Carbon Fiber Reinforced Silicon Carbide Research Articles

A Micromechanical Fatigue Limit Stress Model of Fiber-Reinforced Ceramic-Matrix Composites under Stochastic Overloading Stress.

Fatigue limit stress is a key design parameter for the structure fatigue design of composite materials. In this paper, a micromechanical fatigue limit stress model of fiber-reinforced ceramic-matrix composites (CMCs) subjected to stochastic overloading stress is developed. The fatigue limit stress of different carbon fiber-reinforced silicon carbide (C/SiC) composites (i.e., unidirectional (UD), cross-ply (CP), 2D, 2.5D, and 3D C/SiC) is predicted based on the micromechanical fatigue damage models and fatigue failure criterion. Under cyclic fatigue loading, the fatigue damage and fracture under stochastic overloading stress at different applied cycle numbers are characterized using two parameters of fatigue life decreasing rate and broken fiber fraction. The relationships between the fatigue life decreasing rate, stochastic overloading stress level and corresponding occurrence applied cycle number, and broken fiber fraction are analyzed. Under the same stochastic overloading stress level, the fatigue life decreasing rate increases with the occurrence applied cycle of stochastic overloading, and thus, is the highest for the cross-ply C/SiC composite and lowest for the 2.5D C/SiC composite. Among the UD, 2D, and 3D C/SiC composites, at the initial stage of cyclic fatigue loading, under the same stochastic overloading stress, the fatigue life decreasing rate of the 3D C/SiC is the highest; however, with the increasing applied cycle number, the fatigue life decreasing rate of the UD C/SiC composite is the highest. The broken fiber fraction increases when stochastic overloading stress occurs, and the difference of the broken fiber fraction between the fatigue limit stress and stochastic overloading stress level increases with the occurrence applied cycle.

C/C‐SiC component for metallic phase change materials

AbstractThanks to their high energy density and thermal conductivity, metallic Phase Change Materials (mPCM) have shown great potential to improve the performance of thermal energy storage systems. However, the commercial application of mPCM is still limited due to their corrosion behavior with conventional container materials. This work first addresses on a fundamental level, whether carbon‐based composite‐ceramics are suitable for corrosion critical components in a thermal storage system. The compatibility between the mPCM AlSi12 and the Liquid Silicon Infiltration (LSI)‐based carbon fiber reinforced silicon carbide (C/C‐SiC) composite is then investigated via contact angle measurements, microstructure analysis, and mechanical testing after exposure. The results reveal that the C/C‐SiC composite maintains its mechanical properties and microstructure after exposure in the strongly corrosive mPCM. Based on these results, efforts were made to design and manufacture a container out of C/C‐SiC for the housing of mPCM in vehicle application. The stability of the component filled with mPCM was proven nondestructively via computer tomography (CT). Successful thermal input‐ and output as well as thermal storage ability were demonstrated using a system calorimeter under conditions similar to the application. The investigated C/C‐SiC composite has significant application potential as a structural material for thermal energy storage systems with mPCM.

Effect of shear strain rate on interlaminar shear behavior of 2D-C/SiC composites: A damage transition from notch ends initiation to gauge section initiation

Two-dimensional carbon fiber reinforced silicon carbide composites (2D-C/SiCs) exhibit excellent mechanical properties at high temperature. However, the weak interfacial performance limits range of their applications. In the present work, interlaminar shear strength (ILSS) of 2D-C/SiC was investigated. By using an industrial camera and an acoustic emission (AE) detection system, quasi-static tests at the shear strain rates from 10−5/s to 10−3/s were conducted. Strain contours revealed the damage evolution process. Peak frequencies of AE signals were clustered into three groups, corresponding to matrix damage, interfacial debonding and fiber fracture. Dynamic tests at the shear strain rates of 200/s and 600/s were conducted using a modified split Hopkinson bar (SHPB). The dynamic deformation phenomenon was captured by a high-speed camera. The high-speed images and digital image correlation (DIC) strain contours revealed the damage initiation under dynamic loading. Damage morphologies were observed by a scanning electron microscope (SEM). The real-time images and damage morphologies explained the mechanisms of shear strain-rate effect on ILSS. The proposed experimental method elicited a fresh perspective on designing dynamic interlaminar shear experiments. Moreover, the interlaminar shear performance over a wide range of shear strain rates enhanced our understanding of the strain-rate sensitivity of compressive strength and tensile strength of 2D-C/SiCs.

