硬质涂层力学性能可靠测量的两步压入法

正确测量涂层的硬度等力学性能一直是硬质涂层生产和研究中亟待解决的问题。本文提出的采用力学探针对涂层进行两步压入的实验方法可以在未知涂层厚度的条件下通过大载荷逐步加载展示出涂层厚度对载荷选择的要求，从而正确选择加载载荷进行小载荷压入实验。由此方法得到的涂层硬度值和其它力学性能指标具有准确和可靠的特点。     

Effective elastic modulus and micro-structure damage of particle-reinforced composites

A new analysis method of effective elastic modulus for composites has been developed by combining Eshelby’s equivalent inclusion method and self-consistent method. The equations obtained can describe the evolution of debonding damage of the composites with multi-phase particles and single-phase particles. Based on the incremental relation between particles and the matrix, the incremental constitutive relations of composite, matrix, particles and voids have been developed. Numerical analysis has been conducted for Ramburg–Qsgood function incorporating with equivalent elastic modulus obtained. The constitutive equation curves for different particle volume fractions can describe the influence of debonding damage on effective elastic modulus of the composites. Numerical results of the present study have a better agreement with the experimental results.     

Effective elastic properties of solids with irregularly shaped inclusions

A unit rectangular cell is usually cut out from a medium for investigating fracture mechanism and elastic properties of the medium containing an array of irregularly shaped inclusions. It is desirable to clarify the geometrical parameters controlling the elastic properties of heterogeneous materials because they are usually embedded with randomly distributed particulate. The stress and strain relationship of the rectangular cell is obtained by an ad hoc hybrid-stress finite element method. By matching the boundary condition requirements, the effective elastic properties of composite materials are then calculated, and the effect of shape and arrangement of inclusions on the effective elastic properties is subsequently considered by the application of the ad hoc hybrid-stress finite element method through examining three types of rectangular cell models assuming rectangular arrays of rectangular or diamond inclusions. It is found that the area fraction (the ratio of the inclusion area over the rectangular cell area) is one dominant parameter controlling the effective elastic properties.     

Radial mechanical properties of single-walled boron nitride nanotubes

The radial mechanical properties of single-walled boron nitride nanotubes (SW-BNNTs) are investigated by atomic force microscopy. Nanomechanical measurements reveal the radial deformation of individual SW-BNNTs in both elastic and plastic regimes. The measured effective radial elastic moduli of SW-BNNTs are found to follow a decreasing trend with an increase in tube diameter, ranging from 40.78 to 1.85 GPa for tube diameters of 0.58 to 2.38 nm. The results show that SW-BNNTs have relatively lower effective radial elastic moduli than single-walled carbon nanotubes (SWCNTs). The axially strong, but radially supple characteristics suggest that SW-BNNTs may be superior to SWCNTs as reinforcing additives for nanocomposite applications.     

Reflective properties of nanoparticle-arrayed surfaces

The reflective properties of nanostructured surfaces, fabricated by laying nanoparticles in a square arrangement on the substrate, were investigated theoretically. Maxwell's equations relating to the subwavelength structure were solved by a rigorous coupled-wave analysis (RCWA), and the results were compared with those of two approximation methods, i.e., the effective medium theory (EMT) and the effective single-layer model (ESL), which have been used extensively in the prior literature. The study presents an analysis of the reflectance characteristics subject to the influences of the size of the nanoparticles, their refractive index, and the surface nanoparticle density. The calculated results revealed that, disregarding variations in the refractive index of the nanoparticles and the surface nanoparticle density, a nanostructured surface with particles of ∼ 120 nm in diameter yields the optimal performance for antireflection with respect to the visible-light region. It was found that, for large particle sizes and refractive indices of the nanoparticles, the results calculated by EMT and ESL may result in considerable deviations relative to those calculated by RCWA and that regarding the nanoparticle-arrayed structure as a gradient refractive-index layer or as a homogeneous layer is inappropriate.     

