On the extent of fracture toughness transfer from 1D/2D nanomodified epoxy matrices to glass fibre composites

Nadiim Domun,Anthony J Kinloch,Homayoun Hadavinia,Tao Zhang,Keith R Paton,Bamber R K Blackman,Cihan Kaboglu,Samireh Vahid,John P Dear

doi:10.1007/s10853-019-04340-8

Abstract

In this study, the effects of adding nanofillers to an epoxy resin (EP) used as a matrix in glass fibre-reinforced plastic (GFRP) composites have been investigated. Both 1D and 2D nanofillers were used, specifically (1) carbon nanotubes (CNTs), (2) few-layer graphene nanoplatelets (GNPs), as well as hybrid combinations of (3) CNTs and boron nitride nanosheets, and (4) GNPs and boron nitride nanotubes (BNNTs). Tensile tests have shown improvements in the transverse stiffness normal to the fibre direction of up to about 25% for the GFRPs using the ‘EP + CNT’ and the ‘EP + BNNT + GNP’ matrices, compared to the composites with the unmodified epoxy (‘EP’). Mode I and mode II fracture toughness tests were conducted using double cantilever beam (DCB) and end-notched flexure (ENF) tests, respectively. In the quasi-static mode I tests, the values of the initiation interlaminar fracture toughness, G_{text{IC}}^{text{C}} , of the GFRP composites showed that the transfer of matrix toughness to the corresponding GFRP composite is greatest for the GFRP composite with the GNPs in the matrix. Here, a coefficient of toughness transfer (CTT), defined as the ratio of mode I initiation interlaminar toughness for the composite to the bulk polymer matrix toughness, of 0.68 was recorded. The highest absolute values of the mode I interlaminar fracture toughness at crack initiation were achieved for the GFRP composites with the epoxy matrix modified with the hybrid combinations of nanofillers. The highest value of the CTT during steady-state crack propagation was ~ 2 for all the different types of GFRPs. Fractographic analysis of the composite surfaces from the DCB and ENF specimens showed that failure was by a combination of cohesive (through the matrix) and interfacial (along the fibre/matrix interface) modes, depending on the type of nanofillers used.

Highlights

Since the 1980s, various types of fillers have been used by many researchers as a secondary reinforcement for toughening fibre-reinforced polymer (FRP) composites in addition to the primary reinforcing fibres [1,2,3]
Incorporation of nanofillers into the epoxy matrix may increase somewhat the value of the E2 modulus of the glass fibre-reinforced plastic (GFRP) composite when using the ‘EP ? carbon nanotubes (CNTs)’ and the ‘EP ? boron nitride nanotubes (BNNTs) ? graphene nanoplatelets (GNPs)’ matrices, with an increase of about 25% being recorded for these GFRP composites, compared to using the neat epoxy (‘EP’)
As noted above, the GFRP composite with the hybrid ‘EP ? boron nitride nanosheets (BNNSs) ? CNT’ matrix had a somewhat lower value of coefficient of toughness transfer (CTT) of 0.65, but gave the maximum value of GCIC 1⁄4 181 Æ 48 J m-2. These results show the transfer of toughness from the matrix, GmIC, to the initiation interlaminar fracture toughness, GCIC, of the GFRP composite is always less than unity

Summary

Introduction

Since the 1980s, various types of fillers have been used by many researchers as a secondary reinforcement for toughening fibre-reinforced polymer (FRP) composites in addition to the primary reinforcing fibres [1,2,3]. The type and volume fraction of filler particles, their size and shape, and the degree of interfacial bonding all play important roles in influencing the extent of these toughening micromechanisms in a given polymer nanocomposite When such polymer nanocomposites are used as the matrices for fibre-reinforced plastic (FRP) composites, it has been shown [13, 14] that the nanofillers can improve the mode I fracture toughness, GmIC, of the polymer matrix but that commensurate increases in the modes I and II interlaminar fracture toughnesses, GCIC and GCIIC, respectively, of the FRP composite may be observed. Quasi-static mode I double cantilever beam (DCB) and mode II end-notched flexure (ENF) delamination tests were conducted, and the extent of transfer of the mode I matrix toughness, GmIC, of the bulk epoxy polymer nanocomposites to the interlaminar fracture toughnesses of the corresponding GFRP composites under both mode I, GCIC, and mode II loadings, GCIIC, has been assessed.

Results of tensile and shear tests

Conclusions

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