Abstract
In-situ thermoforming and overmolding of continuous fiber-reinforced thermoplastic composites by hybrid injection molding enables the mass production of thermoplastic lightweight structures with a complex geometry. In this study, the anisotropic mechanical behavior of such hybrid injection molded short and continuous fiber-reinforced thermoplastics and the numerical simulation of the resulting mechanical properties under flexural loading were investigated. For this, the influence of the volume flow rate between 25 and 100 cm3/s during injection molding of a PP/GF30 short fiber-reinforced overmolding material was studied and showed a strong effect on the fiber orientation but not on the fiber length, as investigated by computer tomography and fiber length analysis. Thus, the resulting anisotropies of the stiffness and strength as well as the strain hardening investigated by tensile testing were considered when the mechanical behavior of a hybrid test structure of short and continuous fiber-reinforced thermoplastic composites was predicted by numerical simulations. For this, a PP/GF60 and PP/GF30 hybrid injection molded test structure was investigated by a numerical workflow with implemented injection molding simulation data. In result, the prediction of the mechanical behavior of the hybrid test structure under flexural loading by numerical simulation was significantly improved, leading to a reduction of the deviation of the numerically predicted and experimentally measured flexural strength from 21% to 9% in comparison to the isotropic material model without the implementation of the injection molding data.
Highlights
IntroductionThe process flow of this technology is comparable to the already implemented process flow of continuous fiber-reinforced thermoplastics consisting of textile fiber components and consist of the heating, hot handling and thermoforming of the TPC with subsequent overmolding in the same mold [8,9]
Short fiber-reinforced thermoplastic composites processed by injection molding show anisotropic mechanical behavior, which is dependent on the local fiber orientation resulting from part design and process parameters
As shown in this study for PP/GF30 test plates, the volume flow rate during injection molding has a significant influence on the fiber orientation of such short fiber-reinforced composites with a higher orientation in flow direction and at lower volume flow rates
Summary
The process flow of this technology is comparable to the already implemented process flow of continuous fiber-reinforced thermoplastics consisting of textile fiber components and consist of the heating, hot handling and thermoforming of the TPC with subsequent overmolding in the same mold [8,9] Typical applications of such thermoplastic lightweight structures are automotive parts with large-scale production [10]. Deviations between the predicted mechanical behavior by the numerical simulations and the experimental results, especially for complex part geometries, are still a problem and can be attributed to imprecise mapping of the local fiber orientation of the overmolding material from the injection molding simulation to the structural analysis [14]. Howcontinuous fiber-reinforced composites with anisotropic but local nearly homogenous ever, such aThus, phenomenological modelling has a limited applicability only to properties
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