东方龙虱鞘翅内表皮层及断面硬度和弹性模量

研究了东方龙虱去除外表皮后的鞘翅内表皮层及其鞘翅断面的力学性能。利用纳米压痕仪测得鞘翅内表皮层硬度和弹性模量分别为(0.065±0.007) GPa和(0.704±0.013) GPa, 均远远小于鞘翅外表皮层的硬度和弹性模量。鞘翅断面的力学性能测试结果表明: 在鞘翅横断面上, 靠近联接部位的硬度和弹性模量略大于鞘翅中部和外侧; 而在鞘翅纵向断面上, 鞘翅中部的硬度和弹性模量明显大于头部和尾部, 其断面力学性能呈现一定的分布规律。      

铜/钢爆炸焊接头界面组织及力学性能研究

为了揭示铜/钢爆炸焊接的结合机理,采用光学显微镜(OM)、扫描电子显微镜(SEM)和纳米压痕仪等对T2纯铜/Q245钢爆炸焊接头结合界面组织和微力学性能进行了分析.结果表明:T2纯铜/Q245钢爆炸复合板结合界面呈现较规则的正弦波形,界面结合良好,界面处原子发生强烈扩散,形成了过饱和铜钢固溶体;界面不同区域固溶体微力学性能不同,纳米硬度在2.02~3.08 GPa,弹性模量在129.6~172.1 GPa;由界面弹性模量分布云图可知,固溶体层连续分布在界面上,由于界面原子扩散程度不同,部分区域的固溶体层厚度很薄,在光镜下很难识别,而在波峰处固溶体则比较明显.固溶体的弹性模量均比铜基体的大,其原子键合强度强于铜基体原子,在一定程度上增强了界面的结合强度,从而使界面的结合强度高于铜基体;爆炸焊接头的拉剪试验断裂位置均位于铜侧,也证实了界面结合强度高于铜基体的强度。     

Influence of reinforcement and processing on steel-based composites: Microstructure and mechanical response

Steel matrix composite reinforced with 2–4 vol.% titanium diboride particles was fabricated successfully by powder metallurgy route through hot pressing method. Influence of sintering parameters on densification was investigated by measurement of density of resultant composites. Microstructural analysis of hot-pressed materials was performed. Hardness and deformation behavior under constant load were evaluated by conducting microhardness and nanoindentation tests. The addition of titanium diboride proved to be effective for enhancement of hardness and strength. Composite with 4 vol.% titanium diboride sintered at 1100°C resulted in improved hardness and elastic modulus which could be related to Orowan strengthening resulting from homogeneous distribution of fine titanium diboride particles in steel matrix. The results indicate that proposed method is economically feasible to process steel matrix composites with improved properties. A comparatively lower temperature and pressure offers better control of interface kinetics and microstructure.     

Effective mechanical properties of EM composite conductors: an analytical and finite element modeling approach

An analytical model and numerical approach to predict the effective mechanical properties of a composite conductor consisting of metallic core and insulation layers are presented in this paper. The analytical model was developed based on a two-step homogenizations and mechanics analysis for composite unit cell. The Step 1 homogenization derives the effective properties of the out-wrapped composite insulation layers. The Step 2 homogenization further smears the metallic core and the effective composite insulation layers to develop homogenized mechanical properties for composite conductor according to appropriate homogenization sequences. The procedure of using numerical approach and finite element method to determine the unit cell effective constants were also described and the results of the FEA prediction were presented. The analytical predictions were compared well to the numerical results for the nine material constants that characterize the effective mechanical properties of the composite conductor.     

Ultrasonic technique as tool for determining physical and mechanical properties of frozen soils

Ultrasonic velocities of compressional and shear waves in frozen sand, silty-sand and silt were measured at subfreezing temperature and the relationship between acoustic and physical-mechanical properties examined. Ultrasonic measurements revealed that the influence of temperature on ultrasonic velocities is due to the phase transition from water to ice. Different methods were proposed to determine the amount of unfrozen water in frozen soils. The unfrozen water content was measured directly by time domain reflectometry and compared to predicted values using different theoretical approaches. The prediction models showed good agreements with measured values at low temperatures. However, the shape of the curves obtained did not completely satisfying as the estimated unfrozen water fraction near 0 °C was significantly greater than the measured values. Finally, based on the elastic wave theory and measured acoustic velocities the elastic constants of the frozen soils were calculated. The changes in elastic constants were found to be related to the increase in ice content, ice stiffness by ice cementation and a decrease in unfrozen water content.     

