High Fiber Volume Content Research Articles

Influences of Fiber Volume Content on the Mechanical Properties of 2D Plain Carbon-Fiber Woven Composite Materials.

The influence of fiber volume content on the mechanical properties of two-dimensional (2D) plain carbon-fiber woven composites is a crucial concern that necessitates immediate attention for large-scale applications in wind turbine blades. In this study, various mechanical tests were conducted on 2D plain carbon-fiber woven composites with different fiber volume contents, and the influences of fiber volume content on the mechanical properties and failure mode of the composite material were analyzed. Using carbon fiber as reinforcement and epoxy resin as a matrix, three types of plates with fiber volume contents of 47%, 50% and 53% were fabricated by using autoclave technology. The tensile, compression and interlaminar shear tests of the two-dimensional woven composites were carried out using MTS series testing machines. The influences of fiber volume content on tensile strength and modulus, compressive strength and modulus, interlaminar shear strength and shear strain energy were investigated. Additionally, the progressive damage development of these two-dimensional woven composites under different stress states was studied using scanning electron microscopy (SEM). The results indicate that the tensile strength and compressive strength increase almost linearly with the increase in fiber volume content, while the interlaminar shear strength increases slowly at low fiber volume content and rapidly at high fiber volume content. The tensile modulus of elasticity slightly increases as the fiber volume content increases, whereas the compressive modulus remains stable at low fiber volume content but gradually decreases at high fiber volume content. With the increase in fiber volume content, the shear strain energy of the specimen increases significantly.

Permeability and fabric compaction in forming of fiber metal laminates

Significant fluid–structure interaction is present in fiber metal laminate forming with a low viscous matrix. A modular, process-inspired test setup is presented for one-dimensional saturated and unsaturated infiltration experiments for fiber metal laminates. Permeability measurements for different fabric orientations, fabric layers, and fiber volume contents show low scatter and good repeatability for fiber volume contents up to 65%. Fiber metal laminate specimens were formed by exchanging the mid-segment of the test setup with a punch and die. The stiffness differences between metal and fabric lead to remarkably high compactions in the bending radii, significantly reducing the flow during infiltration. Contrary to resin transfer molding processes, no formation of resin-rich zones along bending edges occurs due to the high normal pressures from metal forming. A numerical forming simulation was developed to predict the local fiber volume content. Comparing the experimental results with the numerical simulation shows that the high fiber volume content in the radii almost exclusively impacts the overall permeability. Implications for fiber metal laminate processing and modeling are outlined.

The Significance of Multi-Size Carbon Fibers on the Mechanical and Fracture Characteristics of Fiber Reinforced Cement Composites

One of the main challenges of using a high fiber volume content in a cement composite is the narrow margin of fiber volume content beyond which fibers can cause an adverse effect on the mechanical properties. In this paper, the significance of fiber size distribution and fiber volume content of different proportions of chopped and milled carbon microfibers are investigated. The mixes’ flowability showed improvement with altering the fiber size distribution despite having a high fiber content. Uniaxial compression cylinders and unnotched and notched beams were cast and then tested at 7 and 28 days of age. It was found that the compressive strength is significantly affected by fiber size distribution more than fiber volume content. On the other hand, the modulus of rupture and fracture toughness are proportional to the fiber volume content with little effect of fiber size distribution. Finally, neither high fiber volume content nor altered fiber size distribution significantly affected the elastic modulus of the fiber cement composites.

Process Chain Development for the Fabrication of Three-Dimensional Braided Oxide Ceramic Matrix Composites.

