Delamination failure in ceramic matrix composites: Numerical predictions and experiments

The cohesive-zone finite element approach is used to predict initiation and propagation of delamination in relatively complex ceramic matrix composite sub-elements. Two different generic attachment sub-elements are analyzed and tested under applied uniaxial load. Pre-test analyses predict that delamination initiation and growth are the predominant failure mechanism for both of the sub-elements. Experimental results confirm the finite element predictions, and a good qualitative and quantitative agreement is found between the two.     

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.     

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。     

The first matrix cracking behavior of fiber-reinforced ceramic matrix composites

First matrix cracking stress in fiber reinforced ceramic composites is an important design parameter as it signifies the onset of mechanical damage and subsequent degradation of fiber and interface properties due to oxidation and corrosion. In this study, the influence of variation in the matrix crack length and fiber volume fraction on the first matrix cracking stress of ceramic matrix composites is investigated. To this end, zircon matrix composites uniaxially reinforced with silicon carbide fibers and monolithic zircon were fabricated. The monolithic and composite samples were microindented to create flaws of controlled size on the surface, and were then tested in 3-point flexure to obtain the matrix cracking stress. The results obtained from this study clearly indicated the non-steady state (short crack) and steady state (long crack) matrix cracking behaviors in ceramic matrix composites. The experimental results are compared with the theoretical results based on the fracture mechanics analyses published previously.     

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…     

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.     

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.     

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.     

Non-destructive testing of barely visible impact damage in polymer matrix composites

Barely visible impact damage (BVID) is developed when polymer matrix composites are subjected to impact loading. The damage has an adverse effect on structural integrity, and potentially leads to catastrophic failure.Thus it is important to employ a variety of advanced non-destructive testing (NDT) techniques in parallel to unambiguously determine the integrity of composite systems. This study deals with damage evaluation using visual inspection, ultrasonic C-scan, electronic speckle pattern interferometry (ESPI), electronic shearography (ES) and optical deformation and strain measurement system (ODSMS). Internal damage was introduced using an instrumented falling weight impact test (IFWIT) machine by controlling the combination of striker mass and releasing height. It was found that different NDT techniques were successfully employed to identify and visualise the impact induced internal damage. Experimental results generated from these techniques show a good agreement in damage identification and determination. The features, capabilities and limitations associated with these techniques were briefly discussed.     

A numerical strength analysis of metal matrix composites considering the interface and matrix damage evolution

A numerical micromechanical method is adopted here to investigate the tensile strength of metal matrix composites (MMC) by considering interface and matrix damage evolution. A cohesive zone model is employed to simulate the fiber/matrix interface damage. The damage in the matrix, which characterizes microvoid nucleation, growth and coalescence, is described in term of the Gurson-Tvergaard material model. These damage models are performed to a boundary value problem that involves a double periodic array of elastic continuous fibers in the elastic-plastic matrix subjected to transverse loads. The main attempt is made to investigate effects of interface strength and toughness on tensile strength of MMC.     

Processing and properties of metallic and ceramic matrix composites by a novel spraying technique

A concurrent fiber winding and low pressure plasma spraying process has been developed to manufacture multi-ply fiber reinforced metallic and ceramic matrix composites in a single spraying operation. In this study, four-layer SiC fiber reinforced Ti−6Al−4V and SiAlON−MoSi₂ composites have been manufactured, and the composite coupons have been evaluated in terms of fiber breakage, fiber distribution, matrix microstructure, interfacial reaction, and fiber damage. This novel spraying route enabled a wide range of composite systems to be produced, offering rapidly solidified matrix microstructure, regular fiber spacing and minimized interfacial reaction. Fiber damage was considered as a potential major disadvantage, but compared with the more widely investigated foil-fiber-foil route, this novel spraying approach resulted in less degradation in fiber strength. Further minimization of fiber damage could be achieved by precise control over processing conditions and large damage tolerance of fiber coating.     

Microstructure and wear characteristics of ATZ ceramic particle reinforced gray iron matrix surface composites

The alumina toughened zirconia(ATZ) ceramic particle reinforced gray iron matrix surface composite was successfully manufactured by pressureless infi ltration. The porous preform played a key role in the infi ltrating progress. The microstructure was observed by scanning electron microscopy(SEM); the phase constitutions was analyzed by X-ray diffraction(XRD); and the hardness and wear resistance of selected specimens were tested by hardness testing machine and abrasion testing machine, respectively. The addition of high carbon ferrochromium powders leads to the formation of white iron during solidifi cation. The wear volume loss rates of ATZ ceramic particle reinforced gray iron matrix surface composite decreases fi rst, and then tends to be stable. The wear resistance of the composite is 2.7 times higher than that of gray iron matrix. The reason is a combination of the surface hardness increase of gray iron matrix and ATZ ceramic particles and alloy carbides protecting effect on gray iron matrix.     

