Azobenzene (AZO)-based supramolecular photosensitive hydrogels exhibit great potential in biomedical and flexible electronics fields owing to their light-induced gel-sol transitions. To investigate the dynamic rheological mechanisms of these hydrogels before and after irradiation, we develop a fractional four-element rheological model that accounts for hierarchical relaxation governed by memory effects. This model incorporates multiscale microstructural dynamics, including segmental mobility, water molecular motions, single chain conformational changes, and network deformations, offering a new perspective on the rheological behavior. The model's validity is verified through quantitative simulations of storage and loss moduli for representative AZO-based hydrogel systems. Parameter analysis reveals that memory effects arising from complex micro-hierarchical structures determine the nonlinear frequency responses of storage/loss moduli. Furthermore, loss factor analysis reveals a key finding. The mismatch between hierarchical structural motions and external loads, which varies with frequency, regulates the governing microstructure during gel-sol transitions. This regulation causes a shift from network-dominated to segment/water molecule-dominated behaviors. As frequency increases, the transition changes from unidirectional to bidirectional. Time-domain analysis of the model also clarifies low-frequency response mechanisms. It shows that gel-sol transitions are driven by two concurrent mechanisms: modulation of interchain slippage and alteration of entanglement point number density. This study not only reveals dynamic mechanisms in photosensitive hydrogels, but also provides a predictive tool for precisely engineering their effect irradiation on rheological behaviors.

This study presents a comprehensive transient modeling framework to characterize the stress-diffusion behavior of fiber-reinforced hydrogel composites. The proposed model introduces an intermediate configuration to effectively decouple swelling and elastic deformation, while employing Fick’s diffusion law to describe solvent transport within the hydrogel matrix. Unlike previous models, our model accounts for both highly nonlinear behavior and dispersibility of the fibers. We have developed a finite element implementation that incorporates diffusion effects, which has been successfully integrated into Abaqus through a user element subroutine. Numerical results demonstrate excellent agreement with both theoretical predictions and existing numerical solutions. Within this computational framework, we systematically investigate the stress-diffusion coupling in entanglement chain hydrogels and fiber-reinforced hydrogel composites. The parametric studies provide valuable insights into how key factors, including entanglement chain ratio, fiber content, stiffness, and distribution, govern the mechanical and mass transport properties of these materials. These findings elucidate the fundamental mechanisms behind the anisotropic mechanical and diffusion behavior observed in hydrogel systems and their composite variants.

Flexible hydrogel films are critical for flexible electronics and wearable devices, yet they face an inherent trade-off between interfacial peel resistance and structural integrity─an issue traditional methods (e.g., surface modification, uniform property tuning) cannot resolve. This study proposes a gradient-softening strategy to address this bottleneck. Hydrogel films with a through-thickness decreasing modulus gradient (0.24-0.034 MPa) were fabricated by adjusting cross-linker content (0.04-0.005 g) and water content (45-66 wt %): the surface layer maintained high stiffness for structural stability, while the substrate-adjacent layer softened to enable deformation and energy dissipation. Pure shear tests, multiangle (0°, 90°, 180°) peel tests, and finite element analysis (FEA) were conducted to characterize their performance and underlying mechanisms. The gradient-softening films exhibited a fracture toughness of 1253.5 J/m2, which significantly exceeded that of low-stiffness (526.1 J/m2) and high-stiffness (762.1 J/m2) uniform films. They also showed superior peel resistance: 914.6 N/m (90° average peel strength), 538.6 N/m (180° stick-slip amplitude), and 1544 N/m (0° maximum shear strength)─2.1-3.6 times higher than uniform films. Deformation observations and FEA show that the high fracture toughness of gradient-softening films is converted into superior interfacial peel resistance through "stiff-soft synergy": the stiff surface layer provides structural load-bearing capacity to avoid excessive deformation, while the soft substrate-adjacent layer enables strain redistribution and crack blunting to alleviate stress concentration, collectively increasing the energy required for peeling and thus realizing enhanced antipeeling performance; a quantitative correlation between gradient ratio and peel resistance was also revealed. The films remained stable after a 6 day sealed storage and 1000 cyclic bending tests. This strategy provides a novel solution for flexible electronics. It can be integrated with advanced manufacturing (e.g., multimaterial 3D bioprinting) to develop biomimetic interfaces, driving progress in wearable sensing and soft robotics.

