共查询到20条相似文献,搜索用时 0 毫秒
1.
The change in mechanical properties of a fiber-reinforced ceramic from notch insensitivity at room temperature to notch sensitivity at elevated temperature has been investigated. The change in behavior has been attributed primarily to a correspondingly large variation in the shear resistance of the fiber/matrix interface caused by oxidation effects at that interface. The transition in behavior has been correlated with a fracture model based on the incidence of fiber failure in the crack wake. 相似文献
2.
3.
Symmetric (0°/90°) composite laminates consisting of SiC fibers in a lithifum aluminosilicate matrix have been tested intension and flexure. The various modes of damage, consisting of matrix cracks, delamination cracks, and fiber bundle failure, have been examined and related to features of the stress-strain curves. The materials exhibit a relatively lower shear strength (20 MPa), measured in flexure, than tensile strength (200 MPa), because of the formation of matrix microcracks. The stress-strain characteristics of the laminates are shown to be predictable, based on strength measurements obtained on the individual laminate layers, in conjunction with knowledge of the residual stresses. 相似文献
4.
Effects of Matrix Porosity on the Mechanical Properties of a Porous-Matrix, All-Oxide Ceramic Composite 总被引:5,自引:0,他引:5
Michael A. Mattoni James Y. Yang Carlos G. Levi Frank W. Zok 《Journal of the American Ceramic Society》2001,84(11):2594-2602
The effects of matrix porosity on the mechanical properties of an all-oxide ceramic composite are investigated. The porosity is varied through impregnation and pyrolysis of a ceramic precursor solution. Mechanical tests are performed to assess the role of the matrix in both matrix-dominated and fiber-dominated loading configurations. The results demonstrate a loss in damage tolerance and tensile strength along the fiber direction as the porosity is reduced. Concomitantly, some improvements in interlaminar strength are obtained. The latter improvements are found to be difficult to quantify over the entire porosity range using the standard short beam shear method, a consequence of the increased propensity for tensile fracture as the porosity is reduced. Measurements of interlaminar shear strength based on the double-notched shear specimen are broadly consistent with the limited values obtained by the short beam shear method, although the former exhibit large variability. In addition, effects of precursor segregation during drying on through-thickness gradients in matrix properties and their role in composite performance are identified and discussed. An analysis based on the mechanics of crack deflection and penetration at an interphase boundary is presented and used to draw insights regarding the role of matrix properties in enabling damage tolerance in porous-matrix composites. Deficiencies in the understanding of the mechanisms that enable damage tolerance in this class of composites are discussed. 相似文献
5.
Jean-Marc Domergue Fernando E. Heredia Anthony G. Evans 《Journal of the American Ceramic Society》1996,79(1):161-170
Hysteresis measurements obtained on 0/90 SiC/CAS and SiC/SiC have been used to analyze the interface responses. Four parameters have been derived from these measurements. These relate to the compliance change caused by matrix cracking, the frictional resistance of the interface, the interface debond resistance, and the residual stress. These parameters have been used to predict the stress/ strain curves. Preliminary estimates of stress partitioning between the plies have been used to estimate constituent properties, such as the friction stress. 相似文献
6.
Hui Mei Yongdong Xu Laifei Cheng Litong Zhang 《International Journal of Applied Ceramic Technology》2007,4(4):378-386
A C/SiC composite panel with defects of known size and of familiar nature was manufactured successfully for nondestructive evaluation. A computed tomography (CT) system was used to detect embedded defects. The results show that CT imaging corresponds well with the designed defects. The defect-embedded composites undergo relatively greater loss in tensile strength and failure strain than the as-received samples, although their initial Young's moduli are almost identical. It is also observed that the embedded defects make a significant contribution toward the initiation and accumulation of the damage in the composites, which result eventually in the early failure of the composite. 相似文献
7.
