Large Deformation Range Research Articles

An adhesive, highly stretchable and low-hysteresis alginate-based conductive hydrogel strain sensing system for motion capture

A strain sensor stands as an indispensable tool for capturing intricate motions in various applications, ranging from human motion monitoring to electronic skin and soft robotics. However, existing strain sensors still face difficulties in simultaneously achieving superior sensing performance sufficing for practical applications like high stretchability and low hysteresis, as well as seamless device fabrication like desirable interfacial adhesion and system-level integration. Herein, we develop a highly stretchable and low-hysteresis strain sensor with adhesive poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/polyacrylamide (PAAm)‑sodium alginate (SA) composite hydrogel, allowing the successful construction of a wireless motion capture sensing system that can provide precise data collection within a large deformation range. The resultant composite hydrogel displays favorable interfacial adhesion and robust mechanical stability, and the fabricated strain sensor demonstrates a wide working strain range (up to 500 %) with high sensitivity (gauge factor = 11) and ultra-low hysteresis (1.52 %), outperforming previous PEDOT-based hydrogel strain sensors. Enabled by the intriguing material properties and high sensing performance, we further demonstrate the fabrication and integration of a wireless motion capture sensing system for diverse applications like human motion monitoring, gesture recognition, and interactive communication.

Facial feature point detection under large range of face deformations

Facial Feature Point Detection (FFPD) plays a significant role in several face analysis tasks such as feature extraction and classification. This paper presents a Fully Automatic FFPD system using the application of Random Forest Regression Voting in a Constrained Local Model (RFRV-CLM) framework. A global detector is used to find the approximate positions of the facial region and eye centers. A sequence of local RFRV-CLMs are used to locate a detailed set of points around the facial features. Both global and local models use Random Forest Regression to vote for optimal positions. The system is evaluated in the task of facial expression localization using five different facial expression databases of different characteristics including age, intensity, 6-basic expressions, 22 compound expressions, static and dynamic images, and deliberate and spontaneous expressions. Quantitative results of the evaluation of automatic point localization against manual points (ground truth) demonstrated that the results of the proposed approach are encouraging and outperform the results of alternative techniques tested on the same databases.

Study on dynamics of thin shell elements of composite materials based on absolute nodal coordinate formulation

Most solar panels use composite materials to suit the development objectives of large-scale and lightweight spaceship components, resulting in complex nonlinear dynamic characteristics. When describing the dynamic characteristics of thin shell elements in composite materials, the standard 48-DOF fully parameterized thick plate element based on absolute nodal coordinate formulation cannot accurately account for the coupling between the large range of motion and large deformation of thin shell elements, exposing issues such as shear locking, slow convergence, and low computational efficiency. In this study, the absolute nodal coordinate formulation is used to create the 36-DOF reduced-order composite thin shell element. The strain and strain energy of the thin-shell element are calculated using the Green-Lagrange strain tensor, while the bending deformation energy of the thin shell element is calculated using the exact expression of curvature, based on continuum mechanics theory and the constitutive relation of the composite material. The generalized mass matrix and stiffness matrix are developed, and the nonlinear dynamic model of the thin shell element is established using the virtual work principle, with numerical simulation used to validate the dynamic characteristics. The results reveal that the dynamic characteristics of the 36-DOF reduced-order composite thin shell element are consistent with those of the virtual prototype, confirming the validity of the model. The proposed model not only addresses the element locking issue, but it also creates a more realistic dynamic model and increases simulation accuracy. The findings could serve as a theoretical foundation for satellite solar panel on-orbit operations.

