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.

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 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.

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.

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.

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.

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.

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.

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.

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.