Single-Walled Carbon Nanotube-Enhanced Bagasse-Epoxy Hybrid Composites under Varied Low Tensile Strain Rates

Abstract

The production demand of high-performance polymer composites utilizing natural and renewable resources, especially agricultural waste fibres, is rapidly growing. However, these polymers’ mechanical properties are strain rate-dependent due to their viscoelastic nature. Particularly, for natural fibre-reinforced polymer composites (NFPCs), the involvement of fillers has caused rather complex failure mechanisms under different strain rates. Moreover, unevenly and micro-sized bagasse-reinforced polymer composites often cause the formation of micro-cracks and voids in composites. Consequently, the rates of crack initiation and propagation of these composites become extremely sensitive. This, in turn, causes low and unpredictable tensile performance at higher tensile crosshead speeds, even within the low strain rate range. In this study, single-walled carbon nanotubes (SWCNTs) were applied to enhance the bagasse-epoxy composites’ strength. The effects of the weightage in the SWCNT loadings on the composites’ tensile properties were subsequently investigated under low strain rates of 0.0005 s−1, 0.005 s−1 and 0.05 s−1. The composites’ failure shifted to a higher distribution (65.7% improvement, from 37.23 to 61.68 MPa, across strain rates) due to the addition of 0.05% SWCNTs, as indicated in a Weibull distribution plot. The high aspect ratio and strong interface adhesion of SWCNTs in and toward the epoxy matrix contributed significantly to the composites’ strengths. However, a further increase in SWCNT content in the tested composites caused early embrittlement due to agglomeration. The toughness and characteristic strength improved significantly as the strain rate increased. A scanning electron microscopic (SEM) analysis revealed that the SWCNTs’ high aspect ratios and large surface areas improved the interface bonding between the filler and matrix. However, higher SWCNT loadings (0.15% and 0.25%) caused a reverse effect in the same properties of these composites under the same strain rate variations, due to agglomeration. Finally, an empirical relationship was developed to describe the strain rate effect of tensile properties containing 0.05% SWCNT-reinforced bagasse-epoxy composites.

Weibull reliability plots to study the strain rate effect on interfacial strengths of carbon fiber reinforced epoxy composites

“…The Weibull modulus ( m ) values in Figure 9 indicate a moderate decrease for laminate construction type 2 with strain rates. These results are inline with the strain hardening effect reported by Khieng et al [ 22 ]…”

“…The fact that the Weibull statistical analysis revealed a strain rate effect on the Weibull modulus, m, is in agreement with findings reported by Yunfu et al [14] It is generally recognized that strain rate dependency is related to the material ability to redistribute the local maximum stresses under varying strain rate loading conditions. For laminate type 1, Weibull modulus (m) showed slight decrease inline with similar behavior reported by Khieng et al [22] matching strain rate hardening effect of Epoxy material encountered in composite materials.…”

“…Weibull reliability analysis [ 20 ] has been widely applied to composite materials (e.g., References [ 21,22 ] ). The two‐parameter Weibull distribution is given by where, P f is the probability of failure at stress σ , m is the slope of the log–log curve (Weibull modulus), σ 0 is a scale parameter (a normalized stress value), and is the stress distribution (failure stress is reported at probability of failure, P f = 63.1%).…”

“…Weibull reliability analysis [20] has been widely applied to composite materials (e.g., References [21,22] ). The twoparameter Weibull distribution is given by…”