Effect of the Slenderness Relation on In-Plane Deformation in Stack Compression Tests

In forming technologies and their simulation, knowing the flow curve characteristic of the material is an essential parameter. Acquiring this knowledge is particularly challenging for sheet materials in high strain ranges. It is well-known that friction and geometric relationships have a distorting effect on the flow curves, thus compensation is necessary. However, the geometric ratio can not only influence the formation of the flow curve, if our material shows anisotropic behaviour. In our research, using compression tests, we examined the deformation relations of deformed specimens through digital imaging methods. The stack compression test is widely used to determine the flow curve in a broad range of large deformation. During the test, several disk specimens with the same geometric characteristics were stacked on top of each other to form a final test piece, and then compression tests were conducted on these assemblies. We found that at low values of the geometric ratio (0.1 in our study), the proportion of plastic, planar principal strains indicating anisotropic behaviour is greater than at higher geometric ratios (0.5 and 1.0 in our study).

The influence of spark plasma sintering on multiscale mechanical properties of nickel-based composite materials

The paper presents a comprehensive investigation of the influence of the main process parameters of spark plasma sintering on the mechanical and microstructural properties of nickel-silicon carbide composites at various scales. Microstructure analysis performed by scanning and transmission electron microscopy revealed a significant interfacial reaction between nickel and silicon carbide due to the decomposition of silicon carbide. The chemical interaction of the matrix and reinforcement results in the formation of a multicomponent interphase zone formed by silicides (Ni31Si12 or/and Ni3Si) and graphite precipitates. Furthermore, several types of structure defects were observed (mainly nano/micropores at the phase boundaries). These significantly influenced the mechanical response of nickel-silicon carbide composites at different levels. At the macroscopic scale, uniaxial tensile tests confirmed that applying a 1000 °C sintering temperature ensured that the manufactured composite was characterised by satisfactory tensile strength, however, with a considerable reduction of material elongation compared to pure nickel. Moreover, the fractography study allowed us to identify a significant difference in the damage mode for certain nickel-silicon carbide samples. Secondly, the interface of the nickel matrix and silicate interphase was tested by bending with microcantilevers to evaluate its deformation behaviour, strength, and fracture characteristics. It was confirmed that a diffusive kind of interface, such as Ni-NiSi, demonstrates unexpected bonding properties with a relatively large range of plastic deformation. Finally, the nanoindentation of three main components of the nickel-silicon carbide composite was executed to evaluate the evolution of nanohardness, Young's modulus, and elastic recovery due to the application of various spark plasma sintering conditions.

Tough soldering for stretchable electronics by small-molecule modulated interfacial assemblies

The rapid-developing soft robots and wearable devices require flexible conductive materials to maintain electric functions over a large range of deformations. Considerable efforts are made to develop stretchable conductive materials; little attention is paid to the frequent failures of integrated circuits caused by the interface mismatch of soft substrates and rigid silicon-based microelectronics. Here, we present a stretchable solder with good weldability that can strongly bond with electronic components, benefiting from the hierarchical assemblies of liquid metal particles, small-molecule modulators, and non-covalently crosslinked polymer matrix. Our self-solder shows high conductivity (>2×105 S m−1), extreme stretchability (~1000%, and >600% with chip-integrated), and high toughness (~20 MJ m−3). Additionally, the dynamic interactions within our solder’s surface and interior enable a range of unique features, including ease of integration, component substitution, and circuit recyclability. With all these features, we demonstrated an application as thermoforming technology for three-dimensional (3D) conformable electronics, showing potential in reducing the complexity of microchip interfacing, as well as scalable fabrication of chip-integrated stretchable circuits and 3D electronics.

Effect of steel fiber on the permeability of freeze-thaw damaged concrete under splitting tensile and compressive loads

