Analytical study of the interface in fibre-reinforced 2D composite material

Imperfect bonding between the constitutive components can greatly affect the properties of the composite structures.An asymptotic analysis of different types of imperfect interfaces arising in the problem of 2D fibrereinforced composite materials are proposed.The performed study is based on the asymptotic reduction of the governing biharmonic problem into two harmonic problems.All solutions are obtained in a closed analytical form.The obtained results can be used for the calculation of pull-out and pushout tests,as well as for the investigation of the fracture of composite materials.

Numerical Simulation of Dynamic Response of Fiber Reinforced Ceramic Matrix Composite Beam with Matrix Cracks Using Multiscale Modeling

A multiscale method for simulating the dynamic response of ceramic matrix composite （CMC） with matrix cracks is developed. At the global level, the finite element method is employed to simulate the dynamic response of a CMC beam. While at the local level, the multiscale mechanical method is used to estimate the stress/strain response of the material. A distributed computing system is developed to speed up the simulation. The simulation of dynamic response of a Nicalon/CAS-II beam being subjected to harmonic loading is performed as a numerical example. The results show that both the stress/strain responses under tension and compressive loading are nonlinear. These conditions result in a different response compared with that of elastic beam, such as： 1） the displacement response is not symmetric about the axis of time; 2） in the condition of small external load, the response at first order natural frequency is limited within a finite range; 3） decreasing the matrix crack space will increase the displace- ment response of the beam.

Improvement of the matrix and the interface quality of a Cu/Al composite by the MARB process

The matrix accumulative roll bonding technology （MARB） can improve the matrix performance of metal composite and strengthen the bonding quality of the interface./n this research, for the fwst time, the technology of MARB was proposed. A sound Cu/AI bonding composite was obtained using the MARB process and the bonding characteristic of the interface was studied using scanning electricity microscope （SEM） and energy-dispersive spectroscopy （EDS）. The result indicated that accumulation cycles and diffusion annealing temperature were the most important factors for fabricating a Cu/AI composite material. The substrate aluminum was strengthened by MARB, and a high quality Cu/AI composite with sound interface was obtained as well.

EFFECT OF FIBER FAILURE ON QUASI-STATIC UNLOADING/RELOADING HYSTERESIS LOOPS OF CERAMIC MATRIX COMPOSITES

The two-parameter Weibull model is used to describe the fiber strength distribution.The stress carried by the intact and fracture fibers on the matrix crack plane during unloading/reloading is determined based on the global load sharing criterion.The axial stress distribution of intact fibers upon unloading and reloading is determined based on the mechanisms of fiber sliding relative to matrix in the interface debonded region.The interface debonded length,unloading interface counter slip length,and reloading interface new slip length are obtained by the fracture mechanics approach.The hysteresis loops corresponding to different stresses considering fiber failure are compared with the cases without considering fiber failure.The effects of fiber characteristic strength and fiber Weibull modulus on the fiber failure,the shape,and the area of the hysteresis loops are analyzed.The predicted quasi-static unloading/reloading hysteresis loops agree well with experimental data.

Static Crack Propagation of Carbon Nanotube through Non-Bonded Interface of Nanocomposites

This study presents an analytical shear-lag model to illustrate the interface crack propagation of carbon nanotube (CNT) reinforced polymer-matrix composites (PMCs) using representative volume element (RVE). In the model, a 3D cylindrical RVE is picked to present the nanocomposite in which CNT/polymer chemically non-bonded interface is taken into consideration. In the non-bonded interface, the stress transfer of CNT is generally considered to be controlled by the combined contribution of mechanical interlocking, thermal residual stress, Poisson’s contraction and van der Waals (vdW) interaction. Since CNT/matrix interface becomes debonded due to crack propagation, vdW interaction which is a function of relative radial displacement of the CNT/matrix interface makes the modeling of the interface tricky and challenging. In order to solve this complexity, an iterative approach is proposed to calculate the vdW interaction for debonded CNT/matrix interface accurately. The analytical results aim to obtain the characteristics load displacement relationship in static crack propagation for CNT reinforced PMCs.

