The deformation and fracture behaviors of magnetoelectric materials under mechanical loading are affected considerably by an external electric or magnetic field. To provide a deep understanding of the intrinsic coupling properties, several macro/micro-nano multi-field instruments have been designed and constructed, including an electro-magneto-mechanical nanoindentation apparatus and a multi-field bulge-test instrument. With these instruments, several new experimental results have been observed, such as multi-field indentation scaling relationship and magnetic field control of 180° ferroelectric domain switching for magnetoelectric laminates. Furthermore, an electro-magneto-mechanical coupling model considering the effects of surface stress and a finite element based real-space phase field model are developed, which provide reference for structure design of magnetoelectric intelligent device at small scale.

A novel deep-blue emitter PhImPOTD based on phenathroimidazole was synthesized, which is incorporated by an electron-donating dibenzothiophene unit and electron-withdrawing phenanthroimidazole and diphenylphosphine oxide moieties. Furthermore, the weak π–π stacking and intermolecular aggregation render the photoluminescence quantum yield is as high as 0.34 in the solid state. Non-doped organic light emitting diodes (OLEDs) based on PhImPOTD emitter exhibits a low turn-on voltage of 3.6 V, a favorable efficiency of 1.13 cd A−1 and a deep blue emission with Commission Internationale de l’Eclairage (CIE) coordinates of (0.15, 0.08). The CIE is very close to the NTSC (National Television Standards Committe) blue standard (CIE: 0.14, 0.08). PhImPOTD is also utilized as blue emitter and the host for a yellow emitter (PO-01) to fabricate white organic light-emitting diodes (WOLEDs). This gives a forward-viewing maximum CE of 4.83 cd A−1 and CIE coordinates of (0.32, 0.32) at the luminance of 1000 cd m−2. Moreover, the single-carrier devices unambiguously demonstrate that typical bipolar-dominant characteristics of PhImPOTD. This work demonstrates not only that the phenanthroimidazole unit is an excellent building block to construct deep blue emission materials, but also the introduction of a diphenylphosphine oxide deprotonation substituent is an efficient tactic for harvesting deep-blue emitting devices.

Introducing gradient into cellular materials has been envisioned as an effective way to improve their performance. In this study, a novel in-plane graded honeycomb is proposed and its dynamic behavior under out-of-plane compression is investigated using numerical simulation and theoretical analysis. The in-plane gradient is introduced by changing the thickness of each cell wall of honeycomb unit cell along its side length. Numerical results show that the crushing strength and energy absorption capacity of honeycombs with positive gradient are substantially enhanced compared to those of honeycombs without gradient. To explore the enhancement, theoretical and numerical analyses on the energy absorption mechanism of honeycombs are performed. It is found that severe plastic deformation is mainly concentrated near the intersecting edge of cell walls, and the energy absorption can be further improved by distributing more material near the intersecting edge when the total mass remains constant. In addition, analytical formulas for the crushing strength and energy absorption of graded honeycombs are developed, and good agreement is obtained with numerical results.

Nowadays, radomes that are employed to protect antennas inside from physical environment are required to have dual-band or even multi-band transmission performance. In this paper, a design scheme based on the theory of small reflections is proposed for the design of dual-band and multi-band A-sandwich radomes. Subsequently, two A-sandwich composite radome walls are designed and fabricated according to the design scheme. Finally, both numerical simulations and experiments are conducted to verify the electromagnetic characteristics of the radome walls. Results indicate that one of the A-sandwich radome walls has two passbands in 4.0–11.4 GHz and 25.2–40.0 GHz, while the other one has three passbands in 4.0–8.2 GHz, 18.0–20.5 GHz, and 29.1–40.0 GHz, respectively. The proposed method is experimentally demonstrated to be an effective approach for designing dual-band and multi-band dielectric radome walls for both centimeter and millimeter wave applications.

•A new model for depicting temperature dependent fracture toughness is proposed.•Temperature dependent fracture strength model for pUHTCs is developed.•Effects of temperature, microstructures and residual stress are included in model.•The model has no any fitting parameters.•Excellent agreement is obtained between prediction and experimental measurements.The particulate-reinforced ultra-high temperature ceramics (pUHTCs) have been particularly developed for fabricating the leading edge and nose cap of hypersonic vehicles. They have drawn intensive attention of scientific community for their superior fracture strength at high temperatures. However, there is no proper model for predicting the fracture strength of the ceramic composites and its dependency on temperature. In order to account for the effect of temperature on the fracture strength, we proposed a concept called energy storage capacity, by which we derived a new model for depicting the temperature dependent fracture toughness of the composites. This model gives a quantitative relationship between the fracture toughness and temperature. Based on this temperature dependent fracture toughness model and Griffith criterion, we developed a new fracture strength model for predicting the temperature dependent fracture strength of pUHTCs at different temperatures. The model takes into account the effects of temperature, flaw size and residual stress without any fitting parameters. The predictions of the fracture strength of pUHTCs in argon or air agreed well with the experimental measurements. Additionally, our model offers a mechanism of monitoring the strength of materials at different temperatures by testing the change of flaw size. This study provides a quantitative tool for design, evaluation and monitoring of the fracture properties of pUHTCs at high temperatures.

