View source for Glass Fibre Orientation

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<span style="font-size:1.2em;font-weight:bold;">Glass fibre orientation; see also: [[Fibre Orientation|Fibre orientation]] </span>
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==General==

The orientation of short glass fibres is of essential importance for the design and dimensioning of [[Plastic Component|plastic components]], as, alongside fibre geometry – specifically the aspect ratio (''l''/''d'') – and the fibre volume fraction, it has a significant influence on the stiffness, strength and deformation behaviour, as well as on the [[Processing Shrinkage|processing shrinkage]] and warping of the components [1].

==Layer structure in injection moulding of fibre-reinforced plastics==

In the injection moulding process, the filling process within the tool results in a characteristic cross-sectional layer structure, which can vary depending on the distance from the gate and the injection conditions [2, 3]. In the simplest case, the layer structure can be described by a 3-layer model (see also: [[Short-fibre Reinforced Plastics|short-fibre reinforced composites]]) with a core and two edge regions, which can be explained by the flow behaviour within the cavity. In the core region, a virtually constant laminar flow velocity dominates, resulting in a transverse to random orientation of the fibres. Near the edge of the tool, the contact between the melt and the already solidified edge zone results in high shear rates, which, due to the resulting shear forces, create [[Fibre Orientation|fibre orientations]] in the direction of injection ('''Fig. 1''').

[[File:Glass Fibre Orientation Fig-1.jpg]]
{| 
|- valign="top"
|width="50px"|'''Fig. 1''': 
|width="600px" |Fluid flow conditions within the cavity during injection moulding [4]
|}

If one defines a transition zone between transversely and longitudinally oriented layers and takes into account an outer layer that is low in fibres and disoriented, the 3-layer model gives rise to a 7-layer computational model, which can be extended to 9 to 11 layers by including a transition layer from the edge to the highly oriented zone ('''Fig. 2'''). 

[[File:Glass Fibre Orientation Fig-2.jpg]]
{| 
|- valign="top"
|width="50px"|'''Fig. 2''': 
|width="600px" |9-zone layer model of fibre orientation in short-fibre reinforced thermoplastics
|}

==Dimensioning of plastic components==

Provided that the properties of these layers, in particular the [[Fibre Orientation|fibre orientation]] and fibre content (see: [[Ashing Method|ashing method]]), are known, this model can be used for the design and dimensioning of [[Plastic Component|plastic components]] using finite element analysis (FEM) software. A fundamental theoretical determination of fibre orientation is provided by the use of mould flow simulations, e.g. M.Tec Moldflow, Mold Flow Plastic Inside [5] or Autodesk® MoldFlow®, can be calculated in advance and represented as tensors in a property matrix. This calculated data can then be transferred directly to the FEM programs and, together with the local stiffness matrix, is used to determine the dimensions and simulate the [[Fracture Behaviour of Plastics Components|behaviour of the component]] under complex loading conditions.

==Verification of orientation using direct and indirect testing methods==

Regardless of the method used to predict [[Fibre Orientation|fibre orientation]], however, this must be verified experimentally, particularly where dynamic [[Weld Line|weld lines]] are present.

Various indirect and direct testing methods exist for determining fibre orientation, but these are generally relatively time-consuming and costly.

Indirect testing methods include the determination of the [[Elastic Modulus|modulus of elasticity]] in [[Bend Test|bending]] or [[Tensile Test|tensile tests]], or the measurement of the shrinkage force or [[Processing Shrinkage|shrinkage]] (see also: [[Shrinkage Test|shrinkage test]]) using [[Thermal Stress Analysis|thermal stress analysis]] (TSA) or [[Thermal Strain Analysis|thermal strain analysis]] [3, 6]. By determining the [[Stiffness|stiffness]] or shrinkage of test [[Specimen|specimens]] with defined preferred orientations, the fibre orientation can then be determined recursively.

The oldest direct method involves preparing micrographs of the cross-sectional surface of test specimens or using [[Ashing Method|ashed]] and detached fibres, followed by microscopic analysis using light or [[Scanning Electron Microscopy|scanning electron microscopy]]. The fibres are visible on the cross-section as circles or ellipses and can be analysed using image analysis methods [13] with regard to their position (angle of inclination ''Θ'' relative to the normal) and orientation angle ''Φ'' ('''Fig. 3'''), whereby plastic-specific contrast agents must be used to ensure optimal visibility of the [[Phase Boundary Surface|phase boundaries]] between the matrix and the fibre.

