Microwave Absorption and Mechanical Properties of Short-cutted Carbon Fiber/glass Fiber Hybrid Veil Reinforced Epoxy Composites

This work aims at investigating the microwave absorption and mechanical properties of short-cutted carbon fiber/glass fiber hybrid veil reinforced epoxy composites.The short-cutted carbon fibers(CFs)/glass fibers(GFs)hybrid veil were prepared by papermaking technology,and composites liquid molding was employed to manufacture CFs/GFs hybrid epoxy composites.The microstructure,microwave absorbing properties and mechanical properties of the hybrid epoxy composites were studied by using SEM,vector network analyzer and universal material testing,respectively.The reflection coefficient of the composites were calculated by the measured complex permittivity and permeability in the X-band(8.2-12.4 GHz)range.The optimum microwave absorption properties can be obtained when the content of CFs in the hybrid veil is 6 wt%and the thickness of the composites is 2 mm,the minimum reflection coefficient of-31.8 dB and the effective absorption bandwidth is 2.1 GHz,which is ascribed to benefitting impedance matching characteristic and dielectric loss of the carbon fiber.Simultaneously the tensile strength and modulus can achieve 104.0 and 2.98GPa,demonstrating that the CFs/GFs hybrid epoxy composites can be a promising candidate of microwave absorbing materials with high mechanical properties.

Impact Responses of the Carbon Fiber Fabric Reinforced Composites

To study the response characteristics of the carbon fiber fabric reinforced composites under impact loading, one dimensional strain impact test, multi gauge technique and Lagrange analysis method are used. The decaying rule of the stress σ , strain ε , strain rate ε · and density ρ with time and space is obtained. By the theory of dynamics, the impact response characteristics of the material is analyzed and discussed.

Study of damage behavior and repair effectiveness of patch repaired carbon fiber laminate under quasi-static indentation loading

Damage caused due to low-velocity impacts in composites leads to substantial deterioration in their residual strength and eventually provokes structural failure.This work presents an experimental investigation on the effects of different patch and parent laminate stacking sequences on the enhancement of impact strength of Carbon Fiber Reinforced Polymers(CFRP)composites by utilising the adhesively bonded external patch repair technique.Damage evolution study is also performed with the aid of Acoustic Emission(AE).Two different quasi-isotropic configurations were selected for the parent laminate,viz.,[45°/45°/0°/0°]s and[45°/0°/45°/0°]s.Quasi Static Indentation(QSI)test was performed on both the pristine laminates,and damage areas were detected by using the C-scan inspection technique.Damaged laminates were repaired by using a single-sided patch of two different configurations,viz.,[45°/45°/45°/45°]and[45°/0°/0°/45°],and employing a circular plug to fill the damaged hole.Four different combinations of repaired laminates with two configurations of each parent and patch laminate were produced,which were further subjected to the QSI test.The results reveal the effectiveness of the repair method,as all the repaired laminates show higher impact resistance compared to the respective pristine laminates.Patches of[45°/0°/0°/45°]configuration when repaired by taking[45°/45°/0°/0°]s and[45°/0°/45°/0°]s as parents exhibited 68%and 73%higher peak loads,respectively,than the respective pristine laminates.Furthermore,parent and patch of configuration[45°/0°/45°/0°]s and[45°/0°/0°/45°],respectively,attain the highest peak load,whereas[45°/45°/0°/0°]s and[45°/45°/45°/45°]combinations possess the most gradual decrease in the load.

