Search

Copyright of Automobile Technology & Material is the property of Automobile Technology & Material Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Hydroforming is a modern metal-forming process prominently used in the shipbuilding, aerospace, and automotive industries for forming lightweight, complex-shaped geometries due to their inherent process benefits. But this process faces challenges such as limited material selection, high tooling costs, and complex process control for obtaining a defect-free part with uniform thickness. Researchers are constantly innovating and advancing hydroforming technologies to overcome these limitations. This work reviews emerging tube and sheet hydroforming technologies, considering parametric effects and design considerations, particularly for micro-domain applications. Further, a wider acceptance of the hydroforming process in different industries is explored by discussing the studies that tried to improve the efficiency and quality of the hydroforming process. This study observed that better formability could be achieved in hydroforming with appropriate intermediate heat treatment, proper lubrication, the correct design of loading paths, and temperature distribution. In tube hydroforming, wrinkles, necking, and cracking observed to be largely reduced by properly selecting the internal pressure and feeding. The precise protrusion height and uniform thickness at different joint cross-sections in tube forming are found to be significantly influenced by the strain-hardening exponent, loading path, and friction coefficient. Electrohydraulic forming is found being increasingly used due to its higher productivity and lower product cost. However, further research is required to achieve complex sheet geometries with sharp corners. This research emphasizes that advanced research, artificial intelligence integration, and the exploration of alternative materials can improve the performance of the hydroforming process. [ABSTRACT FROM AUTHOR]

This paper presents an asymptotic two-dimensional (2D) finite-deformation theory for a thin magnetoelastic sheet starting from a three-dimensional (3D) variational form. This theory is used to model wrinkling phenomena under applied traction and external magnetic field. The resulting 2D potential energy is specialized to an isotropic, in compressible material, and the expressions for material constants, i.e., elasticity tensor, magnetoelastic coupling constant, and permeability, are obtained as a function of the applied magnetic field. The formulation is further simplified assuming reflection symmetry about the mid-surface of the sheet. Strong form of the resulting 2D governing equations are obtained by setting the first variation of potential energy functional to zero. The resulting governing equations are used to analyze wrinkling in a stretched rectangular sheet placed in a uniform magnetic field. Approximate analytical solutions are obtained by linearizing the 2D plate equation for small slopes. The effect of magnetic field and applied stretch on onset of wrinkling and amplitude of wrinkles is studied. [ABSTRACT FROM AUTHOR]

Honeycombs are commonly used as core materials in sandwich panels, and the core geometry significantly impacts the bending behaviour of these structures. Understanding how core characteristics influence the mechanical properties of sandwich panels is essential. The comparison between different honeycomb sandwich panel configurations is quite complex. This study delves into the intricate comparison between various honeycomb sandwich panel configurations, serving as a benchmark for integral 3D printed panels featuring hexagonal cores in both L- and W-directions, and circular cores. Notably, wrinkling phenomena are observed in the L-direction of the hexagonal cores. Circular cell panels exhibit increased load capacity, flexural modulus, and toughness. Additionally, hexagonal L-core panels demonstrate a higher toughness modulus than their W-core counterparts, making them less rigid yet stronger. Furthermore, L-cell core panels possess a lower density than circular cores, whereas W-cell cores exhibit higher density, compromising their specific mechanical properties. [ABSTRACT FROM AUTHOR]

Wrinkling is a typical failure mode of sandwich structures with thin skins, where the bending deformation of face skins occurs simultaneously in conjunction with transverse stretching deformation of core layer. To analyze the three-dimensional (3D) deformation of wrinkling, a model is required to possess a capability describing completely different deformations at each ply. Therefore, by utilizing the Chebyshev polynomial at each layer of sandwich panels, this paper focuses on proposing a higher-order model to individually illustrate deformations of the skins and the core. By means of the proposed model, a refined triangular element has been constructed. By analyzing the stability of a sandwich plate without stiffeners, the finite-element formulation has been verified by comparing it to the quasi-3D elasticity solutions. In addition, it is anticipated that wrinkling failure can be effectively restrained by designing the stiffener layout. To this end, the influence of stiffener layouts on wrinkling behaviors of sandwich plates has been investigated in detail, and it is found that the capability of resisting the wrinkling deformation can be obviously improved by designing reasonable stiffener layouts. Moreover, the translation between buckling and wrinkling behaviors of sandwich panels with different stiffeners has been also explored, which can help to better understand wrinkling deformation mechanism. In summary, the proposed model can be used to design a reasonable arrangement of stiffeners to resist the wrinkling failure of sandwich panels. [ABSTRACT FROM AUTHOR]

