Search

The paper proposes a novel approach to model the in-plane resin flow in deformable thin-walled fiber preforms for liquid composite molding processes. By ignoring the through-thickness flow in large scale thin-walled components, the 3-D resin flow is simplified to an in-plane flow inside the preform by a specialized divergence theorem. Shell kinematics are used to describe the fiber preform deformation, and the compressible flow is modeled in the context of the free surface flow in porous media. For simplicity and efficiency, the normal stretch, which is driven by the internal fluid and applied external pressure, represents the fiber preform expansion and compression. As compared with full 3-D models, the proposed shell model significantly reduces the problem size, while it still represents the primary physical phenomena during the process. The effects of neglecting the through-thickness flow are illustrated in a numerical example that compares the flow for a set of preforms with different thickness. The model is demonstrated from the numerical example of the mold filling in a doubly curved thin-walled fiber preform. Due to the applied vacuum and the consequent resin flow motion, the relevant deformation of the preform is observed. [ABSTRACT FROM AUTHOR]

Abstract CFRP hat-shaped structure is a typical stiffened structure used in aerospace field. In this work, aimed to provide a theoretical basis for manufacturing CFRP hat-shaped structure, the multi physical field coupling model considering influence of mandrel was established. Effect of mandrel on resin flow and fiber compaction during curing process was studied by simulation and experiment. Results showed that temperature and curing degree affected by mandrel can be negligible in hat-shaped structure, and the distribution of temperature and curing degree was relatively homogeneous. However, the behavior of resin flow and fiber compaction during curing process was not uniform. There was a larger gradient among resin flow, pressure, fiber volume fraction and laminate thickness. Presetting a suitable hole in mandrel can effectively improve the uniformity of resin flow and fiber compaction. By simulation analysis and optimization, the acceptable aperture of 11.5–12.5 mm was obtained. Finally, the model and simulation developed in this study was validated by experiment. The reliability coefficient of 93.4–99.6% was obtained, which indicated a good agreement between simulation and experiment. [ABSTRACT FROM AUTHOR]

Liquid composite molding (LCM) includes all composite-manufacturing methods, where the liquid state resin is forced into the dry preformed reinforcement. In this study, numerical simulation of the resin infusion is presented based on a coupled approach involving Boundary Element Method (BEM) and Level Set Method. The method developed can handle stationary and transient flows by solving the Stokes equations. The numerical results on a square packed set of fibers show excellent agreement with the analytical model. The comparison between experimental and simulation results of flow front patterns revealed a fair accordance. [ABSTRACT FROM AUTHOR]

In this paper, the effects of graphene oxide (GO) nanoparticles on glass fiber composite processing by incorporating them into epoxy resin were investigated. GO was synthesized from graphite powder and was mixed with epoxy resin. Three different GO contents of 0.05, 0.1, and 0.2 wt% were used. Epoxy/GO samples were tested for rheology and cure kinetics to evaluate the effects of GO content on important resin infusion processing parameters. The results show that adding GO to neat epoxy resin increased the viscosity and affected the resin cure reaction by reducing the resin gel time. After that, glass fiber composites were prepared using the resin infusion process. Samples with 0.2 wt% GO result in very slow resin infiltration time with premature resin gelation. A 30 % increase in flexural strength and a 21 % increase in flexural modulus are manifested by adding GO as the secondary reinforcement to glass fiber composites. [ABSTRACT FROM AUTHOR]

Liquid Resin Infusion (LRI) processes including VARI and VARTM have received increasing attention in recent years, particularly for infusion of large parts, or for low volume production. This method avoids the need for costly matched metal tooling as used in Resin Transfer Moulding (RTM) and can provide fast infusion if used in combination with flow media. Full material characterisation for LRI analysis requires models for three dimensional fabric permeability as a function of fibre volume content, fabric through-thickness compliance as a function of resin pressure, flow media permeability and resin viscosity. The characterisation of fabric relaxation during infusion is usually determined from cyclic compaction tests on saturated fabrics. This work presents an alternative method to determine the compressibility by using LRI flow simulation and fitting a model to experimental thickness measurements during LRI. The flow media is usually assumed to have isotropic permeability, but this work shows greater simulation accuracy from combining the flow media with separation plies as a combined orthotropic material. The permeability of this combined media can also be determined by fitting the model with simulation to LRI flow measurements. The constitutive models and the finite element solution were validated by simulation of the infusion of a complex aerospace demonstrator part. [ABSTRACT FROM AUTHOR]

Compression resin transfer molding (CRTM) is an effective process for the manufacturing of composite parts with large size and high fiber content, while the existence of open gap, the dynamically changing dimensions of cavity geometry and the deformation of preform during filling process bring great difficulties to the three-dimensional simulation of resin flow in CRTM. In order to develop a convenient and efficient three-dimensional simulation approach for CRTM filling process, a unified mathematical model for resin flow in both open gap and preform is established instead of considering the gap as high permeability preform, then the analysis of the clamping force and stress distribution are presented. In order to avoid direct solving the coupled equations of resin flow and cavity deformation, volume of fluid (VOF) multiphase flow technology and dynamic mesh model are applied to track the resin flow front and update the cavity geometry during filling simulation, respectively. The master-slave element method is used to modify the amount of resin release and ensure the resin mass conservation. The validity of the numerical approach is verified by comparison with analytical and experimental results, three-dimensional simulation examples are also presented. [ABSTRACT FROM AUTHOR]