In this study the frequency dependence of harmonic hysteretic magnetoelectric (ME) effect in magnetostrictive-piezoelectric laminate was investigated. Taking into account the nonlinear magnetostrictive effect and the structural vibration, a ME dynamic model was proposed to quantitatively describe the frequency-dependent hysteretic characteristics. The model was validated by comparing the simulated ME response with experiment at both the quasi-static and high frequency conditions. As the frequency increases, the shape evolution of the ME hysteresis loop from crescent to butterfly and ellipse was observed. Moreover, the influences of the magnetic bias field, damping ratio and magnetostrictive loss factor were also investigated. It was found that the dynamic ME hysteresis was the combined result of competition between the first two orders of harmonic components and the corresponding phase shift. The former was controlled by the frequency doubling and the mechanical resonance effect, and the latter was originated from the magnetostrictive loss and mechanical damping.

Lightweight composite structure has been widely used in various applications such as aerospace, transportation, and marine. The aim of present paper was to design and fabricate a bogie frame composite element of urban maglev train. It was an attempt to use lightweight composite as the primary load carrying structure in rail transit. A combined mold which can be used in autoclave molding process was developed and a multi-cavity composite casting block was manufactured. Three-point bending test and finite element analysis (FEA) were respectively conducted to evaluate the static strength of this structure. The experimental results revealed that the glass fiber reinforced casting block could satisfy the load bearing requirement for application and the weight reduction was approximately 30.9% in contrast with the traditional metal material. Therefore, it was found that the lightweight composite has a significant potential as the load bearing structure for the rail transportation application.

Photopolymerization is one of the most widely used methods for additive manufacturing and microfabrication of polymer structures. However, the mechanical properties of these materials, formed incrementally or layer-by-layer by photopolymerization, remain unclear. One critical issue is the strength of the interfaces between adjacent layers. During free radical photopolymerization, these interfaces are exposed to atmospheric oxygen, which is detrimental to the polymerization reaction due to radical inhibition. The influence of oxygen on the interfacial properties, however, is still not well understood. This paper investigates the effect of oxygen on the mechanical behavior of interfaces. In order to facilitate mechanical tests, the interfacial strength is investigated using a part-by-part method that mimics the conventional layer-by-layer photopolymerization process. The experiments found that oxygen enhances the interfacial strength by improving interfacial bridging macromolecular links. A theoretical model is developed to capture the interfacial evolution. Numerical studies further illustrate the role of several processing parameters such as curing condition and resin component.

Light activated polymers are a novel group of active materials that deform when irradiated with light at specific wavelengths. This paper focuses on the understanding and evaluation of light activated covalent adaptable networks formed by radical polymerization reactions, which have potential applications as novel actuators, surface patterning, and light-induced bending and folding. In these polymer networks, free radicals are generated upon light irradiation and lead to evolution of the polymer network structure through bond exchange reactions. It is well known that oxygen is an important inhibitor in radical-based chemistry as oxygen reacts with free radicals and renders them as inactive species towards further propagation and reaction. However, it is unclear how radical depletion by oxygen may affect the light-induced actuation. This paper studies the effects of oxygen on both stress relaxation and bending actuation. Light induced stress relaxation experiments are conducted in an environmental chamber where the concentration of oxygen is controlled by the nitrogen flow. A constitutive model that considers oxygen diffusion, radical termination due to oxygen, and the polymer network evolution is developed and used to study the stress relaxation and bending, and the model predictions agree well with experiments. Parametric studies are conducted to identify the situations where the effects of oxygen are negligible and other conditions where they must be considered.

