Influence of aggregate and curing regime on the mechanical properties of ultra-high performance fibre reinforced concrete (UHPFRC)

A new generation of concrete, Ultra-high performance fibre reinforced concrete (UHPFRC) has been developed for its outstanding mechanical performance and shows a very promising future in construction applications. In this paper, several possibilities are examined for reducing the price of producing UHPFRC and for bringing UHPFRC away from solely precast applications and onto the construction site as an in situ material. Recycled glass cullet and two types of local natural sand were examined as replacement materials for the more expensive silica sand normally used to produce UHPFRC. In addition, curing of UHPFRC cubes and prisms at 20 degrees C and 90 degrees C has been investigated to determine differences in both mechanical and ductility.

Effect of processing parameters on the mechanical properties of short Kevlar aramid fibre-thermoplastic polyurethane composite

The effect of various processing parameters, such as nip gap, friction ratio and roll temperature, on the tensile properties of short Kevlar aramid fibre-thermoplastic polyurethane composite has been investigated and the tensile and tear fracture surfaces have been characterised using a scanning electron microscope. A nip gap of 0.45 mm, a friction ratio of 1.15 and a roll temperature of 62°C was found to give optimum mechanical properties. Scanning electron microscopy study revealed a higher extent of fibre orientation in the milling direction in the above condition.

Impact properties of glass/plant fibre hybrid laminates

The use of plants fibre reinforced composites has continuously increased during recent years. Their low density, higher environmental friendliness, and reduced cost proved particularly attractive for low-tech applications e.g., in building, automotive and leisure time industry. However, a major limitation to the use of these materials in structural components is unsatisfactory impact performance. An intermediate approach, the production of glass/ plant fibre hybrid laminates, has also been explored, trying to obtain materials with sufficient impact properties, whilst retaining a reduced cost and a substantial environmental gain. A survey is given on some aspects, crucial for the use of glass/plant fibre hybrid laminates in structural components: performance of hybrids when subjected to impact testing; the effect of laminate configuration, manufacturing procedure and fibre treatment on impact properties of the composite. Finally, indications are provided for a suitable selection of plant fibres with minimal extraction damage and sufficient toughness, for introduction in an impact-resistant glass/plant fibre hybrid laminate.

Properties of hemp fibre reinforced concrete composites

This research is concerned with the mechanical and physical properties of hemp fibre reinforced concrete (HFRC). An experimental program was developed based on the statistical method of fractional factors design. The variables for the experimental study were: (1) mixing method; (2) fibre content by weight; (3) aggregate size; and (4) fibre length. Their effects on the compressive and flexural performance of HFRC composites were investigated. The specific gravity and water absorption ratio of HFRC were also studied. The results indicate that the compressive and flexural properties can be modelled using a simple empirical linear expression based on statistical analysis and regression, and that hemp fibre content (by weight) is the critical factor affecting the compressive and flexural properties of HFRC.

The mechanical properties of natural fibre reinforced cementitious composites

This thesis examined the mechanical properties of natural fibre reinforced cementitious composite materials. The results have provided essential data for the design of these composite materials for different applications. The theoretical model developed also allows accurate prediction of composite behaviour under different loading conditions.

High strain rate tensile properties of rapidly cured woven carbon fibre composites

Tensile tests at high speeds corresponding to automotive crash events were conducted to understand the dynamic properties of rapidly cured woven carbon fiber composites. The High Strain Rate (HSR) experiments were conducted on a servo-hydraulic machine at constant velocities up to a maximum of 25 m/s (82 ft/s). Results from HSR tests were compared with the static results to determine the rate sensitivity of the composite. A high speed camera was used to capture the failure at HSR. The tensile properties of rapidly cured laminate were compared to oven cured laminate to justify its productivity while maintaining the desired properties. The methodology used to achieve constant velocity during HSR tests is discussed in detail. The specimen geometry was specially designed to suit the test rig and to achieve high speeds during tests. All the specimens failed with linear elasticity until sudden brittle fracture. The Scanning Electron Microscopy (SEM) images of the fracture zone were used to identify the failure modes observed at static and high strain rates.

Properties of a carbon-fibre composite modified by electrospun poly (vinylidene fluoride)

The interlaminar toughening of a carbon-fibre reinforced composite by incorporation of electrospun polyvinylidene fluoride (PVDF) nanofibrous membranes was explored in this work. The nanofibres were electrospun directly onto commercial pre-impregnated carbon fibre materials under optimised conditions and PVDF was found to primarily crystallise in its β phase polymorphic form. There is strong evidence from DMTA analysis to suggest that a partial miscibility between the amorphous phases of the PVDF nanofibres and the epoxy exists. The improved plastic deformation at the crack tip after inclusion of the nanofibres was directly translated to a 57% increase in the mode II interlaminar fracture toughness (in-plane shear failure). Conversely, the fracture toughness in mode I (opening failure) was slightly lower than the reference by approximately 20%, and the results were interpreted from the complex micromechanisms of failure arising from the changes in polymorphism of the PVDF.

Effects of ultrasonic treatment on wool fibre and fabric properties

The protein structures of wool, treated in fabric form with ultrasonics for different time durations, were analysed by X-ray diffraction (XRD) and Fourier transform infrared (FTIR), in comparison with the wool without ultrasonic treatment. Fabric water absorption and tensile properties were measured in addition to the fibre micro-structure analysis. It is shown that while the ultrasonic treatment had little effect on the fibre crystallinity, some chemical structures in the protein were altered to some extent during the process. Disruption of fibre internal waxy lipids upon ultrasonic treatment provided the fibres with increased water absorption. Protein chains in the macro fibrils were shown to be rearranged to a more regular and less flexible structure, as a result of the ultrasonic treatment. Fabric tensile tests showed an increased tenacity and a reduced extensibility to the ultrasonically treated fabric. Prolonged ultrasonic treatment, however, significantly reduced both fabric tenacity and extensibility.

Effect of fibre, yarn and knitted fabric attributes associated with wool comfort properties

In this replicated experiment, we investigated the comfort properties of single jersey fabrics composed of cashmere in blends with superfine wools of different fibre curvature (crimp) where the fibre diameter of the wool and cashmere were tightly controlled. The 81 fabrics were evaluated using the Wool ComfortMeter (WCM) which has been calibrated using wearer trials of wool knitwear. General linear modelling determined the best prediction models for log10 transformed fabric WCM values using 27 fibre, 16 yarn and 30 fabric attributes. Tighter fabrics were less comfortable. Progressively blending cashmere with wool progressively increased comfort assessment. The WCM was able to detect differences between fabrics which were more supple and springy, thinner and lighter, and were composed of more elastic, uniform and stronger yarns. Together these attributes explained 82% of the variance in WCM value.