Time filter

Source Type

Coelho R.,University of Sao Paulo | Assis C.,University of Sao Paulo | Rodrigues A.,University of Sao Paulo | Militao A.,Institute of Technological Research
Proceedings of the 15th International Conference of the European Society for Precision Engineering and Nanotechnology, EUSPEN 2015 | Year: 2015

Production of microchannels used in heat microsink has been improved given the advances in precision machining. A variety of part materials (e.g. silicon) can be applied to yield microsinks although metallic coating still needs to be applied to improve surface quality. The main problem to micromachine steel-based materials is to guarantee geometric precision and to minimize burr formation. Among several manufacturing processes, micromilling allows creating 3D structures with vertical sidewalls, good smoothness, external sharp corners and complex geometries, but parts with coarse microstructure can impair the machining efficiency. Thus, homogenous microstructure of the part materials has been investigated given the significant improvements in the cutting process which benefit the microchannels roughness. This surface integrity parameter is the most relevant one when machining channels for microsink. This papers aims to investigate the fabrication of bio-inspired heat microsinks by using micromilling process. This kind of device is more thermally efficient because the channels follow the vascular shape of plant leaves. Ultrafine-grained aluminium (1 μm grain size) was used to match machining scale (milling microparameters) to the workpiece microstructure (micrograin size) aiming at improving the surface generation and part-tool interaction. Surface analyses were carried out using laser 3D microscope. 0.2, 0.4, 0.8 and 2.0 mm diameter tungsten carbide end-mills were used in micromilling tests. The cutting parameters varied along the micromilling due to the different micromill diameters and microchannels geometry. Only feed per tooth (ft) was at the same range of the cutting edge radii (re). The main results indicated that micromilling with ft≈ re reduced the surface roughness. In addition, no deformation of the microsink slots and small burrs on the top of the walls were found, respectively. Thus, micromilling process associated to a homogenous microstructure of the workpiece suggests to favour the microslots production of bio-inspired heat microsinks. Source

Autocondensation and copolymerization reactions of the Acacia nilotica subspecies tomentosa (Ant) and the subspecies adansonii (Ana) tannins extracts solutions have been studied at several pH values by thermomechanical analyzer. Results of chemical analysis of these tannins revealed that the studied tannins, Ant and Ana contained high percentages of extractable tannins (54 and 57 %) for and polyphenolic materials (78 and 80 %) respectively. Different hardeners such as paraformaldehyde, Urea and pMDI were added at different ratios and their polycondensation reactions was studied and compared with their autocondensation ones. The aim was to evaluate the tannins suitability for the production of commercially and technically viable tannin adhesives with reduced Formaldehyde emission for wood products and to study the interference between the autocondensation and the copolymerization reaction. The obtained results of autocondensation reaction for both of the tannins studied showed that the best Young's modulus values for Ant (3,500 and 2,750 MPa) and Ana (2,650 and 2,620 MPa) were obtained at pH 5 and 7. The Young's modulus values obtained by the tannins Ant were higher than those achieved by Ana. This indicates that the Ant is more reactive than Ana. These results were also in line with results achieved by the gel time for both of the tannins. Gel time results indicate that the reactivity of both tannins increased towards alkalinity with Ana being more reactive at alkaline pH. Addition of 8 % of paraformaldehyde was adversely affecting the autocondensation reactions, as the best Young's modulus values were achieved at pH 4 for Ant tannins. As for Ana the higher Young's modulus values (2,000 and 2,310 MPa) were achieved at pH 5 and 7. This indicates that autocondensation reaction was contributed to the final network of the copolymerization reaction. When smaller ratio of paraformaldehyde and Urea (5 %) was added to Ant tannins it favors the autocondensation reaction and the best Young's modulus values were obtained at pH 5 and 7. Addition of pMDI (10-30 %) was found to decrease the temperature of copolymerization and the obtained Young's modulus values by Ant were lower than those obtained by autocodensation reaction. Best Young' modulus values were obtained by Ant at pH 5 and 7. Ana gave the best Young's modulus values at pH 4 and 5 indicating that the autocondensation appears to depress the copolymerization reactions. The obtained results by both reactions were very important from technical and economical point of view as they concluded that it is very possible to produce adhesives system with zero emission depending on the tannins autocondensation reaction and pH values. Reduction of formaldehyde emission was also possible upon addition of smaller amount of paraformaldehyde and Urea. © 2013 Springer Science+Business Media New York. Source

Osman Z.,Institute of Technological Research
Journal of Thermal Analysis and Calorimetry | Year: 2012

