A Single-Layer Piezoelectric Composite Separator for Durable Operation of Li Metal Anode at High Rates

Piezoelectric ceramic and polymeric separators have been proposed to effectively regulate Li deposition and suppress dendrite growth,but such separators still fail to satisfactorily support durable operation of lithium metal batteries owing to the fragile ceramic layer or low-piezoelectricity polymer as employed.Herein,by combining PVDF-HFP and ferroelectric BaTiO_(3),we develop a homogeneous,single-layer composite separator with strong piezoelectric effects to inhibit dendrite growth while maintaining high mechanical strength.As squeezed by local protrusion,the polarized PVDF-HFP/BaTiO_(3)composite separator generates a local voltage to suppress the local-intensified electric field and further deconcentrate regional lithium-ion flux to retard lithium deposition on the protrusion,hence enabling a smoother and more compact lithium deposition morphology than the unpoled composite separator and the pure PVDF-HFP separator,especially at high rates.Remarkably,the homogeneous incorporation of BaTiO_(3)highly improves the piezoelectric performances of the separator with residual polarization of 0.086 pC cm^(-2)after polarization treatment,four times that of the pure PVDF-HFP separator,and simultaneously increases the transference number of lithium-ion from 0.45 to 0.57.Beneficial from the prominent piezoelectric mechanism,the polarized PVDF-HFP/BaTiO_(3)composite separator enables stable cyclic performances of Li||LiFePO_(4)cells for 400 cycles at 2 C(1 C=170 mA g^(-1))with a capacity retention above 99%,and for 600 cycles at 5 C with a capacity retention over 85%.

Research into Applicability of Wöhler Curve Method for Low-Cycle Fatigue of Metallic Materials

Recently,a description on a practicability of the Wöhler Curve Method for low-cycle fatigue of metals was given by the author.By the description and the low cycle fatigue test data of 16 MnR steel,it is important to show that,for low cycle fatigue of metals,such a way that a stress-based intensity parameter calculated by the linear-elastic analysis is taken to be a stress intensity parameter,S,to establish a relationship between the stress intensity parameter,S,and the fatigue life,N,is practicable.In this paper,many metallic materials from the literature are given to show that the Wöhler Curve Method is well suitable for low-cycle fatigue analysis of metals.

A surfactant-modified composite separator for high safe lithium ion battery

Separators have been gaining increasing attention to improve the performance of lithium ion batteries(LIBs),especially for high safe and long cycle life.However,commercial polyolefin separators still face the problems of rapid capacity decay and safety issues due to the poor wettability with electrolytes and low thermal stability.Herein,a novel composite separator is proposed by introducing a surfactant of sodium dodecyl thiosulfate(SDS)into the polytetrafluoroethylene(PTFE)substrate with the binder of polyacrylic acid(PAA)through the suction filtration method.The introduction of PAA/SDS enhances the adsorption energy between PTFE substrate and electrolyte through density functional theory calculations,which improves wettability and electrolyte uptake of the separator significantly.The asachieved composite separator enables the LIBs to own high Li^(+)conductivity(0.64×10^(-3)S cm^(-1))and Li^(+)transference number(0.63),further leading to a high capacity retention of 93.50%after 500 cycles at 1 C.In addition,the uniform and smooth surface morphology of Li metal employed the composite separator after cycling indicates that the lithium dendrites can be successfully inhibited.This work indicates a promising route for the preparation of a novel composite separator for high safe LIBs.

Intelligent Molding Proceeding of Composites and Intelligent Manufacturing Systems for Composite Materials

The technology of Intelligent cure operation is set forth according to developing tendency of smart material and structure. Intelligent-system-based tool was developed in order to operate the autoclave cure of a fiber reinforced thermosetting matrix composite laminate in an optimal manner. The objective function is comforts for minimizing the total cure time, uniforming the temperature distribution, controling exothermal and minimizing the process-induced residual stresses in the laminate. Data is analyzed on-line to determine the trends in real-time. The results from application of this overall strategy for the curing of composites are presented.

