Processing and properties of solution impregnated carbon fiber reinforced polyethersulfone composites

Carbon fiber reinforced polymer composites are attractive because of their high stiffness and strength‐to‐weight ratios. In order to fully utilize the stiffness and strength of the reinforcement fiber, it is necessary to bring the polymer matrix and the reinforcement fiber together with homogeneous wetting. In this paper, a solution processing technique and the mechanical properties of carbon fiber reinforced polyethersulfone composites were investigated. The polymer was dissolved in cyclopentanone and fed onto a continuous carbon fiber tow using a drum winder. The solution‐processed composite prepregs were then layed up and compression molded into unidirectional composite panels for evaluation. The composite samples showed uniform fiber distribution and reasonably good wetting. The longitudinal flexural modulus was as high as 137 GPa, and longitudinal flexural strength 1400 MPa. In addition, the effects of polymer grade and processing conditions on the mechanical properties of the composites were discussed. It is suggested that the transverse properties and interlaminar fracture toughness could benefit from higher polymer matrix molecular weight. A careful design in the spatial distribution of the molecular weight would be necessary for practical applications.     

Microstructure and Mechanical Properties of Three-Dimensional Textile Hi-Nicalon SiC/SiC Composites by Chemical Vapor Infiltration

Three-dimensional textile Hi-Nicalon SiC-fiber-reinforced SiC composites were fabricated using chemical vapor infiltration. The microstructure and mechanical properties of the composite materials were investigated under bending, shear, and impact loading. The density of the composites was 2.5 g·cm⁻³ after the three-dimensional SiC perform was infiltrated for 30 h. The values of flexural strength were 860 MPa at room temperature and 1010 MPa at 1300°C under vacuum. Above the infiltration temperature, the failure behavior of the composites became brittle because of the strong interfacial bonding and the mismatch of thermal expansion coefficients between fiber and matrix. The fracture toughness was 30.2 MPa·m^1/2. The obtained value of shear strength was 67.5 MPa. The composites exhibited excellent impact resistance, and the dynamic fracture toughness of 36.0 kJ·m⁻² was measured using Charpy impact tests.     

Investigation on mechanical and thermo‐mechanical properties of granite powder filled treated jute fiber reinforced epoxy composite

In the present study, two sets of jute epoxy composites are fabricated by varying first fiber loading from 10 to 50 wt% at an interval of 10 wt% and then granite powder incorporated from 0 to 24 wt% in an interval of 8 wt% in the composites. The initial study is to prepare polymeric composites for wind turbine blade application and study the following physical to thermo‐mechanical properties including fracture toughness of the composites. The void content of the unfilled composites show in decreasing order (from 6.37 to 3.07%) with the increasing in fiber loading which satisfied well with the increasing in tensile strength from 28.33 to 34.2 MPa and flexural strength from 44.2 to 97.8 MPa, respectively. As far as particulate filled composites the void content shows reverse in trend (from 2.99% to 9.68%) with the increasing in filler content and which justifies the mechanical properties i.e tensile strength decreases from 33.72 to 32.27 MPa and similarly in case of flexural strength also. Whereas, hardness shows a unique behavior both in fiber reinforced and particulate filled composites in an increasing order from 29 to 44 Hv, respectively. Fracture toughness is observed to be constant for all considered crack lengths however, its value significantly improved with both type of reinforcement. The dynamic mechanical analysis shows positive effect of both the reinforcement for mechanical performance under cyclic stresses. Finally, Cole–Cole plot is drawn from the dynamic mechanical analysis results to verify the homogeneity of the composites. POLYM. COMPOS., 38:736–748, 2017. © 2015 Society of Plastics Engineers     

Interlaminar mechanical properties of carbon fiber reinforced plastic laminates modified with graphene oxide interleaf

By taking the advantage of the excellent mechanical properties and high specific surface area of graphene oxide (GO) sheets, we develop a simple and effective strategy to improve the interlaminar mechanical properties of carbon fiber reinforced plastic (CFRP) laminates. With the incorporation of graphene oxide reinforced epoxy interleaf into the interface of CFRP laminates, the Mode-I fracture toughness and resistance were greatly increased. The experimental results of double cantilever beam (DCB) tests demonstrated that, with 2 g/m² addition of GO, the Mode-I fracture toughness and resistance of the specimen increase by 170.8% and 108.0%, respectively, compared to those of the plain specimen. The improvement mechanisms were investigated by the observation of fracture surface with scanning electron microscopies. Moreover, finite element analyses were performed based on the cohesive zone model to verify the experimental fracture toughness and to predict the interfacial tensile strength of CFRP laminates.     

