Comparison of several closure approximations for evaluating the thermoelastic properties of an injection molded short-fiber composite (original) (raw)
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2015
ABSTRACT: The accurate prediction of both the elastic properties and the thermal expansion coefficien very important for the precise simulation of such processes as injection molding of short-fiber polymer-m composites. In this work, a two-step homogenization procedure is applied and compared with experim values obtained on a polyarylamide/glass fiber composite for a broad range of temperatures. It is obse that the stiffness averaging version of the model surpasses the compliance averaging variant, especially w it is combined with a precise evaluation of the fourth-order orientation tensor. It is also demonstrated tha orthotropic closure approximations are significantly better than previous ones (linear, quadratic, and hy and than a very recent one. Among the orthotropic closure approximations, the fitted ones lead to accep results, which are very close to those obtained with the experimentally measured fourth-order orient tensor
3D microstructure modeling of long fiber reinforced thermoplastics
Composites Science and Technology, 2014
A novel procedure for the generation of a representative volume element for long fiber reinforced thermoplastics and materials with a similar microstructure is presented here. It is characterized by a maximum fiber aspect ratio of approx. 5000 and a maximum fiber volume fraction up to 25%. The modeling procedure is based on characteristic values describing the microstructure in a statistical sense, which are the fiber orientation distribution, the fiber length distribution and the fiber volume content. The resulting mesh for finite element analysis represents the microstructure with a relatively low element count, modeling each fiber only by a single element per cross section. Hence, the model is computationally very efficient and allows the analysis of comparably large structures which include the complete fiber length spectrum of the investigated material. The procedure is validated against the elastic properties of three material variants with different fiber volume fractions, incorporating their experimental measured fiber orientation and length distributions.
Prediction of Young’s Modulus for Injection Molded Long Fiber Reinforced Thermoplastics
Journal of Composites Science
In this article, the elastic properties of long-fiber injection-molded thermoplastics (LFTs) are investigated by micro-mechanical approaches including the Halpin-Tsai (HT) model and the Mori-Tanaka model based on Eshelby’s equivalent inclusion (EMT). In the modeling, the elastic properties are calculated by the fiber content, fiber length, and fiber orientation. Several closure approximations for the fourth-order fiber orientation tensor are evaluated by comparing the as-calculated elastic stiffness with that from the original experimental fourth-order tensor. An empirical model was developed to correct the fibers’ aspect ratio in the computation for the actual as-formed LFTs with fiber bundles under high fiber content. After the correction, the analytical predictions had good agreement with the experimental stiffness values from tensile tests on the LFTs. Our analysis shows that it is essential to incorporate the effect of the presence of fiber bundles to accurately predict the com...