Libo Yan

Improving the mechanical properties of natural fibre fabric reinforced epoxy composites by alkali treatment

In this article, three bio-composites, i.e. flax, linen and bamboo fabric reinforced epoxy resin, were manufactured using a vacuum bagging technique. The influence of alkali treatment (with 5 wt% NaOH solution for 30 min) on tensile properties of flax, linen and bamboo single-strand yarns, surface morphology and mechanical properties (with respect to tensile and flexural properties) of the composites were investigated. It was found that the failure mechanism of single-strand fibres under tension consists of fibre breakage and slippage simultaneously. The alkali treatment had a negative effect on the tensile strength and modulus of the flax, linen and bamboo single-strand yarns. However, after the treatment, the tensile and flexural properties of all the composites increased, e.g. the tensile and flexural strength of the treated flax/epoxy composite increased 21.9% and 16.1%, compared to the untreated one. After the treatment in all the composites, the tensile fractured surfaces exhibited an improvement of fibre/epoxy interfacial adhesion.

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.

Dynamic and static properties of flax fibre reinforced polymer tube confined coir fibre reinforced concrete

Flax and coir fibres have the potential to be used as reinforcement in fibre reinforced polymer and concrete, respectively. This study investigates the effect of coir fibre inclusion and flax fibre reinforced polymer thickness on the dynamic and static properties of flax fibre reinforced polymer tube confined coir fibre reinforced concrete. Plain concrete and coir fibre reinforced concrete beams are considered as references. The properties investigated include natural frequencies, dynamic and static modulus of elasticity, Poisson’s ratio, damping ratio, compressive strength, stress–strain behaviour, ductility and confinement effectiveness. Axial compression test revealed that flax fibre reinforced polymer tube confinement significantly increases axial compressive strength and ductility of the confined concrete composite. The increase in compressive strength and structural ductility is directly proportional to an increase in tube thickness. Dynamic test revealed that both coir fibre and flax fibre reinforced polymer tube improve the damping of the structure considerably, thus reducing the effect of dynamic loading on the structural response.

A comparative study of steel reinforced concrete and flax fibre reinforced polymer tube confined coconut fibre reinforced concrete beams

This paper experimentally investigates the flexural behaviour of circular steel rebar-coconut fibre reinforced concrete and flax fibre reinforced polymer tube-confined coconut fibre reinforced concrete composite beams. Conventional steel reinforced concrete beam and flax fibre reinforced polymer tube-confined plain concrete were considered as reference. A total of 18 beams were tested under 4-point bending. For flax fibre reinforced polymer-confined concrete specimens, two different tube thicknesses were used, i.e. 2-layers and 4-layers fabric. The effect of coconut fibre inclusion on the flexural behaviour of steel rebar-coconut fibre reinforced concrete and flax fibre reinforced polymer tube confined coconut fibre reinforced concrete beams were evaluated. In addition, the performance of flax fibre reinforced polymer tube-confined plain concrete and flax fibre reinforced polymer tube-confined coconut fibre reinforced concrete composite beams were compared with steel reinforced concrete and steel rebar-coconut fibre reinforced concrete beams. The test results indicate that coir inclusion slightly increased the load-carrying capacity but significantly enhanced the energy absorption of the steel rebar-coconut fibre reinforced concrete beam, compared to the steel reinforced concrete beam. For both flax fibre reinforced polymer-confined plain concrete and coconut fibre reinforced concrete, an increase in tube thickness provides a larger ultimate load, deflection and ductility of the beams. In comparison with the brittle failure of flax fibre reinforced polymer tube-confined plain concrete, coconut fibre inclusion modified the failure modes of flax fibre reinforced polymer tube-confined coconut fibre reinforced concrete to be ductile. The comparative study showed that 4-layer flax fibre reinforced polymer plain concrete and flax fibre reinforced polymer tube-confined coconut fibre reinforced concrete beams experienced lower deflection, higher ultimate load and higher energy absorption than the steel reinforced concrete beam.

Effect of bond on compressive behaviour of flax fibre reinforced polymer tube–confined coir fibre reinforced concrete

This study investigated the effect of flax fibre reinforced polymer and concrete bond on the compressive behaviour of flax fibre reinforced polymer–confined plain concrete and coir fibre reinforced concrete. Three types of bond were considered, i.e. concrete confined by (1) flax fibre reinforced polymer tube, (2) flax fibre reinforced polymer tube with internal flax fibre reinforced polymer rings and (3) flax fibre reinforced polymer wrapping. They were termed as naturally, mechanically and adhesively bonded, respectively. A total of 18 flax fibre reinforced polymer–confined plain concrete and coir fibre reinforced concrete cylinders were tested under axial compression. The test results indicated that all the three flax fibre reinforced polymer confinements increased the ultimate compressive strength and ductility of the concrete significantly compared to the unconfined concrete. It was found that the type of flax fibre reinforced polymer and concrete bond has a significant effect on the ultimate strength and axial strain of the confined cylinders. The composite cylinder with naturally bonded offered the largest ultimate strength and axial strain. In all cases of flax fibre reinforced polymer–confined coir fibre reinforced concrete, the coir fibre inclusion reduced the numbers and widths of the cracks in the concrete. Additionally, existing confinement stress and strain models were used to predict the experimental results of the confined plain concrete and coir fibre reinforced concrete cylinders.

