Papers by Keyword: TMA

Abstract: Process induced residual stresses may play an important role under service loading conditions for fiber reinforced composite. They may initiate premature cracks and alter the internal stress level. Therefore, the developed numerical models have to be validated with the experimental observations. In the present work, the formation of the residual stresses/strains are captured from experimental measurements and numerical models. An epoxy/steel based sample configuration is considered which creates an in-plane biaxial stress state during curing of the resin. A hole drilling process with a diameter of 5 mm is subsequently applied to the specimen and the released strains after drilling are measured using the Digital Image Correlation (DIC) technique. The material characterization of the utilized epoxy material is obtained from the experimental tests such as differential scanning calorimetry (DSC) for the curing behavior, dynamic mechanical analysis (DMA) for the elastic modulus evolution during the process and a thermo-mechanical analysis (TMA) for the coefficient of thermal expansion (CTE) and curing shrinkage. A numerical process model is also developed by taking the constitutive material models, i.e. cure kinetics, elastic modulus, CTE, chemical shrinkage, etc. together with the drilling process using the finite element method. The measured and predicted in-plane residual strain states are compared for the epoxy/metal biaxial stress specimen.

Abstract: In recent years a number of studies were conducted in order to obtain polymer composites with superior performance when compared to the metallic alloys. However, these new materials must meet a series of rigid project requirements. One way to evaluate the polymer composites is through their transition temperatures, especially the glass transition temperature (Tg). It is possible to evaluate the Tg of a polymeric material through the study of changes in dimensions of a sample as a function of temperature. These measurements can be made on an equipment of thermomechanical analysis (TMA), however, despite great sensitivity, this technique is basically unknown by most users when compared to others such as DSC or DMA. Even with different technical principles of operation, the results show similarity. Thus, this study aims to compare the results of Tg polymer composites obtained via TMA with those obtained from DSC curves in epoxy resin/carbon fiber laminates.

Abstract: Bamboo/HDPE/PA6 composites have been discussed by systematically studying the effect of formulation on thermal expansion properties. PA6 filled HDPE seemed not significantly influence LTEC of HDPE/PA composites system when the PA loading level increased form 0 % to 20%. It was investigated that BF significantly reduced LTEC value compared with LTEC of HDPE/PA. The reduction of the LTEC appear in HDPE/bamboo composites was dependent on the matrix and filler. Coupling agent can make the LTEC of HDPE/bamboo composites reduced, but the reduction was larger than that of only filler.

Abstract: The paper proposes a new method for a targets trajectory, assumed to be linear and uniform, based on the observation of its speed and bearings. After introducing the new method based on assumed model, the paper analyzes the relative error of range estimation caused by speed and bearings estimations relative error; The results of target motion analysis (TMA) is optimized by linearizing the model and using kalman filter. Pond test shows that relative error of range estimation calculated by this method is less than 10^-1.

Abstract: A sensitive cataluminescence (CTL)-based gas sensor using nano-sized Y₂Ti₃O₉ as a probe was proposed for the determination of trimethylamine (TMA) in air. The gas sensor showed high selectivity for TMA at 490 nm and satisfying activity at 320°C. The linear range of the CTL intensity versus concentration of TMA was 1~70 mg/m³ (γ = 0.995), and the detection limit (3σ) was 0.6 mg/m³. No interference was observed while the foreign substances, such as ammonia, ethanol, benzene, carbon monoxide and sulfur dioxide, were passing through the sensor. The gas sensor displayed good stability for continuously introducing TMA over 100 h, and allowed on-line monitoring of TMA in air.

Abstract: Changes in chemical, textural, and volatile flavor properties were investigated for mackerel fish (Scomberomorus niphonius) stored in cold rooms and freezers. Correlation and multivariate analysis showed a significant time-dependent relationship between TVBN/TMA (Y) and storage time (X) for fish stored in cold rooms, with R=0.996-0.997 values of Gompertz model (Y=a*exp(-exp(b-cX)), and there was a good linear relationship between TVBN and TMA. Combined with the textural properties, the polynomial fitting model (Y=a+bX+cX2+…, R=0.982-0.991) was applied and elucidated the correlation between hardness/springiness (Y) and TVBN (X), the rational function model (Y=(a+bX)/(1+cX+dX2), R=0.975-0.979) used for the chewiness (Y) and TVBN (X). The electronic nose analysis revealed that the variation of muscle volatile flavor compounds was found out along the PC1 to the right, and then along the PC2 to the upward and further to the downward based on the principal component analysis (PCA). Furthermore, the linear discriminant analysis (LDA) had better distinction effect for the changes of fish flavor than PCA. Results from this study suggested that the texture analysis in combination with electronic nose techniques might be utilized as a rapid expeditious process for predicting freshness and shelf life of the alive-storage fish or other aquatic products.