Effect of CNT impregnation on the mechanical and thermal properties of C/C-SiC composites

The present study investigates the effect of additional carbon source, in the form of carbon nanotubes (CNTs), on mechanical and thermal properties of carbon fiber reinforced silicon carbide (C/C-SiC) ceramic matrix composites (CMC) produced by liquid silicon infiltration (LSI) technique. The CNTs used in this study were impregnated into the C/C preforms before the liquid silicon infiltration stage. The results showed that the addition of excess carbon to the C/C preforms in the form of CNTs enhanced Si infiltration efficiency significantly resulting in C/C-SiC composites with higher density and microstructural uniformity. Accordingly, the addition of CNTs improved the flexural strength of the composites by 40% with respect to no-CNT-containing composites due to a lower amount of residual porosity and additional reinforcement effect of the unreacted CNTs. The thermal conductivity of the resulting C/C-SiC composites has been also increased by 31% and 18% parallel and perpendicular to the carbon fiber–woven fabric surface, respectively, by CNT addition.

Effect of diamond content on microstructure and properties of C/SiC-diamond composites

Phenolic resin slurry with different concentrations of diamond was introduced into porous carbon fiber-reinforced silicon carbide (C/SiC) composites, and corresponding C/SiC-diamond composites were obtained through the reactive melt infiltration process. The effects of diamond concentration on the microstructure, mechanical properties, and thermophysical characteristics of C/SiC-diamond composites were obtained through observation and analysis. The results indicated that with the increase of diamond concentration, more diamond particles were introduced into the composites; and the density, mechanical properties, and thermophysical properties of the composites were improved. The three-point bending strength of sample D10 (diamond concentration of 10 vol% in slurry) was 309.01 MPa, the coefficient of thermal expansion at 700 °C reached 2.69 × 10−6/K, and the thermal conductivity at room temperature reached 14.68 W/(m·K), which is much higher than twice that of C/SiC composites (5–6 W/(m·K)) prepared by chemical vapor infiltration.

Damage monitoring of carbon fiber reinforced silicon carbide composites under random vibration environment by acoustic emission technology

Carbon fiber-reinforced silicon carbide (C/SiC) composites are widely used in high-temperature thermo-structural applications. They are subjected to extreme loading conditions, such as random vibrations, which are likely to damage the structure. Structural micro-damage identification during vibration is very difficult, owing to the randomness of the environmental vibration and the complicated response it causes in structures. This study aims to determine a method for monitoring the damage properties of a C/SiC structure under a random vibration environment using acoustic emission (AE) technology. First, a pencil break experiment is conducted to verify the feasibility of the AE technology. Then, an AE monitoring experiment of the structural damage in a vibration environment is systematically conducted. Two types of experiments are designed for simulating the damage formation process inside the structure. In addition, the parameter characteristics of typical AE signals in the random vibration test are analyzed, and the relationships between the AE signal parameters and vibration loading are obtained. Lastly, the different stages of material damage development and damage types in each stage are provided to reveal the damage evolution processes of C/SiC composites. The results indicate that AE technology can be effectively applied to investigate the damage behaviors of C/SiC composites in random vibration environments.

