Continuous Fibre-reinforced Plastics Research Articles

A model for permeability in fibre-reinforced plastics

Increased use of continuous fibre-reinforced plastics (CoFRP) is being seen in the automotive industry due to their high strength specific properties. The manufacturing process, however, is still expensive due to the number of critical steps and material costs. Cost reduction is being combated by computational modelling of the infiltration and curing processes to predict void formation and other potential defects. The accuracy of these simulations is highly dependent on capturing the presence of the carbon sheets in the mould due to the large differences in permeability between flows parallel and normal to the fibre tows. This work presents a geometry-based method for locally orienting the fibre and thickness direction for 2D extruded CoFRP components. The capabilities of these methods will be presented by comparing the fibre orientation prediction for two geometries (i.e., hat channel and double dome) using three different draping schemes (i.e., 0°, 45°, and 90°) against the results of a validated draping simulation developed in LS-DYNA.

Optimisation of layup type and fibre orientation in continuous-fibre reinforced components via anisotropy analysis

Continuous-fibre-reinforced plastics (CoFRP) have drawn increasing attention as load bearing structures in weight-sensitive applications. Typically, their full potential only unfolds after careful adjustment to load requirements. However, owing to the multitude of adjustable material parameters, determining a robust optimum is still a great challenge, especially when considering multiple load cases. In extension of existing approaches, this work proposes an optimality criterion (OC) based on principal stress analysis for simultaneous optimisation of layup type and fibre orientation in multi-load case scenarios. Three common layups are considered as layup types: quasi-isotropic (QI), bidirectional (BD) and unidirectional (UD) layups. Iterative application of the OC assigns each component region either QI-, BD- or UD-material at optimal orientation. The methodology is demonstrated using two generic geometries and one real-world structure. It is found to reliably allocate beneficial layup types at low computational effort and is thus deemed to facilitate a lean part design under consideration of multiple load cases.

Load-dependent path planning method for 3D printing of continuous fiber reinforced plastics

3D printing, to print continuous fiber reinforced plastics (CFRPs) has advantages of manufacturing complex shape and short production cycle. Due to anisotropic mechanical properties of continuous fibers, the paving direction of the fibers determines the mechanical strengths of the printed CFRPs. In this paper, a novel load-dependent path planning (LPP) method has been proposed to generate printing path for CFRPs, which exactly follows the load transmission path of the parts and could provide higher mechanical properties. A topology optimization method is applied to simplify the original disordered load distribution. In the developed Stress Vector Tracing (SVT) algorithm, the printing paths are generated along the load transmission path with the variable spacing of adjacent paths. The LPP method has been compared with the state-of-the-art printing path planning method for continuous fibers and shown better load-bearing and printability.

The Impact of Draping Effects on the Stiffness and Failure Behavior of Unidirectional Non-Crimp Fabric Fiber Reinforced Composites.

Unidirectional non-crimp fabrics (UD-NCF) are often used to exploit the lightweight potential of continuous fiber reinforced plastics (CoFRP). During the draping process, the UD-NCF fabric can undergo large deformations that alter the local fiber orientation, the local fiber volume content (FVC) and create local fiber waviness. Especially the FVC is affected and has a large impact on the mechanical properties. This impact, resulting from different deformation modes during draping, is in general not considered in composite design processes. To analyze the impact of different draping effects on the mechanical properties and the failure behavior of UD-NCF composites, experimental results of reference laminates are compared to the results of laminates with specifically induced draping effects, such as non-constant FVC and fiber waviness. Furthermore, an analytical model to predict the failure strengths of UD laminates with in-plane waviness is introduced. The resulting stiffness and strength values for different FVC or amplitude to wavelength configurations are presented and discussed. In addition, failure envelopes based on the PUCK failure criterion for each draping effect are derived, which show a clear specific impact on the mechanical properties. The findings suggest that each draping effect leads to a “new fabric” type. Additionally, analytical models are introduced and the experimental results are compared to the predictions. Results indicate that the models provide reliable predictions for each draping effect. Recommendations regarding necessary tests to consider each draping effect are presented. As a further prospect the resulting stiffness and strength values for each draping effect can be used for a more accurate prediction of the structural performance of CoFRP parts.

