First matrix cracking behavior of ceramic composites at elevated temperatures

The first matrix cracking behavior of a silicon carbide fiber (SCS-6™)-reinforced zircon matrix composite is studied as a function of flaw size and temperature. Flaws of controlled size are created in the monolithic zircon and silicon carbide fiber-reinforced zircon matrix composite by means of a Vicker's indentation technique. The first matrix cracking stress is measured at three different temperatures of 25, 500, and 1200°C as a function of the crack length. The results on ceramic composites demonstrated both steady state and non-steady state matrix cracking behaviors and an increase in the steady state matrix cracking stress with an increase in temperature as predicted by the theoretical models. These results are compared with the predictions of the theoretical models of matrix cracking based on fracture mechanics analysis.     

Mechanical behavior of glass and Blackglas ceramic matrix composites

Room temperature tensile tests are reported on two low-cost ceramic matrix composite materials, comprised of matrices of Blackglas^® and a proprietory glass composition each reinforced with Nicalon^® SiC-based fibers. The measured mechanical behaviors, supplemented by post-fracture analysis of fiber pullout and fiber fracture mirrors, are compared in detail to the performance predicted theoretically. This allows for an assessment of the roles of the matrix, fiber srength, residual stresses, fiber geometry, and the fiber/matrix interfacial properties in determining mechanical response. The Blackglas^® matrix cracks extensively during processing, and so the mechanical response is controlled by the deformation and fracture of the fiber bundle. The interfacial sliding resistance, τ, is determined to be ≈17 MPa and thein-situ (post-processed) fiber characteristic strength,σ_c is found to be ≈2.0 GPa, both similar to values reported in the literature for Nicalon^®/CAS-glass systems. For the glass matrix, the unidirectional and cross-ply materials show marked differences in mechanical behavior. In the cross-ply composites, τ ≈ 14 MPa andσ_c≈2.9 GPa; in the unidirectional variants, these values were 1.7 MPa and 1.6 GPa, respectively. With these data and other derived micromechanical parameters, the stress-strain and failure point of these materials was predicted using existing models, and excellent agreement with the experiments was obtained. These materials thus perform as expected given the in-situ fiber and interface properties. Notably, the cross-ply glass matrix composites exhibit high fiber strength retention and hence show tensile strengths that are better than other Nicalon^®-based materials tested to date.     

A mean-field micromechanical model of thermal-ratcheting behavior in short fiber-reinforced metal matrix composites

Thermal-ratcheting behavior in short fiber-reinforced metal matrix composites has been investigated. The internal stresses due to mismatch in thermal expansion coefficients between the fiber and matrix in the composites can introduce anomalous deformation under thermal-cycling conditions with or without external mechanical loads. This study has resulted in a more comprehensive understanding of such thermal-ratcheting behavior in short fiber-reinforced composites subject to a wide range of external uniaxial loads based on a mean-field micromechanical model considering the local mass transfer by diffusion along the fiber–matrix interface. The validity of the model has been verified through systematic experiments with directionally solidified Al–Al₃Ni eutectic composites.     

陶瓷基复合材料焊接技术研究进展

对陶瓷基复合材料的焊接技术作了总体概述.系统总结了陶瓷基复合材料的可用焊接方法、工艺、焊接过程中易出现的问题及对策,并对陶瓷基复合材料及其焊接技术的发展前景作了展望.     

Tensile behavior and cyclic creep of continuous fiber-reinforced glass matrix composites at room and elevated temperatures

In this study we investigated the stress-strain behavior at room and elevated temperatures and the tensile creep and cyclic creep response of a unidirectional SiC fiber-reinforced aluminosilicate glass matrix composite. The interfacial condition of the as-received material was measured by a push-out indentation technique. The stress-strain behavior was that expected for this kind of composite, i.e. “pseudoductile” behavior with extensive fiber “pull-out” at room temperature and brittle failure at intermediate temperatures (750 °C) due to oxidation embrittlement. The stiffness of the composite at 750°C was analyzed for different loading rates, highlighing the influence of the loading rate on apparent composite stiffness, due to matrix softening. The creep studies were conducted at temperatures above and below the softening temperature of the glass (T _g, 745 °C) in air. The cyclic creep experiments showed the existence of extensive viscous strain recovery during the unloading period. The creep strain recovery was quantified using strain recovery ratios. These ratios showed a slight dependence on the temperatures investigated (700 and 750 °C). The crept composites retained their “graceful” fracture behavior only partially after testing, indicating that oxidation of the fiber/matrix interface due to oxygen diffusion through the matrix occurred in the peripheral area of the samples. Dr. Boccaccini is presently at the Institute for Mechanics and Materials, University of California, San Diego, CA 92093, USA.     

