We examine the electromechanical field and charge redistribution within a flexoelectric semiconductor (FS) nanobeam, accounting for bending, fundamental thickness-shear, and antisymmetric thickness-stretch deformations. The coupled governing equations include microstructure, flexoelectric, and semiconductor effects, highlighting the interplay between mechanical displacement, electric potential, and charge carriers. For applications in flexoelectronic devices, the static bending of a simply supported FS beam induced by uniform pressure and wave propagation in an unbounded FS beam are analytically addressed using the derived framework. The effects of antisymmetric thickness-stretch on mechanical displacements and electron concentration perturbation, as well as size dependence of microstructure and flexoelectric effects, are identified. An interesting finding reveals that wave frequencies of the antisymmetric thickness-stretch mode, as anticipated by the proposed model, are larger compared to those of the model neglecting flexoelectric and semiconductor effects. For the first time, the cutoff frequency of antisymmetric thickness-stretch impacted by the two features is explained mathematically. These findings are beneficial for enhancing the performance of flexoelectronic sensors and electroacoustic devices.

Equiatomic NiTi shape memory alloys (SMAs) can exhibit multiple martensitic transformations from a parent phase, significantly influencing the advanced macroscopic properties of SMAs, such as the large deformation/strain ability. A comprehensive atomic-scale understanding of the selection rule of the martensite phase/variant and its impact on the macroscopic mechanical behavior of SMA could be helpful for the development of high-performance SMAs. This work studies the transformation pathway, preferred martensite variant and corresponding macroscopic behavior of single crystal and bicrystal NiTi SMAs based on molecular dynamics and theoretical analysis. It is found that the transformation strain of single crystal NiTi is significantly influenced by the crystal orientation-dependent transformation pathway and martensite variant. The selection rule is that the transformation pathway and preferred martensite variant, leading to maximum transformation strains for each orientation, are energetically preferred. It can be predicted theoretically and agrees well with the molecular dynamic simulations. In addition, the stress-strain response of bicrystal NiTi can be modulated by changing its transformation pathway based on the orientation effect. This work provides atomic insights into the orientation-dependent deformation ability of NiTi and could be helpful for the development of high-performance SMAs through orientation modulation.

Ceramic matrix composites have broad application prospects in the aerospace field due to their high temperature resistance and oxidation resistance. The effect of temperature and environment atmosphere on the fracture toughness and failure mechanisms of two-dimensional plain-woven SiC_f/SiC composites was investigated. The results show that they exhibit pseudo-plastic deformation behavior at different temperatures. The fracture toughness is as high as 48 MPa m^1/2 at room temperature, and gradually decreases with rising temperature. The difference in fracture toughness between argon and air initially increases and then decreases with rising temperature. Furthermore, the high-temperature failure mechanisms of these composites were analyzed through macro and micro analysis. Based on this, a physic-based temperature-dependent fracture toughness model considering matrix toughness, plastic power, fiber pull-out, and residual thermal stress was developed for fiber-reinforced ceramic matrix composites. The model has been well validated by experimental results. An analysis of influencing factors regarding the evolution of fracture toughness was conducted by the proposed model. This work contributes to a better understanding of the mechanical performance evolution and failure mechanisms of ceramic matrix composites under multifield coupling conditions, thereby promoting their applications.

A multiscale nonlocal continuum model is proposed to describe the superelastic deformation of gradient nano-grained NiTi shape memory alloys (SMAs). At the mesoscopic scale, the polycrystalline aggregate is regarded as a composite, i.e., the grain-interior (GI) phase is assumed to be a cuboidal inclusion embedded in a matrix of grain-boundary (GB) phase. An intrinsic energetic length and a gradient energy are introduced into the Helmholtz free energy of the GI phase. The criterion of martensite transformation (MT) is derived based on the principle of virtual power and second law of thermodynamics. The hindering effect of GB on MT in GI phase is addressed. By deriving the analytical solution of the proposed model and introducing a scale transition rule, the overall and local stress-strain responses of the specimen at the macroscopic scale are obtained. The prediction capability of the proposed model is verified by comparing the analytical solution with the experiment. The influences of the distribution form for the grain size (GS) on the superelastic deformation of gradient nano-grained NiTi SMAs are further predicted and discussed. The analytical form and low computational cost of the proposed model make it an appropriate theoretical tool to design the gradient nano-grained SMAs with desired mechanical property.

