Fiber-reinforced Ceramic Matrix Composites Research Articles

High-temperature transient-induced thermomechanical damage of fiber-reinforced ceramic-matrix composites in supersonic wind tunnel

This article is based on the supersonic directly connected wind tunnel. Through a specially designed experimental chamber, combined with infrared temperature measurement, high-speed camera, etc., in-situ monitoring of composite materials under airflow at Ma 3.0 with a total temperature of 950 ∼ 1473K was carried out. The dimensional analysis method was used to propose dimensionless parameters to characterize the thermal coupling caused by high-speed airflow thermal shock. Research has shown that the thermal coupling effect of supersonic airflow causes uneven temperature inside the material, and the thermal stress caused by temperature gradient changes (including increasing and decreasing processes) is the main reason for material damage. The damage of ceramic matrix composites under thermal shock mainly manifests as a decrease in surface roughness, surface fiber fracture and a decrease in elastic modulus. In addition, the study also found that there are damage thresholds for the thermal shock effect of airflow at different total temperatures, which helps to further understand the thermomechanical damage mechanism and degradation law of composite structure under high-temperature transient conditions.

Al2O3 fiber-reinforced MAX phase ceramic matrix composite

In the aerospace industry, lightweight can reduce the weight of the engine and improve the thrust-weight ratio of the engine. Ceramic matrix composites have attracted widespread attention in the industry due to their much lower density compared to high-temperature alloys and excellent high-temperature performance. SiC fiber-reinforced SiC ceramic matrix composites are the most outstanding representatives, but their long manufacturing cycle and high manufacturing costs limit their widespread use. Ti2AlC is a new type of ceramic material with the characteristics of low density, high melting point, high-temperature resistance, oxidation resistance, and corrosion resistance of ceramic materials, as well as the conductivity and machinability of metals. However, its mechanical properties are slightly inadequate. The use of chopped fibers for toughening can compensate for these deficiencies to a certain extent and improve mechanical properties. This article first explored the influence of various process parameters on the mechanical properties of pure-phase Ti2AlC ceramic materials in SPS preparation technology and then prepared Ti2AlC composites reinforced with 10 vol%, 20 vol%, and 30 vol% Al2O3 chopped fibers. The results showed that the samples prepared at 1300 °C, 40 MPa, and 10 min had a flexural strength of 697 MPa and a fracture toughness of 9.83 MPa m1/2 when the volume ratio of the reinforcement phase was only 10 vol%, which was the same as that of the continuously fiber-reinforced SiCf/SiC composites. This study showed that the MAX phase matrix composites reinforced with chopped fibers have the potential to become high-temperature structural materials by adjusting the composite composition and optimizing the preparation process.

Effect of interphase layer on matrix cracking in fiber reinforced ceramic matrix composites

The onset of matrix steady-state cracking stands as a pivotal mechanical characteristic in fiber reinforced ceramic matrix composites (FRCMCs), garnering substantial attention and investigations. Experimentally, it has been demonstrated that increasing interphase layer thickness may cause non-monotonic changes in matrix cracking stress. However, the existing models can hardly elucidate this phenomenon thoroughly due to the neglect of interphase thickness. This paper presents a comprehensive analytical model for the matrix cracking incorporating interphase, the Poisson effect, Coulomb friction, fiber asperities, residual thermal stress (RTS), and their coupling effects, along with a modified criterion for interfacial debonding that accounts for the presence of the axial RTS. Based on the proposed model, three distinct cracking domains, i.e., perfectly bonded, debonding with and without interfacial separation, have been identified with the critical conditions deduced analytically. Thereby the mechanism of the non-monotonic influence of interphase thickness is thoroughly revealed as the transition of cracking modes. Meanwhile, the role of interphase on the matrix cracking is systematically studied, and the results indicate that interphase has a notable effect through relieving axial RTS, adjusting interfacial friction, altering interfacial shear modulus, and influencing debonding toughness. The outcomes of this study offer valuable guidance for the interphase design of FRCMCs.