Conductive hydrogels face a persistent challenge in reconciling high electrical conductivity with mechanical robustness, limiting their utility in advanced bioelectronics. This study introduces a two-step fabrication strategy that decouples ionic-electronic conductive pathway formation from polymer network crosslinking. Initially, a salt-free precursor hydrogel is synthesized by uniformly dispersing PEDOT:PSS within a polyacrylamide (PAAM)/polyacrylic acid (PAA) matrix, leveraging electrostatic interactions to suppress microphase aggregation. Subsequent immersion in a hybrid Ca2+/Zr4+ solution induces dual reinforcement: Ca2+ enables reversible electrostatic crosslinking between PAA chains, Zr4+ establishes high-density coordination bonds with PAA networks. The optimized hydrogel material achieves a record electrical conductivity of 11.70 S/m (exceeding ionic hydrogels: <6 S/m) and mechanical strength of 2.16 MPa, alongside an elastic modulus of 0.76 MPa. Demonstrating practical efficacy, the hydrogel exhibits ultralow skin-contact resistance (6.78 k Omega) as microneedle-array electrodes, enabling high-fidelity electromyographic (EMG) signal acquisition. In addition, a customizable 3D-printed bioelectrochemical sensor further highlights its versatility. This work establishes a universal paradigm for multifunctional hydrogel design, bridging material innovation with next-generation bioelectronic applications.

In this paper, we suggest a design strategy for multilayer hydrogel beams with controllable swelling deformation and bending, which can be used in soft devices. We adopt a constitutive model that considers the entanglement chains of the hydrogel and an analytical method for solving multilayer hydrogel beams is developed. First, the reliability of the design strategy is provided by comparing analytical solutions and numerical results. Then, guided by the above design strategy, we quantitatively investigate hydrogel beams with gradient distribution and study the effects of material and distribution on the deformation and bending behavior of the structures. The results show that under non-gradient distribution, all structures with an odd number of total layers only undergo in-plane expansion, while all those with an even number of total layers undergo expansion and bending. However, this law will be broken at the gradient distribution. The introduction of entanglement chains and gradient distribution strategy increase the range of adjustment for deformation and bending. This work is expected to provide new insights into the design of multilayer hydrogel beams for material-structure-function integration.

Despite the promising applications of hydrogels, their poor mechanical properties still greatly limit their further applications. To improve the mechanical properties of hydrogels, various strategies have been proposed. Hydrogels with nanoparticle-crosslinked polymer networks show excellent toughness, self-recovery, and other advantages, and thus have great prospects for use in tissue engineering, artificial muscles, flexible electronics, and other fields. There have been experimental and theoretical studies of its damage. However, the underlying microscale physical mechanisms have not been fully elucidated. Herein, we established a physics-based constitutive model to describe the mechanical behavior of nanoparticle-crosslinked hydrogels under cyclic loading. The deformation-induced damage and the rate-dependent damage were explained by the network alteration and kinetics of chain dissociation/association, respectively. The kinetics dissociation/association theory was modified considering the polymer chains that wind around nanoparticles. The Mullins stress softening and recovery during cyclic loading were described. Cyclic loading tests on nanoparticle-crosslinked hydrogels were carried out to verify the proposed constitutive model. It is demonstrated that the model can well describe the mechanical behavior of nanoparticle-crosslinked hydrogels during cyclic loading.

Graphene oxide/epoxy composite coatings have attracted much attention from researchers due to their excellent anti-corrosion properties. Graphene oxide as a two-dimensional nano-filler can enhance the overall properties of epoxy resin coatings. In the paper, models of graphene oxide/epoxy composite coatings with different permeation degrees are constructed respectively. The interfacial interaction between GO and epoxy resin and the adsorption properties of epoxy coating with metal are analyzed from an atomic perspective by molecular dynamics simulations. The results indicate that the interfacial adsorption effect of the epoxy coating on the protected metal is stronger than the interfacial bonding of GO on the epoxy resin matrix. Simulations of models with different degrees of permeation suggest that the permeation of the NaCl solution occupies the interfacial space and reduces the adhesion between the two interfaces.