Thermal expansion and mechanical properties of high reinforcement content SiC_(p)/Cu composites fabricated by squeeze casting technology

High reinforcement content SiCp/Cu composites (φp=50%, 55% and 60%) for electronic packaging applications were fabricated by patent cost-effective squeeze-casting technology. The composites appear to be free of pores, and the SiC particles are distribute uniformly in the composites. The mean linear coefficients of thermal expansion (CTEs, 20-100 ℃ ) of as-cast SiCp/Cu composites range from 8.8×10-6 ℃-1 to 9.9×10-6 ℃-1 and decrease with the increase of SiC content. The experimental CTEs of as-cast SiCp/Cu composites agree well with the predicted values based on Kerner model. The CTEs of composites reduce after annealing treatment due to the fact that the internal stress of the composite is released. The Brinell hardness increases from 272.3 to 313.2, and the modulus increases from 186 GPa to 210 GPa for the corresponding composites. The bending strength is larger than 374 MPa, but no obvious trend between bending strength and SiCp content is observed.

Discussion on electromagnetic crack face boundary conditions for the fracture mechanics of magneto-electro-elastic materials

This paper discusses electromagnetic boundary conditions on crack faces in magneto- electroelastic materials, where piezoelectric, piezomagnetic and magnetoelectric effects are coupled. A notch of finite thickness in these materials is also addressed. Four idealized electromagnetic boundary conditions assumed for the crack-faces are separately investigated, i.e. （a） electrically and magnetically impermeable （crack-face）, （b） electrically impermeable and magnetically permeable, （c） electrically permeable and magnetically impermeable, and （d） electrically and magnetically permeable. The influence of the notch thickness on important parameters, such as the field intensity factors, the energy release rate at the notch tips and the electromagnetic fields inside the notch, are studied and the results are obtained in closed-form. Results under different idealized electromagnetic boundary conditions on the crack-face are compared, and the applicability of these idealized assumptions is discussed.

Review:Recent Progress on Poly(ether ether ketone) and Its Composites for Biomedical, Machinery, Energy and Aerospace Applications

Poly(ether ether ketone)(PEEK)has drown researchers’wide attention because of the exceptional performances such as mechanical properties,thermal stability,chemical resistance,and biocompatibility.These properties endow it with broad potential use in biomedical,engineering,and aerospace applications.In addition,multifunctional fillers have been intensively incorporated into PEEK matrix,as it is conducive to the enhanced properties,and has the desired properties in concrete applications.This review introduced the basic content and synthesis pathway of PEEKs and their composites,focusing on the various applications,including biomedical,machinery,energy storage,and aerospace applications.Considerable efforts have been devoted to explore the concrete modified method to obtain the desired performances of PEEK based materials.At the end,existing problems and development directions for the PEEK based materials were analyzed and predicted.

A subregional model for delamination prediction of rubber composite under fatigue loading

Results from fatigue experiments of cross-laminated steel cord-rubber composites (SCRC) indicate that fatigue damage life can be categorized into three regimes. In terms of fatigue modes, a subregional fatigue model is developed to describe the damages evolution of SCRC under fatigue loads. Firstly, finite element analysis is introduced to determine interply stress distribution of the specimen. Then, based on the experimental fatigue data, subregional models are introduced to simulate relations between maximum strain, effective stiffness, delamination shear stress and fatigue cycles. Relations between crack density, delamination length growth rate, macro crack density and cycles are modeled by two semi-empirical models. A reasonable prediction result was achieved by the current model, where model parameters can be determined by basic outputs of fatigue testing.

Effect of temperature on the compressive behavior of carbon fiber composite pyramidal truss cores sandwich panels with reinforced frames

This paper focuses on the effect of temperature on the out-of-plane compressive properties and failure mechanism of carbon fiber/epoxy composite pyramidal truss cores sandwich panels （CF/CPTSP）. CFJCPTSP with novel reinforced frames are manufactured by the water jet cutting and interlocking assembly method in this paper. The theoretical analysis is presented to predict the out-of-plane compressive stiffness and strength of CFJCPTSP at different ambient temperatures. The tests of composite sandwich panels are per- formed throughout the temperature range from -90℃ to 180℃. Good agreement is found between theo- retical predictions and experimental measurements. Experimental results indicate that the low tempera- ture increases the compressive stiffness and strength of CF/CPTSP. However, the high temperature causes the degradation of the compressive stiffness and strength. Meanwhile, the effects of temperature on the failure mode of composite sandwich panels are also observed.

