Andrew Beehag

Resistance welding of carbon fibre reinforced thermoplastic composite using alternative heating element

The focus of this work is the use of a metal mesh as an alternative heating element for the joining of carbon fibre fabric reinforced polyetherimide composite laminate. A more homogeneous temperature distribution was generated by the metal mesh at the bonding surface. Glass fibre fabric reinforced PEI (GF/PEI) was used as an electrical insulator between the heating element and adherend laminates. Experimental results show that the GF/PEI prepreg could effectively prevent current leakage and enlarge the welding area. Welding parameters, such as input power level, welding time and pressure, were optimized according to the results of mechanical and microstructure characterization. Mechanical performance of composite specimens joined using metal mesh, in terms of lap shear strength and Mode I interlaminar fracture toughness, was equivalent to that of compression moulded benchmarks. Fracture surfaces of welded specimens showed mostly cohesive failure or intralaminar failure, indicating that good bonding between the PEI matrix and metal mesh was achieved.

Fire Performance of Flax Laminates and their Hybrids

In the current age of growing environmental awareness, natural fibre composites have gained wide acceptance in various facets of engineering. However, in industries, such as aerospace and mining, their acceptance is primarily dependent on them meeting the stringent fire test requirements. In this paper, symmetric laminates consisting of only glass, glass/flax hybrid and only flax as reinforcements in thermoset matrices were tested for their time to ignition, heat release rate and smoke constituents as per standard ASTM E 1354 in a cone calorimeter. Four fire retardant versions of resin systems, were used in this study. The laminates were manufactured using wet hand-layup technique that was vacuum bagged and cured between hot platens of a hydraulic press. A constant fibre volume fraction of 0.5 for all the laminates was obtained by maintaining a constant laminate thickness of 4mm. The results from the cone calorimeter tests were compared to examine the influence of natural fibres on the fire properties of the laminates. It was observed that the degree of fire retardance in the polyester based composites decreased with the increase in the flax fibre content; however, in the modified urethane composites, flax fibre composites performed better by exhibiting higher ignition time compared to the hybrid and glass fibre composites. Another important observation was that the carbon monoxide emissions during testing decreased with the increase in flax content in the composites, no matter what resin system was used. These preliminary tests suggest that, by judiciously incorporating natural fibres in a synthetic system, a hybrid system could be designed to sustain loads in environments with high fire risks.

Kenaf–polypropylene composites manufactured from blended fiber mats

Experimental investigations were conducted on kenaf–polypropylene composites manufactured from preformed mats consisting of kenaf and polypropylene fibers in a ratio of 1 : 1 in weight to explore the prospects of annual natural plant fibers as reinforcements for polymer–matrix composites. Surface treatments to the comingled kenaf–polypropylene fiber mats were first carried out using different coupling agents to increase the compatibility of the natural fiber and the polypropylene matrix. Kenaf–polypropylene composite laminates were fabricated from the mats via compression molding. Experimental results indicated that, among the coupling agents chosen, maleated polypropylene was the most effective coupling agent to significantly improve the mechanical performance of the composites. Analyses using Fourier transform infrared spectrometer and scanning electron microscopy revealed that maleated polypropylene was able to promote strong adhesion between the kenaf fibers and the polypropylene matrix at their interfaces. The outcomes of the study indicate that the use of the preformed fiber mats in combination with fiber surface modifications makes it possible to efficiently produce natural fiber reinforced composites with excellent mechanical properties.