Determination of Water Diffusion Coefficients and Dynamics in Adhesive/Carbon Fiber Reinforced Epoxy Resin Composite Joints

To determinate the water diffusion coefficients and dynamics in adhesive/carben fiber reinforced epoxy resin composite joints, energy dispersive X-ray spectroscopy analysis（EDX） is used to establish the content change of oxy- gen in the adhesive in adhesive/carbon fther reinforced epoxy resin composite joints. As water is made up of oxygen and hydrogen, the water diffusion coefficients and dynamics in adhesive/carben fiber reinforced epoxy resin composite joints can be obtained from the change in the content of oxygen in the adhesive during humidity aging, via EDX analy-sis. The authors have calculated the water diffusion coefficients and dynamics in the adhesive/carbon fiber reinforced epoxy resin composite joints with the aid of beth energy dispersive X-ray spectroscopy and elemental analysis. The de- termined results with EDX analysis are almost the same as those determined with elemental analysis and the results al- so show that the durability of the adhesive/carbon fther reinforced epoxy resin composite joints subjected to silane cou- pling agent treatment is better than those subjected to sand paper burnishing treatment and chemical oxidation treat- ment.

Porosity Effects on Interlaminar Fracture Behavior in Carbon Fiber-Reinforced Polymer Composites

Fiber-reinforced polymer composite materials have become materials of choice for manufacturing application due to their high specific stiffness, strength and fatigue life, low density and thermal expansion coefficient. However, there are some types of defects such as porosity that form during the manufacturing processes of composites and alter their mechanical behavior and material properties. In his study, hand lay-up was conducted to fabricate samples of carbon fiber-reinforced polymer composites with three different vacuum levels in order to vary porosity content. Nondestructive evaluation, destructive techniques and mechanical testing were conducted. Nondestructive evaluation results showed the trend in percentages of porosity through-thickness. Serial sectioning images revealed significant details about the composite’s internal structure such as the volume, morphology and distribution of porosity. Mechanical testing results showed that porosity led to a decrease in both Mode I static interlaminar fracture toughness and Mode I cyclic strain energy release rate fatigue life. The fractographic micrographs showed that porosity content increased as the vacuum decreased, and it drew a relationship between fracture mechanisms and mechanical properties of the composite under different modes of loading as a result of the porosity effects. Finally, in order to accurately quantify porosity percentages included in the samples of different vacuum levels, a comparison was made between the parameters and percentages resulted from the nondestructive evaluation and mechanical testing and the features resulted from fractography and serial sectioning.

Preparation of three-dimensional braided carbon fiber reinforced mullite composites from a sol with high solid content

To prepare the three-dimensional braided carbon fiber reinforced mullite （3D C/mullite） composites, an Al2O3-SiO2 solwith a solid content of 20% （mass fraction） and an Al2O3/SiO2 mass ratio of 2：1 was selected as the raw material. Characteristics andmullitization of the sol were analyzed throughly. It is found that the formation of mullite is basically completed at 1300℃ and thegel powders exhibit favorable sintering shrinkage. The 3D C/mullite composites without interfacial coating were fabricated throughthe route of vacuum impregnation-drying-heat treatment. Satisfied mechanical properties with a flexural strength of 241.2 MPa anda fracture toughness of 10.9 MPa·m1/2are obtained although the total porosity reaches 26.0%. Oxidation resistances of the compositesat 1200, 1400 and 1600 ℃ were investigated. Due to the further densification of matrix, the 3D C/mullite composites show tiny massloss and their mechanical properties are well retained after oxidation at 1600 ℃ for 30 min.

Toughness and Fracture Mechanism of Carbon Fiber Reinforced Epoxy Composites

The fracture toughness of carbon fiber reinforced epoxy composite(CFRP)was investigated through mode I and mode II shaped fracture system in this paper.A novel polyimide with trifluoromethyl groups and grafted nanosilica were used to modify epoxy resin.Effect of modified resin and unmodified resin on fracture toughness of CFRP was compared and discussed.Lay-up angles and thicknesses effects on fracture toughness of composites were also investigated.The fracture toughness of CFRP was obtained through double cantilever beam(DCB)and end notched flexure(ENF)tests.The results showed that the composites prepared by modified resin exhibited high fracture toughness compared with unmodified composites.The fracture toughness value of mode I increased from 1.83 kJ/m2 to 4.55 kJ/m2.The fracture toughness value of mode II increased from 2.30 kJ/m2 to 6.47 kJ/m2.