Fiber composites with a three-dimensional braided reinforcement architecture have higher fiber volume content and Z-fiber content compared to a two-dimensional braided reinforcement architecture; as a result, the shear strength increases. Porous oxide fiber composites (OFCs) have the inherent weakness of a low interlaminar shear strength, which can be specifically increased by the use of a three-dimensional fiber reinforcement. In this work, the braiding process chain for processing highly brittle oxide ceramic fibers is modified; as a consequence, a bobbin, which protects the filament, is developed and quantitatively evaluated on a test rig with regard to tension and filament breakage. Subsequently, a braiding process is designed which takes into account fiber-protecting aspects, and a three-dimensional reinforced demonstrator is produced and tested. After impregnation with an Al2O3-ZrO2 slurry, by either a prepreg process or a vacuum-assisted process, as well as subsequent sintering, the three-dimensional braid-reinforced OFC exhibits an interlaminar shear strength (ILSS) which is higher than that of two-dimensional braid- or fabric-reinforced samples by 64–95%. The influence of the manufacturing process on the relative macropore content is investigated and correlated with the mechanical properties.

High-Performance All-Bio-Based Laminates Derived from Delignified Wood

The need for renewable bio-based materials that could replace well-established synthetic composite materials is rapidly growing. For example, bio-based materials are increasingly used in applications where a lightweight design should be combined with sustainability and recyclability. However, it is often very challenging to directly transfer the excellent properties of biological materials to a product in a scalable and cost-efficient manner. In this study, we combined delignified wood layers (veneers) and a starch-based glue into bio-based high-performance composites. First, we investigated the ideal amount of starch-based glue between the layers to prevent delamination in the final composite. Then, we produced laminates in unidirectional, cross-ply, and quasi-isotropic configurations using wet processing. Laminates with tensile properties up to 40 GPa and 200 MPa in tensile stiffness and strength, respectively, were fabricated with a very high fiber volume content of up to 80%. The high fiber volume contents led to mechanical interlocks between neighboring fibers and made the need for an additional matrix unnecessary. The water-based laminate process is cost-efficient and scalable and additionally allows one to make full use of delignified wood’s formability by producing shaped parts for various applications.

Micromechanical modeling of unidirectional composites with random fiber and interphase thickness distributions

Unidirectional composites having random fiber and interphase thickness distributions are considered, and the corresponding transverse effective mechanical properties are determined by the computational homogenization method developed based on linear elastic equilibrium relationship in multi-phase composite. The micromechanical unit cell model including random coated fibers is generated by a simple and efficient algorithm, and the periodic displacement constraints are applied on the cell boundary to keep the cell edges straight after deformation. Then, the effective transverse elastic properties of composites are determined numerically by the present computational model, which is validated through a comparison against available experimental and analytical/numerical results. Finally, the influences of micromechanical parameters on composites are investigated. It is observed that the nonuniformity of interphase thickness has little influence to the overall material properties of composites, which are significantly affected by the interphase thickness and elastic modulus, especially for the case of high fiber volume content.

Material Characterization and Compression Molding Simulation of CF-SMC Materials in a Press Rheometry Test

The compression molding of sheet molding compounds (SMCs) is typically thought of as a fluid mechanics problem. The usage of CF-SMC with high fiber volume content (over 50%) and long fiber reinforcement structures (up to 50 mm) challenges the feasibility of this point of view. In this work a user-defined material model based on a solid mechanics formulation is developed in LS-DYNA®. The material model is built on a modular principle where the different influence factors caused by the material characteristics form building blocks. The idea is that these blocks are represented by simple mathematical models and interact in a way that forms the overall behavior of the SMC material. To analyze the behavior of the SMC material and create input parameters for the material model it is necessary to perform some kind of material characterization experiment. This paper presents the press rheometry test which can be perform in two variations, differing in terms of specimen size and shape and degree of coverage in the tool. Here the material response to the compression molding can be analyzed and by the visualization of the flow front development the anisotropy and homogeneity of the material can be assessed. For a comparison between the material model and reality the two variations of the press rheometry test are simulated. The simulation results show a good prediction of the experiments. The differences between experiment and simulation can be used to further improve the model in a later process.