Revealing thermal ablation mechanisms of C/SiC with in situ optical observation and numerical simulation

Structural ceramics such as C/SiC (carbon fiber reinforced silicon carbide) are of great importance for high temperature applications, where thermal ablation could occur and impair the structural integrity. Here we adopt in situ and real time optical visualization technique and numerical simulation to study the thermal ablation mechanisms of C/SiC subjected to oxyacetylene flame. The in situ optical setup captures the real time surface evolution at temperatures up to 1800℃, demonstrating clearly the formation of surface gas bubble, the flowing and merging process of liquid SiO2, which are later well reproduced and explained by the numerical simulation. Four different surface ablation regions on the sample subjected to thermal ablation have been identified by the captured images and flow field streamlines, which reveal the distribution and flow mechanism of SiO2 droplets on the C/SiC surface.

Laser ablation behavior and mechanism of C/SiC coated with ZrB2 –MoSi2–SiC/Mo prepared by HVOF

Recently, carbon fiber-reinforced silicon carbide (C/SiC) composites are considered important candidates for laser protection materials. In this paper, the ablation mechanism of C/SiC composites and their modified composites under laser irradiation was studied. ZrB2–MoSi2–SiC ternary-phase ceramic was successfully coated on C/SiC composites by using high velocity oxygen fuel (HVOF) technology, with Mo as transition layer. The evolution of phase and morphology of the composites was investigated by X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The ablation behavior of composites was investigated by laser confocal microscopy (LCM). The results showed that the ablation mechanism of composites was controlled by phase transformation, thermal reaction and thermal diffusion. The solid-liquid transition of ZrB2 and MoSi2 was the dominant factor. Thermal reaction and good thermal diffusivity of coatings were also important factors affecting the ablation performance. ZrB2–SiC– MoSi2/Mo coating failed when all phase transitions were completed and no continuous liquid phase was formed, followed by rapid damage of C/SiC substrate. The results of this work can provide theoretical guidance and research ideas for the design and application of laser protective materials.

Effects of the surface processing on the tribological performance of C/SiCs under dry friction

A new friction counterpart for carbon fiber-reinforced silicon carbide ceramic-matrix composites (C/SiCs) and zirconia (ZrO2) toughened by magnesia ceramics is proposed. The effects of the C/SiC surface processing parameters friction on the tribological performance are investigated under dry friction and ambient temperature conditions. The wear tests are carried out using the pin-on-disc friction method. Scanning electron microscopy (SEM) on an instrument equipped with an energy dispersive spectroscopy (EDS) is used to observe the surfaces of the pins and discs before and after the application of friction to reveal the wear mechanism. The results show that surface processing influenced the tribological properties of C/SiC significantly. When the pressure is 30 N, the speed is 0.5 m/s, and the C/SiC surface is ground using 1500# sandpaper, the counterpart tribological performance is the best among the samples considered herein. It is found that the retention ability of the counterparts influenced the tribology performance significantly.

Experimental study on tool wear in ultrasonic vibration–assisted milling of C/SiC composites

Carbon-fiber reinforced silicon carbide matrix (C/SiC) composites are typical difficult-to-cut materials due to high hardness and brittleness. Aiming at the problem of the serious tool wear in conventional milling (CM) C/SiC composite process, ultrasonic vibration–assisted milling (UVAM) and conventional milling tests with a diamond-coated milling cutter were conducted. Theoretical and experimental research on the cutting force during the ultrasonic vibration milling process of C/SiC composites is carried out. Based on the kinematics analysis of tool path during ultrasonic vibration milling process, the cutting force model of ultrasonic vibration milling is established, and the influence mechanism of ultrasonic vibration on the cutting force is revealed. Based on the analysis of the evolution law of tool wear profile and wear curve during the traditional milling and ultrasonic vibration milling of C/SiC, the tool wear forms and mechanism of diamond-coated milling cutters in two processing modes and the influence mechanism of ultrasonic vibration on tool wear are revealed. It is found that the main wear mechanism of the diamond-coated milling cutter is abrasive wear, and the main wear form is the coating peeling. Compared with the traditional milling, the tool wear can be reduced by the ultrasonic vibration milling in machining process. In the range of test parameters, the tool wear decreases first and then increases with the increase of ultrasonic amplitude.