Influence of Fiber and Interfacial Properties on Fracture Behavior of Fiber-Reinforced Ceramic Composites

The fracture and fracture resistance behaviors of zirconmatrix composites uniaxially reinforced with either uncoated or BN-coated silicon carbide fibers are studied by performing experiments in three-point flexure and by analyzing results analytically using a cohesive crack model that incorporates crack bridging and fiber pullout mechanisms. A comparison of experimental results with the model predictions demonstrates good agreement. This analytical approach is then used in a parametrical study to demonstrate the role of fiber and fiber-matrix interfacial properties on the mechanical behavior of fiber-reinforced ceramic-matrix composites. Material parameters that enhance ultimate strength and ductility or toughness are elucidated.     

Effect of geometry and loading fractions on energy absorbing properties of fiberglass polymer composite under quasi‐static and low‐velocity impact loadings

The focus of this study is to experimentally investigate the mechanical properties of fiberglass reinforced composite with various aspect ratios and loading fractions in the quasi‐static and low‐velocity impact loading conditions. In this study, short fiberglass reinforced polycarbonate composite materials were fabricated via a solution mixing method and characterized for their tensile properties by varying both fiberglass loading fraction and aspect ratio. The tensile properties including tensile toughness of the fiberglass reinforced composites were characterized and compared. It was observed in this study that the toughness of the composite was dramatically improved whereas the tensile strength and Young's modulus were moderately enhanced over the neat polymer, which were measured to be only up to 15% and 70% increase, respectively. The low‐velocity impact behaviors of the fiberglass composites were also investigated and compared to the tensile toughness of the corresponding composites. Besides, the effect of thickness on their low‐velocity impact properties was investigated. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40821.     

Effect of stress transfer between fiber and matrix on toughness of polymer composite

Thanks to their lightweight properties, formability and low cost, polymers have become an essential material for manufactured products. To improve the mechanical properties, almost all polymers are blended with some kind of fiber made from glass, carbon, organic or natural material. The importance of interfacial strength between matrix and fiber is a well known requirement for effective mechanical properties and some experimental results indicate that low interfacial strength helps increase the toughness of composites. In this paper, models of composite reinforced by fiber aligned with maximum principal stress under uni‐tensile loading are simulated. Based on the simulation result, we discuss the effect of interfacial strength, aspect ratio of fiber and friction force between matrix and fiber on stable deformation and provide the guidelines for establishing composites with high modulus and toughness. POLYM. COMPOS. 2011. © 2011 Society of Plastics Engineers     

Numerical Simulation of Mesoscopic Mechanical Behaviors of Gradual Multi‐Fiber‐Reinforced Polymer Matrix Composites

Summary: To simulate the deformation and the fracture of gradual multi‐fiber‐reinforced polymer matrix composites, a numerical simulation method for the mesoscopic mechanical behaviors was developed on the basis of the finite element and the Monte Carlo methods. The results indicate that the strength of a composite increases if the variability of statistical fiber strengths is decreased.

Normalized strength distributions plotted in the Weibull form of versus for composites with varying WM.     

A review of the research progress on the interface between oxide fiber and oxide ceramic matrix

Oxide ceramics have excellent high temperature performance, superior thermal and chemical stability, which can be used in high temperature oxidizing environments, while oxide ceramics generally have low toughness and are prone to catastrophic damage... Oxide ceramics can be reinforced by high performance ceramic fibers to improve the fracture strength and fracture toughness, thus expanding its application in high-temperature components such as aero-engine combustion chambers and tail nozzles. The interface between fiber and matrix is an important factor that determines the performance of the composites. By tailoring the interface, the energy dissipation mechanisms such as fiber debonding and fiber pull-out can be brought into play to avoid the catastrophic damage of the composites. This review paper summarizes the recent research progress of the oxide fiber/oxide ceramic matrix composites interface. The mechanical properties of the interface and the design principles of the interface engineering are discussed, and types of interfaces and coating preparation methods are reviewed.     