This study investigated the effect of steel fibers on the permeability and mechanical properties of freeze-thaw damaged concrete under splitting tensile and compressive loads. A specially designed permeability apparatus is used to investigate the continuous permeability performance of steel fiber reinforced concrete (SFRC) subjected to loads. Results demonstrated that for the concrete without load, the addition of steel fibers exhibits a negative effect on the impermeability performance of the concrete matrix without freeze-thaw damage. The initial permeability of SFRC specimens is between 81.7 % and 180 % higher than that of NC specimens. The addition of steel fibers shows a positive effect on the impermeability of concrete subjected to freeze-thaw cycles. The permeability of SFRC under loads can be categorized into two stages. In the first stage, the concrete matrix is the main water channel. The addition of steel fiber can effectively increase the maximum radial deformation of the first stage and maintain low permeability of concrete in a large radial deformation range. In the second stage, concrete cracks are the main water channels. Both the addition of steel fibers and freeze-thaw cycles can reduce the permeability of the concrete in the second stage. Furthermore, under compressive load, with the increasing of stress level, the permeability of SFRC exhibits a slowly decreasing trend, this is followed by a significant increasing trend. The addition of steel fibers can maintain low permeability performance in a large stress level range, and as the steel fiber content increases, the permeability at peak load gradually decreases. The strain–permeability curves of SFRC under splitting tensile and compressive loads subjected to freeze-thaw cycles are investigated. The permeability of SFRC gradually increases with the increasing of the number of freeze-thaw cycles when the compressive strain exceeds 0.002. However, the opposite trend is observed under splitting tensile load. Notably, the reduction in concrete permeability due to the steel fibers is more significant under splitting tensile load than that under compressive load. Future work might integrate this research with stress-strain constitutive equations and finite element analysis. This will offer a foundational framework for engineering applications aimed at enhancing the permeability of steel fiber concrete under freeze-thaw conditions.

Nanoconfined polymerization limits crack propagation in hysteresis-free gels.

Consecutive mechanical loading cycles cause irreversible fatigue damage and residual strain in gels, affecting their service life and application scope. Hysteresis-free hydrogels within a limited deformation range have been created by various strategies. However, large deformation and high elasticity are inherently contradictory attributes. Here we present a nanoconfined polymerization strategy for producing tough and near-zero-hysteresis gels under a large range of deformations. Gels are prepared through in situ polymerization within nanochannels of covalent organic frameworks or molecular sieves. The nanochannel confinement and strong hydrogen bonding interactions with polymer segments are crucial for achieving rapid self-reinforcement. The rigid nanostructures relieve the stress concentration at the crack tips and prevent crack propagation, enhancing the ultimate fracture strain (17,580 ± 308%), toughness (87.7 ± 2.3 MJ m-3) and crack propagation strain (5,800%) of the gels. This approach provides a general strategy for synthesizing gels that overcome the traditional trade-offs of large deformation and high elasticity.

Fatigue life and failure mechanism of nylon 66 cord/rubber composites under wide temperature range

This work simulates the real harsh service conditions of Fiber-reinforced polymer composites (FRPC), and the dynamic adhesion and failure mechanism of nylon 66 (PA66)-reinforced natural rubber (NR) composites under large deformation and wide temperature range are deeply studied by comprehensive analysis of the interfacial adhesion evolution, microstructure and failure damage location of the composites, interfacial heating rate, and modulus ratio of PA66/NR. The failure mechanism of PA66/NR composites is interfacial debonding at −20 °C, 25 °C and 80 °C, whereas that at 120 °C is matrix cracks. Interestingly, at −20 °C, the crack expansion at the interface is slow, and the samples show two-stage damage during fatigue, resulting in the highest fatigue life. At 80 °C, the interface heating rate and modulus ratio of the PA66/NR composites is the lowest, and thus the fatigue life is higher than that at 25 °C and 120 °C. Keywords: fiber reinforced polymer composites, fatigue life, failure mechanism.