内晶结构复相陶瓷的裂纹扩展行为

以ZrO2-Alo2O3微-纳米复合陶瓷为研究对象,采用跟踪压痕裂纹法测试其裂纹扩展阻力曲线.结果表明,三种微-纳复合ZTA陶瓷的阻力曲线均为显著的上升曲线.成分相同、烧结温度高的试样和烧结温度相同、氧化锆含量少的试样,由于内晶颗粒数量多,阻力曲线的上升趋势更加明显.内晶颗粒附近区域产生位错网、亚晶界甚至微裂纹,使微-纳米复合ZTA陶瓷的断裂方式向穿晶断裂方向变化.裂纹穿晶扩展遇到的阻力大,所需要的裂纹扩展动力也大,形成开裂-止裂交替进行的裂纹扩展过程,故其阻力曲线上升明显.     

陶瓷基复合材料与金属连接的研究进展

陶瓷基复合材料是一种新兴的热结构材料，解决其自身及其与金属的连接工艺，是实现其推广应用的重要课题之一。首先分析了陶瓷基复合材料自身连接及其与金属连接的难点，在此基础上从解决被连接材料的化学相容性与物理匹配性两方面出发，综述了陶瓷基复合材料自身及其与金属连接的研究进展，并介绍了几种典型的连接实例——活性金属钎焊、部分瞬间液相扩散连接以及宏观结构梯度中间层设计。     

Thixoforming of SiC ceramic matrix composites in pseudo-semi-solid state

1INTRODUCTIONIt has great economic profit to exploit the uti-lization of SiC ceramic material for its strength,hardness,wear resistance,corrosion resistanceand high temperature resistance,abundant re-source and low price.But the brittle charactergreatly restricts its application in the field of engi-neering structure materials.Recently a series ofceramic matrix composites with exi mious perform-ance have been developed by reinforcing the matrixmaterial with other materials.Al/SiC is a la…     

Elastic properties of short glass fiber-reinforced ZA-27 alloy metal matrix composites

A well-consolidated composite of ZA-27 alloy reinforced with short glass fiber at volume fractions of 2, 7, 12, and 17% was prepared by liquid infiltration techniques and its elastic properties were determined by destructive testing. The results showed that the modulus of elasticity and ultimate tensile strength of the composite gradually increased with increasing volume fraction of the fiber, although the ductility decreased with an increase in volume fraction of the fibers. In addition, the data obtained from Young’s modulus measurements were compared with theoretical results predicted by the shear-lag model, Nielsen-Chen model, and computational model. The experimental results were shown to be in better agreement with those of the latter two models. The ultimate tensile strength test results were also compared with theoretical results predicted by the shear-lag and Miwa models. The Miwa model agreed favorably with the experimental results.     

The prospects for hybrid fiber-reinforced Ti-TiB-matrix composites

Significant cost reductions in continuously reinforced titanium-matrix composites have enabled their successful insertion into two aerospace applications. Additional applications are being pursued, but reduced anisotropy is required to achieve the broadest impact of this technology. Novel hybrid composites consisting of continuous SiC reinforcements and titanium alloys enhanced with TiB and/or TiC particles are being developed to reduce the anisotropy between longitudinal and transverse properties. For more information, contact W.M. Hanusiak, FMW Composite Systems, 1200 W. Benedum Industrial Drive, Bridgeport, WV; (304) 842-1864; fax (304) 842-1866; e-mail: bhanusiak@fmwcomposite.com.     

Damage behavior of tungsten fiber-reinforced copper matrix composite after high-speed impact

Wf/Cu82Al10Fe4Ni4 composite was fabricated by means of infiltration casting. By the microstructure observation of the composite with the aid of scanning electron microscopy(SEM) and transmission electron microscopy(TEM), it can be found that there are(Fe, Ni),AlFe, Al3 Ni, and Cu3 Al precipitated phases existing in the matrix alloy. By two-stage light gas gun, Wf/Cu82Al10-Fe4Ni4 composite hypervelocity projectile into concrete target test with the speed of 2.2 kmás-1is finished. By microstructure observation, it can be found that the failure mode of Wf/Cu82Al10Fe4Ni4 composite projectile during penetration is the rapid peeling of tungsten fibers from the projectile, which makes the projectile display good selfsharpening property. Meanwhile, it can be found that microstructure morphology change of Wf/Cu82Al10Fe4Ni4 composite occurs after hypervelocity impact. The density of dislocations around the large-dimensional(Fe, Ni),AlFe, Al3 Ni, and Cu3 Al precipitated phases in the matrix alloy rises sharply. At the same time, there are largedimensional deformed twins existing in local regions and stacking faults existing inside the twins.     

The mechanical response of ceramic microballoon reinforced aluminum matrix composites under compressive loading

An investigation is performed on the mechanical response of a family of ceramic microballoon reinforced aluminum matrix composites under both uniaxial compression and constrained die compression loadings. The key material parameters that are varied are the matrix strength and the ratio of wall thickness t to radius R of the microballoons. Uniaxial compressive failure initiates at relatively small strains (≈1–2%) and occurs through a process of crushing and collapse of the material within a localized deformation band. Under constrained die conditions, localization is suppressed and the flow stress increases monotonically with increasing strain. The latter response is well described by Gurson's constitutive law for plastic yielding of porous ductile metals, with an effective strength that depends on the relative wall thickness, t/R. Furthermore, the energy absorption capacity (≈60–70 MJ/m³) is extremely high in comparison with values that are typical of metal foams. The results suggest that the microballoon composites may be attractive for applications requiring a high resistance to penetration by projectiles or other forms of local intrusion, in combination with a high compressive strength.     