Abstract: As titanium source tetrebutyl titanate modified by reflux preparation, the clean solution containing the nano-TiO₂ had been prepared by hydrothermal synthesis method. Then the solution was added to the chloroform solution which containing the poly (hydroxybutyrate-co-valerate) (PHBV), and the loading nano-TiO₂ modified PHBV film was prepared by solution casting processes. X-ray diffraction (XRD) and UV-visible transmission spectra (UV-vis) were used to characterized; in the photocatalytic experiment, 10 ml 5 mg/L methyl orange solution with the 10 mg catalyst, the fade rate reached 90% after 120 min. The thin film obtained in this method has characteristics of high transmittance, high photocatalytic activity, recycling, non-toxic and the loading nano-TiO₂ of uniform dispersion.

Abstract: Single-crystalline 3C-SiC epitaxial layers were grown on on-axis Si (001) substrates by low-pressure hot-wall chemical vapour deposition. Aluminium from a trimethylaluminium (TMA) source was used for p-type doping. The atomic Al and carrier concentrations in the layers were determined as a function of the partial pressure of the TMA source gas. Secondary ion mass spectroscopy (SIMS), Hall-effect measurements at room temperature and four-point electrical resistivity method were applied to measure the atomic and electrically active Al concentrations. The crystalline perfection of the layers was characterized by high-resolution x-ray diffraction (HRXRD). At TMA-partial pressures ranging from 510-7 mbar up to 1.510-4 mbar corresponding aluminium concentrations from 21015 cm-3 up to 1.31019 cm-3 were measured in the epitaxial layers. On increasing the Al concentration from 1x1017 cm-3 to 1x1019 cm-3 the layer electrical resistivity decreases from 17 cm to 0.8 cm, while no influence on the crystalline quality of the layers was observed. The average full width at half maximum (FWHM) of the rocking curve for a 5µm thick 3C-SiC layer is about 500 arcsec. With increasing layer thickness (up to 16 µm) the FWHM of the rocking curve decreases to about 300 arcsec.

Abstract: Scaling of CMOS structures through the deep sub-micron range and into the nano-scale range (< 100 nm) has posed a number of difficult problems for processing technology. One main technological approach has been to improve the uniformity and conformality of deposited layers. As the Atomic Layer Deposition (ALD) has already demonstrated that it can overcome many of the limitations of current film deposition techniques, it seems to be the solution for very conformal layers of high quality on severe topography. The ALD method has been developed already in the 1970’s by Tumo Suntola and co-workers [1-4]. However, it has been in the past a rather unused method in the semiconductor industry. This has recently changed. During the last couple of years, the large semiconductor companies have spent a lot of effort in the utilization of ALD, but until now a production worthy ALD tool with low ‘Cost-of-Ownership’ (CoO) numbers was not available. One reason for the late introduction of ALD is that the method is rather slow compared with the state of art methods like CVD, PECVD and PVD. Nevertheless, due to the outstanding properties of the ALD technique, the drawback of slow deposition rate may be balanced by the parallel processing of many wafers in semiconductor furnaces, as described here.

Abstract: The thermal and mechanical characteristics of various Mg-Cu(Ni)-Y(Gd) metallic glassy alloys prepared by melt spinning are examined using differential scanning calorimetry (DSC), thermomechanical analyzer (TMA), and instrumental nanoindenter. The replacement of Y by Gd appears to benefit both the thermal and mechanical properties, while the replacement of Cu by Ni improves only the hardness and modulus, with the sacrifice of thermal characteristics. The amorphous Mg-Cu-Gd based alloys can be fabricated into rods with a diameter greater than 6 mm, with minimum porosity and reasonable toughness.