Design of a variable-diameter wheel with a novel distributed compliant mechanism

Compliant variable-diameter mechanisms enable adaptation of variable-diameter wheels to both road and soft terrain. Conventional compliant variable-diameter mechanisms, in which every wheel-foot is an independent load-bearing structure, rely heavily on rigid-body mechanisms. To overcome the structure restriction and improve their performances, we introduce a novel compliant mechanism in which circumferentially distributed leaf springs or combination springs with large deformation range are used as flexible components. The springs constitute the closed outer ring and the overall load-bearing structure in the wheel. A novel screw transmission mechanism was designed to achieve motions with two degrees of freedom. Based on the geometric relationships, a dimensional design method for the mechanism is proposed. The chained beam-constraint-model and integration methods are introduced to obtain the spring deflections and maximum hub rotation angle. These methods can be used for further design of the transmission mechanism. The wheel design is then verified experimentally. The results indicate that the required design targets were achieved. Thus, the proposed mechanism diversifies the structure type and design of compliant mechanisms and expands the applicability of variable-diameter wheels in mobile platforms.

Advection-enhanced heat and mass transport from neutrally suspended droplet in simple shear flow

Advection-enhanced heat and mass transport from a single droplet neutrally suspended in a simple shear flow has been studied using high-fidelity numerical simulation. The capillary number ranges from 0.01 to 0.5, which encompasses the entire range of small deformation, large deformation, and breakup of the droplets. The Reynolds number is from 0.01 to 1, including regions of both weak and strong advection. The temperature and mass concentration are modeled as the concentration of a passive scalar released at the droplet surface. Two Schmidt numbers, 10 and 100, are considered, for which flow advection plays a role in the transport of passive scalar. For unbroken droplets, the interaction between the carrier fluid and the suspended droplet leads to several different flows around the droplet. The fluid motions together with scalar diffusion constitute a coupled transport mechanism for passive scalar. The dependence of scalar release rate on Reynolds and Peclet numbers can be roughly described by the correlation for a rigid sphere. For broken droplets, the basic flow features around the droplet during the process of elongation and breakup are similar to those of an unbroken droplet. The variation of the scalar release rate can be decomposed into several stages, corresponding to the process of droplet elongation and breakup. The variation of the scalar release rate exhibits a high correlation with the capillary, Reynolds, and Peclet numbers. This suggests that it is feasible to develop an empirical model that incorporates the effects of the number and size distributions of child droplets after breakup.

On a finite strain modeling of growth in budding yeast.

Cell's ability to proliferate constitutes one of the most defining features of life. The proliferation occurs through a succession of events; the cell cycle, whereby the cell grows and divides. In this paper, focus is made on the growth step and we deal specifically with Saccharomyces cerevisiae yeast that reproduces by budding. For this, we develop a theoretical model to predict the growth powered by the turgor pressure. This cell is herein considered as a thin-walled structure with almost axisymmetrical shape. Due to its soft nature, the large deformation range is a priori assumed through a finite growth modeling framework. The used kinematics is based on the multiplicative decomposition of the deformation gradient into an elastically reversible part and a growth part. Constitutive equations are proposed where use is made of hyperelasticity together with a local evolution equation, this latter to describe the way growth takes place. In particular, two essential parameters are involved: a stress-like threshold, and a characteristic time. The developed model is extended to a shell approach as well. In a finite element context, representative numerical simulations examining stress-dependent growth are given and a parametric study is conducted to show the sensitivity with respect to the above mentioned parameters. Finally, a suggestion for natural contractile ring modeling closes this study.

Three-dimensional potential energy surface for fission of 236U within covariant density functional theory* *Supported by the National Natural Science Foundation of China (11875225, 11790325, 11790320), the Special Fund from the China Nuclear Data Center, the Fundamental Research Funds for the Central Universities, and the Fok Ying-Tong Education Foundation

We calculate the three-dimensional potential energy surface (PES) for the fission of the compound nucleus U using covariant density functional theory with constraints on the axial quadrupole and octupole deformations as well as the nucleon number in the neck . By considering the additional degree of freedom , the coexistence of the elongated and compact fission modes is predicted for . Remarkably, the PES becomes shallow across a large range of quadrupole and octupole deformations for small , and consequently, the scission line in the plane extends to a shallow band, leading to fluctuations of several to ten MeV in the estimated total kinetic energies and of several to approximately ten nucleons in the fragment masses.