Orthogonal design of experiment and analysis of abrasive water jet cutting on carbon fiber reinforced composites

The carbon fiber reinforced composite is a new type of composite material with an excellent property in strength and elastic modulus,and has found extensive applications in aerospace,energy,automotive industry and so on.However,this composite has a strict requirement on processing techniques,for example,brittle damage or delamination often exists in conventional processing techniques.Abrasive water jet machining technology is a new type of green machining technique with distinct advantages such as high-energy and thermal distortion free.The use of abrasive water jet technique to process carbon fiber composite materials has become a popular trend since it can significantly improve the processing accuracy and surface quality of carbon fiber composite materials.However,there are too many parameters that affect the quality of an abrasive water jet machining.At present,few studies are carried out on the parameter optimization of such a machining process,which leads to the unstable quality of surface processing.In this paper,orthogonal design of experiment and regression analysis were employed to establish the empirical model between cutting surface roughness and machining process parameters.Then a verified model was used to optimize the machining process parameters for abrasive water jet cutting carbon fiber reinforced composites.

Micro Model of Carbon Fiber/Cyanate Ester Composites and Analysis of Machining Damage Mechanism

Machining damage occurs on the surface of carbon fiber reinforced polymer (CFRP) composites during processing. In the current simulation model of CFRP, the initial defects on the carbon fiber and the periodic random distribution of the reinforcement phase in the matrix are not considered in detail, which makes the characteristics of the cutting model significantly different from the actual processing conditions. In this paper, a novel three-phase model of carbon fiber/cyanate ester composites is proposed to simulate the machining damage of the composites. The periodic random distribution of the carbon fiber reinforced phase in the matrix was realized using a double perturbation algorithm. To achieve the stochastic distribution of the strength of a single carbon fiber, a novel method that combines the Weibull intensity distribution theory with the Monte Carlo method is presented. The mechanical properties of the cyanate matrix were characterized by fitting the stress-strain curves, and the cohesive zone model was employed to simulate the interface. Based on the model, the machining damage mechanism of the composites was revealed using finite element simulations and by conducting a theoretical analysis. Furthermore, the milling surfaces of the composites were observed using a scanning electron microscope, to verify the accuracy of the simulation results. In this study, the simulations and theoretical analysis of the carbon fiber/cyanate ester composite processing were carried out based on a novel three-phase model, which revealed the material failure and machining damage mechanism more accurately.

Resistance welding of carbon fibre reinforced polyetheretherketone composites using metal mesh and PEI film

Weldability of polyetheretherketone(PEEK) with polyetherimide(PEI) is tested. And carbon fiber reinforced PEEK laminates are resistance welded using stainless steel mesh heating element. The effects of the welding time and welding pressure on the lap shear strength of joints are investigated. Results show that PEEK can heal with PEI well in welding condition and the lap shear strength of PEEK/CF(carbon fibre) joint increases linearly with welding time, but reaches a maximum value when welding pressure ranging from 0.3 MPa to 0.5 MPa with constant welding time. The fracture characteristics of surface are analyzed by SEM techniques, and four types of fracture modes of lap shear joints are suggested.

Electromagnetic Shielding and Absorption Properties of Fiber Reinforced Cementitious Composites

In order to investigate the electromagnetic shielding effectiveness （SE） and absorbing properties of fiber reinforced concrete, steel fiber, carbon fiber and synthetic polyvinyl alcohol （PVA） fiber reinforced concrete were researched. The results show that with the increase of fiber Volume fraction, the SE and trend of frequency change of corresponding fiber reinforced concrete are enhanced. When the volume content of steel fiber is 3%, the SE of concrete is above 50 dB and its frequency is above 1.8 GHz. Moreover, in the range of 8-18 GHz, steel fiber, carbon fiber and PVA fiber all can improve the microwave absorption properties of concrete. The concrete with 0.5% carbon fiber can achieve the best absorbing property, the minimum reflectivity is about -7 dB; while steel fiber optimal volume fraction is 2%. The reflectivity curve of PVA fiber reinforced concrete fluctuates with the frequency, and the minimum value of the reflectivity is below -10 dB. The results show that fiber reinforced concrete could be used as EMI（electromagnetic interference） prevention buildings by attenuating and reflecting electromagnetic wave energy.

