A validation of the fibre orientation and fibre length attrition prediction for long fibre-reinforced thermoplastics

Abstract

Abstract. To improve the mechanical performance of polymeric parts, fibre reinforcement has established in industrial applications during the last decades. Next to the widely used Short Fibre-reinforced Thermoplastics (SFT) the use of Long Fibre-reinforced Thermoplastics (LFT) is increasingly growing. Especially for non-polar polymeric matrices like polypropylene (PP), longer fibres can significantly improve the mechanical performance. As with every kind of discontinuous fibre reinforcement the fibre orientations (FO) show a high impact on the mechanical properties. On the contrary to SFT where the local fibre length distribution (FLD) can be often neglected, for LFT the FLD show a high impact on the material's properties and has to be taken into account in equal measure to the FOD. Recently numerical models are available in commercial filling simulation software and allow predicting both the local FOD and FLD in LFT parts. The aim of this paper is to compare i.) the FOD results and ii) the FLD results from available orientation-and fibre length attrition-models to those obtained from experimental data. The investigations are conducted by the use of different injection moulded specimens made from long glass fibre reinforced PP. In order to determine the FOD, selected part sections are examined by means of Computed Tomographic (CT) analyses. The fully three dimensional measurement of the FOD is then performed by digital image processing using grey scale correlation. The FLD results are also obtained by using digital image processing after a thermal pyrolytic separation of the polymeric matrix from the fibres. Further the FOD and the FLD are predicted by using a reduced strain closure (RSC) as well as an anisotropic rotary diffusionreduced strain closure model (ARD-RSC) and Phelps-Tucker fibre length attrition model implemented in the commercial filling software Moldflow, Autodesk Inc., San Rafael, CA, USA.

A novel fiber length measurement technique for discontinuous fiber‐reinforced composites: A comparative study with existing methods

“…This mechanism of fiber pull‐out might occur particularly for longer fibers and would explain the increase of residual fiber length in the molded part towards the end of the flow path. While similar trends were reported in other studies , a thorough study is required to understand and explain the observed phenomenon.…”

Isolation of hydrodynamic parameters for the fibre length attrition in injection-moulded short-fibre polymer composites

“…Works dealing with the experimental analysis and modelling of glass FB in injection moulding or extrusion supported this assumption. 2,3,[5][6][7]16,[19][20][21] For this reason, only the diameter in the as-received pellets was measured in this work.…”

“…Many works have dealt with FB of polymer composites processed by injection moulding. 1,2,[5][6][7] Phelps et al's model 6 and its implementation in mould filling simulators, that is Moldflow and Moldex3D, is probably the most relevant approach in this topic. It is a statistical model, which describes the probability of a fibre breaking due to buckling and shearing forces in a flow field.…”

“…Some experimental studies were proposed as validation methods for this model. 5,6 Hopmann et al 5 and Phelps et al 6 validated the model extracting fibres at different positions of centre-gated and fan-gated plates. These studies did not isolate the different parameters promoting FB.…”

The effective thermal conductivity of double-reinforced composites

“…Alternatively one could use a simulation of the intended production process (CFD simulation of polymer melt [21]) to predict a geometry for the system. Such a simulation would respect the influence of the production process on the geometry, but it requires a lot of material properties, and Hopmann [13] showed, that default values provided by typical CFD software packages often yield unsuitable results. The most feasible approach is to choose a suitable (parametrized) distribution for the directions of the fibres and adjust the parameters to the composite geometry.…”