Effect of fiber roughness on interfacial friction of fiber reinforced ceramic matrix composites

Interfacial friction plays a crucial role on mechanical behaviors of fiber reinforced ceramic matrix composites (FRCMCs), such as matrix cracking, damage evolution, and fracture, and the fiber surface roughness has been shown to enhance the interface friction. However, the influence of interphase thickness and residual stress on the friction enhancement of fiber roughness was neglected in previous works. Therefore, in this paper a thoroughly theoretical model is established and the additional radial stress is derived to intuitively reflect the contribution of fiber roughness to the interfacial friction. The results indicate that the interfacial friction can usually be enhanced by increasing the fiber roughness and reducing the interphase thickness, which however is severely overestimated by more than 5 times by the previous models. Moreover, the residual stress and fiber axial stress have a nonnegligible effect on the contribution of fiber roughness. For a given fiber axial stress, the residual stress that is too large or too small will weaken or even eliminate the contribution of fiber roughness, and only when the residual stress is within a proper range, can the fiber roughness play an effective role. On the other hand, for a given target load and ambient temperature, a critical fiber roughness that can enhance the interfacial friction is analytically derived. This work can provide valuable insights into the design of fiber roughness and interphase thickness for FRCMCs.

Effect of thermo-mechanical and low-cycle preloading on the strength of carbon fiber-reinforced ceramic matrix composites

Fiber-reinforced ceramic matrix composites (CMCs) exhibit excellent thermo-mechanical properties including outstanding resistance against damage and fatigue. Some CMCs show occasionally even a strength enhancement after fatigue, often interpreted with relieve of internal stresses and interfacial degradation. This study reports the influence of low-cycle thermo-mechanical preloading on the bending and tensile strength of carbon fiber-reinforced silicon carbon (C/C-SiC). For this purpose two C/C-SiC materials with the same fiber architecture but different assumed internal stress states were subjected to single and cyclic mechanical preloads up to 90% of their ultimate strength level at room temperature and at 350 °C. Statistical evaluations of the experiments show that the ultimate strength values were surprisingly unchanged after preloading. The results are discussed regarding the thermal residual stresses (TRS).

The oxide-layer configuration alteration and pseudo-ductile crack propagation mechanisms in composites induced by different relative thicknesses of CVI HfC-SiC multiphase matrix

Carbon fiber-reinforced HfC-SiC ceramic matrix composites (Cf/HfC-SiC) with different HfC-SiC matrix thicknesses were prepared by the chemical vapor infiltration method. The microstructure, ablation, and pseudo-ductile fracture behaviors of the composites were studied. The results proved that with the change of the HfC-SiC layer relative thickness, the oxide-layer configuration changed to promote its densification, which improved the ablative protection and mechanical properties of Cf/HfC-SiC composites. After ablation, when the relative volume proportion of the HfC-SiC matrix was the utmost (24.7/15.5), the composites had the best ablation resistance due to the tubular lamination configuration HfO2 layer. This caused the composite to have the highest residual bending strength (215.8 MPa) and strength retention rate (79.7%). In addition, a pseudo-ductile crack propagation model was established to determine the influence of the induction of residual stress and the relative HfC-SiC layer thickness on the fracture behavior in the composites. Results suggested that in the real crack deflection mechanism, due to the induction of residual stress, the stress state in the HfC-SiC matrix with the increase of the HfC layer thickness changed to form more ring deflection cracks at the HfC/SiC interface. It provides a way to study the pseudo-ductility behavior of multiphase matrix composites and explain the improvement of its predictability and failure.

Single-grain scratching of SiCf/SiC composite under minimum quantity lubrication: Force and material removal mechanism study

As one of the most novel fiber-reinforced ceramic matrix composites, SiCf/SiC composites are difficult to be processed machine materials. On top of that, the underlying material removal mechanism not yet completely understood. Along these lines, in this work, single-grain scratching orthogonal tests with different MQL methods were carried out to systematically analyze the influence of the different processing directions and lubrication methods on the material removal lubrication mechanism and the scratching force in the scratched surfaces. From the acquired results, it was demonstrated that the scratch force was the smallest when the processing direction is was 0° to the fiber direction. In addition, the utilization of MQL from vegetable oil can effectively reduce the cutting force. Diamond indenter caused significant damage to the surface of SiCf/SiC composites when the machining direction was 90° to the fiber direction, while narrow but deep grooves on the surface were observed when the angle was 0°. The dominant mode of material removal of SiCf/SiC composites was a brittle fracture, and the damage features mainly included direct fiber breakage, matrix fragmentation, fiber pullout, and fiber outcropping. The increase of the processing ratio of 0° and implementation of vegetable oil for MQL was proven as one of the best methods.

