Acoustic-emission evaluation of the process of destruction of a composite material under tensile,compression, and cyclic loads

Destruction of the structure of polymer composite materials (PCMs) has been studied by acoustic-emission evaluation method under tensile, compression, and alternating-sign cyclic loads. A program of cluster classification of registered data arrays has been developed and used to reveal specific AE signals that are typical of studied load types. Detection of such signals in the course of deformation of the test samples indicates that irreversible structural changes occur in the composite, it is losing its carrying capacity, or a predestruction state that is critical for PCM has been reached.     

Hashin准则的应力应变形式在复合材料渐进损伤计算中的对比

Hashin准则在复合材料渐进损伤分析中得到广泛应用,它的原始形式用应力表达,而在渐进损伤实际计算中用到了应变形式。推导了这两种形式下渐进损伤计算中需要的复合材料非线性本构关系及对应的切线刚度矩阵,对比分析了它们之间的不等价性。将这两种Hashin准则形式与不同损伤演化模型相结合,应用于开孔板的渐进损伤数值模拟,并与试验数据相对比。将Linde损伤演化模型分别与Hashin准则变形式和应力形式组合,前者的计算结果与试验值符合更好;将Sleight损伤演化模型与Hashin准则应力形式相结合,选取不同的衰减控制参数进行数值模拟,控制参数取0.8时比取其他值与试验结果符合更好。理论推导和数值模拟结果对复合材料渐进损伤实际应用中合理选取损伤准则形式和损伤演化模型有指导意义。     

Deformation and strength properties of a carbon–carbide composite with 2D reinforcement under plane stress state

Data of an experimental–theoretical investigation of the deformation and strength characteristics of a carbon–carbide composite with a 2D reinforcement scheme are given. The nonlinear deformation of the material is described using the relationships of nonlinear elasticity of an orthotropic solid. The strength characteristics are calculated by the maximum stress criterion. Calculated deformation diagrams and ultimate strengths are compared with the experimental data of the authors.     

复合材料蒙皮对机身段适坠性能的影响研究

针对运输类飞机复合材料机身段适坠性设计的需要,研究了复合材料蒙皮对典型机身段适坠性能的影响。利用HyperMesh建立机身段模型,采用LS-DYNA设置复合材料蒙皮铺层角度和铺层数,分析模型在6.67 m/s坠撞速度时的动态响应特性。仿真结果得到了机身段结构的变形、位移、应变和应力等数据,给出了座椅与地板连接处的加速度-时间历程曲线和机身段的破坏模式。仿真结果表明选取合适的蒙皮铺层角度和铺层数,可显著降低座椅处的过载峰值,有效提高复合材料机身段适坠性能。     

预应力钢—混凝土组合连续梁的徐变变形研究

为了准确分析钢—混凝土组合连续梁的长期变形性能,基于换算弹性模量法,采用ANSYS建立了组合梁的空间有限元模型,给出了按换算弹性模量法和有限元软件联合应用的计算组合梁徐变变形一般方法,分析了在徐变作用下钢-混凝土组合连续梁的长期变形规律。通过具体算例说明,组合连续梁的徐变变形在2-3年基本能够达到稳定,且徐变变形的计算在组合连续梁的设计中不能忽略。     

含SMA约束层的复合材料矩形板的阻尼能力分析

研究由形状记忆合(shape memory alloy，简写为SMA)SMA约束层、SMA纤维混杂叠层材料构成的复合材料矩形板的阻尼性能。采用多胞模型和细观力学阻尼分析方法，分别预测叠层复合材料单层的弹性性能和阻尼性能，在叠层材料中计入横向剪切变形的影响。在导出矩形板的应变能和耗散能的基础上，根据最大应变能理论建立板的模态阻尼比的数学表达式。数值结果表明，文中提出的含有SMA约束层的SMA纤维叠层复合材料的集成阻尼设计方法，是一种有效的阻尼增强方案。     

某型直升机蜂窝夹层结构有限元分析

对某型直升机蜂窝夹层结构抗弯刚度进行了深入探讨,给出理论上分析计算蜂窝夹层结构抗弯刚度的一般方法,得出了影响弯曲刚度的主要因素。并通过有限元分析软件Nastran对一典型蜂窝夹层结构抗弯刚度进行有限元分析,得出了正确的蜂窝夹层结构应力云图和变形,具有一定的工程指导意义。     

SiCp增强铝基复合材料与Kevlar增强摩擦材料摩擦副摩擦磨损机理研究

采用盘销式摩擦磨损试验机，对SiCp含量为20vol％的铝基复合材料和Kevlar增强摩擦材料组成的摩擦副在于摩擦条件下的摩擦磨损机理进行了实验研究。结果表明：摩擦副在跑合过程中，铝基复合材料中的SiCp颗粒对较软的有机复合材料产生犁削和微观切削效应，磨损机理为铝基复合材料的硬质颗粒对较软的有机复合材料的磨粒磨损；在跑合后的磨损试验中，摩擦材料磨损表面呈现出粘着磨损和塑性变形特征，随着转动速度的增加，塑性流动加剧；摩擦副接触表面发生材料的相互转移，并在铝基复合材料表面形成转移膜，且在较高速度下转移膜更易形成；在高速条件下，摩擦材料表面可见从铝基复合材料的铝合金基体中脱离的SiCp颗粒和熔融迹象；摩擦材料的磨损机理主要为磨粒磨损、粘着磨损和塑性变形。     