Auxetic mechanical metamaterials: from soft to stiff

Auxetic mechanical metamaterials are artificially architected materials that possess negative Poisson’s ratio,demonstrating transversal contracting deformation under external vertical compression loading.Their physical properties are mainly determined by spatial topological configurations.Traditionally,classical auxetic mechanical metamaterials exhibit relatively lower mechanical stiffness,compared to classic stretching dominated architectures.Nevertheless,in recent years,several novel auxetic mechanical metamaterials with high stiffness have been designed and proposed for energy absorption,load-bearing,and thermal-mechanical coupling applications.In this paper,mechanical design methods for designing auxetic structures with soft and stiff mechanical behavior are summarized and classified.For soft auxetic mechanical metamaterials,classic methods,such as using soft basic material,hierarchical design,tensile braided design,and curved ribs,are proposed.In comparison,for stiff auxetic mechanical metamaterials,design schemes,such as hard base material,hierarchical design,composite design,and adding additional load-bearing ribs,are proposed.Multi-functional applications of soft and stiff auxetic mechanical metamaterials are then reviewed.We hope this study could provide some guidelines for designing programmed auxetics with specified mechanical stiffness and deformation abilities according to demand.

Experimental Investigation of Folding Damage for the Rigidizable Carbon-Epoxy Composites

This paper focused on the folding damage behavior of the space rigidizable materials in terms of 3-1ayer composite membranes. An experimental scheme was presented. The composite membranes were folded between the two plates for a short time, and then the unfolded composite membranes were compressively cured in an oven. By adjusting the displacement of one plate, the folding radius was changed. As expected, the strength and effective modulus of the cured composite membranes drop with decreasing the folding radius. When the strain controlled failure rule is appliedto the composite membranes, a minimal folding radius can be reached, beyond which the membranes will keep intact.Furthermore, folding damage due to folding and unfolding processes was evaluated by a simplified model. Compared with the measured residual strength and effective modulus, calculated results have the same trend. A discrepancy is attributed to neglecting the effects of the transverse fibers and the matrix.

Thermal deformation analysis of the composite material satellite antenna

Controlling the thermal deformation is a crucial index for the design of the satellite antenna. To calculate and measure the satellite antenna’s thermal deformation is also an important step for the design of satellite antenna. Based on the foundation of equivalent assumption, the thermal deformation of the parabolic satellite antenna was analyzed by the finite element method for different design project. The best design project that had the minimum of the thermal deformation could be obtained through changing the lay-angle, lay-layers and lay-thickness of each layer. Results show the asymmetry structure has the minimum of thermal deformation. This paper may provide useful information for the further investigation on the coupling of thermal-stress structure.

Measurement of large deformation of nylon cord-rubber composite and effects of perpendicular loads on its stress-strain behaviors

Effects of transverse loads on longitudinal stress strain behaviors and longitudinal constant tensile loads on transverse stress strain behaviors of single ply of nylon cord rubber composite are studied respectively under biaxial tensile condition with cruciform specimen. Effects of transverse constant tensile load on longitudinal tensile mechanical properties are indistinctive compared with corresponding uniaxial longitudinal tensile mechanical properties. It can be relative to larger difference between longitudinal and transverse mechanical properties. Its dominating failure mode is typical fiber dominated mode; However, Experiment results indicate that transverse mechanical properties of nylon cord rubber composite with longitudinal constant tensile loads are distinct from its uniaxial transverse tensile mechanical properties. It can be attribute to action of longitudinal tension that makes material rigidify in the direction perpendicular to fiber, Mode of failure is representative of matrix dominated failure. For the measurement of large deformation up to 50 percent, a special CCD imaging method is employed in the experimental investigation that makes measurement of large deformations more precise.

Fabrication and thermo-physical properties of TiB_(2p)/Cu composites for electronic packaging applications

TiB_(2p)/Cu composites with high reinforcement content(φ_(p)=50%,58%and 65%)for electronic packaging applications were fabricated by squeeze casting technology.The microstructures and thermo-physical properties of the TiB_(2p)/Cu composites were investigated.The results show that TiB2 particles are homogeneous and distribute uniformly,and the TiB2-Cu interfaces are clean and free-from interfacial reaction products and amorphous layers,the densifications of the TiB_(2p)/Cu composites are higher than 98.2%. The mean linear coefficients of thermal expansion at 20-100℃for TiB_(2p)/Cu composites range from 8.3×10^(-6)to 10.8×10^(-6)/K and decrease with increasing volume fraction of TiB2.The experimental coefficients of thermal expansion agree well with the predicted values based on Turner’s model.The thermal conductivities of TiB_(2p)/Cu composites range from 167.3 to 215.4 W/(m·K),decreasing with increasing volume fraction TiB2.