Fine study of hierarchical interphase constructed by Ti3SiC2 and carbon nanotubes in SiCf/SiC composites

The interphase in silicon carbide fiber-reinforced silicon carbide ceramic matrix composites (SiCf/SiC) assumes a significant role in the mechanical properties exhibited at elevated temperatures. The strength, toughness, and chemical stability of a composite is frequently influenced by the optimization of its interphase. In this work, the MAX phase (Ti3SiC2) and carbon nanotubes (CNTs) were successively deposited on the SiCf using the molten salt method and chemical vapor deposition technique, respectively, to create a hierarchical structure. Transmission electron microscopy was employed to undertake a comprehensive investigation of the interfacial component in SiCf/SiC composites. The detailed study of interphases in SiCf/SiC composites has been conducted through the analysis of crystallization, the bonding natures, and the micromorphology, encompassing geometry and constituent characteristics. A bilayer consisting of TiC–Ti3SiC2/Ti5Si3 and a vertical array of carbon nanotubes (CNTs) with a length of 7 μm is fabricated on the surface of SiCf/Ti3SiC2-CNTs. The SiCf/Ti3SiC2/SiC and SiCf/Ti3SiC2-CNTs/SiC composites exhibit lamellar structures of Ti3SiC2, which indicates a further crystallization of Ti3SiC2 resulting from the formation of SiC matrix by PIP procedure. The interphase of SiCf/Ti3SiC2-CNTs/SiC composite may be categorized into four distinct layers: a TiC phase, a TiSi2 phase, a transition phase of TiSi2/TiC, and a Ti3SiC2 phase. This interphase structure is more intricate compared to the interphase structure observed in the SiCf/Ti3SiC2/SiC composite. This research indicates significant value for the future design and optimization of interfaces.

Large-scale material extrusion-based additive manufacturing of short carbon fibre-reinforced silicon carbide ceramic matrix composite preforms

ABSTRACT Large-scale short carbon fibre-reinforced silicon carbide (Csf/SiC) ceramic matrix composites (CMCs) have important applications in the field of aerospace engineering. This study proposed the use of material extrusion based additive manufacturing to fabricate large-scale C sf/SiC CMC preforms. In this paper, we determined how the key material extrusion parameters, including solid loading, nozzle diameter and layer height impact the stability of the additively manufactured C sf/SiC CMCs. The solid loading significantly influenced the stability of the C sf/SiC CMCs, and the slurry with 50 vol.% solid loading was better for additive manufacturing. The layer height played a significant role in the void formation in CMCs. It was appropriate for structure retention to set the layer height as 60–75% of the nozzle diameter. The effect of angle from vertical on the stability of out-of-plane structure was also investigated. When the angle was over 40o, the out-of-plane structure additively manufactured without supports tended to collapse. Large-scale C sf/SiC CMC preforms with out-of-plane structures were finally successfully fabricated. This study is believed to provide some fundamental understanding for the fabrication of large-scale fibre-reinforced ceramic matrix composites.

Experimental investigation and prediction of ECDM parameters on fiber reinforced SiC composite using hybrid ERNN-based Sparrow Search Optimization

The Silicon Carbide (SiC) fiber-reinforced SiC ceramic matrix composites have proved their outstanding performance on high thermal applications such as gas turbine engine parts, turbo-pumps, nozzles, and various other aerospace/aero-propulsion system parts. Regardless of their enhanced strength properties, the SiC fiber-reinforced SiC ceramic composite materials are difficult to process using conventional machining methods. Also, SiC fiber-reinforced SiC ceramic promotes a higher tool wear rate while doing conventional drilling operations. Therefore, this study investigates the Electrochemical Discharge Machining (ECDM) parameters on such SiC fiber-reinforced SiC ceramic composite. Besides, the levels of most influencing ECDM input parameters Voltage, Electrolytic Concentration and Duty Cycle are optimized using a novel hybrid machine learning optimizer called Elman Recurrent Neural Network-based Sparrow Search Optimization (ERNN-SSO). The experiment is planned using Response Surface Methodology based on Box Behnken Design (RSM-BBD) and verified using ANOVA. The Material Removal Rate (MRR), Tool Wear Rate (TWR) and Overcut (OC) are considered output performances during this study. The proposed ERNN-SSO has optimized ECDM input parameters at a maximum of 0.03 root mean square error (RMSE), approximately 33 % and 95 % lower than the conventional ERNN and RSM optimization techniques. This study’s suggested ECDM input parameters for drilling SiC fiber-reinforced SiC ceramic composite are 95 V voltage supply, 10 %Wt. of electrolytic concentration, and 50 % duty cycle. Because, such optimum ECDM parameters produced a maximum MRR of 370 μg/min with minimum TWR and OC of 283 μg/min and 161 µm during this study.