Fabrication of solid-phase-sintered Si C-based composites with short carbon fibers

Solid-phase-sintered Si C-based composites with short carbon fibers（Csf/SSi C） in concentrations ranging from 0 to 10wt% were prepared by pressureless sintering at 2100°C. The phase composition, microstructure, density, and flexural strength of the composites with different Csf contents were investigated. SEM micrographs showed that the Csf distributed in the SSi C matrix homogeneously with some gaps at the fiber/matrix interfaces. The densities of the composites decreased with increasing Csf content. However, the bending strength first increased and then decreased with increasing Csf content, reaching a maximum value of 390 MPa at a Csf content of 5wt%, which was 60 MPa higher than that of SSi C because of the pull-out strengthening mechanism. Notably, Csf was graphitized and damaged during the sintering process because of the high temperature and reaction with boron derived from the sintering additive B4C; this graphitization degraded the fiber strengthening effect.

STUDY ON ULTRASONIC VIBRATION DRILLING IN CARBON FIBER REINFORCED POLYMERS

This paper researches ultrasonic vibration drilling of carbon fiber reinforced polymers composites that are hard, brittle, and have low shear strength between layers. An experiment plan has been developed to reduce the axial force. Experimental studies have been done on the influence of process parameters, tool structures on the drilling axial force. The drilling mechanism is specially investigated. Thus an effective method is presented to reduce the drilling axial force. The authors suppose that ultrasonic vibration drilling is feasible for carbon fiber reinforced polymers composites.

Elevating mechanical and biotribological properties of carbon fiber composites by constructing graphene-silicon nitride nanowires interlocking interfacial enhancement

Carbon fiber reinforced dual-matrix composites(CHM)including carbon fiber reinforced hydroxyapatite-polymer matrix composites(CHMP)and carbon fiber reinforced hydroxyapatite-pyrolytic carbon matrix composites(CHMC)have great potential application in the field of artificial hip joints,where a combination of high mechanical strength and excellent biotribological property are required.In this work,the graphene-silicon nitride nanowires(Graphene-Si_(3)N_(4)nws)interlocking interfacial enhancement were designed and constructed into CHM for boosting the mechanical and biotribological properties.The graphene and Si_(3)N_(4)nws interact with each other and construct interlocking interfacial enhancement.Benefiting from the Graphene-Si_(3)N_(4)nws synergistic effect and interlocking enhancement mechanism,the mechanical and biotribological properties of CHM were promoted.Compared with CHMP,the shear and compressive strengths of Graphene-Si_(3)N_(4)nws reinforced CHMP were increased by 80.0% and 61.5%,respectively.The friction coefficient and wear rate were reduced by 52.8% and 52.9%,respectively.Compared with CHMC,the shear and compressive strengths of Graphene-Si_(3)N_(4)nws reinforced CHMC were increased by 145.4% and 64.2%.The friction coefficient and wear rate were decreased by 52.3% and 73.6%.Our work provides a promising methodology for preparing Graphene-Si_(3)N_(4)nws reinforced CHM with more reliable mechanical and biotribological properties for use in artificial hip joints.

Observation and Study of Fracture Behaviour for Fiber Reinforced Cement

Polypropylene, carbon, aramid and polyethylene fibers reinforced cement composites were fabricated respectively. Their fracture behaviors were observed using scanning electron microscopy and the bonding between fiber and matrix was observed in detail.

