浮空器蒙皮膜复合材料单轴拉伸力学性能及弹性常数

对新型飞艇蒙皮材料在0°、15°、30°、45°、60°、75°、90°七个偏轴方向单轴拉伸循环试验结果进行了分析,给出了残余应变和弹性模量随循环次数的变化规律;得出了由单层板理论推导出的关于弹性模量的本构关系对各功能膜层压合成的平纹织物膜复合材料适用性较差。使用VIC-2D数字散斑测量系统测出膜材在拉伸过程中的位移场和应变场,通过位移场求膜材的泊松比和通过应变场验证分析膜材拉伸破坏机制,并可以预测断口形态和位置。采用两种不同规格的试样测试膜材的单轴拉伸强度,通过对比发现采用试样3更能反应材料Uretek5876实际强度。本文工作对该材料应用于飞艇结构设计和分析具有参考价值。     

A closed form solution for linear and nonlinear free vibrations of composite and fiber metal laminated rectangular plates

In this paper, the nonlinear equations of motion for laminated composite rectangular plates based on first order shear deformation theory, which include shear deformation and rotary inertia, have been derived. Then, through introducing a force function, these equations reduced to a set of coupled nonlinear partial differential equations and a compatibility equation. By using the Galerkin method, for the first time, a nonlinear ordinary differential equation is obtained, which includes nonlinear inertia and stiffness terms. By using the multiple time scales method, analytical relations for nonlinear frequency and transverse displacement have been obtained. Results are compared with the literature and good agreement is achieved for both linear and nonlinear frequencies. After proving the validity of our work for isotropic rectangular plates and laminated rectangular plates, linear and nonlinear free vibration of a Fiber Metal Laminate panel have been investigated. Also the effects of some system parameters on the nonlinear frequency have been investigated.     

Mechanical characterization of steel/CFRP double strap joints at elevated temperatures

This paper examines the mechanical performance of steel/CFRP adhesively-bonded double strap joints at elevated temperatures around the glass transition temperature (T_g, 42 °C) of the adhesive. A series of joints with different bond lengths were tested to failure at temperatures between 20 °C and 60 °C. It was found that the joint failure mode changed from adherend failure to debonding failure as the temperature approached T_g. In addition, the ultimate load and joint stiffness decreased significantly at temperatures near to and greater than T_g, while the effective bond length increased with temperature. Based on the ultimate load prediction model developed by Hart-Smith for double lap joints and kinetic modelling of the mechanical degradation of the adhesive, a mechanism-based model is proposed to describe the change of effective bond length, stiffness and strength degradation for steel/CFRP double strap joints at elevated temperatures. The modelling results were validated by the corresponding experimental measurements.     

Mechanical property of magnesium alloy sheet with hardening deterioration at warm temperatures and its application for failure analysis: Part I - property characterization

The mechanical property of a thin AZ31B Mg alloy sheet (with the thickness of 0.5 mm) was characterized for its anisotropy, temperature-dependent hardening (including its deterioration) and strain rate sensitivity based on simple tension test data measured at 100 °C, 150 °C, 200 °C, 250 °C, respectively, in Part I. As for anisotropy, simple tension tests were performed along three (rolling, transverse and in-between) directions to calibrate the Hill1948 yield function. As for temperature-dependent hardening, the common practice is to characterize hardening only up to the uniform elongation limit and to extrapolate the data to cover the range beyond its limit. In this work, hardening as well as its deterioration (or softening) behavior observed beyond the uniform elongation limit was numerically characterized based on the inverse calibration method, in which strain rate sensitivity was also considered. The mechanical properties were confirmed to properly predict failure by strain localization for all the simple tension tests involved in the characterization procedure. Ultimately, the mechanical properties characterized in Part I were applied in Part II to analyze the failure by strain localization in the cross-shaped cup drawing tests developed as the benchmark problem for the NUMISHEET2011 conference [1].     