自润滑复合陶瓷是极端环境服役运动部件的最佳候选材料之一,其中仿生层状结
构自润滑复合陶瓷由于具有优异的综合性能而倍受人们的青睐。基于宏/微观结构设计是实现其
结构/润滑功能一体化和可靠性提升的关键。本文结合作者所在课题组的相关工作,综述了层状
结构几何参数和界面微结构、参数与组分对氧化铝层状自润滑复合陶瓷力学性能、摩擦学性能
和服役可靠性的影响规律及作用机制,并提出了层状自润滑复合陶瓷的结构与界面优化设计准
则,以期指导自润滑复合陶瓷性能提升和推动其在高技术装备中的应用。 相似文献
8.
In-Plane Mechanical Properties of an All-Oxide Ceramic Composite 总被引:1,自引:0,他引:1
John A. Heathcote Xiao-Yan Gong James Y. Yang Upadrasta Ramamurty Frank W. Zok 《Journal of the American Ceramic Society》1999,82(10):2721-2730
The present article examines the in-plane tensile properties of a two-dimensional (2D) all-oxide ceramic composite. The distinguishing characteristics of the material include fine-scale porosity within the matrix and the absence of a fiber coating. The anisotropy in the elastic-plastic properties has been studied through tension tests in the axial (fiber) direction and at 45° to the fiber axes, both in the presence and the absence of holes or notches. The notch sensitivity in the axial direction is comparable to that of conventional dense-matrix, weak-interface composites, demonstrating the effectiveness of the porous matrix in enabling crack deflection and damage tolerance. Furthermore, the notch sensitivity is rationalized using models that account for the effects of inelastic straining on the local stress distributions around notches and holes, coupled with a scale-dependent failure criterion. In the off-axis orientation, the tensile strength is dictated by a plastic instability, analogous to necking in metals. Following instability, deformation continues within a diffuse localized band, with a length comparable to the specimen width. Similar deformation and fracture characteristics are obtained both with and without holes. The off-axis properties are discussed in terms of the comminution and rearrangement of matrix particles during straining. 相似文献
9.
Effects of Thermal Aging on the Mechanical Properties of a Porous-Matrix Ceramic Composite 总被引:3,自引:0,他引:3
Eric A. V. Carelli Hiroki Fujita James Y. Yang Frank W. Zok 《Journal of the American Ceramic Society》2002,85(3):595-602
The present article focuses on changes in the mechanical properties of an all-oxide fiber-reinforced composite following long-term exposure (1000 h) at temperatures of 1000–1200°C in air. The composite of interest derives its damage tolerance from a highly porous matrix, precluding the need for an interphase at the fiber–matrix boundary. The key issue involves the stability of the porosity against densification and the associated implications for long-term durability of the composite at elevated temperatures. For this purpose, comparisons are made in the tensile properties and fracture characteristics of a 2D woven fiber composite both along the fiber direction and at 45° to the fiber axes before and after the aging treatments. Additionally, changes in the state of the matrix are probed through measurements of matrix hardness by Vickers indentation and through the determination of the matrix Young's modulus, using the measured composite moduli coupled with classical laminate theory. The study reveals that, despite evidence of some strengthening of the matrix and the fiber–matrix interfaces during aging, the key tensile properties in the 0°/90° orientation, including strength and failure strain, are unchanged. This strengthening is manifested to a more significant extent in the composite properties in the ±45° orientation, wherein the modulus and the tensile strength each exhibit a twofold increase after the 1200°C aging treatment. It also results in a change in the failure mechanism, from one involving predominantly matrix damage and interply delamination to one which is dominated by fiber fracture. Additionally, salient changes in the mechanical response beyond the maximum load suggest the existence of an optimum matrix strength at which the fracture energy in the ±45° orientation attains a maximum. The implications for long-term durability of this class of composite are discussed. 相似文献
10.