Ironing roll is vital equipment in the production of wide aluminum foil, which has a significant impact on the wrinkling defects of aluminum foil during the winding process of the cleaning production line. In this paper, wrinkling defects in 4N6 aluminum foils were improved using the ABAQUS finite element software 2020. A dynamic simulation model of the aluminum foil winding process was established. The ethics model first analyzed the causes of wrinkling during the aluminum foil coiling process. Then the influence of each factor on aluminum foil wrinkling was studied for the effect of ironing pressure, ironing roll deviation, the friction coefficient between the ironing roll and the aluminum foil, and the shape of the ironing roll on the wrinkling of the aluminum foil. The friction coefficients between aluminum foil coils and the uneven distribution of coiling tension have different effects on the wrinkling of aluminum foil. By selecting the optimal process parameters, it is possible to improve the forming quality of the aluminum foil sheet and to reduce the wrinkling faults in the winding process. [ABSTRACT FROM AUTHOR]

Abstract Hydroforming is a modern metal-forming process prominently used in the shipbuilding, aerospace, and automotive industries for forming lightweight, complex-shaped geometries due to their inherent process benefits. But this process faces challenges such as limited material selection, high tooling costs, and complex process control for obtaining a defect-free part with uniform thickness. Researchers are constantly innovating and advancing hydroforming technologies to overcome these limitations. This work reviews emerging tube and sheet hydroforming technologies, considering parametric effects and design considerations, particularly for micro-domain applications. Further, a wider acceptance of the hydroforming process in different industries is explored by discussing the studies that tried to improve the efficiency and quality of the hydroforming process. This study observed that better formability could be achieved in hydroforming with appropriate intermediate heat treatment, proper lubrication, the correct design of loading paths, and temperature distribution. In tube hydroforming, wrinkles, necking, and cracking observed to be largely reduced by properly selecting the internal pressure and feeding. The precise protrusion height and uniform thickness at different joint cross-sections in tube forming are found to be significantly influenced by the strain-hardening exponent, loading path, and friction coefficient. Electrohydraulic forming is found being increasingly used due to its higher productivity and lower product cost. However, further research is required to achieve complex sheet geometries with sharp corners. This research emphasizes that advanced research, artificial intelligence integration, and the exploration of alternative materials can improve the performance of the hydroforming process.

The duality between deformations of elastic bodies and noninertial flows in viscous liquids has been a guiding principle in decades of research. However, this duality is broken when a spheroidal or other doubly curved liquid film is suddenly forced out of mechanical equilibrium, as occurs, e.g., when the pressure inside a liquid bubble drops rapidly due to rupture or controlled evacuation. In such cases, the film may evolve through a noninertial yet geometrically nonlinear surface dynamics, which has remained largely unexplored. We reveal the driver of such dynamics as temporal variations in the curvature of the evolving surface. Focusing on the prototypical example of a floating bubble that undergoes rapid depressurization, we show that the bubble surface evolves via a topological instability and a subsequent front propagation, whereby a small planar zone that includes a singular flow structure, analogous to a disclination in elastic systems, nucleates spontaneously and expands in the spherically shaped film. This flow pattern brings about hoop compression and triggers another, symmetrybreaking instability to the formation of radial wrinkles that invade the flattening film. Our analysis reveals the dynamics as a nonequilibrium branch of "jellium" physics, whereby a rate-of-change of surface curvature in a viscous film is akin to charge in an electrostatic medium that comprises polarizable and conducting domains. We explain key features underlying recent experiments and highlight a qualitative inconsistency between the prediction of linear stability analysis and the observed "wavelength" of surface wrinkles. [ABSTRACT FROM AUTHOR]

Wrinkles are detrimental to the performance of composite components. The prediction of wrinkling during forming is challenging because of complex material interactions. Current computational modeling methods are capable of wrinkle prediction but only for one given set of parameters per simulation cycle. To improve the prediction of wrinkles, this article presents a theory that correlates wrinkle formation with factors such as composite layup and part dimension. This theory allows one to perform design of experiments for physical or virtual forming tests and obtain binomial probability distributions capable of wrinkle prediction. The theory is validated with forming experiment data and demonstrates its potential in wrinkle prediction. [ABSTRACT FROM AUTHOR]

A comprehensive modeling framework for the thermoforming of polymer matrix woven laminate composite was developed. Two numerical indicators, the slip path length and traction magnitude, have been identified to be positively correlated to matrix smearing and wrinkling defects. The material model has been calibrated with picture-frame experimental results, and the prediction accuracy for intra-ply shear and thickness distribution was examined with measurements of the physically formed parts. Specifically, thickness prediction for most locations on the formed parts was accurate within an 11.6% error margin. However, at two points with significant intra-ply shear, the prediction errors increased to around 20%. Finally, a parametric study was conducted to determine the relationship between various process parameters and the quality of the formed part. For the trapezoidal part, orienting the laminate at 45 degrees to the mold axis reduces the likelihood of matrix smear and wrinkling defects. Although this laminate orientation yielded a greater spatial variation in part thickness, the thickness deviation is lower than that for the 0-degree orientation case. Two forming analyses were conducted with ramp rates of 25 mm/s and 80 mm/s to match the equipment's operational limits. It was observed that higher forming rates led to a greater likelihood of defects, as evidenced by a 15% and 10% increase in the formed part areas with longer slip paths and higher traction magnitudes, respectively. It was discovered that shallower molds benefit from faster ramp rates, while deeper molds require slower rates to manage extensive shearing, stretching and bending. Faster forming rates lead to smaller thickness increases at high intra-ply shear regions, indicating a shift from intra-ply shear to out-of-plane bending due to the visco-plastic effect of the molten laminate and can negatively impact part quality. Lastly, it was shown that a well-conceived strategy using darts could improve the part quality by reducing the magnitude of the defect indicators. [ABSTRACT FROM AUTHOR]