Hydrostatic extrusion of composite rods with hard cores

The modes of deformation of composite materials with a hard core during hydrostatic extrusion are examined. The experimental work was carried out for Cu-Al composite rods with the fractional cross-sectional area of the copper being 0.16. It has been found that uniform deformation occurs at low extrusion ratios and the copper rod fails in tension at higher ratios; also the critical extrusion ratio increases as the die angle decreases. A theoretical analysis is developed to predict the mode of deformation by using the upper bound method. The effects of the end of the billet, yield stress ratio, fraction of the harder core, extrusion ratio, die angle and frictional shear factors at the interface and die surface are considered in the analysis. The theoretical results show good agreement with the experimental results.     

UHMWPE基水润滑尾轴承润滑特性仿真及试验研究

针对UHMWPE基高分子复合材料水润滑轴承的润滑特性开展研究。采用双向流固耦合算法研究弹性模量和泊松比等材料参数以及转速、负载等工况参数对水润滑轴承偏心率、最大水膜压力、轴承最大变形量、最小水膜厚度、摩擦因数等润滑特性的影响。基于改性UHMWPE高分子复合材料轴承的试验,验证了仿真方法的正确性。研究表明:计入弹性变形的流固耦合算法在研究高分子复合材料轴承性能方面具有更高的精度;随轴瓦材料弹性模量和泊松比的增大,轴承承载力逐渐增大、弹性变形量逐渐减小;随负载增大,轴承最大水膜压力和最大变形量基本呈线性增长;随转速增大,轴承最大水膜压力和轴承最大变形量显著减小;对于高分子复合材料轴承,低速、重载工况下不计入弹性变形的算法误差更大。     

某模拟雷达的天线结构设计与仿真分析

针对模拟雷达低成本的设计需求,在天线设计时采用基础框架与相控阵阵面相结合的复合天线结构,用较少单元的相控阵阵面模拟真实雷达的相控阵阵面。相控阵阵面采用喇叭空馈。这种馈电形式为封闭式,因而能量漏失小,馈电效率高。阵面的输入单元和辐射单元采用开口波导。该波导结构简单,加工成本低。它们通过轴向阶梯面与移相器连接,连接处不会产生电磁波泄漏和空间耦合。文中还建立了天线的有限元模型,进行静力分析,得到了天线在各工况下的应力云图和变形云图。结果表明,天线结构在各种工况下均能满足设计指标要求。     

Plastic deformation behavior of a uniaxial metal matrix composite under transverse compression

Plastic deformation behavior of a stainless-steel/Sn−Bi composite was examined using transverse compression tests on rectangular specimens under plane strain loadings. Based on the anisotropic yield criterion proposed by Hill, a theoretical analysis on the relationship between the yield strength of the matrix material and the yield strength of the composite was developed and compared to experimental results. Experiments were carried out to investigate the effects of the forming parameters such as yield strength of the matrix material, fiber packing patterns, fiber volume fraction, and lubrication of the compression platens, on the plastic deformation behavior of the metal matrix composite. Failure modes of the composite included shear band formation and eye formation at the fiber-matrix interface. Low deformability in the transverse directions was found for the metal matrix composite specimen. The theoretical and experimental results on the effects of the forming parameters provide basic information for further research on the transverse compression of metal matrix composite materials.     

Free-edge stresses in general composite laminates

In the present study, by starting from the reduced form of elasticity displacement field for a long flat laminate, an analytical method is developed in order to accurately calculate the interlaminar stresses near the free edges of generally laminated composite plates under extension. The constant parameter appearing in the reduced displacement field, which describes the global rotational deformation of a laminate, is appropriately obtained by employing an improved first-order shear deformation theory. The accuracy and effectiveness of the proposed first-order theory are verified by means of comparison with the results of Reddy's layerwise theory as a three-dimensional benchmark. Reddy's layerwise theory is then utilized for analytical and numerical investigations of the boundary-layer stresses within arbitrarily laminated composite plates. Various numerical examples are presented for the interlaminar normal and shear stresses along the interfaces and through the thickness of laminates in the vicinity of the free edges. The effects of end conditions of laminates, fibers orientation angles as well as the stacking sequences of the layers within laminates, and geometric parameters on the boundary-layer stresses are presented and discussed.     