Research Progress on Preforms of C/C Composites

Carbon/carbon (C/C) composites are important fundamental thermal-structure materials in aeronautic and astronautic fields. One of the most primary basic technologies of C/C composites is the manufacture of carbon fiber preforms which determines the performances of C/C composites. In this paper, the preforms including needle-punched felt, fine weave pierced and axial carbon rod weave fabric are introduced, and the process, properties and applications of those preforms are compared. Due to the low cost and homogeneous ablation, needle-punched felt preforms are extensively used in solid rocket motor nozzle and aircraft brake disc. Fine weave pierced preforms are applied in SRM because of high fiber volume content, short densification cycle and low ablative rate. With the excellent ablative rate attributed to more than 70% fiber perpendicular to the gas flow direction, axial carbon rod weave fabric is used in large SRM. For the domestic research status of preforms, it is suggested that the research involving the effect of pore structure and fiber distribution on mechanical, thermal physics properties and the subsequent densification of C/C composites should be further enhanced in order to promote the performance of C/C composite material.

Characterization of 3D woven reinforcements for liquid composite molding processes

Compaction and permeability characterization of fibrous reinforcements is fundamental to liquid composite molding (LCM) processes, given that these fabric properties determine the part thickness, fiber volume content and mold filling time and patterns. In this study, the permeability of three different 3D woven carbon fiber reinforcements (orthogonal, angle interlock and layer-to-layer) was studied, each having a different weave style and z-binder pattern. For all reinforcements, single-cycle and multiple cycle compaction experiments were conducted on dry and saturated samples. The orthogonal preforms were more difficult to compact to the target fiber volume fraction of 0.65, with peak stresses reaching up to 2.3 MPa. Cyclic compaction tests were conducted to highlight the importance of permanent deformation in the reinforcements, when higher fiber volume content is desired via manufacturing using an LCM process. Unsaturated in-plane radial and saturated through-thickness permeability data were obtained at several fiber volume fractions. The orthogonal and layer-to-layer fabrics exhibited greater levels of anisotropy in the plane of flow. The rate of change of in-plane permeability with increasing fiber volume content was lower compared to through-thickness values. The effect of cyclic compaction on permeability was greater in the orthogonal and angle interlock reinforcements. Micrographs of infused samples showed significant permanent deformation of the z-binder yarns, an effect that reduced permeability at high fiber volume contents.

Fracture energy of ultra-high-performance fiber-reinforced concrete at high strain rates

The fracture energy of ultra-high-performance fiber-reinforced concrete (UHPFRC) at high strain rates (5–92s−1) was investigated, and specimens with 1–1.5% fibers exhibited very high fracture energy (28–71kJ/m2). Evaluation of the rate effects on the UHPFRC fracture resistance, including fracture strength (ft), specific work-of-fracture (WS), and softening fracture energy (WF), indicated that ft and WS were highly sensitive to strain rate, whereas WF was not. The effects of fiber type, volume content, specimen shape and fiber blending on the fracture resistance at high and static strain rates differed significantly: 1) smooth fibers exhibited higher ft and WS at high rates than twisted fibers; 2) higher fiber volume content did not clearly generate higher WS and WF at high rates; 3) notched specimens generally exhibited higher fracture resistance than un-notched samples at both static and high rates; and 4) UHPFRC blending two fibers produced higher WS and WF than UHPFRC with mono fiber at high rates.

Effect of mineral admixtures and steel fiber volume contents on the behavior of high performance fiber reinforced concrete

High Performance Fiber Reinforced Concrete (HPFRC) is a structural material with advanced mechanical properties. The structural design of HPFRC members is based on the post-cracking residual strength provided by the addition into the mix of the fibers. Moreover, the addition of different types of mineral admixtures influences the overall behavior of this material. In order to optimize the performance of HPFRC in structural members, it is necessary to evaluate the mechanical properties and the post-cracking behavior in a reliable way. As a result, an experimental study on six different sets of HPFRC specimens was carried out. The main parameters that varied were the fiber volume content and the types of mineral addition. The behavior in compression, in flexural tension and the shrinkage properties were evaluated and critically analyzed in order to give a guide for structural use.The results showed that by adding high fiber volume content and the Algerian blast furnace slag into the mix, the HPFRC material obtained has a very good performance and it is suitable for use in practice.