THE EFFECTIVE PROPERTIES OF COMPOSITES WITH FIBER-END CRACKS

The paper describes use of self-consistent finite element method (SCFEM) for predicting effective properties of fiber composite with partially debonded interface. The effective longitudinal Young's modulus and shear modulus for unidirectional fiber reinforced composites with fiber-end cracks are calculated. Numerical results show that the effective properties are considerably influenced by the fiber-end cracks. The effects of microstructural parameters, such as fiber volume fraction, modulus ratio of the constituents and fiber aspect, on the effective properties of the composites were discussed.

Numerical solutions of singular integral equations for planar rectangular interfacial crack in three dimensional bimaterials

Stress intensity factors for a three dimensional rectangular interfacial crack were considered using the body force method. In the numerical calculations, unknown body force densities were approximated by the products of the fundamental densities and power series; here the fundamental densities are chosen to express singular stress fields due to an interface crack exactly. The calculation shows that the numerical results are satisfied. The stress intensity factors for a rectangular interface crack were indicated accurately with the varying aspect ratio, and bimaterial parameter.

增强体表面改性在高导热金属基复合材料中的应用

随着电子技术的高速发展和电子器件的更新换代,电子封装材料的性能需求越来越高。金属基复合材料,尤其是铝基和铜基复合材料具有高导热、低膨胀、高稳定性等特点,是具有广阔应用前景的电子封装材料。然而,金刚石、石墨烯、硅等增强体与基体的润湿性差,或者在高温下与基体发生有害的界面反应,限制了此类高导热金属基复合材料的开发和应用。本文简述了金属基复合材料的界面研究进展,结合影响金属基复合材料界面结合的因素,提出了几种改善界面结合的方法。增强体表面改性是改善金属基复合材料界面的重要途径之一,常用工艺有磁控溅射法、化学气相沉积法、溶胶凝胶法、化学镀法等;最后,对增强体表面改性在高热导金属基复合材料中的应用进行分析和展望。

Damping capacity of BaTiO_3/Al composites fabricated by hot extrusion

To develop new type of high damping metal matrix composites, large grain size barium titanate （BaTiO3） ceramic was sintered and added into Al powder to fabricate BaTiO3/Al composites through the powder metallurgy method and hot extrusion. The damping properties of BaTiO3 ceramic, Al matrix and BaTiO3/Al composites were examined by dynamic mechanical analysis in the temperature range from 273 K to 573 K. The results show that although BaTiO3 exhibits high damping （tan δ=0.12） below 400 K, the damping capacity of 10%BaTiO3/Al （mass fraction） composites below 400 K is not increased as compared to the Al matrix. On the other hand, the damping capacity above 450 K is greatly enhanced due to the motion of dislocations at the interfaces between ceramic particles and Al matrix. The failure of exerting the intrinsic damping of BaTiO3 particles in the composites is attributed to the poor interface bonding between the particles and the matrix. The tensile strength of the composite is 42% higher than that of the Al matrix, which indicates the possibility of obtaining high strength and high damping composites via interface improvement and the addition of high volume fraction of large grain BaTiO3 particles.

Effect of interface debonding on matrix multicracking evolution of fiber-reinfroced ceramic-matrix composites

An analytical methodology was developed to investigate the effect of fiber/matrix interface debonding on matrix multicracking evolution of fiber-reinforced CMCs(ceramic-matrix composites).The Budiansky-Hutchinson-Evans shear-lag model was adopted to analyse the micro-stress field of the damaged composites.The critical matrix strain energy criterion,which presupposes the existence of an ultimate or critical matrix strain energy with matrix,was obtained to simulate the matrix multicracking evolution of CMCs.With the increase of the applied stress,the matrix multicracking and fiber/matrix interface debonding occurred to dissipate the additional energy entered into the composites.The fiber/matrix interface debonded length under matrix multicracking evolution was obtained by treating the interface debonding as a particular crack propagation problem.The conditions for no-debonding and debonding during the evolution of matrix multicracking were discussed in terms of two interfacial properties,i.e.,the interface shear stress and interface debonded toughness.When the fiber/matrix interface was bonded,the matrix multicracking evolution was much more intense compared with the interface debonding;when the fiber/matrix interface was debonded,the matrix crack density increased with the increasing of interface shear stress and interface debonded energy.The theoretical results were compared with experimental data of unidirectional SiC/CAS(calcium alumina silicate),SiC/CAS-Ⅱand SiC/borosilicate composites.

