncovered mechanical principles could potentially guide more studies on epithelial folding in diverse systems.

20 nm-ultra-thin fluorosiloxane interphase layer enables dendrite-free, fast-charging, and flexible aqueous zinc metal batteries

Dendrite growth of zinc (Zn) anode at high current density severely affects the fast-charging performance of aqueous zinc metal batteries (AZMBs). While interfacial modification strategies can optimize Zn performance, challenges such as complicated preparation processes, excessive layer thicknesses, and high voltage hysteresis should be addressed. Herein, we utilize a cost-effective liquid fluorosiloxane, (3,3,3-trifluoropropyl)trimethoxysilane, for scalable modification of Zn foil via drop-casting at room temperature, resulting in an ultra-thin interphase layer of only 20 nm. The Si-O-Zn bonds formed between fluorosiloxane and Zn ensure interfacial stability, and the Si-O-Si bonds between fluorosiloxane molecules help to homogenize the electric field distribution. Additionally, the abundant highly electronegative fluorine atoms on the anode surface act as zincophilic sites, promoting the uniform deposition of Zn2+. Thus, the modified Zn foil (SiFO-Zn) exhibits excellent dendrite suppression, reduced voltage hysteresis, and prolonged cycle life at ultra-high current density (40 mA/cm2), achieving a cumulative areal capacity of 12.9 Ah/cm2. Further, the full cell assembled with 10 μm-thick SiFO-Zn anode and MnO2 cathode achieves 2600 cycles at 5 A/g with minimal capacity degradation, and a large-size (22.5 cm−2) pouch cell powers the light-emitting diode even after reverse bending, demonstrating the potential of AZMBs for fast-charging flexible devices.

Research on the Hot Straightening Process of Medium-Thick Plates Based on Elastic-Viscoplastic Material Modeling.

With the continuous improvement in the strength of medium-thick plate materials, the hot straightening of plates at high temperatures is increasingly influencing the final defect characteristics of products. In the high-temperature hot straightening process, the temperature and straightening speed of the plate significantly influence its intrinsic material properties, which, in turn, affect the straightening characteristics of the plate. However, most current material models used in the straightening process do not consider the relationship between temperature and strain rate, which leads to an inaccurate characterization of the actual material structure. Additionally, the continuous reverse bending mechanics model for straightening does not account for the impact of different bending strain rates on the bending characteristics of the plate in the thickness direction. In this study, a numerical calculation method was employed to investigate the evolution process of stress and curvature in the roll-type hot straightening process of medium-thick plates. Experimental data and mathematical methods were utilized to develop a viscous plastic material model that accounted for temperature and strain rate. Furthermore, a cross-sectional continuous reverse bending model was established, taking into account the temperature and straightening speed, enabling a reasonable interpretation of the mechanical parameter behaviors of medium-thick plates during high-temperature straightening.

Bending and reverse bending during the fabrication of novel GaAs/(In,Ga)As/GaAs core–shell nanowires monitored by in situ x-ray diffraction

We report on the fabrication of a novel design of GaAs/(In,Ga)As/GaAs radial nanowire heterostructures on a Si 111 substrate, where, for the first time, the growth of inhomogeneous shells on a lattice mismatched core results in straight nanowires instead of bent. Nanowire bending caused by axial tensile strain induced by the (In,Ga)As shell on the GaAs core is reversed by axial compressive strain caused by the GaAs outer shell on the (In,Ga)As shell. Progressive nanowire bending and reverse bending in addition to the axial strain evolution during the two processes are accessed by in situ by x-ray diffraction. The diameter of the core, thicknesses of the shells, as well as the indium concentration and distribution within the (In,Ga)As quantum well are revealed by 2D energy dispersive x-ray spectroscopy using a transmission electron microscope. Shell(s) growth on one side of the core without substrate rotation results in planar-like radial heterostructures in the form of free standing straight nanowires.

Single-Material Solvent-Driven Polydimethylsiloxane Sponge Bending Actuators.

Soft robots mimic the agility of living organisms without rigid joints and muscles. Continuum bending (CB) is one type of motion living organisms can display. CB can be achieved using pneumatic, electroactive, or thermal actuators prepared by casting an active layer on a passive layer. The corresponding input actuates only the active layer in the assembly resulting in the bending of the structure. These two different layers must be laminated well during manufacturing. However, the formed bilayer can still delaminate later, and the detachment hampers the actuator's reversible, long-time use. An approach to creating a single material bending actuator was previously reported, for which spatial gradient swelling was used. This authentic approach allows a single material to be manufactured as a bending actuator, allowing easy access to such actuators without lamination. In this study, we show spatial porosity differences in the sponges of polydimethylsiloxane (PDMS) (a common material in soft robotics) can be used to create the required anisotropy for bending. The spongy polymers are manufactured through table sugar templates and actuated by (organic) solvent absorption/desorption. This enables some versatility in the mechanical properties, shape, actuation force, and actuation speed. The one-material system's straightforward production and seamless nature are advantageous for reversible and repetitive bending. This simple method can further be developed in hydrogels and polymers for soft robotics and functional materials.

Biobased Inks Based on Cuttlefish Ink and Cellulose Nanofibers for Biodegradable Patterned Soft Actuators.