The tube hydroforging process (THFG) is an advanced technology for manufacturing tubular components with complex cross-sections. The positive-curvature arc is one of the most fundamental and difficult-to-form features of complex cross-sections. However, its wrinkling mechanism in the THFG process cannot be explained by the existing theory. This restricts the application of the technology. First, because of the bending deformation caused by the excessive circumferential force, compression instability occurs at the positive-curvature arc part. This results in wrinkling similar to that in the conventional linear part. In addition, owing to the existence of the positive-curvature arc, the circumferential force produces a component force along the vertical direction that causes rigid displacement of the materials. This yields another new instability model: motion instability. The corresponding critical pressures for the two instability models were determined by adopting static method and energy methods respectively. Theoretically, motion instability is dominant in the early stages of compression, whereas compression instability is dominant in the subsequent stages. However, considering actual production, the correlations between the critical pressures of the different parts were compared. The wrinkling of the linear part inhibits the occurrence of compression instability in the positive-curvature arc. Thus, wrinkling of the arc can be caused only by motion instability. Therefore, the critical pressure for motion instability is defined as the critical pressure required for the positive-curvature arc. In addition, a forming window that considers the critical pressure of each part was established successfully. [ABSTRACT FROM AUTHOR]

This study looks into the development of wrinkles in a bilayer fused deposition modeling (FDM)‐printed system. The specimen is composed of two polymeric materials (ABS and TPU) to emphasize the difference in stiffness between the two layers, i.e., the film and the substrate. The specimen production process allows to take into account a variety of printing parameters, including infill density, the number of film layers, and printing orientation. During the experimental stage, a distributed compressive force is applied to the specimens, which are confined so as to avoid out‐of‐plane instabilities, allowing wrinkles to form. The research shows that surface instabilities can develop in the surface film depending on the stiffness mismatch and resulting in variations in the wrinkles' magnitude and wavelength during compression. Furthermore, the study observes the transition from wrinkles to folds (creases). The results of this study are a step forward in explaining the mechanisms that govern surface instabilities and promoting advanced application in future research. In fact, understanding the formation of wrinkles in bilayer membranes with a limited stiffness mismatch will allow the development of soft printed matter with adaptable properties that are easily applicable, for instance, in the fields of soft robotics and biomedical engineering. [ABSTRACT FROM AUTHOR]

Background: To evaluate the efficacy and safety of stromal vascular fraction (SVF), platelet rich plasma (PRP), and 1064‐nm Q‐switched Nd:YAG laser in reducing nanofat treated dark circles and wrinkles under the eyes. Method: This study was a single‐blinded randomized clinical trial conducted on patients with suborbital darkening under the eyes that randomly divided into control and case groups. In the control group, 15 patients were treated with one session of nanofat injection only, and five patients of each intervention groups received one session of nanofat+SVF injection, nanofat+PRP injection, and nanofat injection+Nd:YAG laser, respectively. Assessments methods were (1) evaluation of the degree of darkness and repair under the eyes by a blinded dermatologist based on clinical photographs, (2) investigating patient satisfaction, (3) using biometric variables for color, thickness, and density of the skin (only 3 months after the treatment), and (4) recording the possible adverse effects. Conclusion: In terms of the extent of reduction in the intensity of darkness under the eyes, the combined treatment of nanofat injection together with SVF, PRP, and Nd:YAG laser had a much greater therapeutic effect than nanofat injection alone. In all three groups of combined treatments, patients were 100% satisfied. In terms of biometric variables, amount of changes in colorimeter, complete and dermal thickness, complete and dermal density, between the different groups was statistically significant. The use of combined treatments including nanofat with SVF injection, PRP, and 1064 Q‐switched Nd:YAG laser may be more effective than nanofat alone, in reducing infraorbital dark circles and wrinkles. [ABSTRACT FROM AUTHOR]