Uniaxial tensile strain correction of multi-axial warp-knitted fabric

This paper analyzes the error between the theoretical calculated and actual values of single inserting yarn strain of multi-axial warp-knitted fabric under the uniaxial stretching process, and the “open M-shaped curved surface” of error was obtained theoretically. The analysis results show that the error increases with the increase of fabric elongation. The error is smaller in the small deformation range (fabric maximum elongation is 5%) and larger in the large deformation range. In addition, the error is also related to the angle between the single inserting yarn axis and the uniaxial tensile direction. The error varies periodically with the angle ([Formula: see text]), reaching its maximum when it is close to [Formula: see text]. In order to realize the correction of the existing theoretical calculated formula of single inserting yarn strain, the error formula was fitted by combining the laws of errors. The correction of the single inserting yarn strain was successfully achieved by the fitted error formula. The correction equation can correct the inserting yarn at any angle in the fabric strain range of 0–50%. The correction equation has a larger range of use and more accurate results than the theoretical calculated formula for inserting yarn. Finally, the validation was carried out with bias inserting yarn at [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] angles and the results were very good. Therefore, the corrected equation can replace the actual value of bias inserting yarn strain.

Finite Element Parametric Analysis of High-Strength Eccentrically Braced Steel Frame with Variable-Cross-Section Replaceable Link

This paper proposes a new type of variable-cross-section replaceable link that can isolate the plastic deformation. The link and the frame beam connect with the expanding section by a bolt along the flange and web separately. It is easy to design an elastic bolt, reduce bolt slippage, and facilitate link replacement after an earthquake. Considering the large elastic deformation range of high-strength steel and the superior plastic deformation of the new type of replaceable link, a high-strength eccentrically braced steel frame with a variable-section replaceable link is raised by setting a new type of variable-section replaceable link in the eccentrically braced steel frame. Then, the existing end plate connection replaceable link test specimen is simulated and verified by using ABAQUS software. The finite element model of the high-strength eccentrically braced steel frame with a variable-cross-section replaceable link is established, and the bearing capacity, stiffness, plastic rotation, plastic distribution, and other bearing mechanisms of the structure are studied by cyclic loading. The length of the energy-consuming region (e), the steel strength of the link and other components, and the length of the replaceable link (e’) are compared and analyzed with regard to the seismic performance of the structure. The results are of great significance for understanding and exploring the force mechanism, energy dissipation characteristics of the new variable-section replaceable link, and the seismic performance of the high-strength eccentrically braced steel frame, and it also provides a reference for subsequent research.

A novel series of mechanical metamaterials with sign-changing coefficient of thermal expansion and their parameter analysis

Mechanical metamaterials show great application prospects in many fields such as aerospace, biomedical engineering, energy and transportation. The development of mechanical metamaterials with multiple peculiar properties is an important prerequisite for the development of intelligent sensors with excellent performance and the realization of multifunctional integration of structures. In this paper, a series of novel mechanical metamaterials are designed by adding rhomboid negative thermal expansion units into re-entrant hexagonal honeycombs, which have different signs of the coefficient of thermal expansion when the temperature rises or falls, and the analytical formula of their equivalent thermal expansion coefficient are derived. Parameter analysis and numerical simulations show that the metamaterial can realize the sign-changing properties of thermal expansion coefficient without entering the range of large geometric deformation under specific constituting materials and geometric parameters. In addition, this design idea is extended to three-dimensional form.

