Grinding characteristics and removal mechanisms of unidirectional carbon fibre reinforced silicon carbide ceramic matrix composites

The grinding performance of unidirectional carbon fibre reinforced silicon carbide ceramic matrix composites (C_f/SiC) was investigated in this paper. The effects of the fibre orientation and grinding depth on the surface integrity and grinding forces and an understanding of the grinding mechanisms are the primary concerns of this article. This problem is relatively unexplored; therefore, the main value of this research is to improve the processing quality and reduce the production cost. In the C_f/SiC grinding procedure, cracks, fibre wear, interfacial debonding, fibre pull-out and outcrop can be detected on the ground surface. The grinding depth and deflection angle have been shown to have a notable influence on the surface quality in different datum planes. A suitable grinding depth and deflection angle should be carefully chosen to achieve good surface quality in different machined surfaces. Specifically, the surface quality decreases and the grinding forces increase with increasing grinding depth. In addition, greater grinding surface quality is observed at β?=?90°, i.e., γ?=?0°, but poorer machined surfaces are obtained at α?=?0°, i.e., γ?=?90°. The surface topography, roughness and grinding forces of unidirectional C_f/SiC could be forecasted according to the analysis conclusions. This research is expected to offer guidelines for increasing the machining quality of C_f/SiC.     

Effect of fiber loading and orientation on mechanical and erosion wear behaviors of glass–epoxy composites

For a composite material, its mechanical behavior and surface damage by solid particle erosion depend on many factors. One of the most important factors is the fiber content. Similarly, these properties are also greatly affected by the fiber orientation. In this work, a series of experiments were carried out to investigate the influence of fiber loading and fiber orientation on mechanical and erosion behavior of glass fiber‐reinforced epoxy composites. The composites were fabricated with three different fiber loadings (20, 30, and 40 wt%) and at four different fiber orientations (15°, 30°, 45°, and 60°). The conclusions drawn on the basis of the experimental findings are discussed, and composite with 30° fiber orientation shows better microhardness compared with other fiber orientations irrespective of fiber loading. Similar observations are also noticed for other mechanical properties of the composites, such as tensile strength, flexural strength, interlaminar shear strength, impact strength, etc. Finally, the morphology of eroded surfaces is examined using scanning electron microscopy (SEM), and possible erosion mechanisms are identified. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

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

C_f/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. C_f/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 C_f/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.     

The effects of fiber orientation on failure behaviors of 2D C/SiC torque tube

Different failure behaviors were observed in the 2D C/SiC torque tubes which were fabricated by chemical vapor infiltration (CVI) with different fiber orientations (0°/90° and ±45°). CT test was implemented to characterize the density heterogeneity of the ceramic matrix composite (CMC) torque tubes. With the density value measured by Archimedes drainage method, FEM software was implemented to simulate the stress distribution of the ceramic matrix composite torque tubes and calculate the failure stress. Torsional tests were conducted using special attachments to a universal material test machine. Different torsional behaviors of CMC torque tubes with two different fiber orientations were presented in the stress-strain curves. The fracture morphologies were observed by SEM, and the predominant factors of failure were analyzed. CMC torque tubes with fiber orientation of ±45° have a higher torque capacity and modulus. In failure analysis, we found that ±45° fiber orientation CMC torque tubes have reasonable fracture morphologies.     

New observations of the fiber orientations effect on machinability in grinding of C/SiC ceramic matrix composite

In this paper, the effect of machining parameters on cutting force, force ratio, 3D surface roughness was studied, and the surface formation mechanism was deeply analyzed in view of the position relation between machining directions and fiber orientations. New observations of the fiber orientation effect on machinability are attempted to obtain in grinding of 2D C/SiC ceramic matrix composite with electroplated diamond grinding tool. Two machining directions (A and B) on one surface are taken into account to study the effect of fiber orientation on the grinding process. The results indicate that the cutting forces obtained in machining direction of A are greater than that in machining direction of B under all experimental conditions. However, the tangential force is greater than the normal force, which is different from grinding ordinary material. Whether in the machining direction of A or direction of B in grinding C/SiC composite, on the whole the surface roughness values (Sa and Sq) decrease as the feed rate increases. As depth of cut increasing, the surface roughness values in the machining direction of A and B come out inconsistency. At different feed rates, the surface roughness values in the machining direction of A and B also represent inconsistency with the change of cutting speed. The theoretical model of undeformed cutting thickness is unfit for evaluating its effect on the surface roughness. After analyzing of the surface formation, except for some fibers forming extruding fault and fracture, being pulled out, and fracture or broken, a new phenomenon that some fibers forming extruding fault and fracture is observed.     

