Fracture Of Ceramic-matrix Composites Research Articles

Structural effects in ‘brick-and-mortar’ architecture: Bio-inspired ceramic matrix composites developed through a new method

Here, we present a bio-inspired ceramic matrix composites (CMCs) preparation method with highly controllable ceramic-brick size (length-to-thickness ratio, α, ranges from 5 to 40) based on a laser process combined with an adhesive bonding technology. Thanks to the toughening mechanisms such as crack deflection, bifurcation and bridging induced by ceramic-bricks and the strengthening mechanism controlled by ceramic-bridges, the failure displacement and the work of fracture (γwof) in CMCs have significantly improved by more than 15 and 3.5 times, respectively. On this basis, a novel CMCs, composed of layered ceramic and ‘brick-and-mortar’ ceramic, inspired by the compound structure of prismatic- and nacre-like layers in shell were prepared. Such a gradient design brought a improvement of 11.63 kJ/m2 in the γwof value, which was 2.6 times larger than the optimal improvement in pure ‘brick-and-mortar’ structural CMCs (4.45 kJ/m2). Compared with the experimental results, it was found that the strength and failure behavior of CMCs could be reasonably predicted with the help of the Pimenta and Begley models, while no appropriate model has been established as for the γwof prediction so far.

Tensile properties and failure mechanism of the SiCf/SiC minicomposite with multi-layered (BN/SiC)n interfacial coatings at room temperature

To overcome the brittle fracture of ceramic matrix composites, the interfacial coatings between continuous fibers and the ceramic matrix, especially boron nitride (BN) and silicon carbide (SiC) coatings were often introduced into the composites to improve the interface properties. This work focused on the use of chemical vapor infiltration (CVI) and precursor infiltration and pyrolysis (PIP) to fabricated SiC fiber-reinforced SiC (SiCf/SiC) minicomposites with interfacial coatings. Single BN, double-layered BN/SiC, and multi-layered (BN/SiC)2 interfacial coatings were deposited on SiC fibers from BCl3-NH3-H2 and MTS (Methyltrichlorosilane)-H2 systems in a low pressure hot-wall CVI reactor. Room-temperature tensile testing was used to evaluate the influence of different interfacial coatings on the tensile properties and failure mechanism of SiCf/SiC minicomposites. The minicomposites with (BN/SiC)2 coatings performed the highest fracture strength of 630.9 MPa. The mechanical behaviour of the composites was characterized by the universal testing machine with an acoustic emission (AE) detector, a scanning electron microscope (SEM), and an energy dispersive X-ray spectrometer (EDS). The existence of (BN/SiC)2 coatings provoked the interface debonding in the minicomposite both at the BN/fiber interface and the interface between BN and SiC layers, prolonging the crack propagation paths and noticeably improving the fracture properties of the minicomposite.

Full-field characterisation of oxide-oxide ceramic-matrix composites using X-ray computed micro-tomography and digital volume correlation under load at high temperatures

In situ synchrotron X-ray computed micro-tomography and digital volume correlation (DVC) were utilised to understand the failure mechanisms at room temperature and 1050 °C of two Nextel™720/alumina oxide-oxide ceramic-matrix composites (CMCs), termed materials A and B, sintered respectively at 1200 °C and ~1250 °C. At both test temperatures, three-point-bending strengths were ~55–58 MPa for material A and ~94–100 MPa for material B. Damage was associated with three primary types of cracking modes: interfacial delamination, inclined cracks within fibre tows, opening of existing matrix shrinkage cracks. Material A exhibited higher shrinkage cracking, whereas material B displayed more pronounced diagonal matrix microcracking. At 1050 °C, both systems showed less microcracking but more pronounced delamination. Such damage characteristics were rationalised in terms of the corresponding 3D DVC displacement/strain fields. Specifically, global DVC was utilised and maximum principal strain locations prior to failure, which varied from 0.005 to 0.01, correlated well to the fracture initiation sites. Further, abrupt positive to negative transitions of shear strain components were observed and were attributed to the different bonding strengths between 0°/90° fibres and the matrix. The current study demonstrates that in situ high-temperature tomography/DVC is a powerful method for studying the deformation and fracture of oxide-oxide CMCs.

Two Coupled Unit Problems in Shear-Lag Analysis of Fracture in Ceramic Matrix Composites

Two Coupled Unit Problems in Shear-Lag Analysis of Fracture in Ceramic Matrix Composites

Effect of interface damage on tensile behavior of fiber-reinforced ceramic-matrix composites after thermal fatigue loading

ABSTRACT In this paper, the effect of interface damage on the tensile damage and fracture of fiber-reinforced ceramic-matrix composites (CMCs) after thermal fatigue loading is investigated. The damage mechanisms of matrix cracking, fiber/matrix interface debonding and wear, interface and fiber oxidation, and fiber failure after thermal fatigue loading are considered in the tensile stress-strain behavior prediction. The relationships between the thermal fatigue temperature, applied cycle number, composite internal damage, and tensile damage and fracture are established. The effects of thermal fatigue temperature, thermal cycle number, fiber volume, interface shear stress, fiber strength, and fiber Weibull modulus on the tensile damage and fracture of fiber-reinforced CMCs subjected to the thermal fatigue loading are analyzed. The experimental tensile stress-strain curves of different C/SiC composites with and without thermal fatigue loading are predicted. When the thermal fatigue temperature and applied cycle number increase, the composite tensile strength and failure strain decrease, the interface debonding ratio, interface oxidation ratio, and broken fibers fraction increase at low applied stress level.

