Jialu Li

A New Method to Determine Fiber Transverse Permeability

Improving manufacturing technology is one of the greatest challenges for the resin transfer molding (RTM) process. Permeability parameters that include in-plane and transverse permeability are important in simulation codes. Especially, through-thickness permeability is a critical parameter in the optimization of complex shaped and thick-sectioned composites. This research work presents a new method based on radial technology to determine transverse permeability. A key difference when compared to other methods is the layout of reinforcement placement. The fabric is wound and placed on the mold. The fluid flows radially into the reinforcement along the through-thickness direction. The new method avoids racetracking, and it is easy to view the flow front. The measurement of through-thickness permeability is translated into an in-plane measurement of radial technique. The through-thickness permeability for woven fabric tape and fiberglass roving is measured. The experiment shows that the width of the sample has no significant influence on transverse permeability.

Influence of thermo-oxidative aging on the impact property of conventional and graphene-based carbon fabric composites

The effects of reinforced structure (three-dimensional braided preform and laminated plain woven fabric) and graphene nanoplatelet-reinforced hierarchical interface on the impact properties of carbon fabric composites after thermo-oxidative aging were investigated. The results indicated that the impact properties decreased with increasing aging time due to the degradation of the matrix and fiber–matrix interface. After exposure to 140℃ for 1200 h, the peak impact force and impact strength retention rates of 3D-braided graphene nanoplatelet-coated carbon fiber-reinforced composite were 13% and 8% higher than those of the laminated composite, respectively. One of the reasons was the graphene nanoplatelet-reinforced gradient interphase may provide an effective shield against interface oxidation, transfer the localized thermal stress, and restrict the movement of the different phase of the materials at the composites interface. Another reason was the integrated structure of the 3D-braided composite can make the fiber bear impact force together although the resin was damaged and the adhesive force between fiber bundles and resin decreased after thermo-oxidative aging. This synergetic reinforcing effect of 3D-braided structure and graphene nanoplatelet-reinforced hierarchical interface provides an easy and effective way to design and improve the thermo-oxidative stability of carbon fiber-reinforced composites.

Effect of thermo-oxidative aging on three-dimensional and four-directional braided carbon fiber/epoxy composite:

An experimental study was performed to investigate the effect of high temperature exposure on flexural properties of the three-dimensional and four-directional braided carbon fiber/epoxy composite and the corresponding neat resin. For this purpose, samples were exposed to 90℃, 120℃, 150℃, and 180℃ (below and above the glass transition temperature of the matrix resin) for various periods of time up to 13 days. The flexural properties combining with Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), weight loss, scanning electron microscope (SEM), and optical microscope analyses were performed on the unaged and aged samples. The results revealed that the thermo-oxidative behavior of the braided composite was significantly different from the neat resin. The flexural strength of the neat resin decreased dramatically due to the oxidation degradation of the sample surface when the aging temperature was equal to its glass transition temperature. The extensive degradations of both the matrix and the fiber/matrix interface, especially for the interface, were responsible for the significant decrease in flexural strength of the braided composite. The flexural strength retention rates of the braided composite were higher than that of the neat resin after exposure to 90℃, 120℃ and 150℃ because the integral structure of the braided composite can make the fiber bear flexural force together although the matrix resin and the fiber/matrix interface had a certain degree of damage after longtime thermo-oxidative aging.

Measurement Research of Parameter on Three-Dimensional Braided Composite Material Preform Surface

This paper describes a new measuring algorithm for three-dimensional (3-D) braided composite materials preform exterior average braided angle based on image texture. In this project, an advanced nonlinear filtered algorithm for image of 3-D braided composite materials preform was developed. The digital signal processor, TMS320C/F240, has been used as a device for the preform exterior image filtering. The nonlinear filter consisted of minimum, median, and maximum filters. The DUAL PORT RAM, TC514256, has been used as image buffer. The proposed implementations achieve more powerful and stable noise reduction than commercial algorithms. In this research we also propose a more effective and rapid system design method and describe the procedure and how to implement our proposed algorithms by using the surface image testing system. A real time preform surface image collecting and filtering system was developed without PC controlling (the FPGA technology and digital signal process were used). To show the effectiveness of the proposed designing scheme, angular power spectrum algorithms were designed and it generated an optimized and portable code using assemble and VC language; then it was downloaded to a PC. It built programs that helped speed up the system so as to produce high quality results in less time. Experimental results show that the proposed method is feasible. The research was appraised by Science & Technology Committee of Tianjin. The appraisal report shows the research is advanced in the world. So far, the research is a new development for 3-D braided composite material preform measuring. It will provide the perfect data for improving artifact technology for 3-D braided composite material preform.

The effect of reinforced structure on thermo-oxidative stability of polymer-matrix composites:

A new concept in improving the thermo-oxidative stability of carbon fiber polymer-matrix composites (CFPMCs) by adopting integral reinforced structure was investigated. Specimens of three-dimensional and four-directional braided carbon fiber/epoxy composites (BC) and laminated plain woven carbon fiber/epoxy composites (LC) were subjected to isothermal aging at 90℃, 120℃, and 150℃ in air circulating ovens for various durations up to 13 days. The process resulted in progressive deterioration of the matrix reins and fiber/matrix interfaces, in the form of chain scissions, weight loss, and fiber/matrix debonding, which significantly led to the decrease of the flexural strength. Besides, the flexural properties’ retention rates of BC were higher than those of LC at the same aging conditions due to the difference of the reinforced structures. On the one hand, LC lost more weight than that of BC because the percentage of fiber ends area exposure to air in LC specimen was three times more than that in BC specimen. On the other hand, the BC specimens can resist the flexural load as an integral structure although the resin was damaged and the adhesive force between fiber bundles and resin decreased after thermo-oxidative aging, and no delamination happened like the LC specimens. Therefore, adopting three-dimensional and four-directional braided preform as the reinforcement of CFPMCs is an effective way to improve their thermo-oxidative stability.