Application of the J-integral concept for the description of toughness properties of fiber reinforced polyethylene composites

For the determination of toughness properties of HDPE/glass fiber and HDPE/cotton fiber composites, an instrumented Charpy impact test has been used. The interpretation of impact load-deflection curves has been carried out with several concepts of fracture mechanics. Here the limits of linear elastic fracture mechanic (LEFM) have been shown. The change of toughness properties with increasing fiber volume can be described for short fiber reinforced composites with the help of the J-integral concept in a suitable mode. An application of the conventional Charpy impact test will result in an overestimation of material behavior because of the energy of crack propagation. With the help of a micromechanical model to describe failure processes, taking account of energy dissipative processes, it is possible to calculate fracture mechanical material parameters. Because of the peculiarities of deformation and fracture behavior, the application of elastic-plastic fracture mechanic (EPFM)-concepts for fiber reinforced polymers is required.     

Mechanical and thermal shock properties of Cf/SiBCN composite: Effect of sintering densification and fiber coating

In this work, resin-derived carbon coating was prepared on carbon fibers by polymer impregnation pyrolysis method, then silicoboron carbonitride powder was prepared by mechanical alloying, and finally carbon fiber-reinforced silicoboron carbonitride composites were prepared by hot-pressing process. The effects of sintering densification and fiber coating on microstructure, mechanical properties, thermal shock resistance, and failure mechanisms of the composites were studied. Fiber bridging hinders the sintering densification, causing more defects in fiber-dense area and lower strength. However, higher sintering temperature (1800–2000°C) can improve mechanical properties significantly, including bending strength, vickers hardness, and elastic module, because further sintering densification enhances matrix strength and fiber/matrix bonding strength, while the change of fracture toughness is not obvious (2.24–2.38 MPa·m^1/2) due to counteraction of higher debonding resistance and less pull-out length. However, fiber coating improves fracture toughness greatly via protecting carbon fibers from chemical corrosion and damage of thermal stress and external stress. Due to lower coefficient of thermal expansion, lower fiber loading ratio, less stress concentration at the fiber/matrix interface, and better defect healing effect, lower sintering temperature favors thermal shock resistance of composites, and thermal shock recession mechanisms are the damage of interface.     

The effect of loading rate on the interfacial behavior of overmolded hybrid fiber reinforced polypropylene composites

In the present work, the interfacial behavior of overmolded hybrid fiber reinforced polypropylene composites (hybrid composites) under the loading rate of 1, 10, and 100 mm/min are studied by experimental methods. The interfacial mechanical properties of hybrid composites are determined by monotonic and cycle loading-unloading single-lap-shear tests. The experimental results reveal that interfacial shear strength increases with loading rate, while the shear stiffness shows insensitive to loading rate. A regression function is built to describe the variation of interfacial shear strength with loading rate. The cyclic loading-unloading curves of hybrid composites samples indicate that loading rate effects on the interfacial nonlinear behavior of hybrid composites are considered by affecting plastic deformation. In addition, scanning electron microscopy and digital image correlation observations reveal the failure mechanisms of overmolded hybrid composites. The failure behavior of overmolded hybrid composites is mainly CFRT laminate failure for all cases. The evolution of non-uniform strain fields indicates that the fracture of overmolded thermoplastic composites may initiate at the edges and spread out to the far fields.     

Development of Silicon Carbide Reinforced Jute Epoxy Composites: Physical,Mechanical and Thermo-mechanical Characterizations

The aim of the present study was to investigate the physical and thermo-mechanical characterization of silicon carbide filled needle punch nonwoven jute fiber reinforced epoxy composites. The composite materials were prepared by mixing different weight percentages (0–15 wt.%) of silicon carbide in needle punch nonwoven jute fiber reinforced epoxy composites by hand-lay-up techniques. The physical and mechanical tests have been performed to find the void content, water absorption, hardness, tensile strength, impact strength, fracture toughness and thermo-mechanical properties of the silicon carbide filled jute epoxy composites. The results indicated that increase in silicon carbide filler from 0 to 15 wt.% in the jute epoxy composites increased the void content by 1.49 %, water absorption by 1.83 %, hardness by 39.47 %, tensile strength by 52.5 %, flexural strength by 48.5 %, and impact strength by 14.5 % but on the other hand, decreased the thermal conductivity by 11.62 %. The result also indicated that jute epoxy composites reinforced with 15 wt.% silicon carbide particulate filler presented the highest storage modulus and loss modulus as compared with the unfilled jute epoxy composite.     