Laser welding process and strength enhancement of carbon fiber reinforced thermoplastic composites and metals dissimilar joint:A review

Carbon fiber reinforced thermoplastic composites(CFRTP)and metals hybrid structures have been widely used in aircraft lightweight manufacturing.However,due to the significant difference in physical and chemical properties between CFRTP and metals,there are lots of challenges to connect them with high quality.Laser welding has a good application prospect in CFRTP and metals connection,and a significant research progress has been made in the exploration of CFRTP-metal laser joining mechanism,joining process optimization,joining strength improvement and joining defects controlling.However,there are still some problems need to be solved for this technology application.In this paper,the research progress of CFRTP-metal laser joining was summarized in three major aspects:theoretical modeling and simulation analysis,process exploration and parameter optimization,joint performance improvement and process innovation.And,problems and challenges of this technology were discussed,and the outlook of this research was provided.

Research on Lightweight Design of Automobile Lower Arm Based on Carbon Fiber Materials

Based on the principle of lightweight design, a method of using carbon fiber reinforced composite instead of traditional metal materials to design automobile carrier?can be?proposed. The method uses the equal stiffness design principle of the composite material parts to lay out the design of the carbon fiber parts, including the application of the laying angle and the thickness of the laying layer in design. Through the analysis of the actual working conditions of the lower arm, the stress and boundary conditions are obtained. After the design of the stiffness, the geometrical topology of the lower arm is further optimized. Finally, the lower arm of the carbon fiber not only met the performance requirements,?but also to a certain extent, achieved?the purpose of lightweight.

Computational and Experimental Analyses of Detachment Force at the Interface between Carbon Fibers and Epoxy Resin

Herein, we used theoretical and experimental methods to investigate the shear fracture strengths of carbon fiber/epoxy resin interfaces. The shear strengths of carbon fiber and epoxy resin were measured using the microdroplet test, whereas interaction and binding energies were estimated using?Ab initio?and molecular dynamics methods. However, binding energies did not impact the shear strength volumes determined by microdroplet tests,?i.e., bonds between functional groups of the carbon filer and the epoxy resin were difficult to break. On the other hand, the interaction energies calculated for epoxy monomers were in good agreement with experimental data. Moreover, we determined the relationship between the simulated interaction energy and the shear fracture strength volume obtained using the microdroplet test.

含缺陷管道碳纤维复合材料补强数值模拟研究

当代石油、天然气等能源的主要运输方式为管道运输,管道在长期使用时会产生各种缺陷,这些缺陷将对管道的结构和强度产生影响。目前先进的管道修复技术为复合材料补强技术,其中碳纤维复合材料是较优的选择。为了测试有/无碳纤维补强管道缺陷处的效果,开展了不同层数碳纤维复合材料的拉伸实验研究,结合ANSYS数值模拟探究了修复前后不同缺陷管道在承载时的应力、应变分布,分析了修复补强效果的影响因素。结果表明:缺陷减薄厚度对管道的应力、应变状态影响较大,碳纤维复合材料修复技术能在减小管道缺陷处应力、应变的同时优化其应力、应变分布,可以通过增加碳纤维修复层数来提升修复效果,相关研究对于管道的修复补强有一定指导意义。

单脉冲平顶激光清洗CFRP的多物理场特性研究

为探究平顶激光清洗碳纤维增强复合材料(CFRP)的作用机制,本研究考虑CFRP的组分对激光的吸收、反射特性差异显著,将激光载荷分层施加到CFRP的细观有限元模型上,引入热烧蚀-热应力双重作用效果,还原不同能量密度下单脉冲平顶激光清洗形貌,并完成了试验验证。结果表明:分层施加激光载荷较传统表面加载模式能够有效提升仿真精度,采用热烧蚀-热应力双重判据能够进一步提升形貌还原效果,本研究模型的仿真形貌长轴贴合度不低于96.64%,面积贴合度达到80.00%,并通过高精度模型瞬时温度场分布能够指导激光清洗CFRP表面树脂的实际工艺。