Experimental and Numerical Investigation of Dynamic Fracture Toughness of Ceramic Composites

This study focusses on the experimental and numerical investigation of the continuous carbon fiber-reinforced silicon carbide (SiC), and silicon nitride (Si3N4) matrix composites. A testing procedure has been designed to study the Charpy impact testing system. The dynamic elastic-plastic fracture toughness (JdSiC=11.88kJ/m2 and JdSi3N4=1.77kJ/m2) as well as the dynamic stress intensity factors (kdSiC=36.88 MPaem2and JdSi3N4=22.03 MPaem2) have been evaluated. Further on, a good agreement between finite element results and experimental findings was found.

Comparisons of cyclic fatigue hysteresis between C/SiC and SiC/SiC ceramic–matrix composites with different fiber preforms at room and elevated temperatures

In this paper, the cyclic fatigue hysteresis of carbon fiber reinforced silicon carbide (C/SiC) and SiC/SiC ceramic–matrix composites with different fiber preforms at room and elevated temperatures is investigated. The evolution of fatigue hysteresis dissipated energy versus applied cycle number for unidirectional C/SiC ( σmax = 240 MPa at room temperature and σmax = 250 MPa at 800℃ in air atmosphere), cross-ply C/SiC ( σmax = 105 MPa at room temperature and 800℃ in air atmosphere), 2D C/SiC ( σmax = 387 and 425 MPa at room temperature), 2.5D C/SiC ( σmax = 180 MPa at room temperature, σmax = 140 MPa at 800℃ in air atmosphere, and σmax = 230 MPa at 600℃ in inert atmosphere), 2D SiC/SiC ( σmax = 130 MPa at 600℃, 800℃, and 1000℃ in inert atmosphere, σmax = 80 MPa at 1000℃ in air atmosphere, σmax = 100 MPa at 1000℃ in steam atmosphere, σmax = 140 MPa at 1200℃ in air and in steam atmospheres, σmax = 90, 120 MPa at 1300℃ in air atmosphere), and 3D SiC/SiC ( σmax = 100 MPa at 1300℃ in air atmosphere) is analyzed. The change rate of the fatigue hysteresis dissipated energy between C/SiC and SiC/SiC composites is compared. The fatigue hysteresis dissipated energy decreases with applied cycle number for unidirectional, and cross-ply C/SiC composite at 800℃ in air, and 2.5D C/SiC composite at 600℃ in inert; and the fatigue hysteresis dissipated energy increases with applied cycle number for 2.5D C/SiC composite at 800℃ in air, 2D SiC/SiC composite at 600℃, and 800℃ in inert.

Mechanical model and removal mechanism of unidirectional carbon fibre-reinforced ceramic composites

Numerous scholars have researched the influences of grinding parameters on the surface quality and grinding forces of carbon fibre-reinforced silicon carbide ceramic matrix (Cf/SiC) composites. Nevertheless, the relevant mechanical model and removal mechanism have not been investigated from a microscale perspective. To develop a mechanical model, the area of formation of the grinding chips should be analysed in detail and discussed. The supporting conditions and debonding depth are critical to the grinding forces. To validate the reliability of the mechanical model, experiments with the same grinding parameters were performed. The differences between the theoretical and experimental results were small, which indicated that the mechanical model was accurate and reasonable. Based on the theoretical analyses and experimental results, the material removal mechanism was explored in detail. Based on the topographies of the grinding chips and surfaces, the failure processes of the fibre and matrix due to the forward motion of the abrasive grains were analysed. As the grinding depth increased, the evaluation indexes of the debonding depth, grinding forces and grinding chips gradually increased. Moreover, the increasing proportions of fibre pullout and fibre outcrop indicated that the quality of the grinding surface decreased. Based on the research findings, the debonding depths, grinding forces, grinding chips and surface topographies of unidirectional Cf/SiC composites can be determined, which is expected to significantly improve the machining ability of Cf/SiC composites.