Experimental investigations on grinding characteristics and removal mechanisms of 2D–Cf/C-SiC composites based on reinforced fiber orientations

The effects of fiber orientations on the grinding force and ground surface roughness in grinding 2D–C_f/C–SiC composites were investigated in this work. The characteristics of surface microstructure and the mechanism of the grinding phenomena are also discussed. The results show that the prominent removal mechanism for grinding the 2D-C_f/C-SiC composites is the brittle fracture, and the destruction of the composites is mainly via breaking of interfacial bonds, fiber fracture, and matrix cracking. The grinding force of different grinding surfaces follows the order: Surface B > Surface A > Surface C, and the surface roughness follows: Surface C > Surface A > Surface B. Grinding parameters, such as feeding speed, depth of cut, and wheel speed, have a great influence on the grinding force and surface roughness. This result suggests that this body of work offers a useful guideline for improving the design and processing of 2D–C_f/C–SiC composites.     

Effect of the fiber orientation on the sorption kinetics of seawater in an epoxy/glass composite: A free-volume microprobe study

The conventional gravimetric method and positron lifetime spectroscopy have been used to investigate the effect of glass fiber orientation on the diffusion behavior of seawater in epoxy-based composite samples with glass fiber orientations of 0 and 45°. The equilibrium mass uptake of seawater in 45 and 0° orientation composites has been found to be 2.77 and 1.57%, respectively. The diffusion process is non-Fickian in a 45° fiber oriented composite, whereas it is Fickian in a 0° oriented composite. Free-volume data for 45° fiber oriented composites indicates swelling upon the sorption of seawater leading to structural relaxation, and hence the diffusion becomes non-Fickian. On the other hand, a 0° fiber orientation sample exhibits no swelling, and this suggests that water diffusion to the fiber–resin interface through the resin matrix is impeded by the large number of bonds. A polymer–fiber interaction parameter determined from these results also further supports the idea that interface interaction in a 45° fiber oriented composite is less than that in a 0° fiber oriented composite. Positron and gravimetric results support this argument. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of fiber orientation on viscoelastic properties of polymer matrix composites subjected to thermal cycles

Fibers in polymer composites can be designed in various orientations for their usage in service life. Various fiber orientated polymer composites, which are used in aeroplane and aerospace applications, are frequently subjected to thermal cycles because of the changes in body temperatures at a range of −60 to 150°C during flights. It is an important subject to investigate the visco‐elastic properties of the thermal cycled polymer composite materials which have various fiber orientations during service life. Continuous fiber reinforced composites with a various fiber orientations are subjected to 1,000 thermal cycles between the temperatures of 0 and 100°C. Dynamic mechanic thermal analysis (DMTA) experiments are carried out by TA Q800 type equipment. The changes in glass transition temperature (T_g), storage modulus (E′), loss modulus (E′′) and loss factor (tan δ) are inspected as a function of thermal cycles for different fiber orientations. It was observed that thermal and dynamic mechanical properties of the polymer composites were remarkably changed by thermal cycles. It was also determined that the composites with [45°/−45°]_s fiber orientation presented the lowest dynamic mechanical properties. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Enhancing ductile removal of Cf/SiC composites during abrasive belt grinding using low-hardness rubber contact wheels

C_f/SiC composites are used as advanced thermal protection and friction materials. However, machining these materials is difficult because of their hard, brittle, anisotropic, and heterogeneous characteristics. This study investigated the removal behavior and surface integrity of C_f/SiC composites during abrasive belt grinding using rubber contact wheels of various hardness. Additionally, detailed analysis was performed on their thermal-mechanical coupling characteristics, surface integrity (that is, surface roughness, surface micro morphology, and subsurface damages), and the grinding chips produced. Results revealed that with decreasing hardness of the contact wheel, the surface roughness in all directions, grinding force, and temperature decreased significantly. Moreover, the surface removal morphology of the C_f/SiC composites changed from macro-fracture to micro-fracture, and the subsurface morphology changed from SiC matrix cracking and carbon fibers pull-out to matrix plastic flow and fiber micro-fracture, respectively. Furthermore, strip chips with plastically squeezed and cut surfaces were visible in the grinding chips obtained under the 40-HA contact wheel. Therefore, the ductile removal behavior of the C_f/SiC composites was enhanced, and the surface quality in abrasive belt grinding with low-hardness contact wheels was markedly improved.     