Electromagnetic properties of three-dimensional woven carbon fiber fabric/epoxy composite:

To investigate the reinforcement architectures effect on the electromagnetic wave properties of carbon fiber reinforced polymer composites, three-dimensional (3D) interlock woven fabric/epoxy composites, 3D interlock woven fabric with stuffer warp/epoxy composites, and 3D orthogonal woven fabric/epoxy composites were studied by the free-space measurement system. The results showed that the three types of 3D woven carbon fiber fabric/epoxy composites had a slight difference in electromagnetic wave properties and the absorption was their dominant radar absorption mechanism. The electromagnetic wave absorption properties of the three types of composites were more than 90% (below −10 dB) over the 11.2–18 GHz bandwidth, and more than 60% (below −4 dB) over the 8–12 GHz bandwidth. Compared with unidirectional carbon fiber reinforced plastics, the three kinds of 3D woven carbon fiber fabric/epoxy composites exhibited better electromagnetic wave absorption properties over a broadband frequency range of 8–18 GHz. Therefore, the three kinds of 3D woven composite are expected to be used as radar absorption structures due to their excellent mechanical properties and outstanding absorption capacity. The total electromagnetic interference shielding effectiveness of the three types of 3D carbon fiber woven composites are all larger than 46 dB over the 8–12 GHz bandwidth, which is evidence that the three types of 3D carbon fiber woven composites can be used as excellent shielding materials for electromagnetic interference.

Statistics-based full-scale three-dimensional geometric model and fiber length distribution for carbon fiber needled felt

In this study, the fiber-shift method is presented to generate the three-dimensional geometric model of carbon fiber needled felt, and curved carbon fiber is regarded as beam under pure bending. The finite mixture model is applied to describe the fiber length distribution for the experiments and models. Closed model, open model and cut model are proposed, and cut model is thought to be more close to reality. A series of analytical methods are proposed to investigate the full-scale three-dimensional geometric model. The fiber-length distributions of cut models with different dimensions are obtained. The results show that, with the increasing of border length of cut model, the percentage of carbon fiber been cut is getting smaller, and the average fiber length is increased. In addition, the compression and needling process of pre-needling technique are simulated, and the needling hole obtained by simulation is similar to reality.

Improvement of interlaminar shear strength of 2.5D fabric laminated composites with short-cut web interlayer

Abstract In this study, the short-cut web interlayer and three-dimensional (3D) needle-punched technique were used to improve the interlaminar shear strength (ILSS) of 2.5D fabric laminated composites. The ILSS was measured by the short beam testing method, and the tensile and bending tests were carried out to investigate the in-plane mechanical properties. Observations on microstructure and crack propagation were carried out. The damage mechanisms of different 2.5D fabric laminated composites were analyzed. The results showed that the short-cut web interlayer and 3D needle-punched technique resulted in the improvement of ILSS, and they affected the tensile and bending properties of 2.5D fabric laminated composites.

Influence of fabric architecture and weaving parameter on the thermal conductivities of 3D woven composites

To investigate the effect of fabric architectures and weaving parameters on thermal conductivities of three-dimensional woven composites, the 2.5D angle-interlock woven composites, 2.5D angle-interlock (with warp reinforcement) woven composites, and 3D orthogonal woven composites were prepared. The thermal conductivities of these woven composites were measured by using transient hot-wire method in this study. It was indicated that the thermal conductivities of three-dimensional woven composites showed significant differences due to the distribution of continuous fibers in three-dimensional woven composites with different structures, which could influence the sum fiber content on the cross section of heat flow. More importantly, compared with 2.5D angle-interlock woven composites and 2.5D angle-interlock (with warp reinforcement) woven composites, 3D orthogonal woven composites exhibited better performance in thermal conductivity. Overall, it was concluded that the thermal conductivities of three-dimensional woven composites were influenced by the fabric architectures and weaving parameters, such as the volume fraction, density, and types of fibers. Furthermore, the volume fraction of fibers on the cross section of heat flow was the dominant factor for thermal conductivities of different woven composites.

Multi-Scale Finite Element Analyses of Thermal Conductivities of Three Dimensional Woven Composites

This paper summarizes an extensive experimental and prediction study of thermal conductivities of three-dimensional woven composites (3DWCs). Three kinds of innovative 3D woven architectures are examined, including 2.5D angle-interlock, 2.5D angle-interlock (with warp reinforcement), and 3D orthogonal woven architectures. The differences of thermal behaviors of 3DWCs in plane and out of plane are assessed by using multi-scale finite element analysis. For the validation of models, the thickness direction thermal conductivity of 3DWCs are measured. It is indicated that the predicted results are in good agreement with the experimental results. The effects of weave density and fabric architecture on the distribution of heat flux and temperature have been discussed in this work, which determined the thermal conductivities of 3DWCs. From this study, it can be expected that the need of thermal performance of 3DWCs can obtained according to optimize the weave parameters based on the high designability of 3DWCs.