Effective properties of layered magneto-electro-elastic composites

A micro-mechanics model is established to evaluate the effective properties of a layered composite with piezoelectric and piezomagnetic components. In the approach the mechanical and electromagnetic continuity conditions across an interface of two dissimilar media is incorporated, decomposing those quantities such as the stress/strain, electric displacement, electric field intensity, magnetic induction, and magnetic field intensity into two orthogonal complementary parts. Accordingly, the linear coupling effect between elasticity, electricity and magnetism of the composite is derived. Numerical results for a BaTiO₃–CoFe₂O₄ composite with 2-2 connectivity are obtained using the model, and some interesting results are discussed.     

Structural,mechanical, and electrical properties of carbon nanoparticles synthesized from diesel

We studied the elemental analysis, structural morphology, mechanical, and electrical properties of carbon nanoparticles synthesized from diesel. The spherical carbon particle size in the range of about 10 to 80 nm in diameter was observed in scanning electron microscope (SEM) studies that were identified by Atomic force microscopy (AFM) study as an aggregation of carbon particles of average size 2.5 nm. The surface rms of carbon nanoparticle thin film (CNTF) was measured directly by AFM and found 0.22 nm. The Derjaguin–Muller–Toporov (DMT) elastic modulus of carbon nanoparticles (CNPs) was measured by PeakForce QNM mode of AFM. The minimum and maximum elastic modulus was measured of 0.40 GPa and 43.89 GPa, respectively. The resistivity, conductivity, magneto resistance, mobility, and average Hall co-efficient were measured by “Ecopia Hall-effect measurement system” by four-point Van der Pauw approach at ambient condition. We demonstrated I–V characteristic at the Indium/CNTF thin film interface, which is accompanied by rectifying behavior.     

Effective properties of composites with embedded piezoelectric fibres

The present work deals with the modelling of 1–3 and 0–3 composites made of piezoceramic fibres embedded in a soft non-piezoelectric matrix. We especially focus on the longitudinal and transversal effective piezoelectric constants as a function of several micromechanical parameters such as the fibre volume fraction or the aspect ratio. Finite-element results, based on the concept of a cell model, are compared with results of analytical approaches. This study is restricted to linear piezoelectricity and quasistatic cases.     

Effect of the nature of fillers and ultraviolet irradiation on the mechanical properties of epoxy composite coatings

The effect of ultraviolet irradiation, the physical nature and percentage of fine-grained fillers on the mechanical properties of composites has been studied. It has been found that the ultraviolet irradiation of epoxy compositions causes a decrease in the adhesive strength and an increase in the cohesive strength of protective coatings. This has been proved to be due to a change in the course of physicochemical processes at the filler/epoxy oligomer interface, owing to which external surface layers, which have a considerable extent and a high degree of cross-linking, are formed around fine particles in the matrix. Translated from Problemy Prochnosti, No. 4, pp. 117–123, July–August, 2009.     

4J29可伐合金材料低温热物性及弹性模量测试

为了研究4J29可伐合金的低温热物性和机械性能,为低温系统的设计、结构变形、力学稳定性、装调和光学校准等提供技术保障,分别选用"稳态纵向热流法"、"稳态法"测试了4J29可伐合金在77—300 K温区的热导率和比热容,采用弹性模量试验机测试了77—300 K温区的弹性模量系数。通过标准样品材料TC4对比及误差分析,证明热导率测量误差在9%以内,其它误差均控制在6%以内。     

炭基复合材料与人骨的力学性能对比分析

选用3种炭基复合材料,分别为采用化学气相沉积（CVD）工艺和CVD/浸渍复合工艺制备的2种C/C复合材料以及采用CVD/熔融渗硅（MSI）工艺制备的C/C-SiC复合材料,通过对比分析3种炭基复合材料与人骨的微观结构和力学性能,研究了所选用的3种炭基复合材料作为新型骨折内固定材料的可行性。结果表明:3种炭基复合材料与人骨均具有纤维增强、多孔基体的微观结构形态。在力学性能方面,3种炭基复合材料的弹性模量与人骨都较为接近,其中C/C-SiC复合材料的力学性能与人骨最为接近,分别为弯曲强度213.0 MPa、剪切强度19.3 MPa、压缩强度228.1 MPa,有望成为理想的接骨板材料。CVD和CVD/浸渍工艺制备的C/C复合材料,弯曲强度分别仅为161.8 MPa和174.6 MPa,低于人骨的弯曲强度,后期可通过改进坯体结构和制备工艺等方法来使其力学性能与人骨相匹配。      

