Fibre Prestressed Composites: Improvement of Flexural Properties through Fibre Prestressing

Abstract

The effects of fibre prestressing have been investigated on the flexural properties of glass-epoxy composites. Fibre prestressed composites were made by applying and maintaining a known amount of tension on the fibres during the curing process of the epoxy resin. In the next step, bending tests were conducted on a tensile machine using four point bending. In this study the modulus and strength of the fibre prestressed composite increased up to 33%. The experimental data also indicated that there existed a fibre prestressing level at which the flexural properties reached their maximum values. This prestressing level was found to be a function of the curing temperature. A mechanism has been proposed to explain the improvement of the flexural properties by the use of fibre prestressing during the cure process.

Analysis of the tensile behaviour of viscoelastically prestressed polymeric matrix composites

“…For beam-shaped geometries, this elastic prestressing method has been found to increase impact resistance by up to 33%, when compared with unstressed (control) counterparts [1]. A similar increase in flexural stiffness and strength is also reported [2]. Another study [3] indicates that increases of ~25% for tensile strength and ~50% for (tensile) elastic modulus can be achieved.…”

“…Mechanism (iii) relates to an effect proposed by Motahhari and Cameron [2], in that fibres in a prestressed composite can contribute much more effectively to load support. This arises from the ability of taut and straightened fibres to respond 12 instantaneously and more collectively to an applied load.…”

“…The mechanism was proposed for elastically prestressed composites subjected to flexural loads in Ref. [2], and, although a viscoelastically prestressed composite may exhibit some waviness in fibre lay, the fibres are taut and would therefore respond quickly and more collectively to tensile loads, improving mechanical integrity. It should be noted that no significant deviations in fibre alignment (along sample length) could be observed in our composite batches.…”

“…Another study [3] indicates that increases of ~25% for tensile strength and ~50% for (tensile) elastic modulus can be achieved. These improvements, using E-glass fibre in epoxy resin, have been attributed to mechanisms involving compressive stresses within the matrix which (i) impede crack propagation and (ii) reduce composite strain resulting from external tensile and bending loads [1][2][3].…”

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

“…This state of prestress can also be obtained with elastically prestressed PMCs (EPPMCs), the required prestress being produced by maintaining an elastic tensile strain on the fibres whilst the matrix cures. For unidirectional continuous fibre-reinforced composites, improvements in EPPMC mechanical properties [9][10][11] are comparable to those of VPPMCs. In EPPMCs however, fibre length, orientation and spatial distribution are restricted by the application of fibre tension during matrix curing, thereby compromising fibre and mould geometries for more complex situations.…”