Fibre–Matrix Adhesion

Sprachauswahl/Language selection

Dieser Artikel ist auch auf Deutsch verfügbar

A service provided by

Polymer Service GmbH Merseburg
Tel.: +49 3461 30889-50 E-Mail: info@psm-merseburg.de Web: https://www.psm-merseburg.de
Our further education offers: https://www.psm-merseburg.de/weiterbildung
PSM on Wikipedia: https://de.wikipedia.org/wiki/Polymer Service Merseburg

Fibre–Matrix Adhesion

The influence of the fibre–matrix interface is considered significant for strength and toughness properties. Compared to fully bonded fibres, which allow force transfer during mechanical stress, the increase in toughness and strength achievable with non-bonded or only partially bonded fibres is low. With little or no adhesion, less energy is required to detach the fibre and force transfer is not possible due to the absence of interaction at the fibre–matrix interface. Furthermore, with sufficient filler content, the boundary layer leads to local ductility in the adjacent matrix and thus to a reduction in stress concentrations (see: fracture mechanics) [1].

Verification of adhesion

Scanning electron microscope images (SEM images) enable a qualitative assessment of the adhesion of the fibres in the polymer matrix. Figure 1 shows the fracture surface topography (see also: fracture types for plastics) of polypropylene-glass fibre (abbreviation: PP/GF) composites with different adhesion conditions [2].

Fig. 1:

Fracture surface images for evaluating the fracture behaviour of a PP/GF composite with missing (a) and good interfacial adhesion (b); I – fibres not covered by matrix material, II – hole formation due to pulled-out fibres, III – fibre imprint, IV – fibre bonded to the matrix, and V – locally plastically deformed matrix area [2]

Subfigure 1a shows that the fibres are not covered with matrix material (I) and that no plastic deformation can be observed in the area of the fibres and holes (II and III) depending on the matrix properties and the deformation velocity. Subfigure 1b, on the other hand, shows a fracture surface with good interfacial adhesion. Damage initiation (see also: failure analysis – basics) is characterised by the breaking of bonds at the fibre boundary layer (IV), preferably at the fibre ends, and leads to pull-out or fibre fracture with very little matrix deformation in a brittle matrix. In a ductile matrix, the processes of ‘debonding’ and ‘pull-out’ can occur through local plastic flow processes (V), with void formation as the dominant damage mechanisms [1, 3]. Comparable electron microscope images can be found in [1, 4–6].

Figure 2 shows the fibre–matrix adhesion of a polyamide 66/glass fibre composite material as a function of location on the fracture surface.

Fig. 2:

Fracture surface images of polyamide 66/glass fibre composites for investigating fibre–matrix adhesion as a function of location on the fracture surface perpendicular to the surface (a) and at an acute angle to the surface (b) [2]

Preparation of fracture surfaces

If the fracture surface is prepared to check the bonding of the fibres to the matrix, attention must be paid to the location of the specimen. For example, if a crack propagates in a fibre-reinforced plastic, leading to a brittle fracture, brittle material failure (see also: brittle fracture promoting factors) is more likely to occur, especially in thick-walled components. If the crack does not run perpendicular to the surface, i.e. if the direction of crack propagation changes due to geometric features, for example, and runs at an acute angle to the outside near the surface, a peel fracture occurs. Here, the crack propagation speed is reduced, the plastic deformation capacity of the matrix material increases as a result of the transition to a plane stress state, and the fibres are no longer completely separated from the matrix in this area; the material appears to have better fibre--matrix adhesion in this area.

References

[1]	Michler, G. H.: Kunststoff-Mikromechanik – Morphologie, Deformations- und Bruchmechanismen. Carl Hanser, Munich Vienna (1992), (ISBN 3-446-17068-5; see AMK-Library under F 4)
[2]	Kotter, I.; Langer, B.; Bierögel, C.; Grellmann, W.: Technische Kunststoffdiagnostik – Schadensanalyse an Kunststoffbauteilen. In: Pohl, W. (Eds:): Konstruktion, Qualitätssicherung und Schadensanalyse. Conference „Werkstoffprüfung 2007“, November 29–30, 2007, Neu-Ulm, Proceedings, pp. 273–278 (ISBN 978-3-514-00753-6; see AMK-Library under M 14)
[3]	Friedrich, K.: Fractographic analysis of polymer composites. In: Friedrich, K. (Eds.), Application of Fracture Mechanics to Composite Materials. Elsevier Science Publishers B. V., Amsterdam (1989) 425–487 (e-Book: ISBN 978-0-4445-9721-2)
[4]	Michler, G. H.: Electron Microscopy of Polymers. Springer, Berlin Heidelberg (2008) (ISBN 978-3-540-36350-7; see AMK-Library under F 1)
[5]	Michler, G. H., Balta-Calleja, F. J.: Nano- and Micromechanics of Polymers – Structure Modification and Improvement of Properties. Carl Hanser, Munich (2012) (ISBN 3-446-42767-8; see AMK-Library under F 13)
[6]	Sommer, G. S.: Mikromechanische Untersuchungen zur Faser-Matrix-Haftung in Faser-Kunststoff-Verbunden: Einfluss von Härtungsdauer, Feuchtigkeit und Prüfparametern. Technische Universität Dresden, Fakultät Maschinenwesen (2018) (see AMK-Library under C 43)