Effective properties of three-phase electro-magneto-elastic composites

Coupling between the electric field, magnetic field, and strain of composite materials is achieved when electro-elastic (piezoelectric) and magneto-elastic (piezomagnetic) particles are joined by an elastic matrix. Although the matrix is neither piezoelectric nor piezomagnetic, the strain field in the matrix couples the electric field of the piezoelectric phase to the magnetic field of the piezomagnetic phase. This three-phase electro-magneto-elastic composite should have greater ductility and formability than a two-phase composite in which the electric field and the magnetic field are coupled by directly bonding two brittle materials. A finite element analysis (FEA) and micromechanics based averaging of a representative volume element (RVE) are performed in this work to determine the effective dielectric, magnetic, mechanical, and coupled-field properties of an elastic matrix reinforced with piezoelectric and piezomagnetic fibers as functions of the phase volume fractions, the fiber arrangements in the RVE, and the fiber material properties with special emphasis on the poling directions of the piezoelectric and piezomagnetic fibers. The effective magneto-electric moduli of this three-phase composite are found to be less than the effective magneto-electric moduli of a two-phase piezoelectric/piezomagnetic composite, because the elastic matrix is not stiff enough to transfer significant strains between the piezomagnetic and piezoelectric fibers.     

AlTiN layer effect on mechanical properties of Ti-doped diamond-like carbon composite coatings

Ti/Ti-doped diamond-like carbon (DLC) and Ti/AlTiN/Ti-DLC composite coatings were deposited by magnetron sputtering on W18Cr4V high speed steel substrates. The effect of the AlTiN support layer on the properties of these composite coatings was investigated through microstructure and mechanical properties characterization, including hardness, elastic modulus, coefficient of friction and wear properties measured by scanning electron microscopy, Raman spectroscopy, scratch and ball-on-disk friction tests. Ti and AlTiN interlayers have a columnar structure with 50-80 nm grains. The hardness and elastic modulus of Ti/Ti-DLC and Ti/AlTiN/Ti-DLC coatings is 25.9 ± 0.4, 222.2 ± 6.3 GPa and 19.3 ± 1, 205.6 ± 6.7 GPa, respectively. Adhesion of Ti-DLC, Ti/AlTiN/Ti-DLC and AlTiN/Ti-DLC coatings expressed as the critical lateral force is 26.5 N, 38.2 N, and 47.8 N, respectively. Substrate coefficient of friction without coatings is 0.44, and it is 0.1 for Ti/Ti-DLC and Ti/AlTiN/Ti-DLC coatings. Wear resistance of Ti/AlTiN/Ti-DLC composite coatings is much higher than Ti/Ti-DLC coatings based on the wear track width of 169.8 and 73.2 μm, respectively, for the same experimental conditions.     

等离子喷涂热障涂层材料弹性模量与硬度的压痕测试分析

采用纳米压痕法,研究了经高温热循环处理后的等离子喷涂热障涂层材料弹性模量和硬度的抛物线式演变规律,并采用 Weibull统计分析方法对纳米压痕测试数据进行了处理和分析,提高了实验数据的可靠性.结果表明,经过高温热循环处理之后,不同位置处的热障涂层弹性模量和硬度都呈现出明显的各向异性分布.随着热循环次数的增加,涂层表面和...     

Static and dynamic mechanical properties of polydimethylsiloxane/carbon nanotube nanocomposites

The purpose of this study is to investigate the static and dynamic mechanical properties of polydimethylsiloxane (PDMS) and the mixture of PDMS and carbon nanotubes. The PDMS/CNT nanocomposites were stirred by an ultrasonic instrument to prevent agglomerations. The tested specimens of nanocomposites were manufactured by using the thermoforming method at 150 °C for 15 min. A micro tensile tester was adopted in this testing system with a maximum load of 500 mN and a crosshead extension of 150 mm. The static elastic modulus can be calculated by means of a tensile test and the average elastic modulus of pure PDMS is 1.65 MPa. In addition, the Nano Bionix tensile tester was also used to perform the dynamic mechanical analysis. Its dynamic frequency range is from 0.1 Hz to 2.5 KHz. The dynamic properties of PDMS/CNT nanocomposites such as storage and loss modulus can be obtained by this system. The storage modulus increased with the CNT content and also with the higher frequencies. Finally, the nanoindentation measurement system was employed to characterize the mechanical properties of PDMS and PDMS/CNTs. The measurement results of elastic modulus by a nanoindentation test have the similar trend with the results obtained by the tensile test method.