Papers by Author: Li Min Zhou

Abstract: Composites are getting more and more attention in the usage of major structures on ships owing to many advantages such as high specific strength and rigidity. However, composites are sensitive to impact, which indicates that the load-carrying capacity and stability of composite structures will decrease dramatically even for an invisible impact damage. Hence, a real-time impact monitoring system which has already been applied in aviation industry is important for reliability of ships, which inevitably encounter impacts during their lifetime due to different sources. This paper deals with the realization of an operational processing scheme to monitor the impact on composite structures, and estimate the impact location and load history by power distribution approach and system identification method. A PZT (piezoelectric lead zirconate titanate) sensor network was designed and employed to collect sensing signals for monitoring the impact. In the monitoring process, stress wave signals caused by impact were captured, and used to determine the impacted location and load history. Results demonstrate that the proposed method can be successfully applied in identifying the location and load history of impact on composite structures. The impact identification approach is of great significance for marine applications.

Abstract: Shape memory alloy (SMA) has various application fields due to its shape memory effect and super elasticity. It can also be embedded into other material to produce SMA reinforced composite (SMAC). SMAC is a good candidate to realize structural smart control. In this paper the mechanical properties of SMAC in the plane stress state is investigated based on the theory of mechanics of composite material and the constitutive model expressing the thermo-mechanical behaviors of SMA.

Abstract: Shape memory polymer (SMP) is being used in many engineering fields due to its shape memory effect and the advantages of large recoverable strain, excellent manufacturability, light weight, low cost and bio-degradability. Therefore it is of practical interest to investigate its thermo-mechanical behaviors. In this paper, a numerical simulation method is supposed to simulate the thermo-mechanical behaviors of SMP using the finite element software of MSC Marc, which is good at simulating the thermo-mechanical behaviors of viscous elastic material. The comparisons between the numerical results and the experimental results by Tobushi et al. illustrate the supposed numerical simulation method well describes the thermo-mechanical behaviors of SMP during the thermo-mechanical processes realizing shape memory effect.

Abstract: Shape memory alloy (SMA) can be embedded into a host material to achieve shape control, damage repair and self-adaption. It is well recognized that the applications of SMA composites are highly dependent on the integrity of SMA fiber-matrix interface. However, the interfacial debonding often occurs due to the weak bonding of interface between the SMA wire and its surrounding matrix. Therefore, it is necessary to improve interfacial strength of SMA composites. In present paper, the epoxy resin is functionalized by mixing different amount of silane coupling agent to improve the interfacial adhesion of SMA fiber reinforced epoxy matrix composite. The single fiber pull-out test is carried out to evaluate the interfacial strength and the test results indicate that the interfacial strength of SMA composite is improved significantly as compared to the results from unfunctionalized samples.

Abstract: A well-aligned titania nanotube array grown on titanium sheet was fabricated by an anodization process in hydrofluoric acid-phosphoric acid-ethylene glycol aqueous electrolyte. Electroactive ruthenium oxide was filled into independent titania nanotubes or deposited on the surface of planar titanium sheet by an electrodeposition-oxidation process. Electrochemical capacitances of these well-designed ruthenium oxides were investigated for supercapacitor applications. Accordingly, ruthenium oxide-titania/titanium (RuO2-TiO2/Ti) nanocomposite exhibits a much higher specific capacitance, power and energy density than ruthenium oxide/titanium (RuO2/Ti) in sulphate acid electrolyte. The utilization efficiency of RuO2 is intensively improved by introducing a novel electrode substrate with a nanotube array structure. Such a superior performance of RuO2-TiO2/Ti nanocomposite is ascribed to its highly accessible reaction sites of well-tailored RuO2 on TiO2 nanotubes.

Abstract: Porous barium strontium titanate−titania (BST−TiO2) nanocomposite was developed by the combination of electrochemical anodization and hydrothermal synthesis. Self organized titania nanotube arrays were first fabricated by electrochemical anodization of titanium foil in 0.2 wt.% HF. The as-anodized titania was then used as a template and was subject to a hydrothermal treatment in the solution mixture of barium hydroxide and strontium hydroxide with different molar ratios. Well crystallized barium strontium titanate was developed directly from the titania nanotubes. Annealing was carried out to transform residual amorphous titania to crystallized anatase, resulting in the porous BST−TiO2 nanocomposite. The surface morphology and structure of the nanocomposite were characterized. The photoelectrochemical response of the BST−TiO2 composite was investigated and the photocatalytic property was evaluated through the photo-decomposition of an organic dye solution. The effect of hydrothermal parameters on the surface morphology and the photocatalytic activity of the nanocomposite was studied.

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: Highly-ordered titania nanotube array has been fabricated by a potentiostatic anodization process in acidic fluoride electrolyte. Calcination at high temperature is followed to achieve crystallization from amorphous to anatase phase. The approach of embedding bioactive enzymes inside titania tubule channels has been applied for bioactivation modification of titania/titanium. The electropolymerization process is applied by using conductive pyrrole monomer to achieve surface immobilization of enzymes to improve interfacial connection. Characterizations including field emission scanning electron microscopy, nano-indentation and linear sweep voltammetry measurements have been performed to fully evaluate the surface morphology, nanomechanical and electrochemical properties of this composite. Molecule detection application has been investigated by applying such an enzyme-titania/titanium composite.

Abstract: A numerical study of the static behaviours of composite strip with bifurcated type shape memory alloy pins has been conducted. The case of bifurcated type shape memory alloy pins inserted inside the composite strip around the hole to reinforce the laminate, which was subjected to the axial stress was simulated. The models for stress analysis were established by using ANSYS finite element programme. Two types of shape memory alloy pins were proposed to insert along the through thickness direction of the carbon fibre woven fabric composite strip to induce the clamping force. The pre-tensioned load was applied to the shape memory alloy pins in order to reduce occurrence of delamination in the laminate. Three-dimensional elements and contact elements were used to simulate the contact between the composite laminate and shape memory alloy pin to investigate the stress distribution around the hole in the composite strip. The effect of pre-strain of shape memory alloy on the stresses inside composite was studied. The results show that the stress characteristics of the button-shaped and bifurcated shape memory alloy pin models are similar; however, the stresses for the button-shaped pin model are lower. The tensile and compressive stresses, both in button-shaped and bifurcated pin models, are strongly dependent on the percentage of pre-strain of the shape memory alloy. It is therefore concluded that the shape memory alloy pin method was significantly reduced the stress concentration of the composite strip laminate.

Abstract: Fine nickel powders have been prepared by chemical reduction between nickel acetate and alcohol under solvothermal conditions. The effect of adding surfactant and varying solvent on the particle size of the as-synthesized nickel powders have been explored. SEM, XRD and TG were employed to characterize the size, morphology, crystalline structure and the thermal stability of the as-synthesized nickel powders. It is revealed that the FCC-structured nickel powders are of uniform spherical shape with good crystallinity and thermal stability. Typically, nickel powders with an average size of 300 nm were obtained at 200°C for 8 h using 0.04 mol/L solution of Ni(CH3COO)2·4H2O in n-butyl alcohol under solvothermal conditions.