The impact of core-shell nanotube structures on fracture in ceramic nanocomposites

Multi-wall carbon nanotubes (MWCNTs) can be used to create ceramic nanocomposites with improved fracture toughness. In the present work, atomic layer deposition (ALD) was employed to deposit thin oxide layers on MWCNTs. These core-shell structures were then used to create nanocomposites by using a polymer derived ceramic (PDC) to produce the matrix. Variations in both the initial MWCNT structure and the oxide layers led to substantial differences in fiber-pullout behavior. Single tube pullout tests also showed that the oxide coatings led to stronger bonding with the ceramic matrix. With high defect density MWCNTs, this led to shorter pull-out lengths which is consistent with the conventional understanding of fracture in ceramic matrix composites. However, with low defect density MWCNTs longer pullout lengths were observed with the oxide layers. To interpret the different trends that were observed, we believe that the ALD coatings should not be viewed simply as a means of altering the interfacial properties. Instead, the coated MWCNTs should be viewed as more complex core-shell fibers where both interface and internal properties can be controlled with the ALD layers.

Analysis of Heat Generation during Fracture in Ceramic Matrix Composites

Ceramic matrix composites (CMCs) have evolved as potential candidate materials for high-temperature structural applications due to lightweight, high-temperature strength and excellent corrosion and wear resistance. In this investigation, damage evolution and heat generation of CMCs during monotonic loadings were investigated using different types of nondestructive evaluation (NDE) techniques, such as acoustic emission (AE) and infrared (IR) thermography and microstructural characterization. IR camera was used for in-situ monitoring of temperature evolution, and the temperature changes during testing were measured. A significant temperature increase has been observed at the time of failure. Microstructural characterizations using scanning electron microscopy (SEM) were performed to investigate fracture behavior of CMC samples. In this investigation, the NDE technique and SEM characterization were employed to analyze damage evolution and progress of ceramic matrix composites during monotonic loading.

Fracture in Ceramic-Matrix Composites Reinforced with Strongly Bonded Metal Particles

The resistance of a ceramic matrix composite to the cleavage cracking across a field of strongly bonded, uniformly distributed metal particles is studied. The crack trapping and bridging effects of the metal particles are analyzed by means of calculating the strain energy and the traction work. An explicit expression for the critical energy release rate as a function of particle volume fraction has been obtained. The fracture resistance is independent of elastic properties of the matrix and the sample geometry and is predominantly determined by the size/spacing ratio of the particles. It is shown that the theoretical curves agree with experimental data quite well. The methodology developed in this article can be used in studying the fracture resistances of composites with high filler contents and irregular filler geometries.

Direct observation of the fracture of CAS-glass/SiC composites

The fracture behaviour of a CAS-glass/SiC-fibre-reinforced composite was observed by dynamic in situ scanning electron microscopy (SEM). In a companion paper [1], tests on common delamination geometries are described and the basis of micromechanics models is critically evaluated. Flexure geometries and also the unnotched tensile response of ceramicmatrix composites (CMCs) have received considerable attention, both theoretically and experimentally. The effect of through-thickness notches on the tensile fracture of CMCs has however been relatively neglected. Previous work on polymer-matrix composites demonstrates the strong influence of subcritical damage on the fracture behaviour. In this paper we examine failure of notched CAS-glass/SiC composites in tension, under static- and fatigue-loading conditions, using a combination of in situ and conventional test methods. The subcritical damage which forms is compared with that in polymer-matrix composites, and the consequences for prediction of the notched strength are discussed.

Direct observation of the fracture of CAS-Glass/SiC composites

The fracture of ceramic-matrix composites is frequently complex, involving the evolution of subcritical damage which strongly affects the final failure process, and which is very specimen dependent. Observations of fracture mechanisms are described for a calcium-alumino-silicate (CAS) glass reinforced with SiC fibres. The tests were principally undertaken dynamically in situ within a scanning electron microscope. This technique enables detailed characterization of the subcritical damage and of the crack interactions which occur prior to final failure. It is shown that meaningful modelling of fracture processes in these materials generally requires this level of detail in identifying the micromechanisms. We describe a preliminary evaluation of the unnotched tensile response of the material, followed by in situ observations on two common delamination geometries: four-point bending and double cantilever beam. The tensile behaviour of edge-notched specimens is described in part II

The effect of triangularly waved metal fiber on fracture behavior of brittle matrix composites.

From the point of suppressing the crack growth, an attempt to improve the resistance to fracture of ceramic matrix composites was made on Al2O3 matrix/tungsten fiber composite using triangularly waned fiber for the reinforcement.On the monotonic loading flexure test, large plastic deformation was found with holding the maximum strength of the composite, where clear stepwise change in strength against deflection was observed on the load-deflection curve. These phenomena were seen under the condition that fibers were still unbroken.Superior resistance to ratchetting of the deflection against cyclic loading was found on the cyclic loading flexure test, in comparison with straight fiber reinforced composite.No delamination was observed on the Charpy impact test, where straight fiber reinforced composite exhibited serious delamination over the whole test piece.Microscopic observation on the crack extension path clearly showed that triangularly waved fiber had a peculiar effect on suppressing crack growth by way of the branching or turning of the crack path.Mechanism of the crack growth suppression was discussed from a point of the reduction of stress intensity factor induced by serious turning or branching of the crack path.