AbstractSandwich structures are susceptible to wrinkling when subject to in-plane compressive loads, which threatens structural safety. To accurately investigate the failure behavior, the following work is to be required. Firstly, the wrinkling behavior of sandwich plates is a typical three-dimensional (3D) issue. To consider a 3D effect, an enhanced higher-order finite element formulation including transverse normal strain has been proposed for the first time. Utilizing the proposed finite element formulation, a refined quadrilateral element model has been constructed. Secondly, the buckling and wrinkling behaviors of square sandwich plates have been investigated. The performance of the proposed model has been evaluated by comparing it with the quasi-3D solutions, the results obtained from the 3D finite element method (3D-FEM), and other models. The differences between the buckling and wrinkling failure behaviors have been carefully explained. Thirdly, the effects of boundary conditions on buckling and wrinkling deformation have been explored in detail. By utilizing the proposed model, the translation mechanism between the buckling and wrinkling deformations of sandwich plates under different boundary conditions has been revealed, which can help other investigators to well understand the buckling and wrinkling behaviors of sandwich plates. It can be shown that the wrinkling behaviors of thick sandwich plates occur earlier than the buckling behaviors when the thickness ratio of core to face panel is more than 35. Besides, it also can be shown that the buckling and wrinkling loads decrease gradually with the relaxation of the boundary restriction. [ABSTRACT FROM AUTHOR]

Existing studies on wrinkling, an instability phenomenon commonly observed on electro-active polymers (EAP), have largely ignored the unequal-biaxial taut states, focusing instead on the equal-biaxial deformations of such a material class. EAP-based soft actuators, primarily used in soft robotics, frequently exhibit a variety of instabilities, which may adversely affect their functioning and trigger device failure. Conversely, wrinkles can be utilized proactively in specific applications that necessitate an intentional transformation in surface morphology along with functional particle reinforcement on EAP composites. The dielectric elastomer is a promising EAP material class for the same, often filled with functional particles to improve its electromechanical performance. This paper theoretically develops a continuum physics-based unequal-biaxial deformation model incorporating the classical tension field theory to predict the thresholds on the taut domains in the plane of principal stretches. The model solution ties an unanswered ideal remark on the deviations of taut states with the biaxiality ratio of unequal-biaxially deformed wrinkle appearance in EAP composites. The proposed model solution may aid in designing next-generation soft robotic systems by offering guidelines for the wrinkling control of EAP composites. [ABSTRACT FROM AUTHOR]

Tunable electromagnetic (EM) metamaterials have received significant attention due to their compelling advantages of integration and minimization compared with conventional bulky devices. Meanwhile, mechanically reconfigurable metamaterials have witnessed a striving period over recent years due to their simplified structural composition and confined modulation capabilities. Here, a controllable‐wrinkling‐based reconfiguration method is proposed to design split‐ring resonant units with dynamic transmittance spectra by switching between planar and wrinkling morphologies. For the linear polarized incidence, the geometries of planar and wrinkled units are optimized to achieve on‐demanded manipulation of the phases and amplitudes, respectively. By simultaneously implementing the amplitude design and the phase gradient, the mechanically inspired metamaterial is engineered to display a near‐field and a holographic image. For circularly polarized incidences, the spin‐decoupled phases and chiral effects demonstrated in the planar and wrinkled state assist in designing a metamaterial to possess spin‐multiplexed and strain‐modulated fourfold displays. These results demonstrate the practical feasibility of the wrinkling method in engineering tunable metamaterials, and the design flexibility, as well as the mechanical strategy, can extend the potential toward the application scenarios such as information processing, sensing, imaging, flexible meta‐devices, etc. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Dalian Polytechnic University is the property of Journal of Dalian Polytechnic University Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This article discusses a numerical investigation of an extra-deep drawing process using industrial parameters. The study focuses on the formability analysis and process optimization of the drawing process. The authors conducted experiments and simulations to understand the factors that contribute to defects such as rupture and wrinkling in the manufacturing process. They used numerical modeling and measurements to analyze the behavior of the materials and optimize the process parameters. The study provides valuable insights for manufacturers in various industries, including household appliances and automobile construction, to improve the quality and competitiveness of their products. Additionally, there is a document that provides a list of references cited in a research paper on the behavior and processes of deep drawing sheet metal. The references cover various aspects of deep drawing, such as material limits, thinning, wrinkling, spring-back, cracking prevention, lubricants, tribological behavior, and optimization of process parameters. This comprehensive list of sources can be explored by library patrons for further information on these topics. [Extracted from the article]

