Showing papers by "Kin-tak Lau published in 2017"

Enhancement on mechanical strength of adhesively-bonded composite lap joints at cryogenic environment using coiled carbon nanotubes

Abstract: The hardness, tensile and lap joint shear behaviors of pure epoxy, straight multi-walled carbon nanotube (MWNT)/epoxy and coiled multi-walled carbon nanotube (CCNT)/epoxy adhesives conditioned at room temperature (RT) and cryogenic temperature (CT) were investigated in the present study. Experimental results showed that all adhesives had greater Vickers hardness values, Young's moduli and tensile strengths at CT. The performance of CCNT/epoxy adhesive at CT was outstanding due to the enhancement of mechanical interlocking effect between CCNTs and epoxy at low temperature. This effect led to a greater Vickers hardness value, Young's modulus and lap joint shear strength of this adhesive at CT when compared with MWNT/epoxy type. The result from finite element analysis (FEA) also proved that the contraction of matrix at CT induced additional clamping force onto the surface of nanotubes. Due to the larger surface area of CCNTs, a relatively stronger bonding strength was achieved, and thus, CCNT/epoxy adhesive had better mechanical properties at low temperature condition.

Durability characteristics and property prediction of glass fibre reinforced mixed plastics composites

Abstract: This paper presents an experimental and theoretical studies of the durability of composite materials made from mixed plastic solid waste (PSW) containing high-density polyethylene, low-density polyethylene, polypropylene and short glass fibres (10–30% by weight). The effects of exposure to elevated temperatures, UV radiation and moisture ingression were the main parameters considered. The results showed that the exposure to a temperature of 60 °C or higher weakens the adhesion of the glass fibre due to the softening of the mixed PSW and resulting in reduced mechanical properties. Furthermore, exposure to UV radiation results in the shrinkage of the specimens improving the interfacing bonding whereas exposure to moisture results in the swelling of the specimens weakening the interfacial bonding. Besides, the addition of glass fibre reduces the surface degradation of composites under UV and moisture ingression resulting in higher matrix properties. For design purposes, a single equation based on modified rule of mixture was developed to predict the tensile modulus and strength of these composites by introducing environmental factors accounting the effects of different exposure conditions.

Theoretical analysis on the pullout behavior of carbon nanotube at cryogenic environment with the consideration of thermal residual stress

Abstract: A numerical fiber pullout model tailored for carbon nanotube (CNT) reinforced polymer composites is developed based on some classical models, to evaluate the effect of low temperature environment and other parameters to the stress distribution and stress transfer efficiency in CNT/polymer composites. It is assumed that there are no bonding between CNTs and polymer so only frictional slip occurs in the interface. Results show that the required axial stress to pull out a straight CNT at cryogenic temperature is more than 6 times greater than that required at room temperature. Some other parameters, such as the length of CNT and the modulus of polymer, also influence the stresses in the CNT/polymer model. The model is also applied to coiled carbon nanotubes (CCNTs) which are newly-developed carbon nanotubes with a helical configuration. At cryogenic temperature, a greater stress is required to pull out a CCNT than a straight CNT, especially in the case when the pitch angle of CCNT is less than 60°. Hence, the stress transfer in CCNT/polymer composites is better than that in straight CNT/polymer composites.