Computational characterization of micro- to mesoscopic deformation behavior of semicrystalline polymers

In the present study, we clarify the micro- to mesoscopic deformation behavior of semicrystalline polymers by the finite element homogenization method. The crystalline plasticity theory using a penalty method for the inextensibility constraint in the chain direction and the nonaffine molecular chain network theory were used to the representation of the deformation behavior of crystalline and amorphous phases, respectively, in the composite microstructure of a semicrystalline polymer. Various directional tensions are applied to the two-dimensional plane-strain unit cell model of a composite microstructure. The results reveal a highly anisotropic deformation behavior caused by the rotation of the chain direction and lamella interface, which depends on tensile direction and manifests as substantial hardening/softening in the early stage of deformation. The mesoscopic structure of a semicrystalline polymer was modeled using a voronoi polygon comprised of composite microstructures with different lamella interface directions. The initial isotropy of the response of the mesoscopic scale was verified. Due to their interaction with the surrounding grains, the individual grains of the mesoscopic scale show a conservative response as compared with that of the unit cell, and a very nonuniform response depending on the location of the respective grain is observed; these are typical of the mesoscopic response of semicrystalline polymers.     

Vibration of completely free composite plates and cylindrical shell panels by a higher-order theory

This paper deals with the free vibration of open, laminated composite, circular cylindrical panels having a rectangular plan-form and all their edges free of external tractions. The material arrangement of the shell panels considered may vary from this of the single isotropic (or special orthotropic) layer to that of a general angle-ply lay-up. The analysis is based on the application of the Ritz approach on the energy functional of the Love-type version of a unified shear deformable shell theory. A through-thickness parabolic distribution of the transverse shear deformation is mainly assumed but, for comparison purposes, numerical results that are based on the assumptions of the classical Love-type shell theory are also presented. The Ritz method is a powerful analytical technique since, provided that a complete set of trial functions is employed, it can provide the exact solution of the problem considered in infinite series forms. The mathematical formulation is therefore presented in a general form, appropriate for any set of basis functions. The variational approach is, however, finally applied in conjunction with a complete functional basis made of the appropriate admissible orthonormal polynomials.     

Composite,effective, and real hardnesses of thin coatings

The paper presents the results of an analysis of the mechanics of contact between a rigid sphere and an elastic rigidly plastic two-layer half-space that imitates a surface covered with a hard strengthening coating. Analytical dependences are derived which relate the surface hardness to the base and coating hardnesses within the whole possible range of the coating thickness. Analytical dependences that relate the surface hardness to the coating thickness and the indentation depth of a hard tetragonal pyramid are also obtained. A new physical interpretation of the mechanism of the deformation of a layered solid is proposed for the range of the indentation depth that commonly characterizes the domain of the existence of the composite hardness. The term “real coating hardness” is specified and a new term “effective hardness of the coating material” is proposed. The obtained theoretical solutions are used to determine the ranges of the thicknesses within which the composite and effective hardnesses of a hardened surface exist.     

MoS2/C复合涂层在不同对磨副下的冲击磨损行为研究

在基于动能控制的冲击磨损设备上,以球-平面接触的方式,探究304不锈钢基体和MoS_2/C复合涂层在不同对磨副冲击下的磨损行为,并分析摩擦界面响应及磨损机制。结果表明:随着冲击副材料的弹性模量增加,冲击接触峰值力以及能量吸收率逐渐上升,对应的磨损量及磨损率也随之提高;MoS_2/C复合涂层的接触应力、能量吸收率以及磨损均要低于304不锈钢基体;涂层的冲击磨损形式主要为材料的剥落与磨屑堆积,磨损机制为塑性变形以及摩擦氧化。     

铝/铜合金复合材料的多坯料挤压成形

探讨了采用多坯料挤压法制备铝／黄铜复合棒材的可能性, 研究了挤压成形特点、界面结合情况, 分析了沿界面附近合金元素的扩散行为。结果表明, 挤压力变化规律与材料填充焊合腔、挤压复合成形特征相吻合; 复合材界面附近合金元素的扩散明显, 并形成具有不同衬度特征的扩散层; 挤压温度升高, 扩散层厚度增大; 棒材沿纵向和横向复合均匀, 界面为冶金结合, 焊合质量良好。挤压温度过高或过低导致界面结合强度降低。     

Mg/Al合金爆炸焊连接及其界面接合机制

采用爆炸焊接技术制备以AZ31B镁合金为基板,以6061铝合金为覆板的AZ31B/6061合金的层状复合板。对复合板界面的宏观形貌、微观组织、界面元素扩散行为及界面接合性能进行测试、分析。结果表明:AZ31B/6061合金爆炸复合板接合界面呈波状接合;靠近接合界面处的塑性变形程度最大,以孪晶和再结晶形式为主;在AZ31B一侧靠近界面处出现与界面呈45°的绝热剪切带组织,带内为动态再结晶形成的细晶粒组织;接合界面两侧的显微硬度分布为:随着距离接合界面的增大,AZ31B和6061侧的显微硬度值递减趋势;复合板的拉-剪试验结果表明,界面接合强度达193.3 MPa;复合板界面接合机制为压力焊、扩散焊及局部熔化焊综合作用的结果。