Revealing the influential mechanism of strain ranges on cyclic-life saturation during creep-fatigue in Nickel-based superalloy DZ445

The creep-fatigue interaction has been recognized as the main failure mode of most structural components operating in the high-temperature regime. The cyclic life (Nf) usually decreases continuously with the dwell time in their interactions. However, Nf shows an abnormal change, i.e. keeps constant or slightly increases/decreases, in the present studied Nickel-based superalloy, DZ445. This means that generalized “Nf saturation” is achieved by a dynamic equilibrium between the straight single superdislocations and dislocation networks corresponding to local and homogeneous damage, respectively. The saturation appears more easily with the increasing high strain ranges. The variation in the mechanical response parameters, the damage characterizations, and the phase involutions with the increasing dwell time exhibits the low amplitude under the high strain range. The combined characteristics show that the easy occurrence of Nf saturation in the range of large deformations is obtained by increasing the local-damage. The low change rate of straight single superdislocations with the dwell time in the range of large deformation is well confirmed by the above mechanism. The parameters in the different criterion models of the cyclic-life “saturation phenomenon” unify the mechanical response and the damage mechanism soundly. The work provides a new theoretical basis and guidance for the creep-fatigue safety design of high-temperature metallic materials and the establishment of dislocation-based models.

Parametric Study of Non-Load-Bearing Sandwich Wall Panels for Blast Mitigation

AbstractSandwich wall systems provide resistance over a large deformation range, making them useful for blast resistance. This paper analyzed three sandwich panel systems: walls with symmetric conc...

Nonlinear inclusion theory with application to the growth and morphogenesis of a confined body

One of the most celebrated contributions to the study of the mechanical behavior of materials is due to J.D. Eshelby, who in the late 50s revolutionized our understanding of the elastic stress and strain fields due to an ellipsoidal inclusion/inhomogeneity that undergoes a transformation of shape and size. While Eshelby’s work laid the foundation for significant advancements in various fields, including fracture mechanics, theory of phase transitions, and homogenization methods, its extension into the range of large deformations, and to situations in which the material can actively reorganize in response to the finite transformation strain, is in a nascent state. Beyond the theoretical difficulties imposed by highly nonlinear material response, a major hindrance has been the absence of experimental observations that can elucidate the intricacies that arise in this regime. To address this limitation, our experimental observations reveal the key morphogenesis steps of Vibrio cholerae biofilms embedded in hydrogels, as they grow by four orders of magnitude from their initial size. Using the biofilm growth as a case study, our theoretical model considers various growth scenarios and employs two different and complimentary methods – a minimal analytical model and finite element computations – to obtain approximate equilibrium solutions. A particular emphasis is put on determining the natural growth path of an inclusion that optimizes its shape in response to the confinement, and the onset of damage in the matrix, which together explain the observed behavior of biofilms. Beyond bacterial biofilms, this work sheds light on the role of mechanics in determining the morphogenesis pathways of confined growing bodies and thus applies to a broad range of phenomena that are ubiquitous in both natural and engineered material systems.

Pressure-driven micro-poro-mechanics: A variational framework for modeling the response of porous materials

Porous materials are highly relevant in engineering and medical applications due to their enhanced properties and lightweight nature. Current micromechanical models of porous materials can accurately predict the response under the assumptions of small deformations and drained conditions, typically driven by imposed deformations. However, the theoretical framework for the micromechanical modeling of porous material driven by pore pressure in the large-deformation range has been understudied. In this work, we develop a finite-deformation variational framework for pressure-driven foams, i.e., materials where the pore pressure in the cavities produces the deformation. We further consider different kinematical constraints in the formulation of boundary conditions: kinematic uniform displacements, periodic displacements and uniform traction. We apply the proposed model in the numerical simulation of lung porous tissue using a spherical alveolar geometry and an image-based geometry obtained from micro-computed-tomography images of rat lung. Our results show that the stress distributions in the spherical alveolar model are highly dependent on the kinematical constraints. In contrast, the stress distribution in the image-based alveolar model is not affected by the choice of boundary conditions. Further, when comparing the response of pressure-driven versus deformation-driven models, we conclude that hydrostatic stresses experience a marked shift in their distribution, whereas the deviatoric stresses remain unaffected. Our findings of how stresses are affected by the choice of boundary conditions and geometry take particular relevance in the simulation of the lungs, where the pressure-driven and deformation-driven cases are related to mechanical ventilation and spontaneous breathing.