共查询到20条相似文献,搜索用时 15 毫秒
1.
Orfeo Sbaizero Panos G. Charalambides Anthony G. Evans 《Journal of the American Ceramic Society》1990,73(7):1936-1940
Delamination crack propagation has been investigated in a laminated fiber-reinforced ceramic-matrix composite. The crack growth initiation resistance has been shown to be dominated by the critical strain energy release rate for the matrix. However, the resistance increases with crack extension because of bridging effects associated with intact fibers and, in some cases, intact segments of matrix. The delamination cracks also assume a steady-state trajectory within a 0° layer close to the 0°/90° interface. 相似文献
2.
Raj N. Singh 《Journal of the American Ceramic Society》1990,73(10):2930-2937
The first-matrix cracking stress and fiber-matrix interfacial shear stress were measured in zircon-matrix composites uniaxially reinforced with either uncoated or BN-coated silicon carbide filaments to study the role of intentional changes in interfacial shear stress on first-matrix cracking stress. The first-matrix cracking stress was measured by mechanical tests performed in either tension or flexure, and the filament-matrix interfacial shear stress was measured by a fiber pushout test. The first-matrix cracking stress was independent of the measured interfacial shear stress and did not conform to the predictions of a number of energy-based micromechanics models. In contrast, the first-matrix cracking stress showed a good correlation with the first-matrix cracking strain, which is hypothesized to be a more realistic criterion for first-matrix cracking in this class of filament-reinforced ceramic-matrix composites. 相似文献
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Matrix cracking in ceramic-matrix composites with unbonded frictional interface has been studied using fracture mechanics theory. The critical stress for extension of a fiber-bridged crack has been analyzed using the stress-intensity approach. The analysis uses a new shear-lag formulation of the crack-closure traction applied by the bridging fibers based on the assumption of a constant sliding friction stress over the sliding length of the fiber-matrix interface. The new formulation satisfies two required limiting conditions: (a) when the stress in the bridging fiber approaches the far-field applied stress, the crack-opening displacement approaches a steady-state upper limit that is in agreement with the previous formulations; and (b) in the limit of zero crack opening, the stress in the bridging fiber approaches the far-field fiber stress. This lower limit of the bridging stress is distinctly different from the previous formulations. For all other conditions, the closure traction is a function of the far-field applied stress in addition to the local crack-opening displacement, the interfacial sliding friction stress, and the material properties. Numerical calculations using the stress-intensity approach indicate that the critical stress for crack extension decreases with increasing crack length and approaches a constant steady-state value for large cracks. The steady-state matrix-cracking stress agrees with a steady-state energy balance analysis applied to the continuum model, but it is slightly less than the matrix-cracking stress predicted by such theories of steady-state cracking as that of Aveston, Cooper, and Kelly. The origin of this difference and a method for reconciliation of the two theoretical approaches are discussed. 相似文献
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Ramanthan Krishnamurthy Brian W. Sheldon 《Journal of the American Ceramic Society》2001,84(10):2451-2453
Model laminated composites were fabricated with porous-Al2 O3 interfaces between SiC bars. The porous Al2 O3 was deposited using an aerosol spray deposition technique, and the sandwich specimen was fabricated by hot pressing. Residual thermal stresses were present in the interface because of the difference in the coefficients of thermal expansion of SiC and Al2 O3 . Crack deflection was observed with measured interfacial fracture resistances that were considerably higher than the deflection threshold predicted by the He–Hutchinson criterion. Examination of the fracture surface revealed a tortuous crack path and significant crack–flaw interaction. 相似文献
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The fast-fracture and stress-rupture of a crossply ceramic-matrix composite with a matrix through-crack are examined numerically to assess the importance of fiber architecture and the associated stress concentrations at the 0/90 ply interface on failure. Fiber bridging in the cracked 0 ply is modeled using a line-spring bridging model that incorporates stochastic and time-dependent fiber fracture. A finite-element model is used to determine the stresses throughout the crossply in the presence of the bridged crack. For both SiC/SiC and a typical oxide/oxide, the fast-fracture simulations show that as global failure is approached, a significant fraction of fibers near the 0/90 interface are broken, greatly reducing the stress concentration. For fibers with low Weibull moduli ( m < 10), the tensile strength is thus nearly identical to that of a unidirectional composite scaled by the appropriate fiber volume fraction, while for fibers with larger Weibull moduli ( m ≥ 10), there are modest (10−17%) reductions in tensile strength. Stress-rupture simulations show that initially high stress concentrations are relieved as fibers fail with evolving time near the 0/90 interface and shed load away from the interface. For a wide range of fiber properties, efficient load redistribution occurs such that the crossply rupture lifetime is generally within an order of magnitude of the unidirectional lifetime, when the applied stress is normalized by the relevant fast-fracture strength. Overall, stress concentrations at the 0/90 interface are largely relieved with increasing load or time due to the nonlinear bridging response and preferential fiber failure near the interface, resulting in crossplies that respond very similarly to unidirectional composites. 相似文献
7.