Characterization of corrosion resistance of C/C\u2013SiC composite in molten chloride mixture MgCl2/NaCl/KCl at 700\u2009\xb0C

Due to their high thermal stability and low cost, molten chlorides are promising high-temperature fluids for example for thermal energy storage (TES) and heat transfer fluid (HTF) materials in concentrated solar power (CSP) plants and other applications. However, the commercial application of molten chlorides is strongly limited due to their strong corrosivity against commercial alloys at high temperatures. The work addresses on a fundamental level whether carbon based composite ceramics could be potentially utilized for some corrosion critical components. Liquid silicon infiltration (LSI) based carbon fiber reinforced silicon carbide (called C/C–SiC) composite is immersed in a molten chloride salt (MgCl2/NaCl/KCl 60/20/20 mole%) at 700 °C for 500 h under argon atmosphere. The material properties and microstructure of the C/C–SiC composite with and without exposure in the molten chloride salt have been investigated through mechanical testing and analysis with scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) scanning. The results reveal that the C/C–SiC composite maintains its mechanical properties after exposure in the strongly corrosive molten chloride salt. The oxidizing impurities in the molten salt react only with residual elemental silicon (Si) in the area of the C/C–SiC matrix. In comparison, no indication of reaction between the molten chloride salt and carbon fiber or SiC in the matrix is observed. In conclusion, the investigated C/C–SiC composite has a sound application potential as a structural material for high-temperature TES and HTF with molten chlorides due to its excellent corrosion resistance and favorable mechanical properties at high temperatures.

Fracture Strength Behaviors of Ultra-High-Temperature Materials

Abstract Ultra-high-temperature materials have been widely used as key components in high-end equipment. However, the existing studies are mainly conducted at room and moderate temperatures. Besides, they are mainly carried out by experiments. Theories on the temperature dependence of fracture strength are rarely reported. In this work, experimental methods for the ultra-high-temperature tensile properties of advanced materials and the elastic–plastic properties of coatings are developed, respectively, based on induction heating and radiation furnace heating technologies. A temperature-dependent fracture strength model for ceramics is proposed in the view of energy. The experimental methods and theoretical model are verified on the 2D plain-weave carbon fiber reinforced silicon carbide thermal structure composite, yttria-stabilized zirconia thermal barrier coating, and Si3N4 ceramics. The study shows that the mechanical properties of materials decrease significantly at ultra-high temperatures. The results are useful for the applications of ultra-high-temperature materials in thermal structure engineering.

Tensile properties of two-dimensional carbon fiber reinforced silicon carbide composites at temperatures up to 2300 °C

Carbon fiber reinforced silicon carbide (C/SiC) composites are of the few most promising materials for ultra-high-temperature structural applications. However, the existing studies are mainly conducted at room and moderate temperatures. In this work, the tensile properties of a two-dimensional plain-weave C/SiC composite are studied up to 2300 °C in inert atmosphere for the first time. The study shows that C/SiC composite firstly shows linear deformation behavior and then strong nonlinear characteristics at room temperature. The nonlinear deformation behavior rapidly reduces with temperature. The Young’s modulus increases up to 1000 °C and then decreases as temperature increases. The tensile strength increases up to 1000 °C firstly, followed by reduction to 1400 °C, then increases again to 1800 °C, and lastly decreases with increasing temperature. The failure mechanisms being responsible for the mechanical behavior are gained through macro and micro analysis. The results are useful for the applications of C/SiC composites in the thermal structure engineering.