Mode I interlaminar fracture toughness of two-dimensional continuous fiber reinforced ceramic matrix composites using wedge-loaded double cantilever beam method

In this study, the wedge-loaded double cantilever beam (W-DCB) method was applied to evaluate the mode I interlaminar fracture toughness of two-dimensional (2D) continuous fiber-reinforced ceramic matrix composites (CMCs). Based on the elastic foundation theory, a W-DCB model was built and its compliance formula was derived by considering the axial force effect, shear effect, asymmetric propagation, and incomplete interlaminar contact. The friction effect was analyzed and measured using the theory of error transfer and a quasi-in-situ measurement method, respectively. The results reveal that rational selection of the wedge angle and friction coefficient can reduce the friction effect. Meanwhile, the W-DCB formula was comprehensively verified by compliance curves, crack tip behaviors, and the cohesive zone of 2D CMCs, which demonstrates its accuracy in conjunction with the experimental data. Finally, the energy release rate (ERR) of the 2D CMCs calculated using the W-DCB theory was consistent with the measured data.

Codes and standards for ceramic composite core materials for High Temperature Reactor applications

Fiber-reinforced ceramic matrix composites are attractive for high-temperature nuclear applications due to excellent thermal and mechanical properties as well as reasonable-to-outstanding radiation resistance. Over the past 20 years, the use of ceramic matrix composite applications expanded to many commercial non-nuclear industries as fabrication and application of the technologies mature.The ASME Boiler Pressure Vessel Code, under Section III Division 5, provides the design and construction rules for High Temperature Reactor components. It published the first rules for ceramic matrix composites to be used for reactor core components. The rules lay out the quality requirements together with the design and materials criteria for the use and application of silicon carbide- and carbon-based matrix material technologies. As with the established graphite rules, the ceramic composite material rules are structured in Subsection HH (from Section III), that addresses the criteria for class SN nonmetallic core components. The code rules rely heavily on the development and publication of standards for composite specification, classification, and testing of mechanical, thermal, and other properties. These test methods are developed in ASTM Committee C28 on Advanced Ceramics, with a current focus on ceramic composite tubes. This article describes the detail of the composites code, the design methodology and similarities to the graphite code, the guidance for the development of specifications for ceramic composites (for nuclear applications) including recent standard developments, and it mentions the next steps to support licensing aspects by validating the code with benchmarking data.

Estimate constituent properties of 3D needle-punched C/SiC composites from hysteresis loops

To improve the mechanical properties of fiber-reinforced ceramic-matrix composites (CMCs), it is necessary to establish the relationship between the composite’s constituent properties and macro mechanical properties. In this paper, a hysteresis-based micromechanical method was adopted to obtain the constituent properties of four different types of 3D needle-punched C/SiC composites. Hysteresis-based damage parameters (i.e., inverse tangent modulus (ITM), hysteresis width, residual strain, hysteresis modulus, and damage factor) were derived from the hysteresis theory. Through analysis of the experimental monotonic tensile and cyclic hysteresis curves, the composite’s constituent properties (i.e., interface properties and thermal residual stress, etc.) and mechanical properties (i.e., first matrix cracking stress, interface debonding stress, and ultimate tensile strength, etc.) were obtained. Relationship between the composite’s constituent properties and mechanical properties was established. Using the estimated composite’s constituent properties and developed micromechanical constitutive models, the experimental monotonic and cyclic tensile loading/unloading curves were predicted.

