On Mechanical Behaviour of Injection Molded Parts Reinforced with Short Fibres in Rounded Corner's Areas
Oldrich Suba, Miroslav Manas
T.Bata University in Zlin, Czech Republic
Czech Republic

Keywords: short fibre, anisotropy, mechanical behaviour

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Short-fibre-reinforced plastics have been used with increasing
frequency, e.g. to reach higher mechanical properties for the final
products. The choice of short-fibre composites yelds some benefits,
but on the other hand, it is accompanied with some problems as well.
Problems are caused by the structure of injection molded parts associated with the distribution and orientation of short fibres. An
investigation was carried out oriented towards the study of the influence of both material anisotropy and geometrical parameters
of shaped rounded corners of plastic parts reinforced with short fibres on the state of stress. The U-shaped rounded corners of injection molded parts have been solved by FEM for various degrees
of material systems. These systems are characterized by volume
concentrations and aspect ratios of fibres.
The analysis of the mechanical behaviour of an injection molded
part has to be developed on two levels: the micro-mechanical and
macro-mechanical. On the micromechanical level it is necessary to
simulate the linearly elastic behaviour of the totally oriented
3D short-fibre structure. This represents finding five independent elastic constants of a monotropic material. Macro-mechanics then
studies the influence of geometrical and structural parameters
of corner's area.It is shown that the result of the injection molding process is an anisotropic product whose mechanical behaviour is considerably different from the clasical type of isotropic solids.
Unlike the unreinforced plastics, fibre composites exhibit secondary
stress phenomena and secondary properties have to be carefully considered when designing reinforced plastic parts.