Preparation and characterization of new hybrid nanostructured thin films for biosensors design

The present paper reports on an innovative route for the preparation of new hybrid nanostructured thin films based on hydroxyapatite and functionalized polyurethane. Hybrid nanopowders based on hydroxyapatite and functionalized polyurethane have been synthesized by a hydrothermal method with high pressure and low temperature conditions and further used for spin coating deposition. Biocompatible thin films with a thickness of about 50 nm have been deposited onto Si/SiO₂/Ti/Au substrates and their properties recommend them suitable as possible electrodes for the fabrication of impedance biosensors. Hybrid materials with improved properties are obtained, combining the mechanical properties of polyurethane with biocompatible properties of hydroxyapatite (bioactivity and osteoconductivity). The presence of functional groups in polyurethane structure ensures the existence of strong interactions between components and an increased affinity of the thin films for further protein bonding in biosensor design. Hybrid nanostructured thin films based on hydrothermally synthesized hydroxyapatite-polyurethane nanopowders could enhance the amount of immobilized biomolecules in the construction of an impedance biosensor for diagnosis and therapy of bone diseases.     

Mechanical property analyses of porous low-dielectric-constant films for stability evaluation of multilevel-interconnect structures

The mechanical properties of porous low-dielectric-constant (low-k) thin films have been investigated for the stability evaluation of multilevel-interconnect structures using nanoindentation, microscratch, and four-point bending tests. Stress–strain curves of these films are proposed to predict their strengths and to explain their deformation behaviors. Real stress–strain behaviors are analyzed and confirmed by combining the experimental data obtained from nanoindentation and microscratch tests. Soft low-k films exhibit large plastic deformation, while hard and brittle films fracture early. The interfacial adhesion strengths and delamination behaviors between thin-film layers have been also studied using microscratch and four-point bending tests. The mechanical failure of interconnect structures depends on the inferiority of film strength or interfacial adhesion.     

Mechanical property and R-curve behavior of the B4C/BN ceramics composites

The B₄C/BN ceramics composites were fabricated by the hot-pressing process. In this paper, the mechanical property and R-curves behavior of the B₄C/BN composites were investigated. The fracture strength and fracture toughness of the B₄C/BN microcomposites and the B₄C/BN nanocomposites decreased gradually with the increasing content of h-BN. The fracture strength and fracture toughness of the B₄C/BN nanocomposites were significantly improved in comparison with the B₄C/BN microcomposites. The damage resistance and R-curves behavior of the B₄C monolith and the B₄C/BN composites were evaluated by the indentation-strength in bending technique (ISB). The fracture strength of the B₄C monolith, the B₄C/BN microcomposites and the B₄C/BN nanocomposites decreased gradually with the increase of the indentation load. The B₄C/BN nanocomposites retained relative higher fracture strength in comparison with the B₄C monolith and the B₄C/BN microcomposites under the equivalent indentation load. The B₄C monolith, the B₄C/BN microcomposites and the B₄C/BN nanocomposites all exhibited the rising R-curves behavior. The B₄C/BN nanocomposites exhibited the higher rising R-curve behavior than that of the B₄C monolith and the B₄C/BN microcomposites. The toughness mechanisms of the composites were investigated. The B₄C/BN composites with the h-BN content more than 20 wt.% exhibited excellent machinability. The slowly rising R-curves behavior remarkably improved the machinability of the composites.     

Development of viscoelastic/rate-sensitive-plastic constitutive law for fiber-reinforced composites and its applications. Part I: Theory and material characterization

The viscoelastic/rate-sensitive plastic constitutive law to describe the nonlinear, anisotropic/asymmetric and time/rate-dependent mechanical behavior of fiber-reinforced (sheet) composites was developed under the plane stress condition. In addition to the theoretical aspect of the developed constitutive law, experiments to obtain the material parameters were also carried out for the woven fabric composite based on uni-axial tension and compression tests as well as stress relaxation tests, while the numerical formulation and verifications with experiments are discussed in Part II.     