Thomas B. Troczynski Patrick S. Nicholson 《Journal of the American Ceramic Society》1990,73(1):164-166
Bioactive glass was reinforced with 20 vol% Ag particles and 20 vol% SiC whiskers. Fatigue parameters and lifetime data for the two composites were determined via the stressing rate dependence of the bend strength in a bio-simulating buffered solution (pH of 7.4). A lifetime of 10 yr was estimated for the SiC-reinforced composites under bend stresses of 34 MPa and for Ag composites under 23 MPa. Stresses for similar survival of pure bioactive glass are 17 MPa. 相似文献
8.
Boron Nitride Interphase in Ceramic-Matrix Composites 总被引:1,自引:0,他引:1
Roger Naslain Olivier Dugne Alain Guette Jean Sevely Christian Robin Brosse Jean-Philippe Rocher Jacques Cotteret 《Journal of the American Ceramic Society》1991,74(10):2482-2488
A BN interphase has been deposited, by isothermal/isobaric chemical vapor infiltration (ICVI) from BF3 ─NH3 , within a preform made from ex-polycarbosilane (ex-PCS) fibers, at about 1000°C. In a second step, the BN-treated preform was densified with SiC deposited from CH3 SiCl3 ─H2 at about the same temperature. From a thermodynamic standpoint, ex-PCS fibers could be regarded as unreactive vs the BF3 ─NH3 gas phase assuming they are coated with a thin layer of carbon or/and silica. The as-deposited interphase consists of turbostratic BN (N/B < 1) containing oxygen. The SiC infiltration acts as an annealing treatment: (i) the BN interphase becomes almost stoichiometric and free of oxygen; (ii) the fibers undergo a decomposition process yielding a SiO2 /C layer at the BN/fiber interface. The weaker link in the interfacial sequence seems to be the BN/SiO2 interface. Deflection of microcracks arising from the failure of the matrix takes place at (or nearby) that particular interface. 相似文献
9.
Russell H. Jones Charles H. Henager Jr. Charles A. Lewinsohn Charles F. Windisch Jr. 《Journal of the American Ceramic Society》2000,83(8):1999-2005
Ceramic-matrix composites are being developed to operate at elevated temperatures and in oxidizing environments. Considerable improvements have been made in the creep resistance of SiC fibers and, hence, in the high-temperature properties of SiC fiber/SiC (SiCf /SiC) composites; however, more must be known about the stability of these materials in oxidizing environments before they are widely accepted. Experimental weight change and crack growth data support the conclusion that the oxygen-enhanced crack growth of SiCf /SiC occurs by more than one mechanism, depending on the experimental conditions. These data suggest an oxidation embrittlement mechanism (OEM) at temperatures <1373 K and high oxygen pressures and an interphase removal mechanism (IRM) at temperatures of ≳700 K and low oxygen pressures. The OEM results from the reaction of oxygen with SiC to form a glass layer on the fiber or within the fiber–matrix interphase region. The fracture stress of the fiber is decreased if this layer is thicker than a critical value ( d > d c ) and the temperature below a critical value ( T < T g ), such that a sharp crack can be sustained in the layer. The IRM results from the oxidation of the interfacial layer and the resulting decrease of stress that is carried by the bridging fibers. Interphase removal contributes to subcritical crack growth by decreasing the fiber-bridging stresses and, hence, increasing the crack-tip stress. The IRM occurs over a wide range of temperatures for d < d c and may occur at T > T g for d > d c . This paper summarizes the evidence for the existence of these two mechanisms and attempts to define the conditions for their operation. 相似文献
10.
Theory of Mechanical Properties of Ceramic-Matrix Composites 总被引:6,自引:0,他引:6
William A. Curtin 《Journal of the American Ceramic Society》1991,74(11):2837-2845
11.
Thermal expansions of three two-dimensional laminate, continuous fiber/chemical-vapor-infiltrated silicon carbide matrix composites reinforced with either FP-Alumina (alumina), Nextel (mullite), or Nicalon (Si-C-O-N) fibers are reported. Experimental thermal expansion coefficients parallel to a primary fiber orientation were comparable to values calculated by the conventional rule-of-mixtures formula, except for the alumina fiber composite. Hysteriesis effects were also observed during repeated thermal cycling of that composite. Those features were attributed to reoccurring fiber/matrix separation related to the micromechanical stresses generated during temperature changes and caused by the large thermal expansion mismatch between the alumina fibers and the silicon carbide matrix. 相似文献
12.
Antonios E. Giannakopoulos Kristin Breder 《Journal of the American Ceramic Society》1991,74(1):194-202
The improved fracture resistance of whisker-reinforced ceramic-matrix composites involves more than one energy-absorbing mechanism. The possible mechanisms are reviewed and a micromechanical model evaluating the relative contributions to the overall toughness is presented. The mechanisms involve microcracking, load transfer, bridging, and crack deflection. The synergism of these mechanisms is examined using an energy release rate balance equation. The basic assumption of the proposed model is that the load transfer between the matrix and the whiskers is due to Coulomb friction. The model has been applied to an Al2 O3 /SiC whisker composite and shows reasonable agreement with reported experimental results. The role of the thermal residual stresses is also examined in light of the frictional load transfer assumption. 相似文献
13.
