Flax FRP Research Articles

Effect of column parameters on flax FRP confined coir fibre reinforced concrete

This paper experimentally investigated various column parameters on axial compressive and flexural behaviour of a new type of FRP-confined concrete, i.e. natural flax fibre reinforced polymer (FFRP)-confined coir fibre reinforced concrete (CFRC), which is termed as FFRP–CFRC. This new composite structure was composed of an outer FFRP jacket and a CFRC core. Under axial compression, the column parameters examined include types of FFRP/CFRC interfacial bond (i.e. naturally and mechanically bonded), confinement (i.e. FFRP tube and wrapped), and specimen end condition (i.e. flat and grinded tube ends) and tube thickness (i.e. 2, 4, and 6 layers). Push-out test was further performed to find out the relationship between bond strength and level of confinement. In addition, the experimental results were compared with predictions obtained from 25 existing strength models. In flexure, the effects of bond on load–deflection response, ultimate load, energy absorption, failure mode, load–slip behaviour and load–strain responses of the composite beams were evaluated. Results showed that in compression, with an increase of tube thickness, the strength, energy absorption capacity and ductility increased remarkably. The ultimate stress and strain of FFRP-wrapped specimen were lower than the tube-confined specimen and the influence of tube end condition on confinement performance cannot be ignored. It was also found that there was a strong link between FFRP/CFRC interfacial bond and the confinement performance, i.e. with an increase of bond strength, the level of confinement reduced noticeably. In flexure, both naturally and mechanically bonded FFRP tube-confined CFRC composite beams exhibited high load carrying capacity, energy absorption and ductility. Slip between the tube and the concrete was eliminated in the mechanically bonded beams without compromising the peak load, compared to the naturally bonded beams.

An investigation of the damage mechanisms and fatigue life diagrams of flax fiber-reinforced polymer laminates

In this paper we investigated the fatigue damage of a unidirectional flax-reinforced epoxy composite using infrared (IR) thermography. Two configurations of flax/epoxy composites layup were studied namely, [0]16 unidirectional ply orientation and [\textpm45]16. The high cycle fatigue strength was determined using a thermographic criterion developed in a previous study. The fatigue limit obtained by the thermographic criterion was confirmed by the results obtained through conventional experimental methods (i.e., Stress level versus Number of cycles to failure). Furthermore, a model for predicting the fatigue life using the IR thermography was evaluated. The model was found to have a good predictive value for the fatigue life. In order to investigate the mechanism of damage initiation in flax/epoxy composites and the damage evolution, during each fatigue test we monitored the crack propagation for a stress level and at different damage stages, a direct correlation between the percentage of cracks and the mean strain was observed.

Experimental Investigation of Flax FRP Tube Confined Coconut Fibre Reinforced Concrete

The compressive and flexural performance of flax fibre reinforced polymer (FFRP) confined coconut fibre reinforced concrete (CFRC) structures were investigated. The mass content of coconut fibre considered was 1% of cement. Eighteen cylinders were tested under uniaxial compression and 12 beams were tested under four-point bending. Test results show that in compression, both FFRP tube and FFRP wrapping confinements enhance the axial compressive strength and ultimate strain of concrete significantly, e.g. the ultimate strength of 4-layer FFRP tube confined CFRC is 94% larger than that of the unconfined CFRC. In flexure, the FFRP tube increases the lateral load bearing capacity and the deflection several times larger than the unconfined concrete columns, e.g. the ultimate lateral load of 4-layer FFRP confined PC and CFRC are 1066% and 946% larger than the corresponding unconfined PC and CFRC specimens. In flexure, coir inclusion can affect the failure mode of the FFRP-CFRC composite structure significantly.

Experimental study of flax FRP tube encased coir fibre reinforced concrete composite column

The use of natural fibres as building materials is benefit to achieve a sustainable construction. This paper reports on an experimental investigation of a composite column consisting of flax fibre reinforced polymer (FFRP) and coir fibre reinforced concrete (CFRC), i.e. FFRP tube encased CFRC (FFRP-CFRC). In this FFRP-CFRC, coir fibre is the reinforcement of the concrete and FFRP tube as formwork provides confinement to the concrete. Uniaxial compression and third-point bending tests were conducted to assess the compression and flexural performance of the composite column. A total of 36 specimens were tested. The test variables were FFRP tube thickness and coir fibre inclusion. The axial stress–strain response, confinement performance, lateral load–displacement response, bond behaviour and failure modes of the composite column were analysed. In addition, the confined concrete compressive strength was predicted using existing strength equations/models and compared with the experimental results. Results indicate that the FFRP-CFRC composite columns using natural fibres have the potential to be axial and flexural structural members.

Behavior and analytical modeling of natural flax fibre-reinforced polymer tube confined plain concrete and coir fibre-reinforced concrete

As reinforcement flax fibre has the potential to replace glass fibre in fibre-reinforced polymer, composite and coir fibre can be used in concrete. To achieve sustainable construction, this study presents an experimental investigation of a flax fibre-reinforced polymer tube as concrete confinement. Results of 24 flax fibre-reinforced polymer tube-confined plain concrete and coir fibre-reinforced concrete cylinders under axial compression are presented. Test results show that both flax fibre-reinforced polymer tube-confined plain concrete and fibre-reinforced concrete offer high axial compressive strength and ductility. A total of 23 existing design- and analysis-oriented models were considered to predict the ultimate axial compressive strength and strain of flax fibre-reinforced polymer tube-confined plain concrete and fibre-reinforced concrete. It was found that a few existing design- and analysis-oriented models predicted the ultimate strengths of all the flax fibre-reinforced polymer tube-confined plain concrete and fibre-reinforced concrete cylinders accurately. However, no strain models considered match the ultimate strains of these specimens. Two new equations are proposed to evaluate the ultimate axial strain of flax fibre-reinforced polymer tube-confined plain concrete and fibre-reinforced concrete.

Evaluation of interfacial shear strength by tensile tests of impregnated flax fiber yarns

Adhesion of flax fibers and polymer matrix as well as mutual bonding of elementary fibers in a technical fiber are among the principal factors governing the mechanical response of flax fiber-reinforced polymer–matrix composites. A method for evaluation of adhesion is proposed based on tension tests of impregnated fiber yarns, with subsequent characterization by optical microscopy of length distribution of fibers pulled out of the yarn fracture surfaces. An elementary probabilistic model is derived relating aspect ratio distribution of the pulled-out fibers to the fiber tensile strength distribution and the effective interfacial shear strength (IFSS). The method was applied to flax fiber/vinylester resin yarns and an estimate of IFSS at 17 MPa was obtained.

Estimation of the tensile strength of an oriented flax fiber-reinforced polymer composite

Unidirectional orientation of natural fibers in a polymer composite ensures the highest efficiency of reinforcement. Flax fiber reinforcement is discontinuous due to limited fiber length and heterogeneous due to the presence of elementary fibers and their bundles. In order to assess the upper limit of tensile strength of such slightly misoriented, nominally UD natural fiber composite, a statistical strength model of continuous UD fiber reinforced composites is applied. It is found that the experimental strength of UD flax composites, produced from rovings or manually aligned fibers, approaches the theoretical limit only at relatively low fiber volume fraction ca. 0.2, being markedly below it at higher fiber content.