Charles J. Russo Martin P. Harmer Helen M. Chan Gary A. Miller 《Journal of the American Ceramic Society》1992,75(12):3396-3400
Adding aluminum titanate to alumina can result in dramatic improvements in toughness and R -curve properties. However, the improved toughness is offset by a significant reduction in strength at small flaw sizes. This problem can be overcome through the use of a laminated composite construction. By placing a thin layer of high-strength material on the surface of a high-toughness body, the toughness and flaw tolerance of the body material can be maintained without sacrificing small flaw strength. In this study, alumina + 20 vol% aluminum titanate (AAT20) was used for both the surface layer and the bulk material. The surface material was a homogeneous, fine-grained mixture of the two phases, while the bulk was an inhomogeneous mixture having a bimodal grain structure. In monolithic form, the homogeneous AAT20 displays a nearly P −1/3 indentation strength response, and the inhomogeneous material displays a flat strength response, indicative of R -curve behavior. The trilayer material shows a composite indentation strength response, with high strength throughout the entire range of starting flaw sizes. A method for predetermining the optimum surface layer thickness is presented. The processing and mechanical properties of these materials will be discussed. 相似文献
11.
Craig A. Folsom Frank W. Zok Fred F. Lange David B. Marshall 《Journal of the American Ceramic Society》1992,75(11):2969-2975
The mechanical properties of a noval laminar composite are investigated. The composite consists of dense alumina sheets bonded between sheets of a uniaxial carbon-fiber-reinforced epoxy tape. The behavior of the composite in both flexural and tensile loading is characterized and the results are related to the properties of the constituents. The role of the interlaminar interface in composite behavior is also examined. Implications for the design of laminar composites with complex shapes are briefly discussed. 相似文献
12.
Zhang Zuoguang Wang Mingchao Li Min Sun Zhijie 《Journal of the American Ceramic Society》2009,92(5):1129-1132
In order to improve the mechanical properties of boron carbide (B4 C) ceramic, a mullite-reinforced B4 C matrix ceramic with complete densification was fabricated via hot pressing for the first time. The dense sintering mechanism of mullite-reinforced B4 C ceramic was discussed through the phase and element analysis. A new dense sintering mechanism was found in which the diffusion of Si in mullite through the B4 C matrix enhances the sintering of mullite-reinforced B4 C ceramics effectively. The mechanical properties and microstructure of the composite ceramics were investigated in contrast with monolithic B4 C and one kind of commercial B4 C ceramic. The flexural strength and fractural toughness of B4 C with 3 vol% mullite addition reached 560 MPa and 3.33 MPa·m1/2 , which is 154% and 96% higher than that of monolithic B4 C, respectively. 相似文献
13.
Sung R. Choi D. Calvin Faucett Donald J. Alexander 《Journal of the American Ceramic Society》2014,97(12):3926-3934
Foreign object‐damage (FOD) phenomena of an N720/alumina oxide/oxide ceramic matrix composite (CMC), impacted by 1.59‐mm spherical chrome steel projectiles up to Mach 1, were assessed at ambient temperature at a normal incidence angle in both partial and full supports. The impact damage was in the form of craters, matrix/fiber tow breakage, compaction of the material, delamination and cone cracks, and their occurrence and degree depended on both impact velocity and type of target supports. The partial support resulted in significant damage with increasing impact velocity, accompanying substantial strength degradation. The presence of tensile stress and presumably stress wave interaction at the backside of a target could have been responsible for greater impact damage in partial support. Although the CMC targets impacted at 340 m/s were on the verge of being penetrated, the targets still survived catastrophic failure retaining about 68% of the as‐received strength, indicative of relatively superior FOD resistance as compared to monolithic ceramic counterparts. A quasi‐static analysis of impact force prediction was made based on the energy balance principle and was validated indirectly using the experimental data on frontal impact damage size. 相似文献
14.
15.