Vacuum assisted resin transfer molding (VARTM) is one of the important processes to fabricate high performance composites. In this process, resin is drawn into the mold to impregnate the fiber reinforcement to a form composite. A resin distribution layer with high permeability was often introduced on top of the fiber reinforcement to accelerate the filling speed. Due to the difference of the flow resistance in the resin distribution layer and the reinforcement as well as the resulting through thickness transverse flow, the filling flow field is intrinsically three-dimensional. This study developed a two-layer model with two-dimensional formulation to simulate the filling flow of the VARTM process with a resin distribution layer. Two-dimensional flow was considered in each layer and a transverse flow in the thickness direction was estimated between the two layers. Thermal analysis including the transverse convection was also performed to better simulate the temperature distribution. [ABSTRACT FROM AUTHOR]

The soft-mold aided co-curing process which cures the skin part and ribs part simultaneously was introduced for reducing the cost of advanced grid-stiffened composite structure (AGS). The co-curing process for a typical AGS, preformed by the prepreg AS4/3501-6, was simulated by a finite element program incorporated with the user-subroutines 'thermo-chemical' module and the 'chemical-flow' module. The variations of temperature, cure degree, resin pressure and fiber volume fraction of the AGS were predicted. It shows that the uniform distributions of temperature, cure degree and viscosity in the AGS would be disturbed by the unique geometrical pattern of AGS. There is an alternation in distribution of resin pressure at the interface between ribs and skin, and the duration time of resin flow is sensitive to the thickness of the AGS. To obtain a desired AGS, the process parameters of the co-curing process should be determined by the geometry of an AGS and the kinds of resin. [ABSTRACT FROM AUTHOR]

In the autoclave process, resin flow is a primary mechanics for the removing of excess resin and voids entrapped in the laminate and obtaining a uniform and void free composite part. A numerical method was developed to simulate the resin flow in the laminate and the bleeder, and the effects of 'bleeder flow' on the resin flow and fiber compaction were conducted. At the same time, fiber distribution in the cured laminates was investigated by both experiments and simulations for the CF/Epoxy and CF/BMI composites. The data of the experiments and simulations demonstrated that fibers consolidated and reconsolidated in the laminate and it was impacted by the viscosity and gel time of the resin system. Compared to the post study in which only resin flow in the laminate are considered, these results will deepen the understanding of the consolidation process, resin pressure variation and void control during the autoclave process, which is valuable for the study of the performance of composite parts, provided that fiber distribution does affect some properties of composite material. [ABSTRACT FROM AUTHOR]

A multiobjective surrogate-based inverse modeling technique to predict the spatial and temporal pressure distribution numerically during the fabrication of sheet moulding compounds (SMCs) is introduced. Specifically, an isotropic temperature-dependent Newtonian viscosity model of a SMC charge is fitted to experimental measurements via numerical simulations in order to mimic the temporal pressure distribution at two spatial locations simultaneously. The simulations are performed by using the commercial computational fluid dynamics (CFD) code ANSYS CFX-10.0, and the multiobjective surrogate-based fitting procedure proposed is carried out with a hybrid formulation of the NSGA-IIa evolutionary algorithm and the response surface methodology in Matlab. The outcome of the analysis shows the ability of the optimization framework to efficiently reduce the total computational load of the problem. Furthermore, the viscosity model assumed seems to be able to re solve the temporal pressure distribution and the advancing flow front accurately, which can not be said of the spatial pressure distribution. Hence, it is recommended to improve the CFD model proposed in order to better capture the true behaviour of the mould flow. [ABSTRACT FROM AUTHOR]

We tested the hypothesis that compensatory fertilization of Scots pine (Pinus sylvestris L.) stands polluted by the Harjavalta copper-nickel smelter in SW Finland alleviates the stress imposed by metal-contaminated soils. The treatments in the experiment consisted of control, liming, slow-release mineral mixture and stand-specific fertilization, which comprised at least methylene urea and ammonium nitrate. Stress was assessed by needle fluctuating asymmetry (FA) which increases with an increase in developmental instability. Seven years after the treatments, we found pronounced variation in both FA and needle length among study sites (0.5, 2, 4 and 8 km from the smelter) and among treatments. FA increased and needle length decreased with proximity to the pollution source. Variation in FA was independent of tree size (used as index of growth rate in even-age stand); the effects of the treatments on needle length, on the other hand, were expressed only in medium-sized and large trees. Liming best alleviated pollution stress, while the application of a slow-release mineral mixture increased FA by 30%. In pollution-stressed stands FA correlated positively with constitutive resin flow but was independent of volume growth. Our findings suggest that physiological stress (indicated by increase in developmental instability) and tree growth or stand productivity are not directly linked to one another, and that some increase in productivity can be achieved without the alleviation of pollution-induced stress. [ABSTRACT FROM AUTHOR]