Soft actuators with stimuli-responsive and reversible deformations have shown great promise in soft robotics. However, some challenges remain in existing actuators, such as the materials involved derived from nonrenewable resources, complex and nonscalable preparation methods, and incapability of complex and programmable deformation. Here, a biobased ink based on cuttlefish ink nanoparticles (CINPs) and cellulose nanofibers (CNFs) was developed, allowing for the preparation of biodegradable patterned actuators by direct ink writing technology. The hybrid CNF/CINP ink displays good rheological properties, allowing it to be accurately printed on a variety of flexible substrates. A bilayer actuator was developed by printing an ink layer on a biodegradable poly(lactic acid) film using extrusion-based 3D printing technology, which exhibits reversible and large bending behavior under the stimuli of humidity and light. Furthermore, programmable and reversible folding and coiling deformations in response to stimuli have been achieved by adjusting the ink patterns. This work offers a fast, scalable, and cost-effective strategy for the development of biodegradable patterned actuators with programmable shape-morphing.

Optimization of boron depletion for boron-doped emitter of N-type TOPCon solar cells

During the preparation of boron-doped emitters for TOPCon solar cells, boron atoms accumulate, forming a boron-rich layer (BRL). Oxidation, during the boron diffusion process, can eliminate the BRL. Prolonged oxidation which forms a SiO2 layer can remove the BRL, also act as a protective mask for the front surface. Nevertheless, during high-temperature thermal oxidation, boron will be redistributed. Boron reaches a higher equilibrium concentration in SiO2 than in the silicon wafer, and the SiO2/Si interface shifts inward during SiO2 formation. Simultaneously, the high temperature during oxidation prompts the boron inside the silicon wafer to diffuse deeper. The dual effects of oxidation and diffusion cause boron to be depleted near the surface of the silicon wafer. Boron depletion leads to a reverse bending of the energy band, which hampers carrier collection and impedes further enhancement of cell power conversion efficiency. In this paper, the oxidation process was mainly adjusted to reduce surface boron depletion, resulting in approximately 0.09%abs. increase in power conversion efficiency compared to pre-optimization.

Super-Flexible Water-Proof Actuators.

Humidity-responsive materials hold broad application prospects in sensing, energy production, and other fields. Particularly, humidity-sensitive, flexibility, and water resistance are pivotal factors in the development of optimized humidity-responsive materials. In this study, hydrophobic linear polyurethane and hydrophilic 4-vinylphenylboronic acid (4-VPBA) form a semi-intercross cross-linking network. This copolymer of polyurethane exhibits excellent humidity-sensitive, mechanical properties, and water resistance. Its maximum tensile strength and maximum elongation can reach 40.56MPa and 543.47%, respectively. After being immersed in water at various temperatures for 15 days, it exhibited a swelling ratio of only 3.28% in water at 5°C and 9.58% in water at 70°C. While the presence of 4-VPBA network imparts humidity-sensitive, reversible, and multidirectional bending abilities, under the stimulus of water vapor, it can bend 43° within 1.4s. The demonstrated material surpasses current bidirectional humidity actuators in actuating ability. Based on these characteristics, automatically opening waterproof umbrellas and windows, as well as bionic-arms, crawling robots, and self-propelled boats, are successfully developed.

Light- and Solvent-Responsive Bilayer Hydrogel Actuators with Reversible Bending Behaviors.

Light-responsive hydrogel systems have gained significant attention due to their unique ability to undergo controlled and reversible swelling behavior in response to light stimuli. Combining light-responsive hydrogels with nonresponsive polymers offers a unique self-folding feature that can be used in soft robotic actuator designs. However, simple formulation of such systems with rapid response time is still a challenging task. Herein, we demonstrate a simple but versatile bilayer polymeric design combining light-responsive spiropyran-polyacrylamide (SP-PAAm) with polyacrylamide (PAAm) hydrogels. The photochromic spiropyran in our polymer design is a closed-ring, hydrophobic compound and turns into an open-ring, hydrophilic merocyanine isomer under light irradiation. The swelling degree of SP-PAAm and PAAm hydrogels was evaluated using LED lights with different wavelengths and solvent media (e.g., water, ethanol, DMF, and DMSO). We observed that SP-PAAm hydrogels reached a swelling ratio of ∼370% with the illumination of the blue LED in the DMF medium. By combining light-responsive SP-PAAm hydrogels with nonresponsive PAAm, a proof-of-concept demonstration was performed to demonstrate the applicability of our fabricated platforms. Although fabricated one-armed bilayer hydrogels possessed self-folding ability with a folding angle of ∼40° in 30 min, the four-armed bilayer platforms demonstrated more efficient and rapid folding behavior and reached a folding angle of ∼75° in ∼15 min. Given their simplicity and efficiency, we believe that such polymeric designs may offer new avenues for the fields of polymeric actuators and soft robotic systems.

Effects of the yaw error and the fault conditions on the dynamic characteristics of the 15 MW offshore semi-submersible wind turbine

The floating offshore wind turbines (FOWTs) have a higher failure rate compared to onshore wind turbines, which could lead to aerodynamic imbalance on the floating systems. In addition, yaw error presents an inevitable challenge for FOWTs. This study aims to investigate the effects of the yaw error and the fault conditions on the dynamic properties of the IEA 15 MW semi-submersible FOWT using OpenFAST. The fault conditions involve blade seize without shutdown, blade seize with shutdown and grid loss. The platform motions and structure loads under different yaw errors (−20°, −8°, 0°, 8°, 20°) for different fault conditions were investigated. The dynamic response resulting from the fault was compared with the normal condition. Moreover, the optimal yaw angle under fault conditions was investigated in this paper. The results revealed that the fault shutdown conditions significantly impact the motions and loads of the wind turbine, with substantial reverse tower top and base bending moments. The yaw error, conversely, has less effect on the motions of the wind turbine, but can ameliorate the transient effect in the fault shutdown conditions. Additionally, it is recommended to operate the wind turbine at a yaw angle of 25–30° for wind speeds greater than 12 m/s.