Damage Monitoring of Ceramic Matrix Composites Under Tension Loading Via NDE-based DIC Approach

Environmental barrier coatings (EBCs) are used as a coating material on fiber-reinforced ceramic matrix composites (CMC) for various aerospace and turbine engines applications. In order to validate physics-based analytical models for predicting the spallation life of EBCs, the fracture strength of the EBC and the kinetics of crack growth in EBC layers need to be experimentally determined under engine operating conditions. In this study, a coating layer of barium strontium aluminum silicate (BSAS)–based melt-infiltrated silicon carbide fiber-reinforced silicon carbide matrix composite (MI SiC/SiC) is applied on a CMC specimen and tensile tested at room temperature. Multiple tests are performed on a single specimen with increasing predetermined stress levels until final failure. Damage progression due to the load applied is monitored using a digital image correlation (DIC) system. After unloading from the predetermined stress levels, the specimen is evaluated by optical microscopy and computed tomography (CT). The inspection forms the imaging which implied that primary and secondary cracks developed during tensile loading until failure. DIC showed formation of a primary crack at ~50% of the ultimate tensile strength, and this crack grew with increasing stress and eventually led to final failure of the specimen.

Assessment of machined surface for SiCf/SiC ceramic matrix composite during ultrasonic vibration-assisted milling-grinding

As a new advanced material, silicon carbon fiber-reinforced silicon carbon ceramic matrix composite has attracted increasing attention and would have a promising application in prospect owing to its superior properties such as low density, high strength, and high-temperature resistance. However, there is still no such standard criterion for machined surface quality evaluation of fiber-reinforced ceramic matrix composites or fiber-reinforced composites. Thus, in this paper, investigations have been performed on ultrasonic vibration-assisted milling-grinding SiC fiber-reinforced SiC-based ceramic matrix composite. It aims to propose a primary criterion for the machined surface assessment of fiber-reinforced composites. This study considered and tested fiber-reinforced composites such as SiCf/SiC CMC, Cf/SiC CMC, and CFRP. Due to the large size of pits and voids in the machined surface, it was recommended to use non-contact measuring equipment for surface quality measurement. The 2D surface roughness value of every single machined surface differed much along different measuring directions and regions. Then, the 3D surface roughness was suggested for describing the machined surface quality as its data fluctuation was much more minor than the 2D roughness. The comparative analysis found that the measuring area size significantly influenced the 3D roughness result. This study used a measuring area of 13 × 13 mm2, 11 × 11 mm2, 7 × 7 mm2 for SiCf/SiC CMC, Cf/SiC CMC, and CFRP, respectively, taking into consideration the measuring time consumption and the reliability of measured data.

Micromechanical analysis of fiber-reinforced ceramic matrix composites by a hierarchical quadrature element method

This work performed stress predictions of unidirectional fiber-reinforced ceramic matrix composites (CMCs) subjected to longitudinal tension using a hierarchical quadrature element method (HQEM). The HQEM is a p-version finite element method that can present highly accurate results using only a few sampling points. Parametric analysis was conducted to investigate the sensitivity of the HQEM model to interface properties and the detailed process of determining the optimal interface parameters for micromechanical analysis of damaged CMCs has been elaborated. By comparison with the analytical results based on the classical shear-lag model which is commonly adopted to analyze the stress distributions of the damaged fiber-reinforced CMCs, the HQEM estimates of fiber and matrix stress distributions were validated. For uniformly loaded SiCf/SiC composites with a single matrix crack, the micromechanical behaviors of three typical cases during failure process, namely, interface perfectly bonded, interface debonding and fiber failure were analyzed, illustrating the characteristics of CMC failure and providing insight into the mechanisms relating the microstructural behavior to global failure. The present work offers the foundations of the extension of a promising approach for highly accurate and efficient fracture analysis of CMCs.