Controlled energy dissipation in fibrous composites. II: Microscopic failure mechanisms

Mechanical properties and microscopic fracture mechanisms of continuous fiber reinforced polymer composites were investigated. Perforated polyimide films (e.g. Kapton®) were added between composite prepreg layers to modify the interlaminar bonding strength. Addition of highly perforated films can increase the toughness of unidirectional glass/epoxy composites without an appreciable reduction in strength. The fibrous composites studied exhibit two fracture modes (compressive and tensile) when failed by three-point bending. In general, the compressive failure mode preceded the tensile failure mode. Real-time acoustic emission (AE) analysis was found to provide more fracture information which is otherwise not discernible from mechanical testing alone. The crack initiation stress level and the subsequent crack propagation mode were identified by real-time AE during deformation and by post-failure scanning electron microscopy fracture surface analysis.     

Fracture behavior of sisal fiber–reinforced starch‐based composites

The fracture behavior of biodegradable fiber–reinforced composites as a function of fiber content under different loading conditions was investigated. Composites with different fiber content, ranging from 5 to 20 wt%, were prepared using commercial starch‐based polymer and short sisal fibers. Quasistatic fracture studies as well as instrumented falling weight impact tests were performed on the composites and the plain matrix. Results showed a significant increase in the crack initiation resistance under quasistatic loading. This was caused by the incorporation of sisal fibers to the matrix and the development of failure mechanisms induced by the presence of the fibers. On the other hand, a modest increasing trend of the resistance to crack initiation with fiber loading was detected. An improved fracture behavior was also observed when the impact loading was parallel to the thickness direction. Under these experimental conditions, the composites exhibited higher values of ductility index, energy at initiation and total fracture energy than the plain matrix. Furthermore, an increasing trend of these parameters with fiber content was detected in the biocomposites. Overall, the addition of sisal fibers to the biodegradable matrix appears to be an efficient mean of improving fracture behavior under both quasistatic and impact loading conditions. POLYM. COMPOS. 26:316–323, 2005. © 2005 Society of Plastics Engineers     

Physical,mechanical, and water absorption behavior of coir/glass fiber reinforced epoxy based hybrid composites

Fiber reinforced polymer composites has been used in a variety of application because of their many advantages such as relatively low cost of production, easy to fabricate, and superior strength compare to neat polymer resins. Reinforcement in polymer is either synthetic or natural. Synthetic fiber such as glass, carbon, etc. has high specific strength but their fields of application are limited due to higher cost of production. Recently there is an increase interest in natural composites which are made by reinforcement of natural fiber. In this connection, an investigation has been carried out to make better utilization of coconut coir fiber for making value added products. The objective of the present research work is to study the physical, mechanical, and water absorption behavior of coir/glass fiber reinforced epoxy based hybrid composites. The effect of fiber loading and length on mechanical properties like tensile strength, flexural strength, and hardness of composites is studied. The experimental results reveal that the maximum strength properties is observed for the composite with 10 wt% fiber loading at 15 mm length. The maximum flexural strength of 63 MPa is observed for composites with 10 wt% fiber loading at 15 mm fiber length. Similarly, the maximum hardness value of 21.3 Hv is obtained for composites with 10 wt% fiber loading at 20 mm fiber length. Also, the surface morphology of fractured surfaces after tensile testing is examined using scanning electron microscope (SEM). POLYM. COMPOS., 35:925–930, 2014. © 2013 Society of Plastics Engineers     

Degradation of Mode-I Fracture Toughness of CFRP Bonded Joints Due to Release Agent and Moisture Pre-Bond Contamination