Two blue fluorescent phenanthroimidazole derivatives (PhImFD and PhImTD) with a D–π–A structure are synthesized by attaching a hole-transporting dibenzofuran or dibenzothiophene and an electron-transporting phenanthroimidazole moiety and characterized. The nonplanar twisted structures reduce molecular aggregation, which endows both of the compounds with good thermal properties, and film-forming abilities as well as high quantum yields in CH2Cl2 and in the solid state. Non-doped organic light emitting diodes (OLEDs) are fabricated by employing the compounds PhImFD and PhImTD as emitters and exhibited promising performances. The devices show a deep blue emission with Commission Internationale de l’Eclairage (CIE) coordinates of (0.15, 0.11) for PhImFD and (0.15, 0.10) for PhImTD. PhImFD and PhImTD, with the desired bipolar-dominant characteristics, render devices with a low driving voltage of 3.6 V. The energy levels of the materials were found to be related to the donor units in the compounds with different substituents. Device B, using PhImTD as the emitting layer (EML), with well fitting energy levels and increased electron transport ability, possesses favorable efficiencies of 1.34 cd m−2 for CE, 0.82 lm W−1 for PE and 1.63% for EQE. PhImFD and PhImTD are utilized as blue emitters and the host for a yellow emitter, PO-01, to fabricate white organic light-emitting diodes (WOLEDs) that give a forward-viewing maximum CE of 8.12 cd m−2 and CIE coordinates of (0.339, 0.330). The results demonstrated not only that the phenanthroimidazole unit is an excellent building block to construct deep blue emission materials, but also that chemical structure modification by the introduction of a suitable electron-donor substituent could influence the performance of devices.

ZrB2–SiC–graphite ultra high temperature ceramic (UHTC) corrugated panel was firstly proposed and fabricated with potential application for sandwich structured thermal protection system. The compression properties of the as-prepared ultra high temperature ceramic corrugated panel were evaluated at 1600 °C in air. The compression modulus and strength of this ultra high temperature ceramic corrugate panel were 312 MPa and 17 MPa respectively. The design of corrugated panel exhibited an excellent combination of lightweight and excellent compression properties. This study would provide a novel concept of ultra high temperature ceramic corrugated panel for the design of ultra high temperature thermal protection system applications.

This paper studies the dynamic conducting crack propagation in piezoelectric solids under suddenly in-plane shear loading. Based on the integral transform methods and the Wiener-Hopf technique, the resulting mixed boundary value problem is solved. The analytical solutions of the dynamic stress intensity factor and dynamic electric displacement intensity factor for the Mode II case are derived. Furthermore, the numerical results are presented to illustrate the characteristics of the dynamic crack propagation. It is shown that the universal functions for the dynamic stress and electric displacement intensity factors vanish if the crack propagation speed equals the generalized Rayleigh speed. The results indicate that the defined electro-mechanical coupling coefficient is of great importance to the universal functions and stress intensity factor history.

•We report a novel strategy of pre-strain applied to the electrode–collector bilayer.•Pre-strain greatly alleviates built-in stresses due to lithium-ion diffusion.•Owing to pre-strain, stress drop at the electrode–collector interface is suppressed.•Tensile stresses of electrode surfaces should be tailored by tuning pre-strain.Diffusion-induced stresses can break structure integrity of electrodes, and further degrade storage capacity and cycling stability of lithium-ion batteries. To reduce these built-in stresses due to lithium-ion diffusion, we report a strategy of pre-strain applied to the structure of active electrode film bonded to the current collector. Accordingly, a model is developed for the effect of pre-strain on mechanical stress of the electrode–collector structure. The theoretical results show that pre-strain greatly alleviates diffusion-induced stresses of electrode film and current collector, especially stress drop at the electrode–collector interface. In addition, tensile stresses of two electrode surfaces should be modestly tuned by pre-strain, avoiding brittle fracture.

Considering the case of asymmetric oxidation, new elastic and creep analysis models are developed to elucidate the stress evolutions in an oxide scale/metal substrate system during isothermal oxidation, due to the oxidation growth strain in oxide scale. The theoretical works allow for the experimental inference of growth strain and stresses from the curvature measurements during oxidation. Moreover, they provide ways to explore and identify the main mechanisms for oxidation. Two sets of published experimental data are employed and analyzed by the elastic and creep analytical approaches. A novel simple determination method of the growth parameter is proposed and validated.Highlights► The elastic analysis model results confirm the Clarke model. ► A novel simple determination method of growth parameter is proposed and validated. ► The creep analysis model can precisely describe the realistic stress evolutions. ► We find Clarke model can be applied to case considering creep relaxation phenomena. ► The work serves as a basis for experimental work on stress measurement.

