Effect of Fibre Orientation and Hostile Solutions on Stress Relaxation of Glass/Polyamide Composites.

Paulo Nobre Balbis Dos Reis,Maria Augusta Neto,Ana Martins Amaro

doi:10.3390/polym12010020

Paulo Nobre Balbis Dos Reis, Maria Augusta Neto + Show 1 more

Open Access

https://doi.org/10.3390/polym12010020

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Journal: Polymers	Publication Date: Dec 20, 2019
Citations: 5	License type: CC BY 4.0

Affiliation: University of Beira Interior, University of Coimbra

Abstract

Polyamide creates high-performance composite materials, which are replacing the traditional epoxy composites in several applications. In this context, exposure to hostile environments is expected. On the other hand, due to the viscoelastic nature of the matrix, these composite materials are prone to stress relaxation. Therefore, the stress relaxation behaviour of glass/polyamide 6 composites was studied considering different fibre directions, as well as exposure to NaOH and HCl solutions. Stress relaxation tests on the bending mode were carried out, and the stress recorded during the loading time (7200 s). All tests were characterized by a stress decrease over time, but laminates with higher fibre angles were more prone to stress relaxation. However, exposure to hostile solutions promoted more significant decreases, where the highest stress relaxation was achieved for alkaline environments with values that were three times higher for laminates with fibres at 0° and around one and half times higher for 45° fibre alignments when compared with the control samples. Finally, the Kohlrausch–Williams–Watts (KWW) model showed that it can be used to predict stress relaxation time, due to the accuracy that was obtained between the experimental and theoretical results.

Highlights

Composite materials with a polymeric matrix are becoming very common due to their excellent mechanical properties
Arhant et al [3] studied the replacement of carbon/epoxy composites with carbon/polyamide composites for underwater applications, because thermoset-based composites require high thicknesses and reaching such thicknesses without defects is a challenge
Despite the benefits obtained with polyimide laminates, they can microcrack spontaneously when exposed to hostile environments [4]

Summary

Introduction

Composite materials with a polymeric matrix are becoming very common due to their excellent mechanical properties. For example, is an important engineering plastic, with excellent physical and mechanical properties, that creates high-performance composites [2]. Despite the benefits obtained with polyimide laminates, they can microcrack spontaneously when exposed to hostile environments [4]. Han and Nairn [4], for example, observed that polyimide matrix composites present degradation in toughness when exposed to water and high temperature, with consequent microcracking. Several studies can be found in the literature involving such composites, but many of them analysed their mechanical performance only when exposed to wet environments, seawater and/or high temperatures [4,5,6,7,8,9,10]

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