Objective: Platelet‐rich plasma (PRP) is recognized as a safe and effective therapy for regenerative skin healing and rejuvenation, utilizing autologous blood enriched with various growth factors. This review aims to assess the efficacy of PRP treatments for skin rejuvenation. Methods: Keywords such as "platelet‐rich plasma," "rejuvenation," "skin aging," and "wrinkles" were queried on Ovid, PubMed, and MEDLINE to identify pertinent studies on PRP treatment for skin rejuvenation. Results: Analysis revealed that PRP treatment led to significant enhancements in multiple facial parameters after one to three sessions. Improvements were noted in skin pore size, texture, wrinkle reduction, pigmented spots, collagen density, hyaluronic acid levels, and protection against ultraviolet damage. Combining PRP with hyaluronic acid demonstrated a synergistic effect, particularly enhancing skin elasticity in patients with lower body mass index and firmness in individuals aged 50s and 60s. Incorporating both physical and biometric data for assessment proved superior to relying solely on physical observations for evaluating subtle skin quality and structural changes. Conclusion: This study underscores the efficacy of PRP monotherapy for skin rejuvenation and emphasizes the necessity of standardizing PRP preparation protocols in future investigations. Heightened awareness and advancements in technology have contributed to the emergence of higher‐quality, less biased studies supporting PRP as a reliable and safe therapeutic option for skin rejuvenation. [ABSTRACT FROM AUTHOR]

The process of tube nosing is a delicate art that involves forming the end of a tubular part without causing any collapse, buckling, or wrinkling. A recent study has delved into the different modes of failure that can occur during this process and has determined the limits of tube nosing through the use of plasticity and thin/thick-walled tube theories. A finite element simulation was developed to replicate the cold-nosing process using conical dies to validate these theories. The results were compared to experimental outcomes for mild steel, hard steel, and annealed aluminium tubes to ensure accuracy. Through this analysis, we identified and confirmed the modes of failure that can restrict the plastic deformation for the tube nosing process. The outcomes were compared to analytical expressions and showed excellent agreement with the experiments, proving that these expressions provide a reliable reference guide for predicting the limits of the tube-nosing process. The FE simulation method also accurately models critical buckling stresses, nosing loads, and failure modes. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) nanoplatelets can be used to reinforce neat resin or the matrix phase of fiber composites for improved mechanical properties. Although the oxygen content levels in GO and reduced graphene oxide (rGO) strongly influence the interface with the polymer, experimental-based optimization of the oxygen content for enhanced composite properties is difficult and time-consuming. Fortunately, molecular dynamics (MD) simulation can be used to efficiently predict the interfacial properties of composite on the molecular level and provide physical insight into the effect of the oxygen content of rGO. In this study, MD is used to predict the elastic properties of rGO/epoxy interfaces and the corresponding interfacial shear strength (IFSS) for different oxygen content levels. The results indicate that increasing levels of oxygen in rGO results in interfaces with a reduced in-plane elastic modulus but a substantially higher IFSS. These results are important for the design of rGO/epoxy composites for specific engineering applications. [ABSTRACT FROM AUTHOR]

In the deep drawing process of sheet metals, lack of formability and the defects generated as a consequence of friction are two main limiting factors. Using ultrasonic vibration is an impressive way to decrease these limitations. In this paper, the ultrasonic – aided deep drawing process with a novel way of applying radial ultrasonic vibration is presented. The novelty of the presented method is using the bending mode of vibration in the sheet metal and the die using radial ultrasonic vibration. The presented method, contrary to the other techniques of applying ultrasonic vibration, has shown much fewer resonance frequency variations by changing the sheet metal geometry during the process and likewise with a variation of the clearance between the blank holder and the die. For this purpose, the finite element method was used in designing the equipment for the deep drawing process. The experimental test was done on St12 in the presence and absence of ultrasonic vibration. The effect of ultrasonic vibration in the presented method on the wrinkling and thinning defects and likewise the forming forces were experimentally studied. The results indicated the high efficiency of the presenting method in decreasing both the forming forces and the wrinkling and thinning defects. About a 42.3% decrease in the forming forces and a 4.4% decrease in the thinning effect were achieved by applying ultrasonic vibration. [ABSTRACT FROM AUTHOR]

In this work, the formability of copper foils was analyzed based on a series of multi-step micro deep drawing (MMDD) tests. The copper foils were annealed at temperatures ranging from 300 to 700 °C for 5 min, followed by tensile tests and electron backscatter diffraction (EBSD) tests for the exploration of mechanical behavior and microstructural characterization of annealed specimens. The results show that the as-received copper foils exhibit poor formability and cannot form micro cups during MMDD. When the annealing temperature attains 500 °C, a homogeneous microstructure was formed inside copper foils, enhancing the formability of materials and improving the surface quality of formed products. Nevertheless, both the elongation and tensile strength decrease dramatically due to the easy occurrence of incoordination deformation in coarse grain bands with further increase in annealing temperature to 700 °C. Consequently, marked wrinkling is generated on the surface of drawn cups and obvious thinning occurs at the nose radius region due to metal flow. In addition, the results show that the E texture component within the copper foils is favorable for MMDD. Overall, an optimal annealing temperature of 500 °C is obtained with improved formability of copper foils and forming quality of drawn cups.