The permeation of marine water can lead to severe degradation of the protective properties of polymer composite coatings. At present, experimental studies on the anticorrosive and mechanical properties of polymer composite coatings are relatively mature, but the impermeability and mechanical property changes of the coating during the permeation process are challenging tasks to be studied only by experiments. In this paper, molecular dynamics (MD) models of composite coatings consisting of pure epoxy resin (EP), graphene/epoxy resin (Gr/EP), and graphene oxide/epoxy resin (GO/EP) were constructed respectively. MD simulations were performed to reveal the impermeability and mechanical property changes of composite coatings from an atomic perspective. The results show that GO has strong interfacial interaction with EP and the best effect to enhance the impermeability and mechanical properties of epoxy coatings. NaCl solutions can damage the coating microstructure and occupy the Gr and GO surfaces, causing them to no longer have an enhancing effect. The study of GO/EP coatings with different permeation degrees shows that the mechanical properties of the coating decrease as the penetration degree increases.

非标准化考核能够更加真实全面地反映学生学习掌握知识、灵活应用知识以及知识建构的能力,更加有利于培养学生的创新能力、科学思维和质疑精神.本文针对基础力学课程教学进行了非标准化考核模式的探索与实践,以学生的学习成效为导向,以"师生协同、知行合一、育教一体"为教学理念,设计建立了线上线下混合式多元化全过程的考核评价机制,加强学生课堂内外、线上线下学习的评价,提升课程学习的深度、广度和难度.实践表明,非标准化考核模式的实施为基础力学课程教学提供了更加全面合理的课程评价体系.本文考核模式与方法可为基础力学教师提供一些严把质量关的教育教学改革借鉴思路,同时也为学习基础力学的学生提高学业学习水平起到积极的引导作用.

The penetration of salt solution into graphene oxide/epoxy resin (GO/EP) will cause structural damage, decrease in mechanical properties, and reduce service life. In this study, molecular dynamics method was used to simulate the penetration of the 3.5% NaCl solution through the GO/EP. In order to understand the effect of GO surface functional groups on the barrier properties of the GO/EP, a pure graphene model and three kinds of GO models modified with oxygen-containing functional groups (ether, hydroxyl, and carboxyl) were established, respectively. The penetration resistance of GO/EP was analyzed. The type of oxygen-containing functional group affects the penetration rate of the salt solution and the GO/EP interface performance. The spatial distribution and kinetic behavior of the salt solution were studied. The results show that the salt solution molecules trapped in GO/EP were mainly concentrated at the interface between GO and EP, which is the main reason for the degradation of the GO/EP interface performance. Affected by GO, the penetration process of ions can be divided into multiple stages, and its motion state was different depending on the type of functional group.

The potential to provide improved performance for advanced composites through the addition of multi-walled carbon nanotubes (MWCNTs) to carbon fiber composites is of interest in several applications. To investigate performance four types of composite specimens with different off-axis angles were subjected to progressive tensile loading. The results show that MWCNTs can improve the bearing capacity of the composite and the off-axis orientation angle can enhance the toughness of the composite. During loading acoustic emission (AE) signals were collected and they were post-processed using cluster analysis based on a Fuzzy C-Means algorithm. The analysis of the AE signals shows that data can be divided into categories which correlate with three damage modes: matrix cracking, fiber debonding and fiber breakage. The AE peak frequency characteristics of each damage mode were identified. Additional characterization was provided by using micro-computed tomography (Micro-CT) during the progressive tensile loading process. The CT images visualize damage location and evolution in the composites and data exhibit good correlations with the AE data for defects predication. The combination of AE and micro-CT technology were shown to effectively characterize damage evolution of the composites, and such data can potentially serve as a reference for the structural health monitoring of these composites when used in structures.

Applying acoustic emission method to understand the damage and failure mechanism of hybrid composites is challenge for industry. For this study, nine types of carbon/glass fiber-reinforced hybrid laminate composite specimens with different structure and indentation were subjected to tensile experiments. The AE signals collected during the tensile process were post-processed using cluster analysis based on Fuzzy C-Means algorithm. It was found that the AE signals can be divided into three types which correspond to three damage modes, and the AE peak frequency characteristics of each damage mode were found for different specimens. Micro-computed tomography imaging was obtained for specimens with indention before loading and after failure. There is seen to be a good correlation between the damage seen with the Micro-CT imaging, the mechanisms identified and the data cluster analyzed by using AE signals. Results prove that AE signals are reliable and can be used for composite structure health monitoring.