A Novel Model for Predicting the Thermal Conductivity of Fiber Reinforced Ceramic Materials

The prediction of fiber reinforced ceramic is one of the most important procedure when investigating the application of ceramic composite. Numerical simulations were applied and a novel model was brought out in this paper. Firstly, four different models for predicting thermal conductivities of unidirectional fiber reinforced materials were compared, which include the Rayleigh,LN,ST and TE model,. It shows that Rayleigh model and LN model have good precision only in low fiber volume content cases. There existed big differences between the experimental and numerical results if predicted the high fiber volume content with either these four models. Then a novel model based on LN model was studied with the correction of the representative volume element method. Further comparison results indicate that the error can be reduced as 55.6% with this novel model. At the same time, the longitudinal (k11) and transverse (k22) thermal conductivities predicted by the novel model were also analyzed. It was found thatk11had a linear relationship with fiber volume fraction and thermal conductivity ratio (p). Butk22had a nonlinear relationship with fiber volume fraction, which increased much greatly when fiber volume fraction increasing at high fiber volume fraction andp>1.

The micromechanics modeling piezoelectric composite materials by method of homogenization Mori Tanaka: study of piezo-composite SiO2/BaTiO3

In this work, the behavior of piezoelectric composite has been studied in terms of prediction, in order to contribute to understanding the piezoelectricity, perroelectricity phenomenon of these materials. The materials with the piezoelectric intrinsic properties have been added fillers to matrix to obtain the piezoelectric composites materials. The Mori-Tanaka model has been used to predict the mechanical behavior, which is part of the electromechanical formulation. The use of Mori-Tanaka model is based on its compatibility with the composites at high fiber volume content. The results from the Mori-Tanaka model have been compared to Voigt and Reuss models. The models have been simulated using programming language to determine stress-strain behavior.

Effect of Process Variables on the Quality of Compression Resin Transfer Molding

Compression resin transfer molding (CRTM), combining resin transfer molding (RTM) and compression molding, have been developed to fabricate fiber reinforced plastic (FRP) components with large dimensions or high fiber volume content. Although a lot of literature on CRTM is available, relatively little useful technical information is present regarding the proper choice of molding conditions for component optimization. The objective of this research is to investigate the effects of process variables, including injection pressure, mold opening distance, resin temperature, compression pressure, pre-heated mold temperature, and cure temperature, on the quality of CRTM products. The influence of these process variables on the part quality are investigated by applying Taguchi’s method. The ultimate stress measured by tensile test serves as an indicator of the part quality. Experimental result show that the compression pressure and the resin temperature are significant variables for improvements in the mechanical properties of the part, while the effect of pre-heated mold temperature on the mechanical properties appears to be trivial.

3211 FBGセンサによる分布計測を用いたVaRTMプロセス・ヘルスモニタリング技術(J06-3 計測・モニタリングII,J06 知的材料・構造システム)

VaRTM (Vacuum assisted Resin Transfer Molding) process is one of the effective composites manufacturing methods for large composites structure such as hull of yacht, wind turbine blade because of its benefits such as saving cost, high fiber volume content, and void free, etc. However, VaRTM has a lot of problems have to prove in order to increase quality of composites structures. In this study, long gauge FBG (fiber Bragg grating) of about 100mm was adapted to monitor resin flow, resin cure and structural health monitoring of composites structure that was fabricated by VaRTM as distributed sensor. Optical Frequency Domain Reflectometory (OFDR) measurement system was also applied in this study. We could conduct process monitoring of VaRTM and structural health monitoring for composites structure manufactured by that successfully.