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。     

Probing the morphology and nanoscale mechanics of single poly(N-isopropylacrylamide) microgels across the lower-critical-solution temperature by atomic force microscopy

Submicrometer-sized particles of poly(N-isopropylacrylamide) (PNIPAM) are synthesized by surfactant-free radical polymerization. The morphology and nanomechanical properties of individual, isolated PNIPAM microgel particles at the silicon/air and silicon/water interfaces, below and above the PNIPAM volume-phase-transition temperature (VPTT), are probed by atomic force microscopy. In air, and in water below the VPTT, the PNIPAM spheres are flattened and adopt a pancakelike shape. Interestingly, above the VPTT the microgels adopt a more spherical form with increased height and decreased width, which is attributed to reduced interactions of the particles with the substrate. The elastic modulus calculated from force-indentation curves obtained for individual microgel spheres reveals that the stiffness of the particle's surface decreases by two orders of magnitude upon swelling in water. Additionally, the modulus of the PNIPAM spheres in water increases by one order of magnitude when crossing the VPTT from the swollen to the collapsed states, indicating a more compact chain packing at the particle surface.     

多壁碳纳米管增强水泥基复合材料的纳米力学性能

采用纳米压痕技术探讨了多壁碳纳米管(MWCNTs)对有骨料水泥基复合材料纳米尺度上力学性能的影响,分别对压痕模量(M)小于50 GPa和压痕硬度(H)小于4.0 GPa的数据进行了统计,对其频率分布进行了Gaussian函数(PDF)的解卷积分峰处理,并对低密度水化硅酸钙凝胶(LD C-S-H)和高密度水化硅酸钙(HD C-S-H)凝胶进行了定量的体积分数计算。结果表明,除LD C-S-H、 HD C-S-H、 Ca(OH)2(CH)外,还出现了一个假相。MWCNTs降低了水化产物中LD C-S-H的体积分数,提高了HD C-S-H的体积分数,提高了C-S-H凝胶的压痕模量,但利用压痕模量和压痕硬度统计结果计算出的各相体积分数存在一定的差异。MWCNTs作为一种纳米晶核,对HD C-S-H凝胶形成起到了一定的诱导作用,从纳观尺度阐释了MWCNTs对水泥基材料的改性机制。     

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...     

Mechanical properties of concrete containing phase-change material

This study aimed to investigate the mechanical properties of concrete containing solid–liquid phase-change material (PCM) and focused on two key factors. First, a systematic study on the mechanical performance of PCM-modified concretes was conducted, including compressive, elastic modulus, and shrinkage tests. Second, because PCM provides high latent heat during the solid–liquid phase change, the effects of the solid phase and liquid phase on the mechanical properties of concrete were also explored. Results of this study showed that the solid–liquid phase of PCM affected the mechanical properties of concrete. For example, the compressive strength of 10% PCM concrete in solid phase (23 °C) and liquid phase (40 °C) at 28 days was 29.30 and 19.57 MPa, respectively. In addition, with increasing PCM content, the mechanical properties were degraded. For example, 10, 20, and 30% of PCM content lowered the compressive strength by 35.4, 58.4, and 74.3%, respectively. Therefore, concrete with PCM may not be suitable for structural elements. However, PCM is an important solution for optimizing energy consumption in modern buildings. It can absorb or emit large amounts of heat to store or release thermal energy. These properties can be used to control building temperatures resulting in energy saving and carbon reduction.     

香螺壳的结构和微观力学性能

测量产自黄/渤海海域的香螺贝壳的硬度和弹性模量,研究了贝壳的结构与性能之间的关系.结果表明,香螺贝壳主要由方解石和文石两种矿物镶嵌在有机质中构成,方解石结构为不均匀的柱状晶,文石结构为多级超微的交错纹状结构,其中第三级结构为10-80 nm的纳米级纤维.文石的力学性能优于方解石的性能.贝壳类复合材料的压痕效应主要源于裂纹扩展,而微观裂纹扩展与晶体类型以及晶体结构的排列方式是密切相关的.方解石裂纹形状曲折、不规则且沿着方解石层的边界扩展,抗裂纹扩展能力较差;而文石压痕周围平直清晰,裂纹沿着其二级结构界面扩展,性能较好.     

硬化水泥浆体弹性模量细观力学模型

应用复合材料力学理论和有孔介质力学(Poromechanics)理论建立了一个描述硬化硅酸盐水泥浆体弹性模量的细观力学模型, 将硬化水泥浆体从不同尺度上划分为4个层次, 即C-S-H凝胶、 水泥水化产物、 水泥浆体骨架和水泥浆体, 分别应用不同的细观力学模型予以描述: 将C-S-H视为饱和的有孔介质; 应用Mori-Tanaka模型描述水泥水化产物的弹性性质; 应用三相模型(Three-phase model)模拟水泥浆体骨架的有效弹性模量; 最后, 再次应用Mori-Tanaka模型和有孔介质理论, 计算水泥浆体的排水和不排水弹性模量(Drained and undrained elastic moduli)。该模型所需要的参数为水泥浆体各个组成部分的自身弹性性质, 使用方便。通过预测文献中的实测结果, 证明了该模型的有效性。      

Friction and wear properties of quasi-periodic material coatings

Quasicrystalline (QC) materials are of interest not only because of their unique structure, but also because they exhibit unusual properties which are potentially useful in industrial applications. In the present study a range of aluminium-based QC alloys, in the form of plasma-sprayed coatings, has been produced and evaluated. For the first time the influence of heat treatment on the structure and properties of these coatings has been systematically investigated. Of the nine QC coatings investigated, those of the Al-Cu-Fe-Cr system and the Al-Pd-Mn system showed the most promising combination of good hardness with low coefficient of friction.     