Sandwich cylindrical shells are the major components of aerospace structures. In this paper, an analytical investigation was carried out to examine the response of carbon fiber reinforced composite (CFRC) sandwich cylinders with lattice cores. An equivalent monocoque shell theory, was developed in this paper to predict mechanical behaviors of the quasi-isotropic sandwich cylinder, including the deformation and the multi-mode failure criterion. Five failure modes were suggested for the sandwich cylinder, including global buckling, face sheet mono-cell buckling/dimpling, face sheet local buckling, lattice rib crippling and strength failure. Using the suggested criterion, failure mode maps of the sandwich cylinder were acquired to instruct the design of the hierarchical sandwich cylinder with five geometrical variables. The method also correctly predicted the failure modes of the tested sandwich cylinder within acceptable errors.Highlights► An equivalent monocoque shell theory for lattice sandwich cylinders was developed. ► Five failure modes were suggested for lattice sandwich cylinders. ► Failure mode maps were depicted to instruct designing lattice sandwich cylinders. ► Failure mode map correctly predicted the failure style of the tested cylinder.

The thermodynamic behavior of stitched thermal protection structures is simulated using the finite-element method. The effects of stitching step on the thermal protection capability and the induced thermal stress in the stitched sandwich structures are numerically analyzed by ABAQUS codes. The stitched sandwich specimens consist of three components: the upper and lower skins, the heat insulation core and the stitches, and it modeled as a discrete stitched three-layer structure. The structure is subjected to reentry heating corresponding to the Access to Space Vehicle. Two numerical models, for the in-depth heat transfer and for the thermoelastic deformation, are coupled to yield the transient response of the stitched sandwich structures. A heating temperature of 1273 K with constant temperature, isothermal and periodic mechanical boundary conditions are considered. The transient temperature distribution and resultant thermal stresses are then computed. Five different stitching steps are considered and the results of simulations showed that: The ability of stitches in the stitched sandwich structures to improve heat conductivity is limited; however, it has significant influence on thermal stress in the stitched sandwich structures.

Extending the polarization saturation (PS) model and Yoffe crack model for ferroelectric materials, a moving PS model is proposed to study the problems of crack propagation considering the electrical nonlinearity. The model is solved using continuous distribution dislocation method. And the explicit expressions of the size of the electric saturation zone, intensity factors and the local energy release rate for the moving PS model are derived. It can be deducted from this model that the intensity factors and the size of the electric saturation zone are independent of the velocity of the crack. The local energy release rate for the moving PS model has the form of that for a stationary crack multiplied by the local energy release rate universal function f(v). And it increases monotonically with increasing v. When the velocity of the crack v → 0, the moving PS model will reduce to the static PS model. When the size of the electric saturation zone r → 0, the moving PS model is in agreement with the moving linear piezoelectric model.

High-temperature oxidation of metals induces residual stresses both in the metals and in the growing oxide scales. In this work, considering the case of asymmetric oxidation, a new analysis model to elucidate the residual stress evolutions in an oxide scale/metal substrate system during an isothermal oxidation process is developed. Elastic and creep deformations in both oxide and metal phases are considered in this work. The oxidation growth strain generated in oxide scale is also taken into account and is described by the Clarke model, that is, the growth strain rate increases linearly with the oxide thickening rate during isothermal oxidation. A comprehensive numerical study is carried out by the present approach. Results reveal that the proposed model can lead to an excellent agreement with the published experimental results and thus well validate the present model. Effects of the growth parameter, creep constants, Young’s modulus, and substrate thickness on the residual stress evolutions in the oxide scale/metal substrate system have also been discussed.

Based on the principle of superposition and a newly developed stripe method, an analytical equivalent model is proposed to calculate the stress fields in two imperfect planar isotropic lattices: the regular triangular lattice and the Kagome lattice, both containing single bar defects. Finite element simulations are used to validate the model predictions. According to the degree of the imperfection, four types of defects: vacancy defect, weak defect, strong defect, and rigid inclusion are classified and the induced local stress fields are analyzed. The stress concentration factor (SCF) caused by the imperfection is analytically obtained, and the influence of the imperfection degree, loading condition, and relative density on the SCF is quantified. Based on the equivalent model, the interaction of dual defects with the thickness of elastic boundary layer in the two lattices is also estimated. In the presence of a vacancy defect, the distinct deformation mechanism results in only a small knock-down in the strength of a triangular lattice but a substantial strength knock-down of a Kagome lattice. Both lattices exhibit no obvious sensitivity to the presence of a rigid inclusion. It is indicated that compared with the corresponding Kagome lattice, the triangular lattice containing a single missing bar possesses a considerable better strength performance. In addition, the analytical results of imperfection interaction demonstrate that the influence of imperfections on stress field calculations and strength analysis is important for the triangular lattice.