Creep is an important mechanical property of refractory high-entropy alloys (RHEAs) at high temperatures. The existence of short-range order (SRO) and its ability to improve the strength or plasticity of high-entropy alloys (HEAs) have been experimentally proven. However, there is still little research on the correlation between SRO and creep behavior. The mechanism of SRO influencing creep behavior is not yet clear. In this work, the creep behaviors of TiVTaNb RHEA with and without SRO were simulated at various temperatures and stresses using molecular dynamics methods, and the effects of SRO on creep behavior were analyzed. The results show that the SRO is energetically favorable for occurrence in this RHEA. For polycrystalline RHEAs, grain boundary energy is an important driving force for the formation of SRO. Significantly, under the same conditions, the SRO can reduce the steady-state creep rate and change the creep mechanism of the RHEA. Specifically, the models with SRO will exhibit lower stress exponent and grain-size exponent. A mechanism by which SRO reduces the effects of grain boundaries on creep has been discovered. These phenomena can be well explained by the effects of SRO on atomic diffusion. In addition, by analyzing the diffusion ability of different elements, SRO can induce localization of atomic diffusion, resulting in strain localization under high stresses. This work highlights the importance of SRO on the creep of RHEAs and provides a reference for establishing a reasonable creep model of RHEAs.

In this paper, the effect of the morphological profile of dandelion seed on flight lift force under crosswind conditions is explored. Existing studies primarily focus on the flight characteristics of dandelion seed during its fall, emphasizing the influence of the complex filament structure on the formation of wake vortices. However, research on the flight lift force due to the dandelion seed's morphological profile under lateral crosswind conditions is quite limited. This study investigates the aerodynamic behavior of dandelion seed using a novel virtual barrier model. This model is proposed, based on the regular pattern of the filaments' outer contours and the virtual barrier effect produced by their columnar array. Through elaborate numerical simulations, it is found that the morphological profile of dandelion seed possesses superior aerodynamic properties, particularly in generating lift force under crosswind conditions. This characteristic is a crucial mechanism for the long-distance dispersal of dandelion seed. Subsequently, the study extends to examine the aerodynamic performance of the model at varying degrees of opening angles and inflow attack angles, offering a fresh perspective on understanding the flight characteristics of dandelion seed in natural environments. The findings not only contribute to the field of plant aerodynamics but also provide insights into potential biomimetic applications in engineering.

The stability of gaseous detonation waves is crucial for the operation of detonation-based propulsion systems and the assessment of industrial explosion hazards. However, research on the stability of detonation waves in complex reactive systems that are composed of actual fuels and oxidants and can be described by numerous elementary chemical reactions, has not been fully carried out. To investigate the relationship between linear and nonlinear stabilities in gaseous detonation wave propagation for complex reactive systems, the linear stability analysis and the one-dimensionally nonlinear numerical simulations of H₂/O₂/Ar (argon) detonations based on the reactive Euler equations and detailed reaction mechanisms are carried out. The results show that in complex reactive systems characterized by elementary chemical reactions, the results of linear stability computation of detonation are consistent with those from one-dimensionally nonlinear oscillations of detonation wave. Utilizing these linear stability results, a neutral stability curve and a perturbation frequency transition curve in the phase plane of initial pressure versus inert gas (Ar) dilution ratio are derived, especially the new frequency transition curve clearly describes the transition of perturbations from low-frequency to high-frequency mode. One-dimensional nonlinear simulations show that near the perturbation frequency transition curve, the oscillations of the detonation wave can also transform between the low-frequency, high-amplitude oscillation mode and the high-frequency, low-amplitude oscillation mode, with the oscillation frequency corresponding to the mode that exhibits the maximum growth rate identified in the linear stability analysis. This investigation into detonation stability in complex reactive gases offers guidance for selecting appropriate initial conditions and gas compositions in practical applications of detonation.