[[File:GFO_3.jpg]]
{| 
|- valign="top"
|width="50px"|'''Fig. 3''': 
|width="600px" |Diagram illustrating how to determine fibre orientation from polished images 
|}

Equations (1) to (3) can then be used to calculate the components of the fibre orientation:

{|
|-
|width="20px"|
|width="500px" | <math>a_{x}=sin^{2} \theta \cdot cos^{2} \theta </math>
|width="50px" |(1)
|}

{|
|-
|width="20px"|
|width="500px" | <math>a_{y}=sin^{2} \theta \cdot sin^{2} \theta </math>
|width="50px" |(2)
|}

{|
|-
|width="20px"|
|width="500px" | <math>a_{z}=cos^{2}\theta \!</math>
|width="50px" |(3)
|}

with ''a''<sub>x</sub> + ''a''<sub>y</sub> + ''a''<sub>z</sub> = 1.

More modern testing methods are based on the use of [[Non-destructive Testing (NDT)|non-destructive testing]] techniques such as laser diffractometry [7], X-ray refractometry [8, 9], micro-radiography [10], microwave testing [11] or various [[Ultrasound Testing|ultrasonic testing methods]] [12]. One testing technique that is being used with increasing frequency is X-ray-based µ-computed tomography (CT) [14], which directly provides the orientation tensor that can be used in FEM calculations. The CT represents the dependence of the absorption coefficient ''µ'' on the path of the radiation x through the [[Material & Werkstoff|material]] as a greyscale image. As the absorption coefficient ''µ'' is highly dependent on the [[Density|density]] of the heterogeneous material, information regarding the position and the respective [[Density|density]] can be determined, thereby enabling the reconstruction of the volume and the determination of the [[Fibre Orientation|fibre orientation]] ('''Fig. 4''').

[[File:Glass Fibre Orientation Fig-4.jpg]]
{| 
|- valign="top"
|width="50px"|'''Fig. 4''': 
|width="600px" |Micro-CT analysis of a section of test specimens, showing the corresponding Cartesian coordinate system and the orientation of glass fibres in greyscale and false-colour images, following micro-CT scanning and analysis using VG STUDIO MAX V2.2 software [4]
|} 

==See also==

* [[Fibre Orientation|Fibre orientation]]
* [[Fibre Agglomeration|Fibre agglomeration]]
* [[Anisotropy]]
* [[Multiple Fracture UD Tapes|Multiple fracture UD tapes]]
* [[Short-fibre Reinforced Plastics|Short-fibre reinforced plastics]]
* [[Fibre-reinforced Plastics Fracture Model|Fibre-reinforced plastics fracture model]]
* [[Fibre–Matrix Adhesion|Fibre–Matrix adhesion]]