Fiber reinforced lattice composites are light-weight attractive due to their high specific strength and specific stiffness. In the past 10 years, researchers developed three-dimensional (3D) lattice trusses and two-dimensional (2D) lattice grids by various methods including interlacing, weaving, interlocking, filament winding and molding hot-press. The lattice composites have been applied in the fields of radar cross-section reduction, explosive absorption and heat-resistance. In this paper, topologies of the lattice composites, their manufacturing routes, as well as their mechanical and multifunctional applications, were surveyed.

A moving polarization saturation (PS) model is proposed to study the plane problem of a Yoffe-type crack moving with constant velocity in ferroelectric materials considering electric saturation. Based on the extended Stroh formalism, the model is solved using complex function method. The closed-form expressions for the electroelastic fields are obtained in a concise way. Results are shown to converge to known solutions for static PS model and the moving linear piezoelectric model. Numerical results for PZT-5H material are given graphically. It can be deducted that the dynamic intensity factors are dependent of the electric field and the velocity. It predicts that crack propagation may be promoted by a positive applied electrical field and inhibited by the negative one. For high crack velocity, 0.28 times minimum body wave speed, the hoop stress is maximal for an angle θ≠0.Highlights► We propose the moving polarization saturation model in ferroelectric materials. ► Dynamic intensity factors of stress, electric displacement are obtained. ► Results converge to static PS model and the moving linear piezoelectric model. ► Dynamic intensity factors of stress are dependent of electric field and velocity.

Light activated polymers (LAPs) are a class of contemporary materials that when irradiated with light respond with mechanical deformation. Among the different molecular mechanisms of photoactuation, here we study radical induced bond exchange reactions (BERs) that alter macromolecular chains through an addition-fragmentation process where a free chain whose active end group attaches then breaks a network chain. Thus the BER yields a polymer with a covalently adaptable network. When a LAP sample is loaded, the macroscopic consequence of BERs is stress relaxation and plastic deformation. Furthermore, if light penetration through the sample is nonuniform, resulting in nonuniform stress relaxation, the sample will deform after unloading in order to achieve equilibrium. In the past, this light activation mechanism was modeled as a phase evolution process where chain addition-fragmentation process was considered as a phase transformation between stressed phases and newly-born phases that are undeformed and stress free at birth. Such a modeling scheme describes the underlying physics with reasonable fidelity but is computationally expensive. In this paper, we propose a new approach where the BER induced macromolecular network alteration is modeled as a viscoplastic deformation process, based on the observation that stress relaxation due to light irradiation is a time-dependent process similar to that in viscoelastic solids with an irrecoverable deformation after light irradiation. This modeling concept is further translated into a finite deformation photomechanical constitutive model. The rheological representation of this model is a photoviscoplastic element placed in series with a standard linear solid model in viscoelasticity. A two-step iterative implicit scheme is developed for time integration of the two time-dependent elements. We carry out a series of experiments to determine material parameters in our model as well as to validate the performance of the model in complex geometrical and loading configurations. The comparison between the finite element simulations and experiments shows that the model can accurately capture the response of the LAP under a wide range of coupled photo-mechanical loading conditions, such as light induced stress relaxation, creep in tension, and bending. Furthermore, we demonstrate the versatility of the model by simulating a series of examples that exhibit complex three-dimensional, time-dependent photodeformation, including photoorigami, photoforming, and photobulge tests.

Experimental observations have shown the size-dependent residual surface stresses on spherical nanoparticles and their influence on the effective modulus of heterogeneous nanostructures. Based on these experimental findings, this paper proposes a new interface stress theory that considers the curvature effect on the interfacial energy. To investigate this curvature-dependent interfacial energy, we use the Green elasticity theory to describe the nonlinear constitutive relation of the interface at finite deformation, thus explicitly demonstrating the curvature-dependent nature of the interface stress and bending moment. By introducing a fictitious stress-free configuration, we then propose a new energy functional for heterogeneous hyperelastic solids with interfaces. For the first time, both the Lagrangian and Eulerian descriptions of the generalized Young–Laplace equation, which describes the intrinsic flexural resistance of the interface, are derived from the newly developed energy functional. This new interface stress theory is then used to investigate the residual elastic field in a heterogeneous hyperelastic solid containing interfaces. The present theory differs from the existing theories in that it takes fully into account both the curvature-dependence of the interfacial energy and the interfacial energy-induced residual elastic field in the bulk solid. Furthermore, the fundamental equations of the interface are given in Lagrangian description, which are preferable when considering the effects of residual interface stress, residual interface bending moment and interface elasticity. Finally, two examples are presented to shed light on the significance of this new interface stress theory. A more detailed analysis and applications of the new theory will be presented in Part (II) of this paper.

