A model to describe the cyclic anisotropic mechanical behavior of short fiber-reinforced thermoplastics

Abstract

Due to the injection molding process, short fiber-reinforced thermoplastic composites show a complex fiber orientation distribution and, as a consequence, an overall anisotropic mechanical behavior. The monotonic and cyclic mechanical behavior of PolyEtherEtherKetone thermoplastic reinforced with 30wt.% of short carbon fibers was characterized through a series of tests generating various complex loading histories performed at room temperature on samples with various homogeneous and heterogeneous fiber orientation distributions. A three-dimensional model relying on a thermodynamic framework was then developed to represent the anisotropic mechanical behavior of the material, including elastic, viscoelastic and plastic phenomena. The model was implemented into a finite element code to be able to simulate the response of complex parts with a heterogeneous fiber orientation distribution subjected to a heterogeneous loading. Model parameters were identified by applying a robust and original approach relying on a limited number of relevant experiments. The prediction capability of the model was demonstrated by simulating several types of tests not used for the identification, covering a wide range of monotonic and cyclic, homogeneous and heterogeneous, loading conditions, for various simple and complex fiber orientation distributions. In particular, the model is shown to be able to predict the energy dissipated in the material when subjected to cyclic loading.

Fatigue of short carbon fiber reinforced PEEK under compression: Influence of the load ratio and predictions from heat buildup measurements

“…The prediction beyond cycles could be improved by defining a threshold beyond which the fatigue criterion changes or by enriching the energy‐based criterion. To refine the analysis of the heat buildup results and to support the link between heat buildup and fatigue life, it would be necessary (i) to develop a mechanical behavior law able to predict the contributions of the different dissipative phenomena to the total dissipation, as done in by Leveuf et al 1 and Navrátil et al, 29 and/or (ii) to analyze the damage mechanisms, as done by Marco et al 23 for rubber materials for example.…”

“…This limits potential damage accumulation during the heat buildup test. It is assumed that the three regimes correspond to the appearance of different dissipative mechanisms such as viscoelasticity, plasticity, or damage 1,29 . The identification of the regimes for all the conditions tested is presented in Figure 12.…”