The present study proposes a modified random sequential absorption (RSA) algorithm to generate a representative volume element (RVE) model for predicting the elastic properties of discontinuous curved fiber reinforced composites (DCFRCs) with varying fiber waviness functions and orientations. A small-move method was proposed to modify the traditional RSA algorithm. In comparison with the original RSA algorithm, the generation efficiency of the proposed modified RSA algorithm increased by over 40%, and the achievable maximum fiber volume fraction could reach up to 15% with a fiber aspect ratio of 15. The generated RVE model was utilized in conducting finite element analysis to investigate the effect of fiber waviness and wavy functions on the elastic properties of DCFRCs. Finally, a modified rule-of-mixture was proposed to predict the elastic properties of DCFRCs with various fiber orientations. The results indicated that the elastic properties predicted by the modified rule-of-mixture were in good agreement with those obtained from the RVE model, thereby demonstrating its effectiveness.

Non-Schmid (NS) effects in body-centered cubic (BCC) single-phase metals have received special attention in recent years. However, a deep understanding of these effects in the BCC phase of dual-phase (DP) steels has not yet been reached. This study explores the NS effects in ferrite-martensite DP steels, where the ferrite phase has a BCC crystallographic structure and exhibits NS effects. The influences of NS stress components on the mechanical response of DP steels are studied, including stress/strain partitioning, plastic flow, and yield surface. To this end, the mechanical behavior of the two phases is described by dislocation density-based crystal plasticity constitutive models, with the NS effect only incorporated into the ferrite phase modeling. The NS stress contribution is revealed for two types of microstructures commonly observed in DP steels: equiaxed phases with random grain orientations, and elongated phases with preferred grain orientations. Our results show that, in the case of a microstructure with equiaxed phases, the normal NS stress components play significant roles in tension-compression asymmetry. By contrast, in microstructures with elongated phases, a combined influence of crystallographic texture and NS effect is evident. These findings advance our knowledge of the intricate interplay between microstructural features and NS effects and help to elucidate the mechanisms underlying anisotropic-asymmetric plastic behavior of DP steels.

Auxetic metamaterials have attracted much attention due to their outstanding advantages over traditional materials in terms of shear capacity, fracture resistance, and energy absorption. However, there are lack of design inspirations for novel auxetic structures. According to the materials databases of atomic lattice, some natural crystals possess negative Poisson’s ratio (NPR). In this paper, the mechanism of auxeticity in microscale Ti crystal is investigated through density functional theory simulation. Then we propose a macroscopic auxetic metamaterial by mimicking the microscopic atomic lattice structure of the bodycentered cubic Ti crystal. The NPR property of the macroscopic metamaterial is verified by theoretical, numerical and experimental methods. The auxeticity keeps effective when scaling up to macroscopic Ti crystal-mimic structure, with the similar deformation mechanism. Furthermore, from the geometric parameter investigation, the geometric parameters have great influence on the Poisson’s ratio and Young’s modulus of the macroscopic metamaterial. Importantly, an optimized structure is obtained, which exhibits 2 times enhancement in auxeticity and 25 times enhancement in normalized Young’s modulus, compared to the original architecture. This work establishes a link between the physical properties at micro-nanoscale and macroscale structures, which provides inspirations for high load-bearing auxetic metamaterials.

