Prediction of anisotropic mechanical properties in injection molded parts of short fiber reinforced thermoplastics
Tsuyoshi NOMURA, Yoshinori INOUE, Takaaki MATSUOKA
Toyota Central R&D Labs, Inc.
JAPAN

Keywords: anisotropic, elastic, orientarion

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Mechanical properties of injection-molded short fiber reinforced thermoplastics (FRTP) are strongly dependent on orientation of the filled fibers. Because the fibers in injection-molded parts are not uniformly oriented, the mechanical properties are also inhomogeneously anisotropic.

To predict anisotropic mechanical properties of FRTP parts, a new fiber orientation analysis method has been developed by using the particle simulation method(PSM). The PSM is a numerical simulation method that uses arrays of spheres to represent fibers. The reduced model for rigid fibers which has a blank area between spheres was also developed to reduce the number of total spheres to represent fibers. The aim of the reduced model is performance of the calculation of a large scale system.

To analyze fiber orientations in all regions of the FRTP parts, we used a small periodically bounded cube which moves along flow. The cube is filled by PSM fiber models in the same volume fraction ratio as the real FRTP parts. The PSM is executed within the cube and the fiber orientation tensor of the region is calculated.

The mechanical properties were calculated by Advani and Tucker's orientation average method. The orientation average method calculates randomly oriented anisotropic properties from unidirectional anisotropic properties and fiber orientation tensor. The unidirectional anisotropic properties were calculated by Halpin-Tsai equation for elastic constants and by Schapery equation for thermal expansion ratio.

We calculated the mechanical properties of an injection-molded FRTP square plate and compared with experimental results. The calculated results were in agreement with the measured ones.