Nanoindentation of Multifunctional Smart Composites

Abstract

Three multifunctional smart composites for next-generation applications have been studied differently through versatile nanoindentation investigation techniques. They are used in order to determine peculiarities and specific properties for the different composites and to study the charge/matrix, charge/surface, or smart functions interactions. At first, a mapping indentation test was used to check the distribution of hardness and modulus across a large region to examine any non-uniformity due to structural anomalies or changes in properties for a carbon nanotubes (CNTs)-reinforced polypropylene (PP V-2) nanocomposite. This smart composite is suitable to be used in axial impeller fans and the results can be used to improve the process of the composite produced by injection moulding. Secondly, the interfacial properties of the carbon fibre (CF) and the resin were evaluated by a push-out method utilizing the smaller indentation tip to target the individual CF and apply load to measure its displacement under loads. This is useful to evaluate the effectiveness of the surface modification on the CFs, such as sizing. Finally, nanoindentation at different temperatures was used for the probing of the in situ response of smart shape memory polymer composite (SMPC) usable in grabbing devices for aerospace applications. Furthermore, the triggering temperature of the shape memory polymer response can be determined by observing the change of indentations after the heating and cooling cycles.

Keywords: carbon fibre-reinforced composite; interfacial shear strength; nanocomposite; nanoindentation; shape memory polymer.

Figure 1

CNTs-PPV2 plates produced by injection moulding: (a) plates with different thicknesses; (b) an axial impeller fan; and (c) test part in one of the plates.

Figure 2

(a) The disc cut from the mounted composite, (b) specimen and holder for POT, (c) SEM image of the CFs in the CFRP (after POT test).

Figure 3

Shape memory composite sandwich structure.

Figure 4

(a) Scheme of the indenter load versus its displacement during loading and unloading; (b) arrangement of the indenter and the sample on the heating stage in the Micro Materials nano-indentation; (c) schematic of the cone-shaped indenter in a push-out test (POT) setting and a CF after POT.

Figure 5

SEM observation of the CNTs-PPV2 nanocomposite (a) details of CNTs and (b) surface appearance.

Figure 6

The nanohardness (H) and calculated reduced elastic modulus (Er) at the inlet section of the plates, where 0.5, 1.5, and 2.8 mm are the plates’ thicknesses.

Figure 7

(a) Typical indentations and (b) nanohardness and calculated reduced elastic modulus at the centre area of the plates, where 0.5, 1.5, and 2.8 mm are the plates’ thicknesses.

Figure 8

Nanohardness and calculated reduced elastic modulus at the edge area of the plates, where 0.5, 1.5, and 2.8 mm are the plates’ thicknesses (Hardness as circles and Er as triangles).

Figure 9

Nanoindentation test on CFRP: (a) load versus displacement curves for the interface carbon fibre/resin region, the resin and two carbon fibres (CF1 and CF2), and (b) the detailed values of each indentation.

Figure 10

Selected region and the identified CFs in a CFs-reinforced composite (a) before indentation, (b) after indentation.

Figure 11

The loading–unloading vs. displacement curves for different CFs in the CFs-reinforced composite displayed in Figure 10.

Figure 12

Impact of the location of CFs on top of the groove to the POT.

Figure 13

Micro-CT scan views from 3 directions on the shape memory composite.

Figure 14

(a) Load versus displacement at room temperature (RT) with different peak loads (20, 50, 100, 400 mN), and (b) load against displacement curves at different temperatures: RT, 100 °C and 110 °C.

Figure 15

Indentation changes on SMPC: 50, 100, and 400 mN impressions, respectively depicted as 1, 2 and 3, (a) at room temperature; (b) after heating to 110 °C and cooling down; and 100 and 400 mN impressions (c) at room temperature; (d) after heating to 100 °C and cooling down.