Experimental Investigation of Mechanical and Morphological Properties of Flax-Glass Fiber Reinforced Hybrid Composite using Finite Element Analysis

The use of cellulosic fibers as reinforcing materials in polymer composites has gained popularity due to an increasing trend for developing sustainable materials. In the present experimental study, flax and glass fiber reinforced partially eco-friendly hybrid composites are fabricated with two different fiber orientations of 0° and 90°. The mechanical properties of these composites such as tensile, flexural and impact strengths have been evaluated. From the experiments, it has been observed that the composites with the 0° fiber orientation can hold the maximum tensile strength of 82.71 MPa, flexural strength of 143.99 MPa, and impact strength of 4 kJ/m². Whereas the composites with 90° fiber orientation can withstand the maximum tensile strength of 75.64 MPa, flexural strength of 134.86 MPa, and impact strength of 3.99 kJ/m². Morphological analysis is carried out to analyze fiber matrix interfaces and the structure of the fractured surfaces by using scanning electron microscopy (SEM). The finite element analysis (FEA) has been carried out to predict the resulting important mechanical properties by using ANSYS 12.0. From the results it is found that the experimental results are very close to the results predicted from FEA model values. It is suggested that these hybrid composites can be used as alternate materials for pure synthetic fiber reinforced polymer composite materials.     

Crystallographic orientation effect on the polishing behavior of LiTaO3 single crystal and its correlation with strain rate sensitivity

Lithium tantalite (LiTaO₃ or LT) single crystal has been extensively applied in the fields of electro-optical and piezoelectric devices. As a typical anisotropic material, the crystallographic orientation effect on its machining responses, i.e., surface roughness and material removal rate (MRR), is not yet well understood. In the present work, we investigated the polishing responses of the three typical crystallographic orientations for LT single crystal under a series of rotation speeds. The results showed that both the rotation speed and crystalline orientation had little effect on the quality of polished surface. While for the MRR, it was almost linearly increased with increasing rotation speed for all of the three planes, among which the enhancements of MRR on Y-42° and Y-36° planes were more pronounced than that on X-112° plane. The scratch features and friction coefficients were investigated using a nanoindentation system under various velocities. The nano-hardness values were obtained under various strain rates and, hence, the strain rate sensitivities (SRS) were determined as 0.0172, 0.0455, and 0.043 for X-112°, Y-42°, and Y-36° planes, respectively. The better mechanical properties and “plastic” removal mechanism of X-112° plane resulted in the lower value of MRR. Also, the much lower SRS corresponded well with the relatively less sensitivity of MRR with rotation speed on X-112° plane. Results of this study suggested that the plastic parameter of SRS could provide as an excellent indicator to bridge the machining response and intrinsic deformation mechanism for brittle single crystal ceramics.     

Mechanical properties of natural fiber hybrid composites based on renewable thermoset resins derived from soybean oil,for use in technical applications

Natural fiber composites are known to have lower mechanical properties than glass or carbon fiber reinforced composites. The hybrid natural fiber composites prepared in this study have relatively good mechanical properties. Different combinations of woven and non‐woven flax fibers were used. The stacking sequence of the fibers was in different orientations, such as 0°, +45°, and 90°. The composites manufactured had good mechanical properties. A tensile strength of about 119 MPa and Young's modulus of about 14 GPa was achieved, with flexural strength and modulus of about 201 MPa and 24 GPa, respectively. For the purposes of comparison, composites were made with a combination of woven fabrics and glass fibers. One ply of a glass fiber mat was sandwiched in the mid‐plane and this increased the tensile strength considerably to 168 MPa. Dynamic mechanical analysis was performed in order to determine the storage and loss modulus and the glass transition temperature of the composites. Microstructural analysis was done with scanning electron microscopy. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The effect of fiber orientation on failure behavior of 3DN C/SiC torque tube