Ironing roll is vital equipment in the production of wide aluminum foil, which has a significant impact on the wrinkling defects of aluminum foil during the winding process of the cleaning production line. In this paper, wrinkling defects in 4N6 aluminum foils were improved using the ABAQUS finite element software 2020. A dynamic simulation model of the aluminum foil winding process was established. The ethics model first analyzed the causes of wrinkling during the aluminum foil coiling process. Then the influence of each factor on aluminum foil wrinkling was studied for the effect of ironing pressure, ironing roll deviation, the friction coefficient between the ironing roll and the aluminum foil, and the shape of the ironing roll on the wrinkling of the aluminum foil. The friction coefficients between aluminum foil coils and the uneven distribution of coiling tension have different effects on the wrinkling of aluminum foil. By selecting the optimal process parameters, it is possible to improve the forming quality of the aluminum foil sheet and to reduce the wrinkling faults in the winding process.

Copyright of Steel Pipe is the property of Steel Pipe Magazine and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chinese Journal of Computational Mechanics / Jisuan Lixue Xuebao is the property of Chinese Journal of Computational Mechanics Editorial Office, Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Liquid crystal elastomers (LCEs) are becoming increasingly popular as a shape memory material for soft robot actuators that operate in a contractile or flexural mode. There have been previously studies on the use of LCEs for reversible changes in surface topography. However, surface protrusions have typically been limited to the order of 1 μm or depend on light, heat, or electrical stimulation that are difficult to locally control or require relatively high voltage. This article presents a novel operation mode of LCE actuators based on the wrinkling behavior of an LCE‐elastomer bilayer architecture. Embedding a liquid‐metal‐based conductive ink within the LCE enables electrical control of surface wrinkling through Joule heating. The actuator cells can generate wrinkles with amplitudes ranging from 17 to 45 μm within 30 s under an input power of 2 W and a voltage on the order of 1 V. As the bilayer is composed entirely of soft materials, it is highly deformable, flexible, and can be integrated into a multi‐cell array capable of bending on curved surfaces. [ABSTRACT FROM AUTHOR]

Thin film structures will be wrinkled due to buckling deformation under the influence of compressive stress. The wrinkle and tension states of the thin film can be changed by introducing microstructures. So we introduce rigid elements on the thin film to suppress the wrinkling behavior of the thin film, and propose a method to calculate the optimal distribution position of the rigid elements on the thin film. Using this method, the optimal distribution positions of the square rigid elements on the biaxially stretched square thin film were calculated, and the effectiveness of introducing rigid elements on the thin film to suppress the wrinkle was verified through numerical simulation and experimental research. The results show that the wrinkling behaviour of the film can be effectively suppressed by placing rigid elements at the optimal position obtained by the method proposed to this paper. Our findings could provide new design ideas for thin-film antenna structures in aerospace engineering. [ABSTRACT FROM AUTHOR]

In this study, we investigated toroidal shell wrinkling in free hydroforming. We specifically focused on toroidal shells with a regular hexagonal cross-section. Membrane theory was used to examine the distribution of stress and yield load in both preform and toroidal shells. The wrinkling moment was then predicted using an empirical formula of shell buckling. In addition, the wrinkling state was investigated using a general statics method, and the free hydroforming of toroidal shells was simulated using the Riks method. Subsequently, nonlinear buckling and equilibrium paths were analyzed. A toroidal preform was manufactured, and free hydroforming experiments were conducted. Overall, the experimental results confirmed the accuracy of the theoretical predictions and numerical simulations. This indicates that the prediction method used in the study was effective. We also found that wrinkling occurs during hydroforming in the inner region of toroidal shells due to compressive stress. Consequently, we improved the structure of the toroidal shells and performed analytical calculations and numerical simulations for the analysis. Our results indicate that wrinkling can be eliminated by increasing the number of segments on the inner side of toroidal preforms, thereby improving the quality of toroidal shells. [ABSTRACT FROM AUTHOR]

We consider a class of models motivated by previous numerical studies of wrinkling in highly stretched, thin rectangular elastomer sheets. The model is characterized by a finite-strain hyperelastic membrane energy perturbed by small bending energy. In the absence of the latter, the membrane energy density is not rank-one convex for general spatial deformations but reduces to a polyconvex function when restricted to planar deformations, i.e., two-dimensional hyperelasticity. In addition, it grows unbounded as the local area ratio approaches zero. The small bending component of the model is the same as that in the classical von Kármán model. The latter penalizes arbitrarily fine-scale wrinkling, resolving both the amplitude and wavelength of wrinkles. Here, we prove the existence of energy minima for a general class of such models. [ABSTRACT FROM AUTHOR]

In-plane shear deformation is a highly important mechanic that controls the formation of wrinkles during the forming of textile composites. This paper presents two computational formulations that describe the in-plane shear behavior of woven thermoset prepreg fabric. The bias-extension characterization test was used to validate the computational models. One of the two computational models presented is based on linear visco-elasticity and the other is based on visco-hyperelasticity. The comparison of simulation and experiments shows that a visco-hyperelastic model is necessary to accurately capture the behavior of woven composite prepregs. This paper also compares the experimental measurements with calculations based on the pin-jointed net theory to develop a criterion that helps to determine the range of the bias-extension experiment data that can be used to validate and calibrate computational models. [ABSTRACT FROM AUTHOR]

