Advanced Materials Research Vols. 47-50

Abstract: Organic-inorganic hybrid nanoporous materials with silicalite-1 structure were synthesized in one step co-condensation technique and subsequent transformed into solid acid materials. The tetraethoxysilane (TEOS) was used as the primary inorganic silica source with the phenethyltrimethoxysilane (PE) as an organic modifier. The effect of the PE presence in the initial synthesis mixture was studied by varying the molar ratio of PE to TEOS in the range of 0.05 to 0.20. The resulting organic-inorganic hybrid materials were characterized for its crystallinity (X-ray diffraction, XRD), surface morphology (scanning electron microscopy, SEM) and elemental composition (elemental analysis). The degree of chemical interactions between the organic and inorganic phases was determined by Fourier transform infrared spectroscopy (FTIR). The acid strength of the organic-inorganic hybrid solid acid materials was also obtained by titration technique.

Abstract: In this paper, the behaviours of three types of MR fluids under quasi-static loadings in tension mode were investigated. One type of water-based and two types of hydrocarbon-based MR fluids were activated by a magnetic field generated by a coil using a constant value of DC electrical current. Experimental results in terms of stress-strain relationships showed that the MR fluids had distinct unique behaviours during the tension process. A high ratio of solid particles to carrier liquid in the MR fluid is an indication of high magnetic properties. The water-based MR fluid had a relatively large solid-to-liquid ratio. At a given applied current, a significant increase in tensile stress was obtained in this fluid type. On the other hand, the hydrocarbon-based MR fluids had relatively lower solid to liquid ratios, whereby, less increases in tensile stress were obtained. The behaviours of MR fluids were dependent on the relative movement between the solid magnetic particles and the carrier fluid. A complication occurs because, in the presence of a magnetic field, there will be a tendency of the carrier fluid to stick with the magnetic particle

Abstract: In this paper, a stick-slip compensation for the micro-positioning is presented using the statistical rough surface contact model. As for the micro-positioning structure, PZT (lead(Pb) zirconia(Zr) Titanate(Ti)) actuator is used to drive the load for precise positioning with its high resolution incorporating with the PID (Proportional Integral Derivative) control algorithm. Since the stick-slip characteristics for the micro structures are highly nonlinear and complicated, it is necessary to incorporate more detailed stick-slip model for the applications involving the high precision motion control. Thus, the elastic-plastic static friction model is used for the stick-slip compensation considering the elastic-plastic asperity contact in the rough surfaces statistically. Mathematical model of the system for the positioning apparatus was derived from the dynamic behaviors of structural parts. Since the conventional piezoelectric actuator generates the short stroke, a bridge-type flexural hinge mechanism is introduced to amplify the linear motion range. Using the proposed smart structure, simulations under the representative positioning motion were conducted to demonstrate the micro-positioning under the stick-slip friction.

Abstract: A new method to evaluate the relationship between stress intensity factor KI and crack growth rate V of ceramics which is based on Double-Torsion (DT) technique was proposed. Materials were soda-lime glass, glass ceramics and alumina ceramics. Plate type DT specimens were prepared, and rectangular section guide groove was introduced in the upper surface of specimen. As a crack propagation test, a constant loading rate test was performed. Furthermore, a crack growth behavior was monitored by a compliance method. As the results, it was found that the clack growth behavior can be detected with high accuracy by using the proposed method. And it was confirmed that crack growth characteristic over wide range of crack growth rate can be evaluated by single experiment. Furthermore, since the method is based on a simple measurement system, it is considered that the method has a good availability for KI-V evaluation in ceramics.

Abstract: This paper develops one-dimensional and two-dimensional models for bending, coupled bending and extension of isotropic beams/plates with induced strain actuators. The adhesive layer between the actuator and the structure is considered in the Bernoulli-Euler formulation and the results for various models are compared with the uniform strain model which includes the shear lag effects with assumption of a finite thickness of adhesive layer. The reduction in actuation as a result of strain distribution inside the actuator is considered to improve the prediction ability of the existing model based on the Bernoulli-Euler formulation. The FEM model is also developed to study the strain transfer in the beam. Finally, an experimental test employing a macro fiber composite (MFC) actuator is carried out to evaluate the accuracy and limitations of the developed models. The models are in good agreement with the experimental results.