•Hierarchical structures greatly enhance anti-crushing behaviors of tubular structures.•Mean crushing forces of HLTs are three to four times higher in current research.•Improving mechanisms include hierarchical fold, short wave and great bending moment.•Progressive folding and global bending models were proposed.Hierarchy greatly enhances anti-crushing behavior of thin-walled tubular structures. To reveal the energy-absorbing mechanism, hierarchical triangular lattice structures with lattice-core sandwich walls were designed. Crushing experiments were carried out to reveal the progressive collapse modes and folding mechanisms. Compared with single-cell and multi-cell lattice structures, hierarchical structures possess greater mean crushing forces (MCFs), three to four times higher. Three mechanisms, including hierarchical folding, shortening wave length and enlarging plastic bending moment of sandwich wall, help hierarchical structure greatly enhance its anti-crushing behavior. Folding styles turning from single fold, multi-fold, hierarchical fold to single sandwich-fold when increasing micro-cells in the wall were revealed by numerical simulation to propose optimized hierarchical lattice structure possessing the best specific energy absorption (SEA). Based on progressive folding mechanism, global bending mechanism and hybrid folding mechanism, theoretical models were built to predict the MCF. The predictions are reasonable.Download full-size image

The unexpected thermal distortions and failures in engineering raise the big concern about thermal expansion controlling. Thus, design of tailorable coefficient of thermal expansion (CTE) is urgently needed for the materials used in large temperature variation circumstance. Here, inspired by multi-fold rotational symmetry in crystallography, we have devised six kinds of periodic planar lattices, which incorporate tailorable CTE and high specific biaxial stiffness. Fabrication process, which overcame shortcomings of welding or adhesion connection, was developed for the dual-material planar lattices. The analytical predictions agreed well with the CTE measurements. It is shown that the planar lattices fabricated from positive CTE constituents, can give large positive, near zero and even negative CTEs. Furthermore, a generalized stationary node method was proposed for aperiodic lattices and even arbitrary structures with desirable thermal expansion. As an example, aperiodic quasicrystal lattices were designed and exhibited zero thermal expansion property. The proposed method for the lattices of lightweight, robust stiffness, strength and tailorable thermal expansion is useful in the engineering applications.

•Failure modes and energy absorptions of multi-cell lattice tubes were revealed.•Lattice tubes have mean crushing forces 60–103% higher than single-cell tubes.•Plastic models were suggested to predict the mean crushing forces.•Multi-cell mechanisms include shortened wavelength and flange interactions.To enhance the energy absorbing ability of thin-walled structures, multi-cell tubes with triangular and Kagome lattices were designed and manufactured. Quasi-static axial compression experiments were carried out to reveal the progressive collapse mode and folding mechanism of thin-walled multi-cell tubes. Combining with the experiments, deformation styles were revealed and classical plastic models were suggested to predict the mean crushing forces of multi-cell tubes. Compared with anti-crushing behaviors of single-cell tubes, multi-cell lattice tubes have comparable peak loads while much greater mean crushing forces, which indicates that multi-cell lattice tubes are more weight efficient in energy absorption.

The internal temperature is the most effective parameter to determine whether the battery is entering the danger zone. However, it is also the most difficult to be monitored in real time. This paper focuses on the real-time monitor of internal temperature evolution of the lithium-ion coin cell battery during charge and discharge. First, the experimental set-up is introduced, which consists of four parts: the embedded sensor, incubator, data transmission and collection. This shows that the internal temperatures rise rapidly at the end of the discharge process while the difference between internal temperature and surface temperature is insignificant during the 0.5 C rate charge process. With the increasing C-rate, the heat generation rate increases correspondingly. Secondly, the influence of the embedded sensor on electrochemical performance is evaluated at different C-rates. It is found that the capacity difference is about 8.28% for the 0.1 C-rate charge process between the cases with and without the embedded sensor. With the increase of the charge rate, the capacity difference becomes larger and even approached 50% under 2 C-rate. Finally, a novel thermal model is developed to determine the heat transfer parameters for the coin cell based on the monitoring data. The heat flow during 1 C and 2 C discharge tests is calculated by the thermal model and temperature curves, which has the same tendency with the experimental results using the micro-calorimeter technique.