Wrinkles in flat graded elastic layers have been recently described as a time-varying Hamiltonian system by the energy method. Cylindrical core/shell structures can also undergo surface instabilities under the external pressure. In this study, we show that by treating the radial direction as a pseudo-time variable, the graded core/shell system with radially decaying elastic properties can also be described within the symplectic framework. In combination with the shell buckling equation, the present paper addresses the surface wrinkling of graded core/shell structures subjected to the uniform external pressure by solving a series of ordinary differential equations with varying coefficients. Three representative gradient distributions are showcased, and the predicted critical pressure and critical wave number are verified by finite element simulations. The symplectic framework provides an efficient and accurate approach to understand the surface instability and morphological evolution in curved biological tissues and engineered structures. [ABSTRACT FROM AUTHOR]

In this paper, we are interested in the one-dimensional singular optimization problem with constraints:... In the first part of the paper, we show the existence of a critical value d* > 0 such that if d ≤ d*, J admits a minimum in a carefully chosen closed convex set of W1;p0 (-1; 1). The second part of the paper is dedicated to numerical simulations. We elaborate a numerical algorithm that transforms our constrained optimization problem into the solution of a system of ordinary differential equations. Illustrative examples are given to verify the efficiency and accuracy of the proposed numerical method to test the relevance of the proposed approach. We point out that the numerical results obtained are in good agreement with the physical phenomenon of pleated graphene in the particular case p = 4 and γ = 9/5 [12]. [ABSTRACT FROM AUTHOR]

Truncated hemisphere parts were press formed with two commercially available unidirectional thermoplastic composite materials, namely Toray TC1225 and Solvay APC. The width and layup of the laminates were varied to influence the wrinkling severity, to trigger various deformation mechanisms and to influence the amount of in-plane deformation. A total of eight layup/width combinations were selected and formed in triplicate for both materials, resulting in the analysis of 48 parts in total. The wrinkling defects are clearly observed due to an intentional gap between the forming tools at the end of forming. Further, a dot pattern with a resolution of 3 mm was applied to the laminates prior to forming using a photoresist mask, sandblasting and heat resistant spray paint. The locations of the dots before and after forming were measured using photogrammetry and are provided in the dataset as a triangular mesh including a precision metric. Matlab functions, bundled with this dataset, allow for the reproduction of the deformation calculations and averages. Lastly, a Matlab App (GUI) is provided for easy visualization of the data. This dataset can serve as a reference for validation of composite forming simulations.

A simple equation modelling an inextensible elastic lining of an inner-lined tube subject to an imposed pressure difference is derived from a consideration of the idealised elastic properties of the lining and the pressure and soft-substrate forces. Two cases are considered in detail, one with prominent wrinkling and a second one in which wrinkling is absent and only buckling remains. Bifurcation diagrams are computed via numerical continuation for both cases. Wrinkling, buckling, folding, and mixed-mode solutions are found and organised according to system-response measures including tension, in-plane compression, maximum curvature and energy. Approximate wrinkle solutions are constructed using weakly nonlinear theory, in excellent agreement with numerics. Our approach explains how the wavelength of the wrinkles is selected as a function of the parameters in compressed wrinkling systems and shows how localised folds and mixed-mode states form in secondary bifurcations from wrinkled states. Our model aims to capture the wrinkling response of arterial endothelium to blood pressure changes but applies much more broadly.

Fine control over the mechanical properties of thin sheets underpins transcytosis, cell shape, and morphogenesis. Applying these principles to artificial, liquid-based systems has led to reconfigurable materials for soft robotics, actuation, and chemical synthesis. However, progress is limited by a lack of synthetic two-dimensional membranes that exhibit tunable mechanical properties over a comparable range to that seen in nature. Here, we show that the bending modulus, B, of thin assemblies of nanoparticle surfactants (NPSs) at the oil-water interface can be varied continuously from sub-kBT to 106kBT, by varying the ligands and particles that comprise the NPS. We find extensive departure from continuum behavior, including enormous mechanical anisotropy and a power law relation between B and the buckling spectrum width. Our findings provide a platform for shape-changing liquid devices and motivate new theories for the description of thin-film wrinkling.

Liquid crystal elastomers (LCEs) are becoming increasingly popular as a shape memory material for soft robot actuators that operate in a contractile or flexural mode. There have been previously studies on the use of LCEs for reversible changes in surface topography. However, surface protrusions have typically been limited to the order of 1 μm or depend on light, heat, or electrical stimulation that are difficult to locally control or require relatively high voltage. This article presents a novel operation mode of LCE actuators based on the wrinkling behavior of an LCE‐elastomer bilayer architecture. Embedding a liquid‐metal‐based conductive ink within the LCE enables electrical control of surface wrinkling through Joule heating. The actuator cells can generate wrinkles with amplitudes ranging from 17 to 45 μm within 30 s under an input power of 2 W and a voltage on the order of 1 V. As the bilayer is composed entirely of soft materials, it is highly deformable, flexible, and can be integrated into a multi‐cell array capable of bending on curved surfaces.

