Fiber Ceramic Matrix Composites Research Articles

Novel measuring method for prepreg processability of oxide fiber ceramic matrix composites

In this study, the processing behavior of pre-impregnated fabrics (prepregs) for the fabrication of ceramic matrix composites (CMC), specifically oxide fiber composites (OFC), was investigated. The evaluation of rheological slurry properties alone proved to be insufficient for the assessment of their suitability for the cold roll lamination process used in this work. Therefore, a novel testing method was developed, which determined the behavior of a prepreg stack in process-oriented conditions. This provided qualitative information not only on the squeeze flow of the slurry, but also on its ability to maintain this imposed level of compaction with no major rebounding throughout the following processing steps. Tests were performed with three different slurries and the results obtained corresponded well with the fabrication of full-scale OFC plates. Hence, the results gained by this novel method provide a more straight-forward approach for the evaluation of prepreg systems and quality control.

Processing and oxidation response of Cr2AlC MAX-phase composites containing ceramic fibers

Three different ceramic matrix composites (CMCs) were produced using Cr2AlC as a matrix, and carbon, SiC and Al2O3 short fibers as a secondary phase. Cr2AlC powders were synthesized by solid-state reaction, followed by mixing with the fibers, and full densification using a field-assisted sintering technique. Of the three different fiber types, Carbon fibers reacted strongly with Cr2AlC, while the reaction with SiC fibers was more limited and alumina fibers didn’t show any reaction. Oxidation tests of the monolithic Cr2AlC and the composites were performed by thermogravimetric analysis. An alumina layer formed at 1000 ​°C on every sample, well attached and worked as a good oxidation barrier. Under realistic conditions using a burner rig for cyclic oxidation at 1200 ​°C for 500 cycles, the oxidation resistance of the alumina fiber CMC is good, as no defects or degradation are visible and the alumina layer is well attached.

Powder Injection Molding of Oxide Ceramic CMC

Ceramic Matrix Composites (CMC) offer improved mechanical properties, especially higher toughness, preferably at elevated temperatures. Fields of application are, for example, highly hot stressed components of aero engines.Processing of Ceramic Matrix Composites by powder injection molding offers attractive economic benefits, however, it represents a considerable challenge. Development of a process chain for the ceramic injection molding of Al2O3 short fiber CMC had started by feedstock preparation and characterization. Fiber content varied between 10 to 50 vol.% whereas for binder a well-examined system from KIT was chosen. The fiber content showed a minor effect on the rheological properties but fiber orientation depended strongly on the apparent shear profile. The sintering behavior was affected as well, i.e. higher densities were achieved.

Modeling the temperature-dependent non-steady state first matrix cracking stress for fiber ceramic matrix composites

Based on fracture mechanics theory and a temperature-dependent interfacial shear strength model established by the authors, this paper develops a temperature-dependent theoretical model for the non-steady state first matrix cracking stress of fiber ceramic matrix composites. The model unifies the combined effects of temperature, crack length and thermal residual stress on the first matrix cracking stress into a single theory. The model predictions for the first matrix cracking stress of silicon carbide fiber reinforced zircon matrix composite agree well with the experimental results. Compared with the classical models proposed by Danchaivijit and Shetty, Thouless and Evans, and Marshall et al., our model has obvious advantages from the aspects of applicability, convenience and accuracy. Moreover, the analysis of influencing factors for the first matrix cracking stress is conducted systematically. Some new insights into improving the first matrix cracking stress of fiber ceramic matrix composites are obtained.

Velcro-Inspired SiC Fuzzy Fibers for Aerospace Applications.

The most recent and innovative silicon carbide (SiC) fiber ceramic matrix composites, used for lightweight high-heat engine parts in aerospace applications, are woven, layered, and then surrounded by a SiC ceramic matrix composite (CMC). To further improve both the mechanical properties and thermal and oxidative resistance abilities of this material, SiC nanotubes and nanowires (SiCNT/NWs) are grown on the surface of the SiC fiber via carbon nanotube conversion. This conversion utilizes the shape memory synthesis (SMS) method, starting with carbon nanotube (CNT) growth on the SiC fiber surface, to capitalize on the ease of dense surface morphology optimization and the ability to effectively engineer the CNT-SiC fiber interface to create a secure nanotube-fiber attachment. Then, by converting the CNTs to SiCNT/NWs, the relative morphology, advantageous mechanical properties, and secure connection of the initial CNT-SiC fiber architecture are retained, with the addition of high temperature and oxidation resistance. The resultant SiCNT/NW-SiC fiber can be used inside the SiC ceramic matrix composite for a high-heat turbo engine part with longer fatigue life and higher temperature resistance. The differing sides of the woven SiCNT/NWs act as the "hook and loop" mechanism of Velcro but in much smaller scale.