Nacre-like structures exhibit excellent mechanical properties under low-velocity impact, but the effectiveness of the nacre-like designs under high-velocity impact remains unclear. In this study, the process of a spherical projectile impacting on a nacre-like plate over a wide range of velocities is simulated using the finite element method. A three-dimensional finite element model is constructed and validated against the test data of the target perforation in terms of residual velocity and fracture morphology. The effects of impact velocity, interface strengths, and geometric sizes on the impact resistance capabilities are systematically investigated, and a dimensionless geometrical parameter is proposed to reveal the mechanism affecting the fracture toughness of nacre-like materials. It is found that the impact resistance of the nacre-like material gradually weakens with impact velocity increasing and is inferior to that of homogeneous plates under high-velocity impact. Moreover, the fracture toughness of nacre-like materials depends on the competition mechanism between interfacial enhancement and strength weakening at different impact velocities. These findings provide significant guidance on applying bio-inspired structures to design protective materials.

In the theory of two-dimensional linear elasticity, an elliptical inclusion is known to attain a constant stress field when perfectly buried in an infinite homogeneous matrix if a uniform eigenstrain is applied to it. The focus of this paper falls on the question: when the initially elliptical inclusion verges on a bi-material interface, what would happen to its configuration if it is required to retain the internal constant stress? Specifically, we explore the anti-plane shear version of this question (the version of plane deformations or three-dimensional deformations seems, however, insoluble at this stage), in which an inclusion undergoing a uniform (anti-plane shear) eigenstrain is embedded in a bi-material structure composed of two infinite elastic half-planes whose interface is straight and perfectly bonded, and the shape of the inclusion is to be determined such that the eigenstrain-induced stress inside the inclusion appears to be a constant. Unlike most optimization methods-driven solution procedures for finding the shape of the inclusion approximately in which huge computation is required, we derive by a rigorous theoretical analysis an exact integral equation with respect to the boundary curve of the inclusion that is sufficiently and necessarily related to the existence of a constant stress inside the inclusion. We solve this integral equation via the use of some analytic techniques and present in several illustrative examples a variety of shapes of the inclusion achieving constant stresses. We discover some interesting phenomena for the evolution of the shape of the uniformly stressed inclusion relative to the stiffness of the nearby interface.

In order to solve the vertical vibration negative effect problem caused by the increase of the unsprung mass in the hub motor driven vehicle (HMDV), a novel mechatronic suspension using the bridge electrical network is proposed. Firstly, the bridge electrical networks composed of two capacitors, two inductors, and one resistor are summarized and their impedance functions are analyzed forward through the structural method. Then a quarter HMDV model is constructed, and the optimal element parameters in the electrical networks are selected through the Pattern Search algorithm. The influence of element parameters perturbation of the optimal structure on the output response of HMDV suspension is further analyzed. Results show that the proposed bridge electrical network can be realized as a biquartic impedance. It can be equivalent to a mechanical impedance of the suspension through a linear motor. Compared with the conventional suspension, the root-mean-square values of the dynamic tire load and the suspension working space are reduced by 10.76% and 18.10%, respectively. The vibration at low and high frequencies of the unsprung mass is suppressed, effectively improving the grounding and handling stability of the vehicle.

Advancements in dynamic modeling methods of robotic manipulator are critical to the effective implementation of model-based control. Traditional approaches rely on rigorous first-principles-based dynamic modeling and precise parameter identification, while this paper explores an alternative through data-driven model reconstruction. To tackle the curse of dimensionality in the model reconstruction of a serial robotic manipulator with multi-degree-of-freedom, a relative activation indicator is proposed. Based on this indicator, the k-means clustering algorithm is utilized to classify the data under different working conditions. Subsequently, we leverage the fundamental prior knowledge to find the dynamical characteristics of each cluster and reconstruct the dynamic model in a stepwise manner using the method of sparse identification of nonlinear dynamics (SINDy). For the library generation of SINDy, the strategy of double-feature-set for serial manipulators with common joint types is proposed. Simulation results show that the stepwise model reconstruction approach not only reduces the size of the library of candidate functions but also decreases the impact of data noise on the reconstruction results. Finally, controllers based on the reconstructed models are deployed on the experimental platform and the experimental results demonstrate the improvement in trajectory tracking performance and the potential of the proposed method in engineering applications.