Distribution of Matrix Cracks in a Uniaxial Ceramic Composite 总被引:1,自引:0,他引:1
Chongdu Cho John W. Holmes James R. Barber 《Journal of the American Ceramic Society》1992,75(2):316-324
Conventional shear-lag analyses of matrix cracking and debonding in uniaxial composites loaded in tension predict that the matrix stress varies only very slowly with position except near existing cracks. It therefore follows that the location of subsequent cracks is very sensitive to minor local variations in matrix strength, leading to significant statistical variation in crack spacing. This question is investigated using a discrete random process model of a composite and by direct experimental measurements of crack spacing. In the limit of a completely homogeneous composite, it is shown that the crack spacing distribution tends to an inverse square distribution between the theoretical maximum spacing and half that value. The random process model recovers this behavior in the limit and exhibits an approximately Weibull distribution of crack spacings when the matrix strength has significant variance. The theoretical predictions are compared with experimental results obtained for a unidirectional ceramic-matrix composite (SiC fibers in a calcium aluminosilicate matrix). The experimental results exhibit features similar to those predicted by the model and are compatible with a matrix strength whose standard deviation is of the order of 40% of the mean strength. An important point is that, with this magnitude of strength variation, the material exhibits a significant size effect and it is essential to take this into account in estimating the mean crack spacing from the corresponding mean matrix properties. 相似文献
16.
Ahmad C. Solomah Wolfgang Reichert Vincenzo Rondinella Leonardo Esposito Enrique Toscano 《Journal of the American Ceramic Society》1990,73(3):740-743
Zirconia-toughened alumina (Al2 O3 –15 vol% Y-PSZ (3 mol% Y2 O3 )) reinforced with 10 vol% silicon carbide whiskers (ZTA-10SiC w ) ceramic matrix composite has been characterized with respect to its room-temperature mechanical properties, thermal shock resistance, and thermal stability at temperatures above 1073 K. The current ceramic composite has a flexural strength of ∽550 to 610 MPa and a fracture toughness, K IC , of ∽5.6 to 5.9 MPa·m1/2 at room temperature. Increases in surface fracture toughness, ∽30%, of thermally shocked samples were observed because of thermal-stress-induced tetragonal-to-monoclinic phase transformation of tetragonal ZrO2 grains dispersed in the matrix. The residual flexural strength of ZTA–10 SiC w ceramic composite, after single thermal shock quenches from 1373–1573 to 373 K, was ∽10% higher than that of the unshocked material. The composite retained ∽80% of its original flexural strength after 10 thermal shock quenches from 1373–1573 to 373K. Surface degradation was observed after thermal shock and isothermal heat treatments as a result of SiC whisker oxidation and surface blistering and swelling due to the release of CO gas bubbles. The oxidation rate of SiC whiskers in ZTA-10SiC w composite was found to increase with temperature, with calculated rates of ∽8.3×10−8 and ∽3.3×10−7 kg/(m2 ·s) at 1373 and 1573 K, respectively. It is concluded that this ZTA-10SiC w composite is not suitable for high-temperature applications above 1300 K in oxidizing atmosphere because of severe surface degradation. 相似文献
17.
18.
19.
着重研究了5231/T300复合材料的常规力学性能和高温下的力学性能,并与5222/T300复合材料的相应性能进行了对比,试验表明,前者在抗压缩模量和抗剪切性能方面比后者略低,其他力学性能基本相当,耐高温性能良好,另外,5231碳布预浸料可与铝蜂窝直接共固化,抗滚筒剥离强度较高,该复合材料可应用于飞机的结构件上。 相似文献
20.
Rachman Chaim Laura Baum David G. Brandon 《Journal of the American Ceramic Society》1989,72(9):1636-1642
High-density whisker-reinforced composites of an alumina-30 vol% glass matrix material were produced by hot-pressing in the temperature range 1350° to 1400°C in air. Significant improvement was observed in the strength of composites containing 15 vol% SiC whiskers, up to ∼550 MPa, but with only a small effect on the fracture toughness. In composites containing Si3 N4 whiskers, no reinforcement was achieved. Transmission electron microscopy showed the formation of a protective layer of amorphous silica on the SiC whiskers, while the Si3 N4 whiskers were found to react with the matrix. The mechanical properties were related to the microstructure and the density of the samples. 相似文献