==References==

{|
|-valign="top"
|[1]
|[[Menges, Georg|Menges, G.]], Geisbüsch, P.: Die Glasfaserorientierung und ihr Einfluß auf die mechanischen Eigenschaften – Eine Abschätzmethode. Colliod Polym. Sci. 260 (1982) 73–81 
|-valign="top"
|[2]
|Hegler, R. P., [[Altstädt,_Volker|Altstädt, V.]], [[Ehrenstein,_Gottfried_W.|Ehrenstein, G. W.]], Mennig, G., Scharschmidt, J., Weber, G.: Einfluss stofflicher Parameter auf die Faserorientierung beim Verarbeiten kurzfaserverstärkter Thermoplaste. Kunststoffe 76 (1986) 766–771 
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|[3]
|Pflamm-Jonas, T.: Auslegung und Dimensionierung von kurzfaserverstärkten Spritzgussbauteilen. Dissertation, Technische Universität Darmstadt, 2001 ([https://www.deutsche-digitale-bibliothek.de/item/72PJZZ2UCX5PASEYADJTUXVRXC5RRGFO?isThumbnailFiltered=true&query=Auslegung+und+Dimensionierung+von+kurzfaserverst%C3%A4rkten+Spritzgussbauteilen&rows=20&offset=0&viewType=list&firstHit=72PJZZ2UCX5PASEYADJTUXVRXC5RRGFO&lastHit=lasthit&hitNumber=1 Dissertation]) (last access on March 19, 2026)
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|[4]
|Illing, T.: Bewertung von mechanischen und thermischen Eigenschaften glasfaserverstärkter Polyamid-Werkstoffe unter besonderer Berücksichtigung des Alterungsverhaltens von Bauteilen in der Automobilindustrie. Dissertation, Martin-Luther-Universität Halle-Wittenberg (2015), Shaker Publishing GmbH, Aachen (2016), (ISBN 978-3-8440-4212-2; see [[AMK-Library]] under B 1-27)
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|[5]
|Lutz, W., Lasko, G., Schmauder, S., Predak, S., Bullinger, O., Gerhard, H., Busse, G.: Spritzgieß-Simulation eines glasfaserverstärkten Formteils mit Bindenaht zur Berechnung von Faserorientierung und resultierenden mechanischen Eigenschaften. 19th Stuttgarter Kunststoff-Kolloquium 2005, Proceedings 4V5
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|[6]
|[[Bierögel, Christian|Bierögel, C.]]: Prüfkörperherstellung. In: [[Grellmann,_Wolfgang|Grellmann, W.]], [[Seidler,_Sabine|Seidler, S.]] (Eds.): Kunststoffprüfung. Carl Hanser, Munich (2025) 4th Edition, pp. 15–37 (ISBN 978-3-446-44718-9; E-Book: ISBN 978-3-446-48105-3; see [[AMK-Library]] under A 23)
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|[7]
|Maurer, C.: Versagensmechanismen von PVD-Beschichtungen auf CFK unter Erosionsverschleiß. Dissertation, RWTH Aachen, 2014 ([https://d-nb.info/1052162061/34 Dissertation]) (last access on March 19, 2026)
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|[8]
|Bullinger, O., Busse, G.: Röntgen-Refraktions-Topographie − Ein zerstörungsfreies Werkzeug zur Charakterisierung von Schädigungen in Kunststoffen. DGZfP DACH-Jahrestagung, Salzburg, Proceedings 2004
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|[9]
|Günzel, S.: Analyse der Schädigungsprozesse in einem kurzglasfaserverstärkten Polyamid unter mechanischer Belastung mittels Röntgenrefraktometrie, Bruchmechanik und Fraktografie. Dissertation, Universität Berlin, 2013
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|[10]
|Bürger, C., Ehrenstein, G. W.: Darstellung verstärkter Kunststoffe mittels RE-Detektor (REM) und Mikroradiografie. Practical Metallography: 43, 4 (2006) 161−183
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|[11]
|Busse, G.: Zerstörungsfreie Kunststoffprüfung. In: [https://www.researchgate.net/profile/Wolfgang-Grellmann Grellmann, W.], Seidler, S. (Hrsg.): Kunststoffprüfung. Carl Hanser, Munich (2025) 4th Edition, pp. 445–509 (ISBN 978-3-446-44718-9; E-Book: ISBN 978-3-446-48105-3; see [[AMK-Library]] under A 23)
|-valign="top"
|[12]
|Reinfurth, M.: Geführte Ultraschallwellen zur Bewertung der Schadensakkumulation in Faser-Kunststoff-Verbunden. Dissertation, Universität Stuttgart, 2013 ([https://elib.uni-stuttgart.de/handle/11682/2192 Dissertation]) (Last access on March 19, 2026)
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|[13]
|Beller, T.: Erkennung von Faserorientierungen in Kunststoffen mittels Bildanalyse. DGZfP DACH-Jahrestagung, Bremen, Proceedings 2011
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|[14]
|Kastner, J., Schlotthauer, E., Angermaier, D., Zitzenbacher, G.: Quantitative Messung von Faserlängen und -verteilung in faserverstärkten Kunststoffteilen mittels μ-Röntgen-Computertomographie. DGZfP DACH-Jahrestagung, Konstanz, Proceedings 2007 
|}

[[Category:Morphology and Micromechanics]]