Development and application of micromechanical techniques for characterising interfacial shear strength in fibre-thermoplastic composites

Abstract

a b s t r a c tThe development of single fibre pull-out and microbond tests for characterising interfacial strength in thermoplastic composites is reviewed in detail. Manufacture of an experimental jig and sample preparation regimes for both tests are described. The challenges addressed in the sample preparation include the measurement of embedded fibre length for pull-out samples and the low yield rate of axisymmetric resin droplets obtained during sample preparation under nitrogen. The applications of these laboratory developed techniques are demonstrated by characterisation of the interfacial shear strength (IFSS) of glass fibre-polypropylene (GF-PP) and natural fibre-polylactic acid (NF-PLA). The comparison of the IFSS between neat and modified GF-PP showed that both methods were sensitive to the interfacial performance change despite the poor agreement between them for the absolute IFSS values from the same composite. The effect of the material modification was also reflected in load-displacement curves with different behaviour of the frictional motion after complete debonding. When a high level of fibre-matrix adhesion was realised in the composites with weak fibres, the microbond test showed higher feasibility for characterising the IFSS. This was clearly shown in its application to NF-PLA.

In-situ polymerisation of fully bioresorbable polycaprolactone/phosphate glass fibre composites: In vitro degradation and mechanical properties

“…All the composites exhibited properties which were within the range of the flexural properties of cortical bones (E = 5-23 GPa, σ = 35-280 MPa) [30,31]. It is well known that the strength of the fibre/matrix interface is critical to the mechanical properties of fibre reinforced composites [9,[32][33][34]. Although the molecular weight of the ISP composites was much lower than that of LS composites, the flexural properties of the ISP composites were still significantly higher, which proved that ISP process delivered a significantly enhanced interfacial bonding and adhesion.…”

The usability of recycled carbon fibres in short fibre thermoplastics: interfacial properties

“…Further increases in maleic anhydride content resulted in minimal increases in IFSS, with 8 wt% giving a 225 % increase over the unmodified polymer. The maximum IFSS that the authors achieved was approximately 6.5 MPa, which was extremely low compared to GF.mPP systems (approximately, 25 MPa [15]). A suspected cause for the low interface strength results is polymer degradation, which occurs during droplet formation.…”

“…The method used for producing carbon fibre/ polypropylene microdroplet samples was the same as in [15]. Individual pellets of PP were initially melted on a hot plate at 190°C.…”

“…Weibull analysis was subsequently used to characterise the fibre strength, which is a widely used method for this procedure. The two-parameter model is commonly used for the analysis of brittle fibres [12,15,24], as the three-parameter analysis has been previously been shown to lead to unrealistic results [25]. The general three-parameter model was simplified to a two-parameter model by assuming that the threshold stress, r th , is equal to zero for brittle materials [24] …”

“…Yang and Thomason [15] found that adding 2 wt% of maleic anhydride gave an increase in IFSS of 46 and 111 % for the microbond and single fibre pull-out test, respectively. Jannerfeldt et al [16] also used a 2 wt% addition and found a 27 % increase in IFSS over the unmodified polymer using the microbond test.…”