周期性单胞复合材料有效弹性性能的边界力方法

均匀化方法是一种适应于周期性构造复合材料有效性能预测的有效方法。然而均匀化方程数学表达形式复杂, 均匀化方法很难直接应用通用有限元软件进行计算, 因此本文中提出一种便于求解均匀化方程的边界力方法, 利用高斯定理将原均匀化问题转化为普通的三维应力问题, 给出了单胞中不同材料交界面上作用的面分布力形式。运用有限元软件求解了均匀化系数, 预报了单向复合材料和三维四向编织复合材料的有效性能, 计算结果与实验吻合很好。      

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.     

聚四氟乙烯-芳纶/酚醛树脂斜纹织物衬垫不同磨损阶段弹性常数计算模型

为了探究磨损对聚四氟乙烯（PTFE）和芳纶（Kevlar）纤维及酚醛树脂基体（PTFE-Kevlar/酚醛树脂）编织成的斜纹织物衬垫宏观弹性常数的影响。基于复合材料细观力学中的数学模型和体积平均算法,结合斜纹衬垫的细观结构,建立了不同磨损阶段的细观几何模型。从未磨损阶段入手,基于纤维织物几何参数及纤维各自弹性常数,利用MATLAB计算衬垫纤维束和基体的各自体积分数及相关矩阵,实现斜纹织物衬垫局部坐标系与整体坐标系下的弹性常数转化。构建了未磨损阶段衬垫的弹性常数计算模型,并利用算例证明方法的正确性,理论值与试验值的最大误差为5.88%。在此基础上,根据衬垫的结构,把磨损划分为6个阶段,建立不同磨损阶段的弹性常数计算模型。      

Analysis of micro--macro material properties and mechanical effects of damaged material containing periodically distributed elliptical microcracks

The existence of numerous microcracks causes changes in the stiffness or fracture toughness of materials. In this paper, the manifestations of mechanical properties in the damaged materials caused by the microcracks are evaluated by the present homogenization method based on the superposition method together with the VNA solution. Moreover, it is known that the stress concentration at the macrocrack tip decreases due to the stress relaxation effect caused by the existence of the microcracks. In order to evaluate the manifestations of mechanical behavior, the mechanical effects of the existence of the microcracks on the macrocrack, the component separation method for mixed-mode stress intensity factors of the macrocrack in the damaged materials is newly developed in this paper. Various numerical analyses are successfully conducted for the two topics, the mechanical properties of the damaged materials and the mechanical behavior of the macrocrack in the damaged materials.     

Novel approach for fabrication and characterisation of porosity-graded material

A novel continuously graded material that is based on a porosity-graded structure was successfully synthesised via a cold pressing-vacuum sintering-dissolution process (SDP) of powder metallurgy technology. Microscopic observations and the Archimedes method were used to confirm the newly synthesised porosity-graded material, the mechanical properties and the modulus. The results show that the density continuously increased from 1.4 to 2.7?g?cm^?3, and there was no obvious interfacial transition layer. In addition, the hardness and elastic modulus were obtained from nanoindentation tests and display a stepwise feature along the gradient direction. Moreover, we found that the fractography changes from typical ductile fracture to ductile and cleavage fracture with an increase in the porosity.

Highlights

• A porosity graded material has been successfully synthesised by powder metallurgy.

• The density continuously transit from 1.4 to 2.7?g?cm^?3, and it has no obvious interfacial transition layer.

• The stepwise feature of density and modulus shows great potential in the shields of spacecrafts.

     

Procedure for the determination of torsional deformation relationships for anisotropic materials

The paper presents a procedure for the determination of torsional deformation relationships for prismatic specimens made of anisotropic material and construction of deformation curves under these conditions Translated from Problemy Prochnosti, No. 3, pp. 116–123, May–June, 2009.     

Microstructure and fracture morphology of thermally sprayed refractory metals and ceramics

The microstructural characteristics such as porosity, splat morphology and grain size of thermally sprayed coatings made of both ceramic and refractory metals are investigated. Al₂O₃ and Cr₂O₃ coatings represent ceramic materials while pure W and Mo coatings represent the refractory metals. The used deposition technology (RF-plasma, gas stabilized or water stabilized DC plasma) was found to influence the coatings microstructure to a great extent by providing different particle impact velocities and temperatures. At the same time the substrate temperature plays an important role as is shown for refractory metal coatings deposited at different substrate temperatures. Generally, all investigated coatings contained intrasplat cracks, intersplat pores and voids, individual splats of different degree of deformation and different degree of intersplat sintering, crystal grains formed inside individual splats or extending through many of them. It is shown that the size and abundance of the above-mentioned microstructural features predetermine the fracture morphology of the coating as well as mechanical properties. __________ Translated from Problemy Prochnosti, No. 1, pp. 89–92, January–February, 2008.     

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。      

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.     

树脂基深水浮力材料压缩性能研究

为探究空心微珠填充量对树脂基深水浮力材料压缩性能的影响以及材料压缩破坏机理,基于Mori-Tanaka及Turesanyi方法对空心微珠填充环氧树脂基深水浮力材料的有效弹性模量及压缩强度进行了理论预测.制备了空心微珠填充环氧树脂基深水浮力材料,对不同空心微珠填充比的材料体系进行了单轴压缩试验,并通过扫描电镜观察了材料断裂面微观形貌.结果表明:随着空心微珠填充量增加,材料体系耐压强度降低,模量上升,且实验结果与理论预测吻合情况较好;空心微珠破损是深水浮力材料破坏的根本因素.     

On the determination of interfacial stresses in a composite material

The conventional finite element method has been modified to allow the elastic stresses along the fibre matrix interfaces of a composite to be determined with improved accuracy. The results obtained by this 'modified' method are compared with both a photoelastic and some traditional finite element solutions.