In this paper, the 3DN C/SiC torque tubes were fabricated by chemical vapor infiltration (CVI) combined with silicon melt infiltration (SMI) method with different fiber orientations (0°/90° and ± 45°) which leads to different density, torsional behaviors and failure behaviors. CT test was implemented to characterize the density heterogeneity. Using the density measured from Archimedes drainage method, FEM software was implemented to simulate the stress distribution of the tubes and calculate the failure stress. A good agreement with analytical model was obtained which helps a lot to failure analysis. Torsional tests were conducted using special attachments to a universal material test machine, the shear strain was calculated from the strain gauge, the shear strength was calculated by simplified formula, different torsional behaviors of two different fiber orientations were represented in the stress-strain curves. The fracture morphologies were observed by SEM, and the predominant factors of failure were analyzed. Torque tubes with fiber orientations of ± 45° have a higher torque capacity, modulus, and reasonable fracture morphologies, which is in good agreement with simulation results.     

Comparative study of micro topography on laser ablated C/SiC surfaces with typical uni-directional fibre ending orientations

Functional micro-structures on laser-ablated carbon fibre reinforced composites surfaces exhibit distinct advantages. A variety of fibre endings with different orientations may coexist on the C/SiC sectional plane, the anisotropic nature of C/SiC (carbon fibre reinforced silicon carbide) composites present a new challenge to the laser ablation process. However, few reports describing the influence of the fibre ending orientations on the laser-ablated C/SiC surface topography could be found. In this investigation, micro-ridges were established on three typical C/SiC surfaces by laser ablation, and a comparative study was performed to identify the topography variations on these laser-ablated C/SiC surfaces. The results showed that C/SiC surfaces with different fibre ending orientations present distinct surface characters (Sz, Sq) after laser ablation. Although all of the laser ablation processes are similar in nature, the fibre ending variation made the laser and material interaction different greatly. Attention should be devoted to the influence of the fibre ending orientation on surface topography formation before performing the laser ablation of carbon fibre reinforced composite materials. Finally, some typical surface defects on these laser-ablated surfaces were also discussed.     

Short fiber-reinforced oxide fiber composites

This paper presents a novel fiber spraying process for the manufacturing of short fiber bundle-reinforced Nextel™ 610/Al₂O₃-ZrO₂ oxide fiber composites (SF-OFC) and its characterization. First, the influence of varying fiber lengths (7, 14, and 28 mm, continuous fibers) and fiber orientations (unidirectional 0°, quasi-isotropic, ±45°) was investigated using hand-laid SF-OFC. Due to the weak matrix, the hand-laid material exhibited a strongly fiber-dominated material behavior, that is, variations in fiber length and orientation had a strong influence on the material properties. Second, the automated sprayed SF-OFC, however, exhibited a random orientation of the fiber bundles, which resulted in in-plane isotropic material properties. Average bending strengths of up to 177 MPa, strains of .39%, and a quasi-ductile fracture behavior were achieved. The strain was, therefore, in the range of fabric-reinforced OFC. While the bending strength of the SF-OFC was somewhat lower than that of fabric-reinforced OFC with the fiber orientation parallel to the loading direction, it was more than two times higher than the strength in 45° direction relative to the fabric reinforcement. Combined with good drapability and lower material costs compared to fabric-reinforced OFC, SF-OFC is, therefore, a promising material for industrial applications.     

Effect of initial density on thermal conductivity of new micro-pipeline heat conduction C/SiC composites

C/SiC composites prepared by chemical vapor infiltration technique (CVI) have been regarded as thermal structural materials widely. However, these composites still suffer from poor functional properties like low thermal conductivity, especially in thickness direction of the composites, limiting their large-scale applications. Herein, mesophase pitch based carbon fiber (MPCF) and continuous wave laser machining were utilized to construct highly effective heat conductive micro-pipelines within CVI C/SiC composite. The effect of initial density on the final density and thermal conductivity of the as-obtained MPCF-C/SiC composites were investigated. The results revealed that higher initial density would directly enhance the thermal conductivity and reduce the negative impact of the bottle-neck effect. At temperatures between 100°C and 500°C, MPCF-C/SiC composites preserved more than threefold of the thermal conductivity (340%) when compared to reference C/SiC composites. This work provides a highly effective route for enhancing the thermal conductivity of C/SiC, which would broaden their future applications.     