Thomas B. Troczynski Patrick S. Nicholson 《Journal of the American Ceramic Society》1991,74(8):1803-1806
Composite bioactive glass-ceramics reinforced with 30 vol% Ti particles were produced by warm-forging and in situ crystallization. The bend strength of the composite was 87 ± 7 MPa. A fracture mechanical study in air and Ringer's bioactive solution determined crack velocity vs stress intensity factor and the effect of stressing rate on the bend strength. Time to failure of 10 years is predicted for the composite loaded at 10 MPa in Ringer's solution or 50 MPa in air. A disappointing fatigue performance of the relatively tough metal/ceramic composite illustrates that satisfactory short-time fracture resistance does not guarantee lifetime under fatigue conditions (long-term fracture resistance). 相似文献
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16.
Temel Kotil John W. Holmes Maria Comninou 《Journal of the American Ceramic Society》1990,73(7):1879-1883
Possible mechanisms for the hysteresis in stress-strain response observed during fatigue of fiber-reinforced ceramics are examined analytically. In the model developed, the microstructure of a unidirectional composite is divided into adjacent cells, each containing a single fiber. The compliance of each cell is modeled by a series of springs, with frictional sliding of fibers represented by sliding blocks. Fatigue damage is modeled by allowing fibers to debond and fracture on a random cycle-by-cycle basis. The magnitude of the interfacial shear between the fibers and matrix is shown to play a significant role in determining the extent of hysteresis observed during fatigue loading of unidirectional composites. Practical considerations, such as the influence of fiber volume fraction on macroscopic fatigue behavior, are also discussed. 相似文献
17.
Rate of Strength Decrease of Fiber-Reinforced Ceramic-Matrix Composites during Fatigue 总被引:2,自引:0,他引:2
Bent F. Sørensen John W. Holmes Eddy L. Vanswijgenhoven 《Journal of the American Ceramic Society》2000,83(6):1469-1475
An experimental investigation was performed to study the rate at which strength-controlling fatigue damage evolves in a ceramic-matrix composite. Tensile specimens of a unidirectional SiC-fiber-reinforced calcium aluminosilicate matrix composite were cycled to failure or to a preselected number of cycles under similar loading histories. The residual strength of the precycled specimens was found to be similar to that of virgin specimens. Microstructural investigations showed that the fracture surfaces of the specimens cycled to failure had a central region where fiber pullout was negligible. It is proposed that frictional heating (due to interfacial sliding) is the cause of fatigue failure. High interfacial temperatures are assumed to cause the formation of a strong interface bond, leading to internal embrittlement. 相似文献
18.
A model describing the salient features of tensile stress-strain curves of ceramic–fiber composites has been developed. The model incorporates statistics of fiber failure. Furthermore, the compliance of the testing machine is included so that the onset of instability can be predicted. An experiment conducted on a composite consisting of a glass-ceramic matrix reinforced with SiC fibers exhibits excellent agreement with the predicted behavior. 相似文献
19.
Hongxiang Zhai Yong Huang Changan Wang Xin Wu 《Journal of the American Ceramic Society》2000,83(8):2006-2016
The dependence of toughening mechanisms on reinforcement orientation and the toughening effect governed by multiple toughening mechanisms were characterized for ceramic-matrix composites (CMCs) with discontinuous elongated reinforcements. Two kinds of Si3 N4 -based composites, with directionally oriented and randomly oriented SiC whiskers, respectively, were tested by the three-point bending of chevron-notched bars. Based on microscopic observations and micromechanical analyses, three mechanisms were confirmed to dominate the crack-bridging behavior: (1) bridging and breaking of long reinforcements, (2) frictional pullout and breaking of short reinforcements, and (3) local matrix spalling. Both the occurrence of the multiple mechanisms and their toughening effects were proved dependent on the reinforcement orientation. The combined effect of the multiple mechanisms correlated with random orientation thus was characterized by a statistical approach to solve for the crack-bridging stress function. The theoretical model was in good agreement with the experimental results. 相似文献
20.
Kathleen R. McDonald John R. Dryden Arun Majumdar Frank W. Zok 《Journal of the American Ceramic Society》2000,83(3):553-562
The thermal conductance of delamination cracks in a unidirectionally reinforced ceramic composite is investigated. A phase-sensitive photothermal technique is used to measure the crack conductance in situ under load. Special emphasis is given to the effects of the local crack opening displacement (δ). A crack conductance model that considers the contributions from both the air and the fibers within the crack is developed and compared with the measurements. Despite considerable scatter in the experimental data, the model adequately predicts the increased conductance that is associated with fiber bridging, as well as the overall trend that is observed with δ. 相似文献