陶瓷及陶瓷基复合材料连接的研究进展

综述了近年来陶瓷及陶瓷基复合材料连接的研究进展。包括陶瓷及陶瓷基复合材料润湿机理的研究、润湿性的改善、连接界面组织结构的演变及与接头力学性能的关系、接头连接机理及连接应力的缓解方法。同时,对连接中间层的选择,包括玻璃陶瓷中间层、复合中间层、复合钎料及梯度中间层的研究也进行了归纳总结。分析了目前研究已经取得的突破进展及仍然存在的问题,并对未来陶瓷及陶瓷基复合材料连接的研究方向进行了展望。     

Recent progress in ceramic matrix composites reinforced with graphene nanoplatelets

Graphene nanoplatelets(GNPs) are considered to be one of the most promising new reinforcements due to their unique two-dimensional structure and remarkable mechanical properties. In addition, their impressive electrical and thermal properties make them attractive fillers for producing multifunctional ceramics with a wide range of applications. This paper reviews the current status of the research and development of graphene-reinforced ceramic matrix composite(CMC) materials. Firstly, we focused on the processing methods for effective dispersion of GNPs throughout ceramic matrices and the reduction of the porosity of CMC products. Then, the microstructure and mechanical properties are provided, together with an emphasis on the possible toughening mechanisms that may operate. Additionally, the unique functional properties endowed by GNPs, such as enhanced electrical/thermal conductivity, are discussed, with a comprehensive comparison in different ceramic matrices as oxide and nonoxide composites. Finally, the prospects and problems needed to be solved in GNPs-reinforced CMCs are discussed.     

Microstructure evolution of rare earth Pr modified alumina-silicate short fiber-reinforced Al-Si metal matrix composites

Al-Si metal matrix composites (MMCs) reinforced with 20 vol.% alumina-silicate shot fibers (Al2O3-SiO2(sf)) were fabricated by an infiltration squeeze method. Pure Pr metal was added into these composites. The effect of Pr addition on the microstructure evolution of Al-Si MMCs was investigated by SEM,TEM,and EDS. Pr addition is favorable to make uniform microstructures with the modified eutectic Si crystal. PrAlSi phase with high contents of Pr and Si is observed on the interface between the fiber and the m...     

Computer modeling of the mechanical behavior of composites -Interfacial cracks in fiber-reinforced materials-

An interface crack between a fiber and a matrix has been analyzed and results of SIFs for both, mode I and mode II contributions, have been presented graphically. Trends in these SIFs have been identified and rationalized. It was found that the strong variation in SIFs is mainly a function of crack length, elastic mismatch and loading directions.     

石英纤维增强陶瓷基复合材料制孔工艺研究

本试验针对目前硬质合金刀具加工石英纤维增强陶瓷基复合材料时存在的刀具磨损严重、加工质量差、效率低下等问题,对比了硬质合金刀具钻孔、PCD刀具钻孔和电镀金刚石套料钻螺旋铣磨制孔的效果,分析了切削力对制孔质量的影响。研究结果表明:纬纱纤维对X向和Y向切削力的影响明显大于经纱纤维,垂直于纬纱纤维方向的切削力较小,平行于纬纱纤维方向的切削力较大;PCD刀具钻孔质量相对较好,刀具磨损不明显,适用于石英纤维增强陶瓷基复合材料的制孔加工。      

超声辅助螺旋磨削SiCf/SiC陶瓷基复合材料

针对SiC纤维增强SiC陶瓷基复合材料(SiC_f/SiC)存在加工质量差、材料去除困难等问题,开展金刚石砂轮超声辅助螺旋磨削SiC_f/SiC陶瓷基复合材料试验,研究其出口质量、孔壁形貌及孔壁表面粗糙度。结果表明：与传统制孔相比,超声辅助螺旋磨削制孔出口处材料无大面积崩边;砂轮磨削速度方向与纤维方向的夹角θ的周期性变化导致孔壁表面形貌呈现规律性变化。当θ在0°/180°时,纤维与基体多发生脱黏现象;当θ在45°时,纤维多发生剪切断裂;当θ在90°时,纤维多发生挤压断裂;当θ在135°时,纤维既发生剪切断裂又发生挤压断裂;孔壁表面粗糙度Sa在θ为90°时最低,在θ为135°时最高。在一定范围内,表面粗糙度Sa随着超声振幅的增大而降低,最大降幅为38.7%;随着进给速度的增大而升高,最大增幅为39.3%。