Reinforcement Efficiency of Carbon Fiber Composites - A Numerical Study

Long carbon fiber-reinforced thermoplastics (LCFRT) have become popular lightweight automotive materials as they fulfill durability and safety requirements, and the mechanical performance characteristics of carbon fibers are better than those of natural or glass fibers. In practice, a standard shell-core laminate structure is seen in the injection-molded FRT parts. Anisotropic orientation of long fibers intensely influences the improved mechanical properties of an FRT product.

However, when it comes to dealing with higher fiber concentrations and longer fibers, it is difficult to predict the anisotropic orientation. To date, just a few trials have been made to examine the changes of fiber orientation for different fiber composites from a simulation perspective.

Polyamide 6,6 (PA66) and polypropylene (PP) are two polymer matrices that are considered in the current research. The materials of interest are long carbon fiber (LCF)-reinforced thermoplastic composite, including 50 wt% LCF/PA66 and 50 wt% LCF/PP. Figure 1 shows the end-gated plaque of mold filling. The dimensions of plaque were 178 x 178 x 3.175 mm. Unlike the previous technique, the Moldex3D’s model iARD-RPR has only three parameters to exactly predict fiber orientation in injection molding simulations. Figure 2 illustrates the distribution of fiber orientation through the thickness at the center of the Pacific Northwest National Laboratory (PNNL) plaque (Region B, the middle of the plaque) for 50 wt% LCF/PA66 and 50 wt% LCF/PP. On the whole, the iARD-RPR foretelling results matched the experimental data reasonably well.

Illustration of injection molded geometry for the PNNL plaque with three measured regions.

Figure 1. Illustration of injection molded geometry for the PNNL plaque with three measured regions.

A comparison of the 50 wt% LCF/PA66 and 50 wt% LCF/PP composites with the PNNL experimental data and the iARD-RPR curves for orientation components, (a) A11 and (b) A22, through the normalized thickness at Region B measured in the end-gated plaque.

Figure 2. A comparison of the 50 wt% LCF/PA66 and 50 wt% LCF/PP composites with the PNNL experimental data and the iARD-RPR curves for orientation components, (a) A11 and (b) A22, through the normalized thickness at Region B measured in the end-gated plaque.

Digimat-MF (MSC software and e-Xstream engineering), which is a micromechanical material modeling software based on the Mori-Tanaka Mean Field homogenization scheme, was used to determine the mechanical performance of the fiber-reinforced thermoplastic composites. On the basis of the predicted fiber orientation data, Digimat-MF was applied to obtain the flow modulus E1.

As a result, the modulus distribution through the normalized thickness is demonstrated in Figure 3. A further comparison of modulus E1 was made to show that 50 wt% LCF/PA66 is greater than 50 wt% LCF/PP. The value of the thickness-averaged modulus E1 is listed in Table 1, and compared with the experimental data. Approximately, the predicted E1 value is satisfied. When the same fiber concentration of 50 wt% LCFs was added, the reinforcing performance for the PA66 composite was found to be more effective than the PP composite, as demonstrated in Figure 4.

The predicted tensile moduli E1 distribution through the normalized thickness at Region B measured in the end-gated plaque for various fiber composites, 50 wt% LCF/PP and 50 wt% LCF/PA66.

Figure 3. The predicted tensile moduli E1 distribution through the normalized thickness at Region B measured in the end-gated plaque for various fiber composites, 50 wt% LCF/PP and 50 wt% LCF/PA66.

Table 1. The thickness-averaged orientation tensor components (A11 and A22) and tensile moduli (E1) at Region B of the end-gated plaque for different materials with the experimental bulk value of tensile modulus (Eexp).

The thickness-averaged orientation tensor components (A11 and A22) and tensile moduli (E1) at Region B of the end-gated plaque for different materials with the experimental bulk value of tensile modulus (Eexp).

aTaken from Web Page of PlastiComp Technical Data Sheet.

Bar chart of the predictive tensile modulus against various fiber composites with experimental data of pure PP and pure PA66.

Figure 4. Bar chart of the predictive tensile modulus against various fiber composites with experimental data of pure PP and pure PA66.

In brief, an exact prediction of fiber orientation and assurance of structural strength can now be obtained using integrative simulation software from Moldex3D and Digimat-MF computation for actual automotive LCFRT products. Since the complicated geometry of designing high-quality parts necessitates the inclusion of ribs, changes in holes and thickness, as well as various changes in the flow direction; finding how to establish the optimal parameters of the fiber orientation model is a crucial objective for both current and future studies.

This information has been sourced, reviewed and adapted from materials provided by Moldex3D.

For more information on this source, please visit Moldex3D.

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