Simulating Mold Filling in Compression Resin Transfer Molding (CRTM) Using a Three-Dimensional Finite-Volume Formulation

Light-weight structural components are increasingly made of continuous fiber reinforced plastics (CoFRP), but their mass production is still very expensive. Because of its high automation potential, especially the Compression Resin Transfer Molding (CRTM) process gains more and more attention. Numerical mold filling simulations help to optimize this process and can avoid expensive experimental studies. Here, we present a new method to simulate mold filling in CRTM using a full three-dimensional finite-volume (FV) method. In comparison to known finite-element (FE) methods, it contains a compressible two-phase/Volume-of-Fluid description of the air- and resin-phase. This approach is combined with a moving mesh to account for the change of cavity height during the process, which results in a change of fiber volume fractions and thus permeabilities. We verify the method by comparison to analytic solutions of the Darcy equation and to solutions of state-of-the-art mold filling simulation software. The presented method enables CRTM mold filling simulation of complex parts, which is shown in two application examples. Furthermore, this shows the potential of using FV-based tools to simulate mold filling in RTM process variants containing non-constant cavity geometries.

Forming optimisation embedded in a CAE chain to assess and enhance the structural performance of composite components

Virtual process chains (CAE chains) are being increasingly developed to reduce the overall development costs of high-performance continuous fibre reinforced plastics (CoFRP). A current drawback is the need for integrated optimisation methods, which include multiple physical-based simulation steps in an efficient way. The present paper proposes a new two-loop CoFRP optimisation workflow comprising both process and structural simulation. A genetic forming optimisation method features the inner optimisation loop, looking at the process conditions. The resulting fibre orientations and fibre volume fractions are transferred to the structural simulation model. Subsequently, the structural performance is evaluated under consideration of the forming strategy, outlining the outer optimisation loop. The overall optimisation workflow is demonstrated by an automotive reference structure. Its complex geometry makes it challenging to form the textile without inducing manufacturing defects. The results of the optimization workflow show that both process results and structural capability can be considerably improved, if process optimisation is integrated in the composite design process.

Continuous Fiber-Reinforced Plastics and Metal with Integrated Sensor

Continuous Fiber-Reinforced Plastics and Metal with Integrated Sensor

Consistent Simulation of Fibre Reinforced Thermoplastics: Forming Process and FE-Analysis of the Mechanical Behaviour

In the development of continuous fibre-reinforced plastics, the consistent computer-assisted simulation of all the processes involved in the design, production and application is an extremely valuable tool. Especially in the design of fibre-reinforced thermoplastics (TP-FRP) a number of special characteristics have to be taken into account. A new forming simulation program, UFOS-GT, has thus recently been developed at the IKV. UFOS-GT incorporates a new interface between the forming simulation program and a structure simulation program and allows the local mechanical part properties that come into being after the thermoforming process to be taken into consideration at the mechanical design stage. The use of a special kind of volume elements also makes it possible to calculate the non-linear deformation behaviour of these parts under conditions similar to those encountered in practice. This new approach offers a better prediction quality while minimising work for FEA modelling.

Propagation Path of Interlaminar Cracks in Continuous Fiber-Reinforced Plastics under Remote Mode I Loading.

The propagation path of cracks in continuous fiber-reinforced plastics (FRP) under remote mode I loading was studied. Two FRP models are used in the two-dimensional boundary element analysis:the inhomogeneous FRP model which has a laminated structure composed of matrix and fiber, and the three-layered FRP model in which a thin matrix layer is sandwiched between homogenized FRP plates. The matrix stress intensity factors and the non-singular T-stress, Tm, were calculated for a crack parallel to the fiber direction in a matrix layer of these models. When the residual stress in the matrix layer is negligible, Tm is negative for typical FRP composites. For long cracks, the absolute value of Tm for the inhomogeneous FRP model is larger than that for the three-layered FRP model, and the ratio of these values is independent of fiber properties. A crack is predicted to propagate along the centerline of the matrix layer of FRP composites without the matrix residual stress because of a negative Tm value and the sign of the mode II matrix stress intensity factor. The effects of the residual stress, the height of the cracked matrix layer, and the crack length on the crack propagation path were discussed on the basis of the results of the present analysis.

長繊維強化複合材料の層間マトリックスき裂先端の塑性域の簡便評価

長繊維強化複合材料の層間マトリックスき裂先端の塑性域の簡便評価