Single fibre pull-out test

Single fibre pull-out test 179 Site energy distribution 47 Skin 124... 

The effect of AAPP treatment on the properties of namral fibre reinforced cellulose acetate butyrate (CAB) composites was then further studied [66]. At a fibre loading fraction of 30 wt%, the storage modulus of the short fibre composites improved by as much as 370% (Fig. 6.4). This is due to the enhanced interfacial adhesion between the fibres and the matrix as a result of AAPP treatment (as measured by single fibre pull-out test) [79], In addition to this, the increment in the mechanical glass transition temperature and a reduction in the height of tan 5 showed better fibre-matrix bonding and fibre-in-matrix distribution. It is evident that AAPP treatment is able to improve the fibre-matrix interface, resulting in composites with improved mechanical properties. 

Chua, P.S. and Piggott, M.R., The glass fibre-polymer interface, I. Theoretical consideration for single fibre pull-out tests. Compos. Sci. TechnoL, 22, 33-42 (1985). 

Figure 3. Schematic diagrams for single fibre pull-out test and specimen for fibre attached on a card-board window.

Penn, L.S. and Lee, S.M., Interpretation of the force trace for Kevlar/epoxy single filament pull-out tests. Fibre Sci. Technol., 17, 91-97 (1985). 

An assumption implicit in most analytical models and pull-out test configurations is that the faces of the crack across which the fibre is bridging are smooth and straight, with single fibres protruding normal to the faces. However, in an actual composite, the situation is much more complex ... 

Bartos [29] also developed a graphical procedure from which the maximum load vs. embedded fibre length curve (Figure 3.16(c) and (d)) can readi ly be constructed on the basis of the results of a single pull-out test, in which the pull-out load vs. displacement is recorded. 

An interpretation of pull-out tests in terms of interfacial shear bond strength values is only feasible when the fibre geometry is constant and well defined along its length. This is usually the case when using single fibres or an array of parallel fibres, which are straight and circular in cross section. The results of such tests will... 

For the pull-out test, a single crystal of Cgo was vapour deposited on high modulus pitch-based carbon fibres (Young s modulus 700 GPa, Tohnen Co. Ltd.) by the above-mentioned method. The fibres have a diameter of 10 m and their surface structure is similar to that of the CNTs. The shear strength of the interface was estimated from the load-displacement (L-D) curve of the pull-out test, which was performed in an Instron-type tensile testing machine (Autograph AGS-D Type 3, Shimadzu) at room temperature with a cross head speed of 0.5 mm/min. 

The fine single crystal grown on a CNT is faceted by 111 planes of the fee stmeture as in the case of a large bulk specimen. The epitaxial orientation relationship of the Csq/CNT interface is reslricted to the parallel direction because of the cylindrical shape of the CNT. The fibre axis of the CNT is observed to be parallel to <110> of the Cso crystal, as shown in Fig. 14.9. In the case of a carbon fibre-Ceo composite, C o crystals of sizes ranging from micrometres to millimetres were formed on the carbon fibre (Fig. 14.10). As shown in Fig. 14.11, the interfacial structure of Ceo/CNT is morphologically similar to that of the Ceo/carbon fibre. The pull-out tests were performed on three specimens in which the carbon fibre axis was parallel to <110> of the Cgo crystal. The L-D curve exhibits a nonlinear behaviour the steps are indicated by arrows from the beginning of the test (Fig. 14.12). The fibre was pulled out immediately once the maximum load was realised. Load fluctuation due to... 

Pull-out load vs. fibre displacement, obtained in a single test. 

I n the case of a short weft knit fabric the structure of the yarns is quite complex (Figure 13.6), making it difficult or impossible to set up a test for characterization of the pull-out of a single yarn from a fabric which is embedded in a cement matrix. However, indirect indication of the influence of the fibre structure on the nature of bonding may be obtained by considering the relative strength efficiency... 

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