_applied sciences_  
_Article_  
Experimental Investigation and Applicability of Multi-Stage Simulations in the Case of a Thick-Walled Injection-Moulded Composite  
[PERSON],*\(\copyright\), [PERSON] and [PERSON]\(\copyright\)  
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them is the Jeffrey model, in which the motion of an infinite fibre in a dilute suspension is examined qualitatively, but the fibre-fibre interaction is not taken into consideration. The other one is the Folgar-Tucker model, which is more adaptable for polymer composites with massive fibre reinforcements, as mechanical interactions between fibres are taken into account [7; 8]. Nowadays, more and more objective theoretical models have been created in the field of fibre orientation during rheology, for example, the RSC (reduced strain closure) model [9], ARD-RSC (anisotropic rotary diffusion and reduced strain closure) model [10] and iARD-RPR (improved anisotropic rotary diffusion and retarding principal rate) model [11]. In commercial injection moulding simulation software, these novel orientation models have been included, such as Autodesk MoldFlow insight (AMI) and Moldex3D. In most programmes, the result is a second-order orientation tensor main diagonal (A\({}_{\text{ij}}\)) in a 3 \(\times\) 3 matrix, with which the orientation condition of the material in a unit area is described. Orientation tensors were first introduced by [PERSON] and [PERSON] [12]. If the flow direction (usually A\({}_{11}\)) is chosen to be the reference direction, it can be determined whether the orientation of the fibres is perpendicular (usually in the core) (A\({}_{11}\) < 0.30) to the flow direction, completely random (A\({}_{11}\) = 0.5) or parallel to the flow direction (usually in the shell layer) (A\({}_{11}\) > 0.7) [13]. Another interpretation of the orientation tensor can be used [14; 15]. If the fibres are perfectly orientated in the flow direction, then the tensor and the fibre orientation represented in Figure 1a are valid, while, if the fibres are only parallel to a certain plane, then planar isotropy occurs (Figure 1b), and if the same amount of fibres is parallel to the three coordinate axes, then the material is isotropic (Figure 1c). Fibre orientation during injection moulding with a sprue gate of a 1.5 mm thick, circular disk from a polycarbonate composite with a 10 wt% short glass fibre (GF) reinforcement was measured with optical microscopy at three different points and compared to the predictions determined with the Moldflow simulation software in a study carried out by [PERSON] and colleagues [16]. During the comparison of the results, it was found that even though a qualitative agreement between the measured and calculated fibre orientation tensor in the flow direction was established, the difference between the actual values was significant. A quantitative agreement was only found at the wall of the mould and in the middle of the core, which may be the result of shear flow behaviour being less capable of being modelled than extensional flow behaviour.