Preparation, characterization and applications of novel iminodiacetic polyurethane foam (IDA-PUF) for determination and removal of some alkali metal ions from water

The new type of ion chelating resin (IDA-PUF) has iminodiacetic group that was prepared from polyurethane foam (PUF) by the reaction between primary amine of PUF and monochloro-acetic acid. The IDA-PUF was characterized using infrared spectra, elemental and thermal analysis. The exchange properties and chromatographic behaviour of the new chelating resin were investigated for removal of some alkali metal ions (lithium, sodium and potassium) using batch and column processes. The maximum distribution coefficient (K_D) of trace alkali metal ions was in the pH range of 8–10. The kinetics of sorption of the alkali metal ions was found to be fast with average values of half-life of sorption (t_1/2) of 4.93 min. The values of ΔG, ΔS and ΔH were −3.86 kJ mol⁻¹, 57.73 J mol⁻¹ K⁻¹ and 14.41 kJ mol⁻¹, respectively, which reflects the spontaneous and endothermic nature of ion exchanger process. The average sorption capacity of IDA-PUF is 4.8 mmol/g for alkali metal ions, enrichment factors ≈40 and the recovery 95–100% were also achieved with average value of RSD% = 1.67. The proposed method has been successfully applied to preconcentrate, determinate and remove the alkali metal ions from different samples of water.     

Progressive damage modeling for large deformation loading of composite structures

A nonlinear constitutive model for large deformation loading at different strain rate condition was developed to represent tensile progressive damage of the nonlinear large deformation rate dependent behavior of polymer-based composite materials. The material was characterized by using off-axis composite specimens at different strain rates. A new failure criterion was proposed for the analysis of different loading directions and strain rates. Based on a method of combining the nonlinear constitutive theory and the proposed failure criterion for different strain rates, the progressive damage behavior of large deformation composites was represented. The strength of the material was also successfully represented with a single material constant.     

Experimental characterization of phenolic-impregnated honeycomb sandwich structures for transportation vehicles

In the present paper the main outcomes of an experimental characterization on phenolic impregnated honeycomb sandwich structures are presented. The experimental investigations addressed both the static and dynamic properties of novel sandwich material, manufactured expressly for transportation industry and both the structural and impact behavior of the sandwich configuration. Moreover in order to fulfill design requirements, the prediction of the material properties and structural behaviors of sandwich structures due to environmental degradation have been assessed using accelerated aging tests. The outcomes herein presented provide information for the modification of design parameters to minimize the influences of the environmental factors and the adverse effect of in-service impact events.     

颗粒增强金属基复合材料力学行为有限元模拟研究现状

从细观尺度和宏观尺度两个方面分析总结了国内外颗粒增强金属基复合材料有限元模拟研究现状.介绍了基于几何建模的周期性单胞模型、基于实际微观结构的有限元模型及宏观尺度模拟几个方面的内容,并对目前该领域存在的问题及今后的研究方向进行了分析总结.     

Synthesis and characterization of binary chromophore polymers for electro-optic application

We prepared the side-chain electro-optic polymers by the active bonding of cyanate- and hydroxy-functional groups, and employed these side-chain polymers as hosts for the bi-chromophore system to enhance the electro-optic coefficient (r₃₃). In singular chromophore polymer (in PMMA host), the dependence of EO response on loading concentration was examined, r₃₃ about 26 pm/V was obtained. In order to further incorporate the chromophore, the loading behavior in binary chromphore systems was investigated. The optimal r₃₃ more than 40 pm/V was achieved, which was almost the sum of two individual polymers. Furthermore, the temporal stability at room temperature and 85 °C, respectively, over 500 h was evaluated for the potential application on electro-optic devices.     