Optimization analysis on gap size of molding for Pb-GF composite wire

Under the condition of equal flow, the maximum and minimum theoretical values of gap size were studied and an estimation equation was established for the clad extrusion of the brittle core cladded by plastic metal materials. The results show that the gap size is a key parameter for the continuous clad extrusion and the molding speed. Its maximum value (Hmax) is 0.24mm and the minimum one (Hmin) is 0.12mm. At a gap size of 0.18mm, the maximum of metal extrusion per unit of time and the optimal coating speed can be obtained.

Compressive testing and failure analysis of three-dimensionally reinforced carbon/carbon composites

It is important to reveal the performance of carbon/carbon composites subjected to complex loading, which can provide a basis for developing the failure laws of carbon/carbon composites. The uniaxial and biaxial compressive performances of three-dimensional reinforced carbon/carbon composites (3D C/C) were investigated in this paper. The results showed that the compressive strength becomes larger when the loading direction parallels to the z-direction of 3D C/C. The uniaxial compression failure was mainly caused by fracture fiber bundles to form an overall shear fault in the z-direction. The failure mode was delamination of fiber bundle/matrix interface for the x- and y-direction samples. The biaxial compressive failure of x-y direction compressioncompression specimen was caused by the low interlaminar shear strength. In addition,for y-z and z-x direction compression-compression samples,the shear-type failure was formed on the surface of the specimen plumbing the loading direction. Overall,the weak-interface is still a main factor to influent the fracture mechanism of 3D C/C.

Introduction to the Special Issue on Mechanics of Composite Materials and Structures

Plate,shell and panel are basic structures used in engineering and industry.These structures play an important role as main supporting component in all kinds of structures in machinery,civil engineering,ship building,flight vehicle manufacturing,etc.Composite materials and structures are widely used in aerospace,marine,automobile industries due to their designable characteristic,lightweight advantageous,high specific strength and stiffness.Common configurations include laminated materials,hybrid layered materials,sandwich core materials and structures(foam,honeycomb,corrugated and lattice cores,etc.).How to establish an accurate analytical and numerical model is one of the most important subjects in composite materials and structures.The topics discussed in this special issue include aspects of core-face bonding and reinforcement,enhancement of core mechanical properties and panel performance(including the role of structural hierarchy),and multifunctional advantages offered by different core constructions.In addition,the special issue discusses potential applications,including in morphing wing design,impact resistance and ultralightweight applications.Future research directions are discussed.

Functional Composite Materials with Ordered Micro-Structure

Colloidal crystal is an ordered array of monodis-persed colloidal submicrospheres,analogous to astandard crystal whose repeating units are atoms ormolecules.A natural example of colloidal crystalcan be found in the gem opal.The ideal opal struc-ture is a periodic close-packed three-dimensionalarray of silica microspheres.There are some exam-

ON THE CALCULATION OF ENERGY RELEASE RATE FOR VISCOELASTIC CRACKED LAMINATES

The energy release rate(ERR) of crack growth as the energy change at the same time t between the two states of the structure is redefined, one is with crack length a under the loading σ(t), the other is the state with crack length a+ Δ a under the same loading condition. Thus the defined energy release rate corresponds to the released energy when a crack grows from a to a+ Δ a in an infinitesimal time. It is found that under a given loading history, the ERR is a function of time, and its maximum value should correspond with the critical state for delamination to propagate. Following William’s work, the explicit expressions of ERR for DCB experimental configurations to measure the interfacial fracture toughness have been obtained through the classical beam assumption.

Design,fabrication,and dynamic mechanical responses of fiber-reinforced composite lattice materials

Fiber-reinforced composites are a popular lightweight materials used in a variety of engineering applications,such as aerospace,architecture,automotive,and marine construction,due to their attractive mechanical properties.Constructing lattice materials from fiber-reinforced composites is an efficient approach for developing ultra-lightweight structural systems with superior mechanical proper-ties and multifunctional benefits.In contrast to corrugated,foam,and honeycomb core materials,composite lattice materials can be manufactured with various architectural designs,such as woven,grid,and truss cores.Moreover,lattice materials with open-cell topology provide multifunctional advantages over conventional closed-cell honeycomb and foam structures and are thus highly desirable for developing aerospace systems,hypersonic vehicles,long-range rockets and missiles,ship and naval structures,and protective systems.The objective of this study is to review and analyze dynamic mechanical behavior performed by different researchers in the area of composite lattice materials and to highlight topics for future research.