Papers by Author: Alan Kin Tak Lau

Abstract: To characterize the thermomechanical response, especially the superelastic behavior of NiTi shape memory alloys (SMAs), the DSC and tensile cycle test of NiTi of different annealing temperature have been presented. There’s no remarkable phase transformation peak, however, the stable tensile cycle curve and maximum dissipated energy have been observed at annealing temperature of 673K.

Abstract: The aim of this study was to put forward a new method to improve the ballistic impact performance of unidirectional plate (UD plate) by adding shell powder into matrix. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR) spectra revealed that modified shell powder was dispersed uniformly in the matrix. The results of ballistic tests and temperature adaptation tests demonstrated that the bulletproof property of modified UD plate was improved about 20%. The heat-resistant temperature was increased approximately 5°C.

Abstract: Although many studies have been conducted in the past few years on the possibility of using carbon nanotube (CNT) to improve the performance of polymer-based materials, some of the results were contradictory and lack of coherence. Thus, the in-depth understanding of CNT composites is required. In this paper, single-walled carbon nanotubes (SWNTs), which were functionalized by sonicating with nitric and sulfuric acids, will be used to fabricate a SWNT/epoxy composite. There are two reasons for functionalizing the SWNTs, they are (i) to improve the dispersion of the SWNTs in polymer, and (ii) to improve the interfacial bonding properties between the SWNTs and polymer matrix. Tensile property test and micro-hardness test will be carried out to examine the mechanical properties of the composites with different SWNT contents. Thermogravimetry Analysis (TGA) will be used to evaluate the thermal properties of the composites. Scanning Electron Microscope (SEM) will also be used to investigate the failure mechanism of the composites after tensile test. A comparison of the composites with functionalized and non-functionalized SWNTs will be given to elaborate the effect of nanotube functionalization.

Abstract: The applications of carbon nanotubes benefit to a wide range of engineering, applied physics and biomaterials areas for their superior mechanical and electrical properties. Recently, coiled carbon nanotube (CCNT) has opened a new alternative to reinforce traditional advanced composites. Their coiled shapes are considered to induce mechanical interlocking between the nanotubes and matrix which result in the enhancement of fracture toughness and mechanical strength of the composites. In this study, nanomechanical properties of CCNT reinforced epoxy composites with varying weight percentages (0, 1, 3, and 5 wt %) of nanotubes were measured by the nanoindentation technique. Hardness and elastic modulus measurement of the composites were conducted.

Abstract: Mechanical properties of nanoclay/epoxy composites (NC) have been studied by various experimental setups in bulk form recently. Creep mechanism of the NC is an important manufacturing criterion for the aircraft industry. In this paper, nanoindentation was employed to investigate the nano-mechanical creep effects on different wt. % of nanoclay contents in epoxy matrix. Creep behaviors of the nanoclay/epoxy composites with different wt. % of nanoclay contents were modeled by the power-law creep equation. Neglecting the temperature effects on creep, the stress exponents of tested composites were estimated.

Abstract: There has been a concern over many years on the usage of existing metallic and ceramicbased biomaterials for implant design and development due to the necessity of conducting operations for patients to remove and maintain implants after they complete their desired functions. Recently, the development of biodegradable polymers like poly(glycolic acid), poly(lactic acid), and their co-polymers etc. have emerged and provided an entirely new concept to tackle this problem as these polymers can be fully or partly degraded or resorbed by the human body, i.e. an extra operation for removing the implants can be avoided, which can highly alleviate the hard feeling of the patients that come from psychological and physiological pressures. Natural fibres have been well recognized as potential micro-reinforcements for the enhancement of mechanical, thermal and structural properties of biodegradable polymer composites, without generating any harmful by-products and adverse effects during their degrading process to the patients. These natural fibers can be mainly classified depending on their origin into two categories; they are (i) plant-based and (ii) animal-based natural fibers, like spider and silkworm silks. Since the last decade, silkworm silks have been used as reinforcements for fabricating biocomposites. However, no comprehensive study, particularly on the correlation between the mechanical properties of the composites, and fiber orientations and configurations has been done to date. In this paper, an in depth study on the mechanical properties of silk/epoxy composites with different fiber contents and orientations, through experimental approach and fractographic examinations will be conducted. Tensile property tests for all silk/epoxy composite samples will be performed. Failure samples will be examined by using scanning electron microscope (SEM) to investigate the failure mechanism of the composites.

Abstract: Aerodynamic surfaces for subsonic flight vehicles are usually designed primarily with the cruise condition in mind. With this objective in mind, the design of these aerodynamic surfaces, which usually exist as airfoils on the vehicles, are in general suboptimal for actual situation because they must be used for takeoff, landing, and maneuver in addition to cruise condition [1]. Therefore, it would be always desirable to design an airfoil with the ability to adapt to its current flow condition and alter its shape to remain the efficiency at any speed. The present paper reports a design of an airfoil with NACA 0012 profile which aims to deform the airfoil shape under the actuation the shape memory alloy (SMA) actuators embedded in it. The SMA actuators design to alter the aerodynamic lift and drag in a subsonic flow. The feasibility of the design is examined and discussed in the light of the change in lift to drag ratio and the power budget of the actuation.

Abstract: In this paper, fiber Bragg grating (FBG) sensor and piezoelectric (PZT) actuator are used to develop a hybrid system for the evaluation of delamination in glass fiber-reinforced epoxy (GF/EP) composite laminates. The surface-bonded PZT actuator generates ultrasonic Lamb wave in the composite laminates, while the FBG sensor, which is embedded in the composite laminates, captures the Lamb wave signal. Wavelet analysis is introduced to extract signal spectrographic characteristics in the time-scale domain appropriately. Since the propagation characteristics of Lamb wave is altered by the existence of damage in the composite laminates, delamination information can be obtained from the received signal. With the assistance of a signal generation and an acquisition system, this methodology enables active sensing and non-destructive evaluation of delamination in the composite laminates. Experiments have been carried out with GF/EP composite beams to examine the feasibility of the proposed detection technique. The acquired and processed Lamb wave signals corresponding to different delamination sizes are compared.

Abstract: Al2O3-TiC composites were fabricated by hot-pressing Cobalt coated powders at low temperature through liquid phase sintering. Cobalt coating layers effectively hinder the growth of grain and harmful reaction between Al2O3 and TiC particles, which would improve the mechanical properties of Al2O3-TiC composites. The hardness decreases with the increase of Co content and the bending strength was enhanced to 782MPa owing to the grain refinement effect of Co phase. The fracture toughness, about 9.23 MPa.m1/2, was measured for the composites containing 3wt% Co sintered at 1550°C. SEM images of fracture surface show that the toughening effect should be attributed to the conversion of fracture mode caused by the Co phase.

Abstract: This paper demonstrates the use of ultrasound (US) indentation technique for estimating the mechanical properties of tissue- mimicking phantom composites. A tissue-mimicking phantom composite is used to simulate two-layer soft tissue in human. Investigation on the mechanical properties of the phantom composites is extremely important for the understanding of the viscoelastic behaviours of soft tissues and the validation of our proposed US indentation system. The hand-held indentation probe embedded with a US transducer and a load cell together with a US pulser/ receiver. The output of the whole indentation process can be illustrated as force-deformation curves. The mechanical properties of the phantom composites can be estimated by analyzing the force-deformation curves using genetic algorithm (GA).