Influences of clearance angle and point angle on drilling performance of 2D Cf/SiC composites using polycrystalline diamond tools

Cf/SiC composite (carbon fiber reinforced silicon carbide ceramic matrix composites) is a kind of advanced composite material constituted by SiC as matrix and carbon fiber as reinforcing phase. Cf/SiC composites are being extensively used in the modern aerospace industry owing to their excellent physical and mechanical properties. The current work aims to investigate influences of clearance angle and point angle on drilling performance of 2D Cf/SiC composites using PCD (polycrystalline diamond) tools in terms of thrust force, drilling torque, hole surface quality, and material removal mechanism. PCD drill bits with different point angles and clearance angles were used in the experiment. The obtained results indicate that the 150° point angle is beneficial to improve the hole surface quality, and larger clearance angle is helpful to reduce the damage of exits. Additionally, the variation of clearance angle has little effect on the roughness of the machined surface. During the drilling process, the dominated material removal mechanisms are matrix removal, fiber breakage, and matrix-fiber debonding. The brittle fracture mode of carbon fibers, which directly affects surface roughness, can be divided into micro-brittle fractures in carbon fiber and macro-brittle fractures. Besides, the damage identification method of hole entrance and exit based on image processing technology is helping to improve the efficiency of machining quality evaluation.

Experimental investigations of thermal modal parameters for a C/SiC structure under 1600 °C high temperature environment

This work aims to investigate the thermal–mechanical behavior of a carbon fiber reinforced silicon carbide (C/SiC) structure under 1600 °C high temperature environment. In this test, both the contact and non-contact measurement are used. Four laser vibrometers were used for non-contact measurement. The laser reflection characteristics of C/SiC surface under high temperature were tested. The fiber Bragg grating sensor (FBG) sensor network measures both strain and temperature of the test piece, by means of wavelength shifts due to the tensile stress on a Bragg grating. The energy spectrum of the signal is obtained by the time–frequency analysis method, and the peak value is extracted by an algorithm to obtain the time–frequency characteristic of different modes. The result shows that the modal frequencies of C/SiC structure under time-varying thermal loads change with the temperature of the structure, which has a great influence on the modal characteristics of the structure. Besides, this study indicates that the FBG sensor is suitable for structural health monitoring of C/SiC structure under 1600 °C high temperature environment. The results provide an important basis for the dynamic performance analysis and safety design of structure under high-temperature thermal-vibration conditions.

Fabrication of artificial defects and their effect on the mechanical properties of C/C-SiC

Determining the effect of defects in fiber-reinforced materials, such as polymer matrix composites (PMCs), can be studied by creating artificial flaws in these materials, for example by introducing artificial PTFE foil to induce material delaminations. For fiber-reinforced ceramics (CMCs), this approach is more difficult due to the more complicated production routes of CMCs, which involve several processing steps at elevated temperatures. This work deals with the fabrication and introduction of defined defects in carbon fiber reinforced silicon carbide (C/C-SiC) composites in a way, which allows their detection by non-destructive material testing methods during and after each production step of the composite. It was shown that the defects produced using boron nitride (BN) and alumina fiber roving were stable over the entire manufacturing process and could be detected by ultrasound and x-ray tomography techniques. To determine any possible effects, an initial sampling of bending samples with artificial defects was manufactured, tested and compared with defect-free reference materials. These tests showed a lower bending strength and failure strain for the defect samples compared to samples without defects.

A multi-layer integrated thermal protection system with C/SiC composite and Ti alloy lattice sandwich

In this paper, a multi-layer integrated thermal protection system (ITPS) is proposed and compared with two existed ITPS. This multi-layer ITPS consists of a carbon fiber reinforced silicon carbide matrix composite (C/SiC) panel, a glass wool layer and a titanium (Ti) lattice sandwich filled with glass wool. In order to satisfy the aerodynamic shape requirement of hypersonic vehicles, a curved ITPS structure is concerned in this study. Multi-layer curved ITPS and single-layer curved ITPS made of Ti alloy and C/SiC composite are firstly analyzed and discussed under typical aerodynamic heating and pressure loads. Numerical results show that the proposed multi-layer ITPS provides efficient thermal insulation and load bearing properties compared with the C/SiC sandwich ITPS and Ti alloy sandwich ITPS. Secondly, multi-layer curved ITPS samples are fabricated. Experimental tests and numerical validation are carried out to evaluate the heat transfer characteristics of the ITPS samples.