Mechanical characterization and drug permeation properties of tetracaine-loaded bioadhesive films for percutaneous local anesthesia

In the development of bioadhesive patch devices for percutaneous local anesthesia, the tensile properties of the films produced after the casting of the gel intermediates is of key importance to the clinical compliance of the product, and its effective delivery of the local anesthetic agent. A range of bioadhesive patches were formulated and their mechanical and in vitro permeation properties determined. Altering formulation significantly altered the mechanical properties of films. The tensile properties of the films could be modified to allow concomitant benefits in the mechanical and drug permeation properties of the films, ensuring that patches not only exerted clinically beneficial effects, but are also mechanically robust. Tetracaine was found to plasticize films and while this effect was weak, it was significant both statistically and potentially also in the effect it has on the clinical use of these devices. Drug release from tetracaine patches demonstrate the same trends as found previously across polydimethylsiloxane films. By altering the formulation of the patch device, the drug release from the device to the skin is readily and accurately controlled, and was not solely a function of the stratum corneum barrier properties but additionally of the formulation.     

A path-independent integral for the characterization of solute concentration and flux at biofilm detachments

A path-independent (conservation) integral is developed for the characterization of solute concentration and flux in a biofilm in the vicinity of a detachment or other flux limiting boundary condition. Steady state conditions of solute diffusion are considered and biofilm kinetics are described by an uptake term which can be expressed in terms of a potential (Michaelis–Menten kinetics). An asymptotic solution for solute concentration at the tip of the detachment is obtained and shown to be analogous to that of antiplane crack problems in linear elasticity. It is shown that the amplitude of the asymptotic solution can be calculated by evaluating a path-independent integral. The special case of a semi-infinite detachment in an infinite strip is considered and the amplitude of the asymptotic field is related to the boundary conditions and problem parameters in closed form for zeroth and first order kinetics and numerically for Michaelis–Menten kinetics.     

锂离子电池斜方锰酸锂阴极材料的合成与表征

用一步固相法合成了斜方锰酸锂,对其进行了表征并确定了前驱体化合物烧结中的转变过程,以及相互化合间的烧结机制．结果表明,随着煅烧温度的升高,杂相减少,生长出主体相斜方锰酸锂．在700℃以上可以生成均一相的层状斜方类球状和棒状锰酸锂颗粒．两种颗粒的粒度分别为1～5μm和5～15μm．在充放电循环中,斜方锰酸锂结构易于向尖晶石结构转变．在2．5～4．5V范围内以20mA／g电流进行充放电循环,斜方锰酸锂的初始充电容量达到247mAh／g,放电容量为133mAh／g,50次循环后,容量保持率为92％．     

Synthesis, characterization, and gas-sensing property for HCHO of Ag-doped In2O3 nanocrystalline powders

Pure and Ag-doped In₂O₃ nanocrystalline powders with different doping concentrations have been prepared by a sol–gel method, and characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectrum (XPS). The results indicated that these powders had a good crystalline structure with an average crystallite size of 12 nm. The indirect heating structure sensors were fabricated by loading these powders on ceramic tubes with Au electrodes. Gas-sensing measurements indicated that the sensor fabricated from 8 wt.% Ag-doped In₂O₃ could detect HCHO gas down to 2 ppm with a short response time (10–15 s) and an excellent selectivity at 100 °C.     

Creep Behavior of As-Cast Ti-48Al-2Cr Intermetallic Alloy for Aerospace and Automotive Applications

The creep properties of as-cast Ti-48Al-2Cr (at%) alloy which had been strengthen with addition of 2 at% Cr were investigated. Tensile creep experiments were performed in air at temperatures from 600-800°C and initial stresses ranging from 150 to 180 MPa. Stress exponent and activation energy were both measured. Data indicates that the alloy exhibits steady state creep behavior and the steady state creep rate is found to depend on the applied load and temperature. The measured power law stress exponent for steady state creep rate is found to be close to 3 and the apparent activation energy for creep is calculated to be 15.7 kJ/mol. The creep resistance of the present alloy was also compared with binary Ti-48Al (at%) to evaluate the effect of Cr addition on creep resistance of TiAl. It is concluded that addition of 2 at% of Cr does not have significant effect on the creep resistance of TiAl.