Flexural and Thermal Properties of Novel Energy Conservation Slotted Reinforced Concrete Beams

Conventional solid reinforced concrete (RC) beams were modified to slotted beams for consideration as thermal insulation structural components. The slotted beam consisted of an outer and an inner beam, respectively, with a slot located near the middle of the beam along its width direction for filling thermal insulation material. Flexural and thermal behavior of the slotted beams were investigated. Three RC reference solid beams and six slotted beams were fabricated and tested under four-point bending tests. The test results indicated that the failure mode of both slotted beams and the solid beams was flexural failure. However, the damage process of the slotted beams was different from that of the solid beams at the final loading stage. The moment curvature analysis indicated that the tensile reinforcement ratio of the outer and inner beams had an important effect on the flexural behavior, especially the ductility of the slotted beams. Thermal study indicated that the heat transfer coefficient of the slotted beam was greatly reduced and the thermal inertia factor increased a lot, compared with the solid beam. In addition, FE simulation results showed that a new frame structure using slotted beams exhibited obvious and attractive thermal insulation property.

On energy absorption capacity, flexural and dynamic properties of flax/epoxy composite tubes

In this study, energy absorption capacity, flexural and dynamic properties of flax fibre reinforced epoxy polymer composite (FFRP) tubes are investigated. The energy absorption capacity of the tubes is investigated under uniaxial compression. Flexural behaviour of the tubes is studied under four-point bending and the dynamic properties (i.e., natural frequency and damping characteristics) are evaluated by impact hammer vibration testing of the tube specimens. The damping characteristics of the tubes are determined by using both a logarithmic decrement curve and the half-peak bandwidth method. The influence of tube laminate thickness and specimen size on the mechanical properties of FFRP tubes is determined. Compressive testing indicates that the FFRP tube provides a specific absorbed energy of 22 J/g, which is close to the conventional metal energy absorption materials, i.e. stainless steel and aluminium tubes. Flexural study shows that the FFRP tube exhibits a brittle failure as similar to that of the FFRP composites in a flat-coupon tension. The load carrying capacity and deflection of the tube increase with an increase in the tube thickness. Impact loading test concludes that an increase in tube thickness leads to a reduction in natural frequency and damping ratio of the tubes. The FFRP tubes have sizedependent dynamic properties, i.e. an increase in tube size increased the natural frequency but reduced the damping ratio of the specimens remarkably. However, all FFRP tubes have high damping ratios, thus reducing the effect of dynamic loading on the structural response. Therefore, this study suggests that FFRP tubes could be used in several structural applications, i.e. in automotive as energy absorbers and in civil infrastructure as poles.

Reliability assessment of confinement models of carbon fiber reinforced polymer-confined concrete

This paper presented a review of 84 confinement strength models developed for predicting the ultimate compressive strength of carbon fiber-reinforced polymer-confined concrete subjected to uniaxial compression. Among these models, 64 design-oriented models and 12 analysis-oriented models were selected and evaluated by a comprehensive database including the experimental results of 1475 carbon fiber-reinforced polymer-confined concrete specimens through three statistical indicators: the mean (μ), the coefficient of determination ( R 2 ) , and the root mean square error (σ) of the predicted ultimate compressive strength f cc * and the experimental ultimate strength f cc . Based on the results of evaluation, 27 design-oriented models were further considered for reliability assessment and structural reliability analysis. Given the performance of strength predictions and the reliability assessment, it was found that for the design purpose, the 27 design-oriented models are reliable for practical predictions of carbon fiber-reinforced polymer-confined concrete structures subjected to uniaxial compression.

Confinement models of GFRP-confined concrete: Statistical analysis and unified stress–strain models

This paper presented a comprehensive assessment of 22 existing stress models and 13 strain models, which were developed for glass fiber reinforced polymer (GFRP)-confined concrete in uniaxial compression. In addition, a reliability evaluation of these stress and strain models was performed. A database including 212 GFRP-confined cylindrical concrete specimens was collected and analyzed to evaluate the performance of these stress and strain models. The accuracy and applicability assessment of these models were carried out by χ 2 test and the Pearson correlation coefficient r, and the Monte Carlo–JC method was used by for the reliability assessment. Based on the evaluation, it was found that the unconfined concrete strength f co is the most important parameter which determines the accuracy of these stress and strain models for GFRP-confined concrete. Most stress and strain models used in this study can predict the ultimate axial strength and strain of the GFRP-confined concrete appropriately, although some scattered points exist for some models. In addition, it was found that all these models satisfy the command of reliability even some models are too conservative. Based on the database, unified stress and strain models were proposed showing better applicability.

Can Plant-Based Natural Flax Replace Basalt and E-Glass for Fiber-Reinforced Polymer Tubular Energy Absorbers? A Comparative Study on Quasi-Static Axial Crushing

Using plant-based natural fibers to substitute glass fibers as reinforcement of composite materials is of particular interest due to their economic, technical, and environmental significance. One potential application of plant-based natural fiber reinforced polymer (FRP) composites is in automotive engineering as crushable energy absorbers. Current study experimentally investigated and compared the energy absorption efficiency of plant-based natural flax, mineral-based basalt, and glass FRP (GFRP) composite tubular energy absorbers subjected to quasi-static axial crushing. The effects of number of flax fabric layer, the use of foam filler and the type of fiber materials on the crashworthiness characteristics, and energy absorption capacities were discussed. In addition, the failure mechanisms of the hollow and foam-filled flax, basalt, and GFRP tubes in quasi-static axial crushing were analyzed and compared. The test results showed that the energy absorption capabilities of both hollow and foam-filled energy absorbers made of flax were superior to the corresponding energy absorbers made of basalt and were close to energy absorbers made of glass. This study, therefore, indicated that flax fiber has the great potential to be suitable replacement of basalt and glass fibers for crushable energy absorber application.