ANALYSIS OF ENERGY RELEASE RATE FOR CRACKED LAMINATES

An interface crack analysis is presented for further understanding the characteristics of the crack-tip field. The conditions under which the energy release rate components would exist are emphasized and the relations between energy release rate components and the stress intensity factors are given. Combining with the results of chasical plate theory analysis. a closed-form solution for stress intensity factors in terms of external loading as well as some geometric and material parameters for fairly general composite laminates is derived Then. an analytical solution for energy release rate components is deduced. In order to get energy release rate components under general loading condition. a mode mix parameter, Ω, must be determined separately. A methodology for determining Ω is discussed. Finally. several different kinds of laminates are examined and the results obtained could be used in engineering applications.

粘接结构波动特性的矩阵表示法及参数影响

为丰富多层复合材料界面形态检测方式,笔者构建了一种声波传播界面矩阵模型。分别用空气和水模拟粘接结构的界面为脱粘和进水状态,导出了横波入射下的多层结构中的声反射和透射系数表达式;研究了超声波与不同形态界面的相互作用,分析了入射角度对声波传播特性的影响。结果表明:当横波入射角度介于30°~40°或30°~60°之间,分别采用横波的反射系数法或透射系数法可较容易区分出完好连接、脱粘以及进水界面;除了0°、临界角和90°外,采用纵波透射系数法也较容易鉴别界面形态;无论横波入射角度为多大,采用纵波反射系数法均不能很好地区分脱粘和进水界面。该方法为实验时采用超声波检测粘接结构提供了依据。

Fabrication and fracture toughness of macro-toughening-designed composite

A macro-structure-toughened SiC particle reinforced LD2 aluminum alloy matrix (SiCp-LD2/LD2) composite was designed and fabricated based on considering the main factors which result in low room temperature fracture toughness of conventional metal matrix composites. Its room temperature fracture toughness was tested using three-point bending samples with sing1e edge notches. Compared with conventional SiCp/LD2 composites fabricated by stirring casting in case of same particle size and similar reinforcement volume fraction, this composite has a higher room temperature fracture toughness KQ. It shows strong resistance to crack propagating. The crack in it can propagate stably for a long time on the maximum load, therefore abrupt fracture occurring in most conventional composites can be avoided. Bending fractography (SEM) shows that the fracture mechanism of this material is different from SiCp/LD2 composite and the deformation of the unreinforced LD2 matrix and the SiCp-LD2/LD2 interface debonding are the main toughening mechanisms of this composite.

金属基热界面材料研究进展

随着芯片向小型化、集成化和高功率化发展,其在工作时产生的热量增多,若产生的热量不能及时传递到外部,会严重影响电子元件的性能和使用寿命。热界面材料是电子元件散热结构中重要的组成部分,其主要作用是填充电子元件与散热器之间的空气间隙,使电子元件产生的热量快速转移,降低界面热阻。综述了现有热界面材料的种类和特点,详细介绍了金属基热界面材料的类型与性能特征、研究现状及存在的问题等,并对低熔点金属基热界面材料的发展进行了展望。

纳米碳强化钛基复合材料界面结构与性能优化研究进展

钛及钛合金材料因其密度低、比强度高、耐腐蚀性能好等优异特性,在航空航天、汽车和军事等领域具有广阔的应用前景。近10年来,以石墨烯为代表的碳纳米材料由于具有超高的力学特性和独特的二维结构,广泛用作钛或钛合金基体的增强体。然而,纳米碳源的团聚现象以及严重的界面反应使纳米碳强化钛基复合材料的力学性能提升有限。随着对纳米碳强化钛基复合材料制备方法和工艺的深入探索,在其界面-组织-性能关系和强化机制等方面取得了一系列研究进展。在纳米碳强化钛基复合材料的制备过程中,必须从各个方面(如工艺特点、适用范围和应用要求等)衡量,选择合适的制备工艺,并通过界面结构设计优化来进一步改善基体组织,提高钛基复合材料力学性能。因此,系统性介绍近年来纳米碳强化钛基复合材料的制备工艺和纳米碳材料的表面改性及其应用,并对纳米碳强化钛基复合材料的界面结构调控和强化机制进行分析讨论,指出现阶段其制备、性能优化等方面存在的问题,并对其未来发展趋势进行展望。以期对以后纳米碳强化钛基复合材料的发展和应用提供一定的指导和借鉴。