Progressive tensile damage for carbon fiber composites both containing and without multi-walled carbon nanotubes (MWCNTs) is discussed and this work is an extension of a previously published study. The composite specimens were subjected to progressive tensile experiments, and AE signals were collected during loading. The signals were post-processed using cluster analysis based on the Fuzzy C-Means algorithm. The results show that AE signals can be divided into three classes, corresponding to three damage modes: matrix cracking, fiber debonding, and fiber breakage. The AE peak frequency characteristics of each damage mode were found. Samples were also characterized using micro-computed tomography (Micro-CT) imaging and the observed damage shows good correlation with AE signal characterization for defect class prediction. Analyzing the data clusters it can be found that MWCNTs can delay and in some cases prevent both matrix cracking and fiber debonding in laminate composites. It was found that matrix cracking, debonding and fiber break AE signals for composites with CNTs correspond to a higher frequency range than that without CNTs. The results give guidance for composite design when considering MWCNTs and structure health monitoring of these composite materials.

In this paper, an atomistic investigation was performed to reveal the dependence of the graphene content on the shape memory effect of the multilayer graphene reinforced poly (L-lactide-co-ε-caprolactone). Uniaxial compression deformation was carried out to show the shape memory effect of the graphene composites. The temperature response of the composites was obtained during shape recovery. It is observed that the composites with higher graphene content exhibit larger recovery ratio and are more sensitive to temperature during a gradual warming recovery. The graphene composites show good reusable properties and the shape of composites is able to fully recover by constant temperature recovery tests. Especially, the graphene of the composite was subjected to a separate heating test to check the role of the graphene in shape recovery of the composite, where electro-induced indirect heating was qualitatively simulated. It is shown that the recovery first appeared in composites with the most content of graphene. The polymer will have a temperature hysteresis compared with graphene in composites. The shape recovery trajectory of graphene and the evolution of the interaction between graphene and polymers during the process of shape memory were clearly presented to reveal the mechanism how graphene promotes the performance of shape memory. This research can provide a guidance for obtaining composite materials with ideal shape memory effect.

Graphene is a significant reinforcement in metal matrix composites by virtue of its superior mechanical properties. The cracking of metal crystal and the failure of graphene-metal interface are the main reasons for the decrease of mechanical properties of graphene/metal composites, but the damage mechanism of that is not clear. In this paper, a novel two-dimensional microstructure model of graphene/polycrystalline metal composites is established by a self-developed structure modeling procedure. According to the actual structure of graphene/metal composites, the numbers, sizes, orientations, arrangements of graphene and grain can be controlled respectively. Moreover, by employing the method of combining the crystal plasticity finite element method (CPFEM) and the cohesive zone model (CZM), the damage mechanism of graphene/aluminum (Al) composites on polycrystalline Al matrix, graphene-reinforcement and graphene-Al interface under tensile load is revealed from the mesoscale for the first time, then the effects of graphene morphology and initial microcracks on the failure behavior and overall mechanical properties of graphene/Al composites are fully captured. This study provides a strong theoretical support and inspiration for the construction of graphene/Al composites with excellent properties.

随机堆叠石墨烯制成的石墨烯复合材料(GC)的不均匀性,使得GC的压阻传感性能与其细观单元的尺寸密切相关.根据GC的微观结构特点,发展了一种GC压阻传感性能计算方法,依次计算了GC的电子渗流概率、初始方阻和相对电阻-应变关系.结果 表明:GC的电子渗流概率随着石墨烯面分比的增大而增大,大长宽比石墨烯组成的GC的渗流阈值更低,电子迁移网络连通的最小面分比是0.5;GC代表单元的最小边长可由它的初始方阻确定,大面分比GC拥有更小的代表单元,当石墨烯面分比分别为1.2、1.4、1.6、1.8、2.0时,GC代表单元的最小边长与石墨烯边长的比值为35、30、25、20、15.最后,不同石墨烯面分比、长宽比的GC代表单元的计算结果证实,增大石墨烯的面分比与长宽比能够延长GC的线性感知阶段,提高GC的总感知范围.

以毛竹纤维细胞壁(BFCW)为研究对象,运用纳米压痕技术对BFCW的蠕变性能和松弛性能进行了研究.通过设计不同的加载方式,得到了纳米压痕的载荷与压入深度的关系曲线;通过拟合不同应变率的实验结果数据,计算得出了BFCW的蠕变应力指数.研究了BFCW在不同压入深度、加载速率、保载时间下的松弛行为,分析了不同的载荷、加载速率、保载时间对BFCW蠕变行为的影响.结果表明:BFCW纵向和横向具有不同的力学性质,在纵向表现出更明显的松弛特性和更强的抗蠕变变形能力;BFCW的蠕变行为随着压入载荷的增大愈加明显,表现为蠕变位移和蠕变速率增大;BFCW纵向的压入深度和蠕变位移量均比横向的小,在最大压入载荷为15mN时,其差值分别达到了24.96％和32.25％;BFCW的松弛模量、载荷松弛量与压入深度呈正比;BFCW纵向的松弛能力比横向的强,在加载速率为50nm/s时纵向载荷松弛量较横向高34.58％.

