Advanced Materials Research Vols. 123-125

Abstract: Demands for improved aerial vehicle performance have led to the increasing use of composite materials. However, the mechanical behavior and failure modes of composites are not characterized as well as metals, and damages may be more difficult to detect. To overcome this, there is a demand to develop a structural health monitoring (SHM) system for composite aerial vehicles. This paper presents the development of sensor integrated composite wing structure, which is an essential part of SHM system. The composite wing structure was manufactured using an autoclave process, and Fiber Bragg Grating (FBG) optical sensor and piezoelectric (PZT) sensor were installed. The optimal number and location of each sensor system are determined based on the experimental results and Finite Element Analysis (FEA). Installation procedures for FBG and PZT sensor system are developed and validated using tension-tension fatigue tests over 106 cycles.

Abstract: This paper outlines an ongoing SHM project called KASHMOS where the damage detection in composite wing structures using multiple sensors is investigated. The test bed is a composite UAV wing section and the ground structural tests are being performed to evaluate developed systems. Different kinds of damage modes in prearranged areas are intentionally induced. Optical fiber sensors, piezo-electric active sensors and Q-switched pulse lasers are utilized for detecting the damage and monitoring the integrity of the wing structure. Strain-based, impedance-based, and ultrasonic-wave-based damage monitoring methods are studied. Although this investigation is based on the ground tests, the operation concepts for the onboard system as well as the ground system are also considered.

Abstract: This paper describes a new delamination detection technique for a composite structure under varying temperature. Guided waves and impedances have the merits of being sensitive to small defects of a structure. However, they can be vulnerable to environmental and operational variations. In reality, structures are subject to various environmental and operational conditions that affect measured guided wave and impedance signals, and these ambient variations can often lead false alarms. To tackle this issue, a data normalization procedure that distinguishes structural damage from undesirable ambient variations, is developed. The overall procedures of the proposed method are (1) the temperature estimation from impedance data using data normalization, (2) the selection of guided wave signals related to the estimated temperature, and (3) damage classification based on generalized extreme value statistics. In order to validate the proposed method, experimental studies under varying temperature are investigated in a composite plate.

Abstract: Fiber reinforced cement based composites was exposed to high temperature conditions for up to 900oC and up to 2 hours and then they checked about their mechanical response and their convenience for ultrasonic wave transmission. Glass and polypropylene chopped fiber composites showed similar results. For low temperatures of exposure up to 300oC only a small variation of strength is appeared and a slight reduction of ultrasonic wave transmission. This is due to a corresponding water evaporation of wet not even hardened paste that is enclosed in small pores of cement composites. At the next stage and for temperature up to 800oC a steep drop of the mechanical strength of cement based composites is appeared. This reduction is accompanied by a corresponding decrease of ultrasonic wave velocity in the exposed specimens. The characteristic appearance of this stage is due to the dehydration process of calcium hydroxide that takes place at the temperature of about 400oC. At a third stage that starts from 800oC a total destruction of composite is appeared due to the decomposition of carbonate aggregates at 900oC. Typical sigmoidal curves were appeared according to temperature exposure, with that of ultrasonic wave transmission to be less steep, reaching values of 30% for an exposure of 900oC for 2 hours, whereas the mechanical strength for this level of exposure was less that 10% of the unexposed one.

Abstract: The TiO2 thin films were coated on the 100 meshes stainless steel 304 (SS304) sieves by using the sol-gel method followed by a thermal treatment at 200oC. The prepared TiO2-coated sieves were then employed to setup a photocatalytic reactor for evaluating their abilities on the degradation of VOCs (volatile organic compounds). The UV lamp was enveloped with a cylinder TiO2-coated sieve and located in the center of the reactor. A VOCs diffusing tube was applied to yield acetone under water bath. The yielded gaseous acetone was enforced to pass through the TiO2-coated sieves and reacted by photocatalytic reaction. Both the inflow gas and off-gas were monitored by a PID (photoionization detector) sensor for calculating the treat efficiencies under various conditions. The results showed that the amorphous structure was observed on the TiO2 films after sol-gel method, whereas the crystalline anatase phase was found after annealing at 200oC. The SEM images showed that the surface morphology of TiO2 coated SS304 sieves was very similar to that of uncoated sieves, demonstrating a good uniformity and thin thickness of the sol-gel coating method derived in this work. It was observed that most volatile acetone (almost 100%) was removed after treated with the designed photocatalytic reactor under a high fed flow rate (0.5- 2.0 l/min). As compared with the control experiments (UV OFF test), the adequate photocatalytic abilities of this developed TiO2 coated sieves were demonstrated. With the advantages of high contacting area with VOCs, low headloss, durable substrate and easy maintenance, the TiO2-coated sieves possessed a high potential for applying on the photocatalytic degradation of indoor air pollutants.

