Strain Rate Dependent Ductile-to-Brittle Transition of Graphite Platelet Reinforced Vinyl Ester Nanocomposites

Brahmananda Pramanik,P Raju Mantena

doi:10.1155/2014/765698

Brahmananda Pramanik, P Raju Mantena

Open Access

https://doi.org/10.1155/2014/765698

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Abstract

In previous research, the fractal dimensions of fractured surfaces of vinyl ester based nanocomposites were estimated applying classical method on 3D digital microscopic images. The fracture energy and fracture toughness were obtained from fractal dimensions. A noteworthy observation, the strain rate dependent ductile-to-brittle transition of vinyl ester based nanocomposites, is reinvestigated in the current study. The candidate materials of xGnP (exfoliated graphite nanoplatelets) reinforced and with additional CTBN (Carboxyl Terminated Butadiene Nitrile) toughened vinyl ester based nanocomposites that are subjected to both quasi-static and high strain rate indirect tensile load using the traditional Brazilian test method. High-strain rate indirect tensile testing is performed with a modified Split-Hopkinson Pressure Bar (SHPB). Pristine vinyl ester shows ductile deformation under quasi-static loading and brittle failure when subjected to high-strain rate loading. This observation reconfirms the previous research findings on strain rate dependent ductile-to-brittle transition of this material system. Investigation of both quasi-static and dynamic indirect tensile test responses show the strain rate effect on the tensile strength and energy absorbing capacity of the candidate materials. Contribution of nanoreinforcement to the tensile properties is reported in this paper.

Highlights

Vinyl ester based composites are mostly considered in applications such as pipelines and chemical storage tanks
The quasi-static indirect tensile stress-strain history for pure vinyl ester, xGnP reinforced, and carboxyl terminated butadiene nitrile (CTBN) toughened samples are shown in Figures 8(a)(i) and 8(b)(i)
It can be observed in Figures 8(a)(ii) and 8(b)(ii) that tensile strength of pure vinyl ester is reduced by the addition of xGnP reinforcement (Figure 8(a)(ii)) and even with CTBN toughening (Figure 8(b)(ii))

Summary

Introduction

Vinyl ester based composites are mostly considered in applications such as pipelines and chemical storage tanks. The vinyl ester molecule features fewer ester groups, exhibits better resistance to water and to some chemicals [1, 2]. The reactive sites in vinyl ester resin are positioned only at the ends of the molecule and it helps in improving the length of molecular chain. This long-chain molecular structure maskes vinyl ester resin somewhat tough and resilient. This candidate material is being considered in ship superstructures which may be subjected to shock waves, impact, and high-strain rate loading

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