Nanolaminated metal/graphene composites can have many special mechanical properties, thanks to a high density of interfaces. Even though the interface effect is a key mechanism for the propagation of dislocations in nanolaminated metal/graphene composites, it is not well understood. In this paper, simulations of the molecular dynamics of nanolaminated polycrystalline aluminum/graphene (PAl/Gr) composites are performed. The results provide insight into the grain-size effect on plastic flow stress of nanolaminated PAl/Gr composites and the underlying mechanism. Extended dislocations are found to dominate the plastic deformation of the PAl/Gr composites. Both the PAl/Gr interface and the Al grain boundaries (GBs) interact with the dislocations. Three dislocation propagation forms are observed in the PAl/Gr nanolaminated composite based on the Al grain-size. By decreasing the laminate thickness, the dislocation-GB interaction can transition to a dislocation-graphene interaction. When the Al layer thickness is smaller than the in-plane grain size, the strain-hardening capability is increased due to greater ability of the dislocation/graphene-interface to store dislocations than the GBs. Besides, geometrically necessary dislocations are induced because of the deformation gradient between the graphene and Al grains, which lead to back-stress strengthening and thus strain hardening. Accordingly, a confined layer slip mechanism, which considers back-stress, is used to predict the flow stress of the PAl/Gr composites.

In this paper, we developed a new design and preparation method of 2D and 3D composite metamaterial with adjustable isotropic negative hydration expansion (NHE) function based on re-entrant auxetic honeycomb. The metamaterial is composed of composite lattice microstructure with hydrogel driving layer and re-entrant framework and prepared by multi-material 3D printer. Experimental, simulation and theoretical investigation were carried out to demonstrate the design method and NHE deformation effects of the metamaterial. It was shown that the effective NHE coefficient depends on the length of the driving layer and the straight bar connecting the lattice microstructures. In addition, a non-monotonic relationship was found between the bandings angle θ2 and the length ratio (s/a) due to the constraint effect on both ends of the composite beam. Through the parameter design of the lattice microstructure, the NHE coefficient of can be adjusted within the range of 0–22.4%. For the 3D sample, the value of the NHE coefficient is among the largest achieved in experiments to date. This work provides a practical method for obtaining 2D and 3D metamaterial with adjustable NHE and can be applied to the design of macro-, micro- and nano-metamaterial.

Many experimental researches on the in-plane random stacked graphene composites (GC) for wearable sensors have been carried out. Due to the limitation of experimental technology, its piezoresistive sensing mechanism and piezoresistive performance are still an open problem. Based on the microstructure characteristics of GC, the position and direction of graphene flakes in GC are determined by the uniformly distributed random numbers between 0 and 1, and a novel two-dimensional GC model is established. According to the uniform deformation characteristics of GC, the finite element method for piezoresistive performance of GC is developed. The relative resistance, gauge factor, morphology of graphene flakes and current density contour of GC are obtained. By connecting them, it is revealed that the substantial cause of piezoresistive effect is the change of graphene flakes density and the specific reason is the variation of the electron migration pathway and the invalid flakes number. The increase of the length of electron migration pathway caused by the relative sliding of overlapped graphene flakes leads to the linear sensing characteristics, while the cut of the number of electron migration pathway and the increase in the number of invalid flakes induced by the separation of graphene flakes bring about the non-linear sensing effect. In addition, the results show that GC with high area fraction and GC with large-scale graphene flakes have a large sensing range, while GC with low area fraction and GC with small-scale graphene flakes have a higher gauge factor. Finally, the in-plane resistivity of contact surface of overlapped graphene flakes is assumed as a function of strain and the influence of contact resistance on piezoresistive effect of the GC is investigated, to understand the mechanism of the GC piezoresistive performance. These results can contribute to the improvement or innovation of GC fabrication method and the production of the GC piezoresistive sensing devices for expected sensing performance.