•Diffusion-induced stress of composition-gradient electrode plates is formulated.•Delamination of composition-gradient electrode plates is investigated.•Symmetric NE-gradient active plates can alleviate stresses and retard delamination.•PE-gradient bilayer active plates can alleviate stresses and retard delamination.Diffusion-induced stress can result in failure of layered electrodes in lithium-ion batteries during the process of fast lithiation and delithiation. Recent studies have demonstrated that the electro-chemo-mechanical properties of compositions-gradient nanoparticles are superior to those of homogeneous ones. In light of this aspect, we develop a theoretical model to probe the effects of composition-gradient on the stress evolution in layered electrodes. Our analysis concludes that, compared with the corresponding homogeneous structure, symmetrical negative-exponent gradient active plates or positive-exponent gradient bilayer electrodes can significantly reduce the maximum compressive stress and the stress drop at the electrode–collector interface, while the energy release rate of interface delamination is slightly weakened by it. These results, again, show that the composition-gradient could improve the mechanical performance of electrodes in lithium-ion batteries, and are instrumental to the design of electrode structures.

The low fracture toughness of the widely used piezoelectric and ferroelectric materials in technological applications raises a big concern about their durability and safety. Up to now, the mechanisms of electric-field induced fatigue crack growth in those materials are not fully understood. Here we report experimental observations that alternative electric loading at high frequency or large amplitude gives rise to dramatic temperature rise at the crack tip of a ferroelectric solid. The temperature rise subsequently lowers the energy barrier of materials for domain switch in the vicinity of the crack tip, increases the stress intensity factor and leads to unstable crack propagation finally. In contrast, at low frequency or small amplitude, crack tip temperature increases mildly and saturates quickly, no crack growth is observed. Together with our theoretical analysis on the non-linear heat transfer at the crack tip, we constructed a safe operating area curve with respect to the frequency and amplitude of the electric field, and validated the safety map by experiments. The revealed mechanisms about how electro-thermal-mechanical coupling influences fracture can be directly used to guide the design and safety assessment of piezoelectric and ferroelectric devices.

In this paper, the mode-I transient response of a semi-infinite conducting crack propagating in a piezoelectric material with hexagonal symmetry under normal impact loading is investigated. The integral transform methods together with the Wiener–Hopf technique are used to solve the mixed boundary value problem under consideration. The solutions of the coupled fields are derived for two cases, i.e., generalized Rayleigh wave exists or not. The dynamic stress intensity factor and dynamic electric displacement intensity factor as well as their universal functions are obtained in a closed form. The numerical results for two universal functions are provided to illustrate the characteristics of dynamic crack propagation. It is found that the universal functions for the dynamic stress and electric displacement intensity factors vanish when the crack propagation speed reaches the generalized Rayleigh speed which is the propagation speed of surface wave in a piezoelectric half-space with metallized surface. It is noted that the electromechanical coupling coefficient has an important influence on the dynamic fracture characteristics.

In this paper, a novel atomic-level computational method of perovskite ferroelectrics is established by combining the shell model and atomic-scale finite element method (AFEM). Its applicability is carefully testified for both bulk and nanoscale ferroelectrics, by comparing the calculated structural parameters and polarizations with the molecular dynamics (MD) simulations, first-principles calculations and experiment results. A comparison of the CPU time demonstrates that the developed method has a computational speed about 10 times over that of shell model MD method and its advantage becomes more evident as the computational scale becomes larger. Moreover, two effective calculation skills of long-range Coulomb force are introduced which can further enhance the computational efficiency by about 10 times. Using the developed atomic-level method, we investigate the various patterns of nanoscale domain structures in BaTiO3 and their evolutions under electrical loadings. A domain structure with coexistence of vortex and streamline polarization patterns is revealed. Furthermore, the simulations of domain evolutions not only reproduce well the two-step 90° domain switching process observed in experiments on single domain under an anti-parallel electric field, but also provide a full evolution diagram among different domain patterns under various electric fields. A quantitative analysis indicates that the direction-dependent coercive field of multi-domain structure can be well described by that of single domain based on a simple analytical model. This study on domain patterns and evolutions may help us understand the behaviors of ferroelectrics from the atomic level.