Abstract: The Dye-Sensitized TiO2 thin film fabricated by TiO2 nanoparticles is a novel technology with advantage in low cost, little pollution and simple in manufacturing process. The fiber-shaped reacting sites provide enlarged photo-sensing area of the TiO2 thin films. Natural dye of TCPP was applied to improve the photo absorbability in this study. Besides, a novel plasma surface activation technique employed on the thin film showed well performance compared with previous reports by heating methods. The SEM images demonstrate that the nano-TiO2 composites deposited on the fiber substrate. Degradation of acetone under 365 and 420 nm light irradiation were conducted to evaluate the photocatalytic ability of the TiO2 and TCPP/TiO2 thin films. While TiO2 thin films gel catalyst showed good photocatalytic performance with a high degradation efficiency of 99.9%, only about 80% conversion efficiency was achieved by the TCPP/TiO2 thin films reactor under 365 nm light irradiation. Although the TCPP dye on TiO2 nanoparticle shows beneficial reflection intensity in 420 nm, the acetone degradation capability of TiO2 and TCPP/ TiO2 thin films reactor decreased about 30% and 25% respectively compared with the degradation efficiency under 365 nm.

Abstract: Pd/SDB (Styrene Divinylbenzene Copolymer), a hydrophobic catalyst, has been used for the destruction of volatile organic compounds (VOCs) in wastewater. Although the catalysts performed well in low VOC concentrations, they were not as effective in high VOC concentrations because of the heat removal problem. On the other hand, Pt/Zeolite contains a high silica to alumina ratio, which gives it hydrophobic characteristics and allows it to endure significantly higher temperatures than Pd/SDB. Hence, they were chosen for the treatment of wastewater containing high VOC concentrations. As expected, the catalysts presented both high conversion rates and good stability maintenance. Because of their high stability and rapid regeneration, the catalysts were regarded to be promising for industrial applications. In this study, the noble metal content of Pt/Zeolite amounted to 1.5 wt.%, and that the different temperatures and pressures collocating with different weight hourly space velocity (WHSV) were used to test the VOCs conversion efficiency. The results showed that the best reduction temperature was 450°C below the temperature- programmed reduction (TPR) process. The reaction system consisted of a continuous dripping flow with a fix-bed system and proportional integral derivative (PID) temperature controller. Selected VOCs such as methanol, ethanol, propanol and formaldehyde were investigated over the catalyst. Qualitative and quantitative analysis of the reagents and the potential organic intermediates was determined using gas chromatography with a flame ionization detector (FID). The experimental results indicated that the reaction rate is inversely proportional to the molecular weight for the compounds with the same functional group. For the same molecular weight, aldehyde is easier to destroy than alcohol. Ethanol and propanol, atypical products of incomplete oxidation of alcohols, were detected in the reaction gas. To minimize the energy consumption, we preferred liquid phase reaction since the heat of reaction could maintain the reaction temperature.

Abstract: On the basis of measuring the viscosity of Sn melt and referring to analysis of high temperature XRD, the change of viscosity and structure for Sn melt with temperature were carried out. The results show that there is discontinuous change of viscosity for Sn melt with the temperature. The state of Sn melt are divided into high, middle and low-temperature region according to the change of viscosity, and there is an anomalous point of viscosity change between different temperature region. There is a correlation between the viscosity change of and the structure change of Sn melt. The coordination number and correlation radius, and the fluid cluster size of Sn melt decrease with the increase of temperature, so that the viscosity of Sn melt decrease. But there is an anomalous change in the vicinity 673 K and 1073 K, it results in discontinuous change in viscosity of Sn melt.

Abstract: Melt blowing(MB) is a process for producing fibrous webs or articles directly from polymers or resins using high-velocity air or another appropriate force to attenuate the filaments. This process is one of the newer and least developed nonwoven processes. This process is unique because it is used almost exclusively to produce microfibers rather than fibers the size of normal textile fibers. MB microfibers generally have diameters in the range of 2 to 4 ㎛, although they may be as small as 0.1 ㎛ and as large as 10 to 15 ㎛. The material acoustic property for noise absorption is principally based on the efficiency of material structures for damping sound wave reflections. In this paper, the sound absorbing material was designed with three layer composite sturcture. Sound absorbing material with fine meltblown(0.5~3 ㎛, 80%) and high modulus hollow fiber(30 ㎛, 20%) as a surface layer and bulky non-woven(15~30 ㎛) as middle layer, meltblown(3~10 ㎛) as bottom layer were manufactured. Their noise absorption were measured using the acoustic duct instrurment. The effect of the sound absorbing on the properties of PP/PET bico MB webs was investigated including the fiber diameter, weight, thickness and air permeability.

Abstract: Shape memory polymers (SMPs) can have a large frozen strain but providing much lower recovery stresses. To overcome such disadvantage, sandwich structures consisted of a SMP core and two thin metallic skins was considered. Due to much compliance of the SMP core, SMP sandwich beam is buckled at a lower packaging strain. Buckling is the fundamental character of SMP sandwich beam under bending. The critical buckling parameters about two types of SMP sandwich beams were theoretically derived.