To avoid collisions between a suspended object, cables, towing robots, and obstacles in the environment in a multi-robot suspension system, obstacle avoidance planning was studied based on a collaborative optimization method for force and position. Based on the analysis of the kinematics and dynamics of the system, the inverse kinematics and inverse dynamics of the system are solved using the least variance method. The obstacle avoidance planning is performed in the solved collisionfree feasible space using the stable dung beetle optimization (SDBO) algorithm, which ensures that the suspended object can move stably to the target point in the workspace. The optimal obstacle avoidance trajectory of the multi-robot suspension system can be accurately determined by using the collaborative optimization method for force and position to plan the towing robot and the cable. Finally, the correctness of the obstacle avoidance planning method is verified by simulations. By taking a special scenario, the remarkable findings reveal that the SDBO algorithm outperforms the dung beetle optimization algorithm by reducing the length of the planned trajectory of the suspended object by 14.51% and the height by 79.88%, and reducing the minimum fitness by 95.84% and the average fitness by 94.77%. The results can help the multi-robot suspension system to perform various towing tasks safely and stably, and extend the related planning and control theory.

Dielectric elastomer (DE) is an electroactive polymer with the characteristics of high energy output, great flexibility, lightweight, mechanical compliance, and low cost, which are particularly suitable for DE energy generators. Energy harvesting efficiency is a key index to evaluate the performance of the energy generator, which depends on the structural configuration and the mechanical and dielectric properties of the DE material. This paper proposes a fractional viscoelastic polarization(FVP) model by combining the fractional viscoelasticity model and the polarization-based lumped parameter model. A dynamical model of a cone dielectric energy generator (CDEG) considering stretch-dependent electrostriction and nonlinear viscoelasticity is established. Additionally, a deep neural network (DNN) model is developed to explore the relationships between various parameters and the output energy of CDEGs to efficiently and accurately predict the energy output of CDEGs. Based on the DNN model, optimal parameter designs for CDEGs are obtained by using non-dominated sorting genetic algorithm II (NSGA-II). The experiments verified that the FVP model predicts accurately the output energy of CDEG and the established optimal design framework can accurately provide the optimal design parameters of CDEG, which offers deep insights for the design and fabrication of a high-efficiency dielectric energy generator.

Osteoarthritis is one of the most common joint diseases, leading to joint pain, dysfunction, and a reduced quality of life for patients. Therefore, it is particularly important to explore more effective prevention, treatment and management methods to relieve patients’ pain and enhance their quality of life. Among physical therapies, pulsed electrical stimulation (PES) is considered to be a promising treatment method due to its high safety and ease-of-use features. PES provides a non-invasive, safe and effective option for patients. However, there are fewer studies on the biomechanical changes of PES in periarticular tissues, and its effects on the biological behavior of chondrocytes remain unknown. This study investigated the effects of PES on the biomechanical properties of osteoarthritic joints and the biological behavior of chondrocytes. The results showed that PES with an intensity of 10 mA and a frequency of 4 Hz increased the cross-sectional area of muscle fibers, prevented muscle atrophy and loss of function, and restored the mechanical properties of muscle tissue. PES also effectively increases the resistivity of knee osteoarthritis cartilage tissue, as well as the elastic modulus of cartilage, which can enhance the biomechanical characteristics of cartilage tissue. PES also promoted the metabolic activity of chondrocytes and increased cartilage matrix synthesis, thereby improving the overall structure and mechanical properties of cartilage tissue. Additionally, cellular experiments showed that 5 consecutive days of 800 mV PES significantly increased the expression level of Piezo1 gene in chondrocytes. At the same time, the expression of type II collagen and transforming growth factor beta increased, while the expression of matrix metallopeptidase 13 decreased. These changes favored the promotion of cartilage matrix synthesis. This has a positive effect on protecting and improving joint health and reducing the impact of osteoarthritis, and is important for understanding the mechanism of action of PES on chondrocytes and the development of related therapeutic strategies.