单向SiC/SiC复合材料拉伸行为模拟研究

理解单向SiC/SiC复合材料在拉伸过程中的损伤破坏机制对掌握SiC/SiC复合材料的力学行为有着至关重要的意义。本文构建了一个单向SiC/SiC复合材料微观二维有限元模型,基于强度判定模拟纤维随机断裂过程;基于内聚力模型模拟界面脱粘现象;特别针对基体裂纹现象,通过均匀质方法和断裂能释放率建立了基体的连续介质损伤模型。结果显示,模型成功模拟了单向SiC/SiC复合材料在拉伸过程中的微观破坏机制和宏观力学行为。基体裂纹、纤维断裂、界面脱粘这3种微观破坏机制之间共同作用、相互影响,最终造成了材料整体的失效。本文中获得的结果将有助于进一步理解单向SiC/SiC复合材料拉伸行为,有利于材料性能的提高。

预紧力对EPGC204材料螺栓连接时基体开裂的影响研究

EPGC204一种环氧玻璃布层压板复合材料,具有良好的力学、电气绝缘和阻燃性能,广泛应用在小批量、多品种,有阻燃和绝缘、耐高温要求的电器、机械等设备中。在装配使用过程中主要通过螺栓连接,经常因为预紧力不合适导致基体开裂,运用数值仿真计算的方法,在ANSYS中建立不同几何尺寸的零件装配三维模型,分组计算在不同预紧力下EPGC204零件螺栓连接时所受的应力,建立预紧力与应力的关系曲线,研究预紧力对基体开裂的影响,寻找避免基体开裂的临界预紧力,为工艺参数制定提供参考依据。

ELASTIC SH WAVE PROPAGATION IN PERIODIC LAYERED COMPOSITES WITH A PERIODIC ARRAY OF INTERFACE CRACKS

The interaction of anti-plane elastic SH waves with a periodic array of interface cracks in a multi-layered periodic medium is analyzed in this paper. A perfect periodic structure without interface cracks is first studied and the transmission displacement coefficient is obtained based on the transfer matrix method in conjunction with the Bloch-Floquet theorem. This is then generalized to a single and periodic distribution of cracks at the center interface and the result is compared with that of perfect periodic cases without interface cracks. The dependence of the transmission displacement coefficient on the frequency of the incident wave, the influences of material combination, crack configuration and incident angle are discussed in detail. Compared with the corresponding perfect periodic structure without interface cracks, a new phenomenon is found in the periodic layered system with a single and periodic array of interface cracks.

EPGC204材料螺栓连接时避免基体开裂的临界几何参数研究

针对EPGC204复合材料螺栓连接时基体开裂问题,运用数值模拟有限元仿真计算的方法,建立EPGC204零件螺栓连接时几何参数(宽径比W/D,端径比E/D)与应力的关系曲线,研究几何参数对基体开裂的影响,寻找避免基体开裂的临界几何参数,为零件设计提供参考依据。

单向纤维增强陶瓷基复合材料单轴拉伸行为

采用细观力学方法对单向纤维增强陶瓷基复合材料的单轴拉伸应力-应变行为进行了研究。采用Budiansky-Hutchinson-Evans(BHE)剪滞模型分析了复合材料出现损伤时的细观应力场,结合临界基体应变能准则、应变能释放率准则以及Curtin统计模型三种单一失效模型分别描述陶瓷基复合材料基体开裂、界面脱粘以及纤维失效三种损伤机制,确定了基体裂纹间隔、界面脱粘长度和纤维失效体积分数。将剪滞模型与3种单一失效模型相结合,对各个损伤阶段的应力-应变曲线进行模拟,建立了准确的复合材料强韧性预测模型,并讨论了界面参数和纤维韦布尔模量对复合材料损伤以及应力-应变曲线的影响。与室温下陶瓷基复合材料单轴拉伸试验数据进行了对比,各个损伤阶段的应力-应变、失效强度及应变与试验数据吻合较好。