陶瓷及陶瓷基复合材料高温钎料的研究现状与进展

为充分发挥高温结构陶瓷材料的高温件能优势,针对陶瓷及陶瓷基复合材料的高温钎料的研究一直足陶瓷连接领域的发展方向.文章综述了SigN4、SiC陶瓷和C/C复合材料对应的高温钎料的研究难点和研究现状.虽然高温钎料的研究获得一些进展,但仍缺乏对陶瓷具有连接强度岛而且耐高温性能好的实用高温钎料.指出对于Si3N4陶瓷,以V为活性元素的高温钎料值得深入研究;而在设计和研制SiC连接用的高温新钎料时.应该允分考虑钎料与SiC之间的界面反应并予以控制.并对C/SiC陶瓷基复合材料用高温钎料的研究进行了简要的探讨.     

Thermal explosion synthesis of aluminum matrix composites reinforced with TiC-TiB2 ceramic particulates

In situ TiC-TiB2 diphase ceramic reinforced aluminum metal matrix composites were successfully fabricated via thermal explosion （TE） reaction in the Al-Ti-B4C system, Using DTA and XRD analyses, the combustion reaction characteristic was examined. The results show that Al serves not only as a diluent but also as a reaction participant, affecting the reaction process and its final products. Combining with the DTA and the TE temperature-time curves, the ignition temperature is estimated to be about 970 K. With increasing Al content, the adiabatic combustion temperature is lowered and the sizes of the TiC and TiB2 particulates decrease. When the Al content in the reactants is more than 50%, AlaTi intermediate phase is detected in the synthesized products. SEM observations reveal that the nearly spherical TiC particles and hexagonal or rectangular TiB2 particles distribute relatively uniformly in the Al matrix.     

Surface treatment effects on ceramic matrix composites: Case of a thermal sprayed alumina coating on SiC composites

High-temperature-resistant ceramics are already used for many industrial applications. In response to the growing demand, the need for further research considering the final application and the global behaviour of the material is becoming increasingly apparent. In general, it is possible to comply with many specifications, just by treating the surface of the ceramics. For instance, it is possible to achieve an adequate mechanical strength by depositing a protective layer with different structure and/or chemical composition. Regardless to the specification, the adhesion coating/substrate is the most crucial property to be considered. Conventionally, surface degreasing (applying solvents to remove organic impurities) and grit blasting (corundum) are carried out as a two steps pretreatment prior to the thermal-spraying operation to guarantee a mechanical anchorage of the molten particles to the substrate. However, some substrates are grit-blasting sensitive and therefore, alternative treatments should be considered. In these cases, the adherence of the coating must be attained by others means, either from a chemical point of view by modifying the surface wettability, or from a photonic one.Within this context, this study aims to explore the surface modifications induced on SiC composites (Ceramic Matrix Composites, CMC) before plasma spraying of alumina coatings. The effect of two different pre-treatments, deposition of a silicon bonding layer and short-pulse laser treatment (Nd:YAG), on the coating-substrate interface is investigated. A better chemical affinity between the alumina coating and the silicon carbide CMC has been observed with the silicon bond coating. On the other hand, a mixture of chemical and mechanical interaction induced by a cone-like structure occurs when treating the SiC CMC surface by laser prior thermal-spraying.     

热压烧结TZ3Y20A-SrSO4陶瓷基复合材料的高温摩擦学性能

采用化学沉淀法制备出粒径约80nm的等轴状SrSO4粉体。选用ZrO2(3mol%Y2O3)-20wt%Al2O3(TZ3Y20A)陶瓷为基体,采用热压烧结法制备出TZ3Y20A-SrSO4陶瓷基复合材料,并对复合材料的组织结构和力学性能进行了研究。采用球盘式高温摩擦磨损试验机测定复合材料从室温到800℃的摩擦学性能。TZ3Y20A-SrSO4复合材料在室温至800℃范围内摩擦系数在0.31～0.42之间,磨损率为10-5mm3/Nm数量级。加入SrSO4后复合材料的磨损表面形成了一层润滑膜,有效地改善了其高温摩擦磨损性能。     

2D-C/SiC陶瓷基复合材料拉伸试验的声发射特性

对2D-C/SiC陶瓷基复合材料试样在室温条件下单调拉伸试验和循环拉伸试验的损伤声发射信号进行研究,利用无监督层次聚类分析方法对单调和循环拉伸试验的声发射信号进行损伤模式识别,得出了两种拉伸试验下试样都有相同的损伤分类。对每次单调加/卸载试验分别进行应力和声发射信号分析,得到了在循环加载区间和卸载区间试样的损伤情况。对比分析两种拉伸试验的声发射信号,得到两次试验中首次加载相同应力时,两个试样有同一种类的声发射损伤信号,从而说明循环加载对试样的主要损伤影响较小。