Inspection of geometry influence and fiber orientation to characteristic value for short fiber reinforced ceramic matrix composite under bending load

For use of short fiber reinforced ceramics the knowledge of the influence of coupon geometry on the failure mode and the determined resistance in bending tests is necessary. In contrast to the continuous fiber reinforced ceramic matrix composites (CMC), for short fiber reinforced CMC there are only few studies and no standard on consideration of size effects. In the present work, the influence of coupon geometry and test conditions on the average value and distribution of flexural strength has been investigated. Two short fiber CMCs with different fiber length were examined under four point bending load. Moreover, the relationship between fiber orientation in the loaded area, failure location and measured flexural strength was investigated through high resolution X-ray computer tomography (μCT) and SEM. The presented outputs will be proposed to a future standard for bending test of short fiber reinforced CMC materials with different fiber length.

FEM predictions of damage in continous fiber ceramic matrix composites under transverse tension using the crack band method

This paper develops a numerical micromechanics fracture model based on the crack band methodology for the prediction of damage in continuous fiber ceramic matrix composites (CMCs). The energy based crack band formulation offers mesh objective predictions in finite element simulations. Detailed finite element models of CMCs are created based on the actual microstructure and compared with randomly created representative volume elements (RVE). The influence of geometrical inhomogeneities, such as fiber clustering and variations of the fiber coating thickness, on the stress-strain response and the crack development are investigated. Furthermore, FEM models of multi-layer cross-ply laminates are created including thousands of explicitly modeled fibers and fiber coatings. Crack density predictions are compared with well established analytical models by Laws and Dvorak [1] and Nairn [2]. An eight layer FEM model is used to predict damage propagation within each layer. The Numerical prediction of the stress-strain response is compared with experimental results of smooth bar tensile coupons.

Multiscale damage characterization in continuous fiber ceramic matrix composites using digital image correlation

Damage in continuous fiber CMCs with weakly bonded fiber–matrix interfaces evolves in several stages that span multiple length scales. Comprehensive damage characterization necessitates identifying how damage initiates as well as how it accumulates (through final failure), which is not feasible with information gathered from a single length scale. Using digital image correlation to measure full-field surface deformations, damage evolutions in continuous fiber SiC/SiC laminates were analyzed at three distinct length scales: constituent, lamina, and laminate. Constituent scale analyses indicated that fine matrix cracks initiated in localized regions of transverse fiber coatings at low stresses. Investigations at the larger lamina scale revealed that some, but not all, of the coating cracks evolved into matrix cracks, the propagation of which was dependent on the state of stress near the crack tip and the local microstructure. Many of these matrix cracks morphed into cracks large enough to be detected at the (largest) laminate scale. The density of the large matrix cracks increased with load, reaching saturation prior to failure. While the constituent scale identifies when (with respect to stress state) and where (with respect to local microstructure) damage initiates, the lamina scale elucidates damage progression between neighboring constituents. Only laminate scale fields of view are large enough to capture the accumulation of the large matrix cracks that ultimately lead to final fracture. However, as spatial resolution is reduced at this scale, finer cracks (which may provide pathways for environmental ingress) go undetected. As each length scale provides a unique perspective of damage evolution in CMCs, multiscale analysis is essential for comprehensive damage characterization.

Poly(borosiloxanes) as precursors for carbon fiber ceramic matrix composites

Ceramic matrix composites (CMCs), constituted of a silicon boron oxycarbide (SiBCO) matrix and unidirectional carbon fiber rods as a reinforcement phase, were prepared by pyrolysis of carbon fiber rods wrapped in polysiloxane (PS) or poly(borosiloxane) (PBS) matrices. The preparation of the polymeric precursors involved hydrolysis/condensation reactions of alkoxysilanes in the presence and absence of boric acid, with B/Si atomic ratios of 0.2 and 0.5. Infrared spectra of PBS showed evidence of Si-O-B bonds at 880 cm-1, due to the incorporation of the crosslinker trigonal units of BO3 in the polymeric network. X ray diffraction analyses exhibited an amorphous character of the resulting polymer-derived ceramics obtained by pyrolysis up to 1000 °C under inert atmosphere. The C/SiBCO composites showed better thermal stability than the C/SiOC materials. In addition, good adhesion between the carbon fiber and the ceramic phase was observed by SEM microscopy