Gradient ultra-low temperature forming is a novel process for improving the forming limit of thin-walled aluminum alloy components. However, it is critical to prevent wrinkling defects through blank holding. It is not clear whether the gradient temperature can meet the deformation requirements for preventing wrinkling defects with draw beads and blank holding. The effects of a draw bead and the blank-holder force on the wrinkling behavior in gradient ultra-low temperature forming of a 7075 aluminum alloy hemispherical shell were investigated experimentally in this study. The wrinkle control mechanism was revealed through stress and strain analyses. The blank-holder force required to prevent wrinkling could be reduced significantly by setting a draw bead. A blank-holder force of 120 kN could be used to form a sound hemispherical specimen with a diameter of 200 mm, which was 31.5% of the force without the draw bead. This benefited from the reduced hoop compressive stress in the unsupported region, which decreased to 165 MPa from 516 MPa. The hemispherical shell formed using gradient ultra-low temperature forming was twice as high as that at room temperature. The deviation in thickness was only 7.2%. Moreover, microstructural observations revealed the reason for this enhanced formability. The uniformly distributed high-density dislocations at ultra-low temperatures significantly improved the strain-hardening ability, thus allowing the deformation to be withstood and transferred. This could prevent splitting of the unsupported region when using a draw bead to prevent wrinkling. This is beneficial for significantly reducing the tonnage requirements, particularly for large-sized thin-walled components, which can expand the application range of gradient ultra-low temperature forming. [ABSTRACT FROM AUTHOR]

Abstract This paper presents analytical solution for wrinkling of thin film bonded to anisotropic substrate by complex function method and linear perturbation analysis, which is verified by FEM. Effect of material parameters along principal axes on critical strain is illustrated. Furthermore, due to effective modulus determined by Voigt assumption, a fiber-reinforced substrate is considered, and results indicate that both Young’s modulus perpendicular to wrinkling direction and in-plane shear modulus have significant influence on wrinkling onset point. The most effective fiber layout in resisting wrinkling is at about 45°inclined to wrinkling direction and arranging at the upper area of the substrate. [ABSTRACT FROM AUTHOR]

The total shear force induced on a profiled sandwich panel by an external load is distributed between the profiled face and core. Sandwich panel with a discrete core material such as mineral wool consists of multiple transverse lamella joints across the full width of the panel, affecting the overall shear performance of the panel as these joints have negligible resistance to shear. Additionally, in some cases the core material is partially bonded only to the lower flange of the profiled face which increase the concentration of stresses in the bonded area leading to the crushing of the core on the support. This work studies the distribution of shear force in mineral wool core sandwich panels with one profiled face utilizing a shear beam test on a specimen cut from the panel including the profiled part. Based on the results and failure modes obtained, this work investigates the behavior and role of the profiled face on the shear resistance of profiled sandwich panels. The distributed shear force between the core and profiled part obtained from the shear beam tests are compared with full‐scale tests suggested by the European Standard EN 14509:2013, thus, exploring the applicability of the devised shear beam test method for assessing the shear properties of profiled sandwich panel. [ABSTRACT FROM AUTHOR]

A new kind of self-organized pattern formation process has been found during laser irradiation of polymer films in water confinement just below the laser ablation threshold, resulting in a randomly oriented pattern with a period of about 475 nm. The morphology, orientation, period, and amplitude of these patterns are inconsistent with both laser-induced periodic surface structures that typically consist of linear grooves with periods smaller the laser wavelength and wrinkling patterns that feature a much larger period and appear at layered systems. Excimer laser (λ = 248 nm, tp = 25 ns) exposure of 650 nm thick photoresist films on silicon wafers cause the growth of irregular submicron patterns. The pattern morphology that is examined with imaging techniques is correlated to processing parameters. The amplitude of these laser-induced self-organized (LISE) submicron structures are strengthened with pulse number and laser fluence. The experimental results are discussed together with simulations of laser heating the photoresist film in water confinement. The proposed pattern formation mechanism of such laser-induced self-organized submicron structures at temporal excitation of a confined polymer surface comprises the formation of an oriented roughness based on LIPSS that are developed to wrinkled structures due to the transient formation of a soft subsurface area that provides conditions for wrinkling of the water cooled, stiff polymer surface by laser-induced stress fields. Size, amplitude, and morphology of the LISE pattern provide good properties for applications in such fields as wetting, friction, optics, and bioactivity. [ABSTRACT FROM AUTHOR]