Viscoelastically generated prestress from ultra-high molecular weight polyethylene fibres

Abstract

The viscoelastic characteristics of ultra-high molecular weight polyethylene (UHMWPE) fibres are investigated, in terms of creep-induced recovery strain and force output, to evaluate their potential for producing a novel form of prestressed composite. Composite production involves subjecting fibres to tensile creep, the applied load being removed before moulding the fibres into a resin matrix. After matrix curing, the viscoelastically strained fibres impart compressive stresses to the surrounding matrix, to produce a viscoelastically prestressed polymeric matrix composite (VPPMC). Previous research has demonstrated that nylon fibre-based VPPMCs can improve mechanical properties without needing to increase mass or section dimensions. The viability of UHMWPE fibre-based VPPMCs is demonstrated through flexural stiffness tests. Compared with control (unstressed) counterparts, these VPPMCs typically show increases of 20-40 % in flexural modulus. Studies on the viscoelastic characteristics indicate that these fibres can release mechanical energy over a long-timescale and fibre core-skin interactions may have an important role.

UHMWPE fibre-based composites: Prestress-induced enhancement of impact properties

“…After releasing an appropriate creep load, UHMWPE fibres have been shown to produce a viscoelastic recovery force; but the force reaches a maximum value followed by a gradual decline in output with time [13]. This is in contrast with equivalent findings from nylon 6,6 fibres, which show a progressive increase in force output with time [21].…”

“…Nevertheless, other researchers have successfully demonstrated VPPMCs based on bamboo and, although flexural moduli were increased by only 12%, flexural toughness was improved by 28% [12]. Most recently, we have found increases of 20-40% in flexural modulus from VPPMCs based on ultra-high molecular weight polyethylene (UHMWPE) fibres [13]. This paper reports the first findings from Charpy impact tests on UHMWPE fibre-based VPPMCs and our results lead to a previously unrecognised energy absorption mechanism being identified.…”

“…Materials and moulding procedures were similar to those employed for flexural stiffness evaluation [13] and are summarised here. The UHMWPE fibre was Dyneema SK60, supplied by Goodfellow Cambridge Ltd., UK.…”

“…A bespoke stretching rig [6][7][8]13] was then used to subject the test yarn to a 24 h creep load of 1.3 GPa, whilst the control yarn was positioned (unconstrained) in close proximity for exposure to the same ambient conditions (19.5-21.0°C). These were the conditions previously developed for UHMWPE fibre composite production [13].…”

“…We suggested in Ref. [13] that the rise and fall in force output may emanate from two competing mechanisms: this could arise from skin-core interactions within the fibres, caused by differences in viscoelastic properties between skin and core regions.…”