Abstract: Recently, there is interest in triggering shape recovery of shape-memory polymers(SMPs) by novel non-external heating. In this paper, many hard works have been carried out to make SMP induced by solution. The main challenge in the development of such polymer systems is the conversion of solution-induced effects at the molecular level to macroscopic movement of working pieces. This paper presents a systematic study on the effects of solution on the glass transition temperature (Tg). The results reveal that the hydrogen bonding of shape memory polymer (SMP) was aroused by the absorbed solution that significantly reduces Tg of polymer. The mechanism behind it is solution firstly intenerates polymeric materials till the Tg of polymer lowered down to the temperature of ambient, then hydrogen bonding interaction improves the flexibility of polymeric macro-molecular chains. Thus, the shape memory effect (SME) can undergo solution-driven shape recovery. In addition, it provides a new approach that the SMP can be induced by applying non-energy stimulus. The Dynamic Mechanical Analyzer (DMA) results reveal that the modulus of polymer was softened gradually with immersion time increasing. The experimental result is approximate to the theory.

Abstract: In this research permendur (49Fe-49Co-2V) and nickel were used to make a novel bimetal actuator. The actuator consists of a main body and core with energizing coil. The main body of actuator is made of annealed permendur with two magnetostrictive bimetal arms. The magnetostrictive bimetal technique is used to enhance the small displacement of permendur. Static and dynamic behaviors of the actuator are investigated at both, room temperature (RT) and 77 K. The actuator magnified the small displacement of permendur strip (1.8 µm) and large displacement of 9 and 5 µm are achieved at RT and 77 K, respectively when the coil was energized by ± 5 A current. Additionally, it is found that resonance frequency of actuator is 1240 Hz at 77 K and 1125 Hz at RT. Since the stiffness of actuator increases at 77 K, the displacement of actuator is reduced 33-50% when the coil is energized with different amplitudes at cryogenic environments.

Abstract: This study presents the hot embossing micro-forming of the V-groove and micro-lens array on the Au-based bulk metallic glasses (BMGs). The thermal and thermomechanical properties were firstly investigated by using thermomechanical analysis (TMA). Based on the results, the temperature of the hot embossing experiment was set at 177oC. The formability of the Au-based BMGs were evaluated under different embossing pressures and time durations, and the results showed the increasing trend of the forming quality with increasing forming pressure and time. The Au-based BMGs are considered to be promising for micro-electro-mechanical system applications.

Abstract: Flexible polymer heart valves are promising clinical prostheses for replacement of diseased or malfunctioned natural heart valves. However, the flexible polymer leaflets are prone to fatigue fracture, which hinders their practicality in clinical applications. In this study, micro strain sensor (gauge) for strain measurement is designed in the polyurethane (PU) thin film to measure the stress/strain in situ. In our design, the strain gauge is embedded in PU which is different to the commercial strain gauge of sticking to the sample. The metal layer of strain gauge used in this study is gold. The overall size of the designed strain gauge is 1 mm x 1 mm x 0.1 μm and the resistance value was measured to be 200±30Ω. The static test of strain gauge without damp proof shows that gauge sensitivity G was measured to be 4 and 1.8 when strain range is less than 1% and between 1-1.5%, respectively. While, the static test of strain gauge with damp proof shows that gauge sensitivity G was measured to be 2.6 when strain range is less than 1.2%. Dynamic test of strain gauge was also applied in this study.

Abstract: In this study, the microstructure and mechanical properties of 0.63C-12.7Cr martensitic stainless steel during various tempering treatments were investigated. Experimental results demonstrate that finely distributed primary carbides can be observed in 0.63C-12.7Cr martensitic stainless steel. It was also found that the measured hardness of 0.63C-12.7Cr martensitic stainless steel after 300°C tempered treatment for 60 minutes can still reach to 677Hv. The variation of measured hardness was found not significant during tempering treatments (200°C-500°C). Moreover, owing to lower concentration of C and Cr, the matensitic transformation temperature Ms can be increased to 96.4°C comparing to -127°C of SUS440C materials.