Interface wear effects in ceramic composite crack opening

For fiber-reinforced ceramic-matrix composites (CMCs), crack opening behavior controls oxidation atmosphere ingress into the internal composite, which affects the operation reliability and durability of engineering CMC components. Under cyclic fatigue loading, interface wear affects the crack opening behavior in CMCs. In this paper, the stress/cyclic-dependent crack opening behavior in CMCs is analyzed considering interface wear effect. The analytical crack opening displacement (COD) and related damage parameters (e.g., interface debonding ratio (IDR)) are determined based on the microstress analysis in the fiber and the matrix. Experimental CODs of different matrix cracks in SiC/SiC minicomposite are predicted under tensile loading. Considering cyclic-dependent interface wear effect, CODs and related damage parameters are analyzed for different cycles. Theoretical relationships between the COD, peak stress level, cycle number, and composite constitutive properties are established. Effects of constitutive properties, peak stress level, and damage state on cyclic-dependent COD and related damage parameters are discussed. Under tensile loading, with increasing tensile stress, COD first increases nonlinearly and then linearly with applied stress corresponding to change of the interface debonding from partial to complete debonding. The increasing rate of COD curve is relatively low upon initial loading due to short interface debonding range. However, the increasing rate of COD curve decrease again at high stress level at the condition of complete interface debonding. Under cyclic fatigue loading, the change of interface debonding condition with increasing applied cycles affects the COD and IDR curves.

Characterization of carbon fiber-reinforced ultra-high temperature ceramic matrix composites fabricated via Zr-Ti alloy melt infiltration

Carbon fiber-reinforced ultra-high temperature ceramic matrix composites (C/UHTCMCs) were fabricated via Zr-Ti alloy melt infiltration (Zr-Ti MI) using carbon-carbon composite (C/C) preforms and alloys with three different compositions. Alloys were successfully infiltrated into C/C to form solid solutions of TiC and ZrC, with melting temperatures > 2900 °C. Notably, residual alloys were not observed after MI occurred at 1750 °C. Bending strength and fracture toughness of the C/UHTCMCs at room temperature and 1500 °C in air/Ar revealed that mechanical properties of the composites were similar to those of the C/C preform. During arc wind tunnel tests at 2000 °C, a recession of C/UHTCMCs fabricated using Ti-rich alloys was observed; however, this behavior was not observed for the composites prepared using Zr-rich alloys owing to the formation of a ZrO2 solid solution. Accordingly, Zr-Ti MI is a viable method for preparing C/UHTCMCs without degrading the mechanical properties of the C/C preform, while increasing the ablation resistance.

Investigation on scratching force and material removal mechanism of 3D SiCf/C–SiC composites during single grain scratching

As one of the novel fiber-reinforced ceramic matrix composites, SiCf/C-SiC composites are difficult to machine materials and the material removal mechanism is not completely clear yet. Single grain scratching tests with gradual depth have been carried out to analyze the influence of fiber orientation and woven structure on the material removal mechanism and scratching force in three typical scratched surfaces defined by the fiber orientation. Results indicate that the scratching force waveform is affected by the weaving method, fibers orientation, and porosity distribution of the scratched area, resulting in periodic fluctuations. Diamond indenter causes greater damage to the surface of SiCf/C-SiC composites when scratching along transverse fibers, while leaving narrow but deep grooves on the surface when scratching along perpendicular fibers. The dominant mode of material removal of SiCf/C-SiC composites is brittle fracture, and the damage features mainly include direct fiber breakage, matrix fragmentation, fiber pullout, fiber outcropping.

Drilling process of Cf/SiC ceramic matrix composites: Cutting force modeling, machining quality and PCD tool wear analysis

Cf/SiC composites are continuous fiber-reinforced ceramic matrix composites with excellent properties, such as high-temperature resistance, high specific strength, and low coefficient of thermal expansion. However, Cf/SiC composites often cause severe tool wear and quality problems. In this paper, tool wear is studied during the machining of Cf/SiC materials. The cutting force model is applied to understand the correlation between cutting force and tool wear. Polycrystalline Diamond (PCD) tools with various point and clearance angles are designed to carry out drilling experiments on Cf/SiC composites with different machining parameters. During experimental investigations, force and acoustic emission signals are analyzed, and PCD tool wear and material machining quality are observed using scanning electron microscopy. Results indicate that PCD tools with a point angle of 140° and a clearance angle of 20° demonstrate the lowest tool wear during machining. Moreover, low-speed and feed machining parameters can effectively reduce tool wear and prolong its life. By observing fracture patterns of hole wall fibers and chip shapes at different stages of tool wear, and combined with the frequency domain distribution of AE signal, the effects of tool wear on the material removal mechanism are summarized. Before tool wear, fiber fracture is flatter, the matrix is mainly removed via crushing. After tool wear, although fiber fracture is more uneven, the matrix is changed from crushing to friction removal, leading to lower surface roughness of the hole wall.