In Situ Nondestructive Evaluation of the Accumulative Damage in Continuous Ceramic Fiber-Ceramic Matrix Composites (CFCCs) using Submillimeter Range Electromagnetic Wave

Monolithic ceramic materials usually show catastrophic failure behavior and this property limits application as structural components because the failure occurs easily from a small flaw that usually exists in the materials. To overcome this, incorporation of a fine ceramic fiber into a brittle ceramic has been examined and the obtained material is named as continuous fiber-ceramic matrix composites (CFCCs).

繊維強化複合材料の新展開 連続繊維強化セラミックスの破壊と力学特性

繊維強化複合材料の新展開 連続繊維強化セラミックスの破壊と力学特性

Nondestructive Characterization of Ceramic Composites Used as Combustor Liners in Advanced Gas Turbines

Nondestructive characterization (NDC) methods, which can provide full-field information about components prior to and during use, are critical to the reliable application of continuous fiber ceramic matrix composites in high-firing-temperature (>1350°C) gas turbines. [For combustor liners, although they are nonmechanical load-bearing components, both thermal characteristics and mechanical integrity are vitally important.] NDC methods being developed to provide necessary information include x-ray computed tomography (mainly for through-wall density and delamination detection), infrared-based thermal diffusivity imaging, and single-wall through-transmission x-ray imaging (mainly for fiber content and alignment detection). Correlation of the data obtained from NDC methods with subscale combustor liner tests have shown positive results at thermal cycling temperatures from 700°C to 1177°C.

Processing of damage-tolerant, oxidation-resistant ceramic matrix composites by a precursor infiltration and pyrolysis method

Damage-tolerant, continuous fiber ceramic matrix composites have been produced by an inexpensive method. According to this method, the space between the fibers is filled with a powder. The powder particles are heat treated to form a porous framework without shrinkage, which is then strengthened with an inorganic synthesized from a precursor. High particle packing densities can be achieved within the fiber preform provided that the particle-to-fiber diameter ratio is small. Filling the interstices with a powder increased the composite density and also limits the size of the crack-like voids within the matrix. In this review we describe the mechanical properties of partially dense materials produced from powders to show that a porous matrix can be strong. We demonstrate that the packing density of particles around fibers is highest when the particle-to-fiber diameter ratio is small. The kinetics and mechanical behavior of composite systems is summarized to demonstrate the requirements of damage-tolerant properties. An all-oxide ceramic matrix composite produced by this method is discussed.

High-speed photographic studies of laser drilling of ceramics and ceramic composites

High-speed photographic techniques were used to study plumes generated above a material during drilling of ceramics and ceramic composites with a carbon dioxide laser. The prinicipal objectives were to identify the mechanism of material removal (spattering, particulate and fiber debris, liquid droplets) and plume phenomena (plume shapes and sizes) for ceramics and ceramic composites. High-speed photographic (1000 frames per second) visualization of laser drilling was undertaken for two monolithic ceramics, (sintered α-silicon carbide (α-SiC) and hot-pressed silicon nitride (Si3N4)) and two continuous fiber—ceramic matrix composites, (carbon fibers in a silicon carbide matrix (C–SiC) and silicon carbide fibers in a silicon carbide matrix (SiC–SiC)). The results of this study indicate that each of these ceramic materials decomposes differently during laser processing and that the material removal mechanism for a given material is possibly different at different stages of the process. In all cases, material removal is initially through high-temperature decomposition and/or vaporization. As the hole depth increases, the walls of the hole become steeper resulting in a substantial reduction of the laser flux incident on the surface; this in turn appears to modify the mechanism of material removal depending upon the composition and porosity of the material. The photographic evidence presented here clearly shows ablative material removal for sintered α-silicon carbide (α-SiC), periodic ejection of liquid silicon during laser drilling of silicon nitride and ejection of particulate/fiber debris during laser processing of the composite materials SiC–SiC and C–SiC.

The topology of percolating porosity in woven fiber ceramic matrix composites

Three-dimensional x-ray microtomography has been used to visualize porosity in ceramic matrix composites during chemical vapor infiltration processing. The topology of percolating pores was determined in both 0°/90° and 0°/45° architectures. At densities greater than 75%, consolidation can be described with percolation theory.