Material interfaces can be regarded as two dimensional curved surfaces since their thickness is negligibly small in comparison with their planar dimensions. Experiments and materials simulation have demonstrated that the elastic energy of interface depends not only on its strain but also on its curvature. In this paper, first, the curvature-dependence of interfacial energy is studied and an interfacial energy formula is formulated, which has simple form and clear physical meanings. Next, a linear small deformation interface stress model is developed. It considers the curvature effect on interfacial energy and suggests that it would be convenient and advantageous to employ the Lagrangian description-based fundamental equations of the interface to study interface problems, especially the effect of residual interface stress. Then, a micromechanics framework considering both the interface effect and particle size distribution is proposed to predict the overall elastic properties of nanocomposites. Finally, the developed interface model and micromechanics approach are applied to study the effective modulus of nanoparticle reinforced composites. The results show that the curvature effect causes a much stronger size dependence of the effective modulus and the influence of particle size distribution becomes obvious when the dispersion of the particle radius is large.

The ductile fracture behavior of two-dimensional imperfect lattice material under dynamic stretching is studied by finite element method using ABAQUS/Explicit code. The simulations are performed with three isotopic lattice materials: the regular hexagonal honeycomb, the Kagome lattice and the regular triangular lattice. All the three lattices are made of an elastic/visco-plastic metal material. Two typical imperfections: vacancy defect and rigid inclusion are introduced separately. The numerical results reveal novel deformation modes and crack growth patterns in the ductile fracture of lattice material. Various crack growth patterns as defined according to their profiles, “X”-type, “Butterfly”-type, “Petal”-type, are observed in different combinations of imperfection type and lattice topology. Crack propagation could induce severe material softening and deduce the plastic dissipation of the lattices. Subsequently, the effects of the strain rate, relative density, microstructure topology, and defect type on the crack growth pattern, the associated macroscopic material softening and the knock-down of total plastic dissipation are investigated.

This paper addresses the development of a magneto-elastic coupling dynamic loss hysteresis model for giant magnetostrictive materials (GMMs). Considering the eddy current loss and anomalous loss, a dynamic constitutive model is proposed to predict the dynamic hysteresis behavior of GMMs. The model is validated by comparing the predicted results with experiments. At first, the frequency effect and anisotropy effect on the domain distribution can be obtained. Moreover, the magnetostriction cannot return to the initial value near the coercive field as the magnetization does with the increasing frequency. It can be explained that the domain distribution changes with the increasing energy loss. The model is benefit for the design and control of GMMs actuators.

•A novel bulge apparatus was designed to study electromagnetic materials.•The mechanical-magnetic features of Ni film were studied by this new apparatus.•The ΔE effect of Ni film was observed and analyzed.•The mechanical electronic-magnetic characteristics of PZT/Ni film were discussed.A novel multiple functional bulge apparatus was designed to study the mechanical-electronic-magnetic characteristics of electromagnetic materials. The elastic modulus difference effect of Ni thin film was observed and it was about 22.16% in the demagnetized and magnetization saturated states. The mechanical-magnetic behaviors of Ni and lead-titanate zirconate (PZT)/Ni films were in-situ measured by using the new bulge systems, respectively. The evolutions of three key material properties in hysteresis loop including saturation magnetization, remanent magnetization and coercive field were discussed in detail, respectively. The mechanisms of mechanical-magnetic coupled behaviors of Ni and PZT/Ni films were analyzed with the aid of the competitive relationship of stress and magnetization. Similarly, the electronic-magnetic characteristics of PZT/Ni films were in-situ measured by using this experimental system. The evolution of saturated magnetization, remanent magnetization and coercive field Kerr signals were discussed with the magneto-elastic anisotropy energy point. In this paper, a suitable mechanical-electronic-magnetic bulge measurement system was established, which would provide a good choice for further understanding the multi field coupling characteristics of electromagnetic film materials.

In the literature, it has been demonstrated that residual surface stress and surface elasticity are two equally important parts of surface stress theory and that, generally, neither of these aspects can be neglected. In this paper, we develop a non-classical formulation of the Boussinesq problem with the surface effect, in which both the residual surface stress and the surface elasticity are considered. To take into account the surface effect, a Lagrangian description of the governing equations of the surface is adopted. The theoretical and numerical results in this paper show that the contributions of the residual surface stress and the surface elasticity to the stresses and displacements at the surface are not always equal. The residual surface stress mostly influences the normal stress, whereas the surface elasticity is a dominant factor in the in-plane shear stress. As an application of this formulation, the three-dimensional Hertzian contact problem at the nanoscale is studied. It is concluded that the surface effect strengthens the elastic contact stiffness. The smaller the contact region, the larger the contact stiffness. Finally, in terms of the dimensionless surface parameters, the influences of the residual surface stress and the surface elasticity on the stresses and displacements are further studied, and a simple scaling law for the stresses and displacements at the surface is constructed for the first time.