Creep properties of melt infiltrated SiC/SiC composites with Sylramic™-iBN and Hi-Nicalon™-S fibers

Isothermal tensile creep tests were conducted on 2D woven and laminated, 0/90 balanced melt infiltration (MI) SiC/SiC composites at stress levels from 48 to 138 MPa and temperatures to 1400°C in air. Effects of fiber architecture and fiber types on creep properties, influence of accumulated creep strain on in-plane tensile properties, and the dominant constituent controlling the creep behavior and creep rupture properties of these composites were investigated. In addition, the creep parameters of both composites were determined. Results indicate that in 2D woven MI SiC/SiC composites with Sylramic™-iBN or Hi-Nicalon™-S fibers, creep is controlled by chemical vapor infiltration (CVI) SiC matrix, whereas in 2D laminated MI SiC/SiC composites with Hi-Nicalon™-S fibers, creep is controlled by the fiber. Both types of composites exhibit significant variation in creep behavior and rupture life at a constant temperature and stress, predominantly due to local variation in microstructural inhomogeneity and stress raisers. In both types of composites at temperatures >1350°C, residual silicon present in SiC matrix to reacts with SiC fibers and fiber coating causing premature creep rupture. Using the creep parameters generated, the creep behaviors of the composites have been modeled and factors influencing creep durability are discussed.     

Effect of precoated carbon layer on microstructure and anti‐erosion properties of SiC coating for 2D‐C/C composites

To improve the erosion resistant of carbon‐carbon composites, an SiC coating was synthesized on carbon‐carbon composites by the in situ reaction method. They are firstly coated with carbon layer by slurry, and then SiC coatings are obtained by chemical vapor reaction. The effects of precoated carbon layer on the microstructure and anti‐erosion properties of SiC‐coated C‐C composites were studied and characterized. The thickness of the SiC coating increased with the increase in the precoated carbon layer thickness. The different thickness of carbon layer affects hardness of the SiC coatings, resulting in diverse erosion resistance of the coatings. The SiC coating prepared with moderate thickness of precoated carbon layer exhibits the best erosion resistance, and show better resistance at an impact angle of 30° than 90°. The eroded surface revealed that coating cracking and brittle fracture, fiber‐matrix debonding, fiber breakage, and material removal, and the additional microcutting and microploughing at oblique impact angle are the major erosion mechanism of SiC coating for C/C composites.     

Mechanical and morphological properties for sandwich composites of wood/PVC and glass fiber/PVC layers

This work manufactured sandwich composites from glass fiber/poly(vinyl chloride) (GF/PVC) and wood/PVC layers, and their mechanical and morphological properties of the composites in three GF orientation angles were assessed. The effects of K value (or viscosity index) of PVC and Dioctyl phthalate (DOP) loading were of our interests. The GF/PVC was used as core layer whereas wood/PVC was the cover layers. The experimental results indicated that PVC with low K value was recommended for the GF/PVC core layer for fabrication of GF/WPVC sandwich composites. The improvement of PVC diffusion at the interface between the GF and the PVC core layer was obtained when using PVC with K value of 58. This was because it could prevent de‐lamination between composite layers which would lead to higher mechanical properties of the sandwich composites, except for the tensile modulus. The sandwich composites with 0° GF orientation possessed relatively much higher mechanical properties as compared with those with 45° and 90° GF orientations, especially for the impact strength. Low mechanical properties of the sandwich composites with 45° and 90° GF orientation angles could be overcome by incorporation of DOP plasticizer into the GF/PVC core layer with the recommended DOP loadings of 5–10 parts per hundred by weight of PVC components. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Off-axis tensile properties and fracture in a unidirectional graphite/polyimide composite (celion 6000/PMR 15)

Tensile properties of unidirectional Celion 6000 graphite/PMR 15 polyimide composites prepared by hot molding and cold molding processes were measured at room temperature and 316°C, the upper use temperature of the polyimide resin, at both 45 and 90° to the fiber axis. The resulting fractures were characterized by scanning electron microscopy and materialographic techniques. Variation in tensile properties with processing history occurred in the elastic modulus and strain to failure for specimens loaded at 90° at 316°C, and in the fracture stress, and hence the in-plane shear stress, for those loaded at 45° at room temperature. Significant plastic deformation was observed in the 45° orientation at 316°C for material produced by both processing methods. In general, fracture occurred by both failure within the matrix and at the fiber-matrix interface; the degree of interfacial failure increased with temperature. Secondary cracking below the primary fracture surface also was observed.