An experimental investigation of the effects of pre-bond contamination on Mode-I fracture toughness of carbon fiber reinforced plastic (CFRP) bonded joints is presented in this paper. Two pre-bond contamination scenarios were considered; namely, the silicon-based release agent and moisture. The two contamination scenarios were realized in one of the composite substrates prior to bonding. The common characteristic of the two contamination scenarios is that they lead in the formation of defects in the form of weak bonds that cannot be detected by conventional non-destructive testing techniques. The contamination effects on Mode-I fracture toughness of the bonded joints were investigated by conducting mechanical tests on double-cantilever beam specimens and comparing the results with relative measurements taken from reference specimens. Prior to mechanical testing, the bonding quality of the specimens was tested using ultrasonic C-scan inspection. Both the release agent and moisture are found to significantly degrade the Mode-I fracture toughness of the joints. For the release agent, the effect was more significant for silicon concentrations over 5 at%; a complete lack of adhesion was observed for silicon concentrations over 7 at%. At low values of relative humidity, there was a small increase in Mode-I critical energy release rate while at larger values there is a decrease which reaches 26% for the higher relative humidity percentage. The results from the Non-Destructive Testing (NDT) tests verify the inability of conventional NDT to detect the defects resulting at the interface between the contaminated adherend's surface and the adhesive for both contamination scenarios.     

Fracture behavior of polyetherimide (PEI) and interlaminar fracture of CF/PEI laminates at elevated temperatures

To investigate the effects of environmental temperature on fracture behavior of a polyetherimide (PEI) thermoplastic polymer and its carbon fiber (CF/PEI) composite, experimental and numerical studies were performed on compact tension (CT) and double cantilever beam (DCB) specimens under mode‐I loading. The numerical analyses were based on 2‐D large deformation finite element analyses (FEA). Elevated temperatures greatly released the crack tip triaxiality (constraint) and promoted matrix deformation due to low yield strength and enhanced ductility of the PEI matrix, which resulted in the greater plane‐strain fracture toughness of the bulk PEI polymer and the interlaminar fracture toughness of its composite during delamination propagation with increasing temperature. Furthermore, the high triaxiality was developed around the delamination front tip in the DCB specimen, which accounted for the poor translation of matrix toughness to the interlaminar fracture toughness by suppressing the matrix deformation and reducing the plastic energy dissipated in the plastic zone. Especially, at delamination initiation, the weakened fiber/matrix adhesion at elevated temperatures led to premature failure of fiber/matrix interface, suppressing matrix deformation and preventing the full utilization of matrix toughness. Consequently, low interlaminar fracture toughness was obtained at elevated temperatures. POLYM. COMPOS., 26:20–28, 2005. © 2004 Society of Plastics Engineers.     

Fracture behavior of short fiber reinforced thermoplastics I. Crack propagation mode and fracture toughness

The fracture behavior of several short glass fiber reinforced thermoplastics has been studied. The fracture toughness of these materials may be related to local crack propagation mode, which is found to be highly rate dependent. At low test rates the crack growth in the reinforced polymers tend to follow a fiber avoidance mode, creating a greater area of new surfaces, which in conjunction with greater degree of interfacial debonding and fiber pullout friction leads to a higher fracture resistance. An increase in loading rate in general results in a more straight and flat crack path, as well as a lesser extent of fiber debonding and pullout. Therefore the fracture toughness is reduced although the frequency of fiber breakage is increased. The fracture behavior of these short fiber reinforced polymers appears to be dictated by the matrix properties when the loading rate is high.     

A review on machining of carbon fiber reinforced ceramic matrix composites

Carbon fiber reinforced ceramic matrix ceramic/polymers composites have excellent physical-mechanical properties for their specific strength, high hardness, and strong fracture toughness relative to their matrix, and they also possess a good performance of wear resistance, heat resistance, dimensional stability, and ablation resistance. It is a choice for thermal protection and high temperature structural materials. However, this kind of composites owning characteristics of high hardness and abrasion is difficult to machine which impedes the large-scale industrial application of manufacturing. This paper mainly reviews the research on machining status of carbon fiber reinforced ceramic matrix composites including carbon fiber reinforced polymer matrix composites from the aspects of conventional machining and unconventional machining method. The machining trends, problems existing in various machining methods and corresponding solutions are generalized and analyzed.