In this article, autocondensation reactions of Acacia nilotica spp. nilotica (Ann) tannin extracts solutions have been studied at several pH values by thermomechanical analyzer (TMA). TMA has been chosen for this study as it has been shown to give results more rapidly and more precisely than panels. It also tends to exaggerate the differences in results which render it an excellent tool for comparison. Therefore, autocondensation reactions were studied and compared with its polycondensation reactions upon addition of different hardeners such as paraformaldehyde, urea, and PMDI at same pH values. The aim was to evaluate the tannin's reactivity and therefore its suitability for the production of commercially and technically viable tannin adhesives for wood products. The results of autocondensation showed that the maximum Young's modulus values (3300 and 3600 MPa) were obtained at pH 4. However, these values have been achieved at high temperature (160 and 208 °C). Results of copolymerization reaction of the tannins with different hardeners revealed that some of these co-reactants were found to depress tannins autocondensations, while others appear to enhance the formation of the final networking. Polycondensation of the Ann tannins with 8% paraformaldehyde and 10% PMDI gave the maximum Young's modulus values at lower temperature (91-101 °C) and acidic pH5. However, the addition of 20 and 30% PMDI achieved the best Young's modulus values 2300 and 3300 MPa, respectively, at pH 4. Furthermore, the obtained values were comparable to those obtained by the addition of urea and the self condensation reactions. This is very important for particleboard production from economical and technical point of view. It has been noticed that the addition of hardeners lowered the temperature of hardening, and the obtained values were more consistent with the pH acidity. The study concluded that the tannins of Ann were very reactive, and therefore, it could be a potential precursor for particleboard adhesives. The results also indicated that the tannins can be used alone, and it would possibly produce zero emission environmentally friendly particleboard. © Akademiai Kiado, Budapest, Hungary 2011. Source

Suhir E.,Portland State University | Suhir E.,Vienna University of Technology | Suhir E.,ERS Co. | Bensoussan A.,Institute of Technological Research | And 2 more authors.
IEEE International Reliability Physics Symposium Proceedings | Year: 2015

The recently suggested probabilistic design for reliability (PDfR) concept of electronics and photonics (EP) products is based on 1) highly focused and highly cost-effective failure oriented accelerated testing (FOAT), aimed at understanding the physics of the anticipated failures and at quantifying, on the probabilistic basis, the outcome of FOAT conducted for the most vulnerable element(s) of the product of interest, for the most likely applications and for the most likely and meaningful combination of possible stressors (stimuli); 2) simple and physically meaningful predictive modeling (PM), both analytical and computer-aided, aimed at bridging the gap between the obtained FOAT data and the most likely actual operation conditions; and 3) subsequent FOAT-and-PM-based sensitivity analysis (SA) using the methodologies and algorithms developed as important by-products at the two previous steps. The PDfR concept proceeds from the recognition that nothing is perfect, and that the difference between a highly reliable and an insufficiently reliable product is 'merely' in the level of the probability of its field failure. If this probability (evaluated for the anticipated loading conditions and the given time in operation) is not acceptable, then a SA can be effectively employed to determine what could/should be changed to improve the situation. The PDfR analysis enables one also to check if the product is not 'over-engineered', i.e., is not superfluously robust. If it is, it might be too costly. The operational reliability cannot be low, but it does not have to be higher than necessary either. It has to be adequate for the given product and application. When reliability and cost-effectiveness are imperative, ability to optimize reliability is a must, and no optimization is possible if reliability is not quantified. We show that optimization of the total cost associated with creating a product with an adequate (high enough) reliability and acceptable (low enough) cost can be interpreted in terms of an adequate level of the availability criterion. The major PDfR concepts are illustrated by practical examples. Although some advanced PDfR predictive modeling techniques have been recently developed, mostly for aerospace applications, the practical examples addressed in this talk employ more or less elementary analytical models. In this connection we elaborate on the roles and interaction of analytical (mathematical) and computer-aided (simulation) modeling. We show also how the recently suggested powerful and flexible Boltzmann-Arrhenius-Zhurkov (BAZ) model and particularly its multi-parametric extension could be successfully employed to predict, quantify and assure operational reliability. The model can be effectively used to analyze and design EP products with the predicted, quantified, assured, and, if appropriate and cost-effective, even maintained and specified probability of operational failure. It is concluded that these concepts and methodologies can be accepted as an effective means for the evaluation of the operational reliability of EP materials and products, and that the next generation of qualification testing (QT) specifications and practices for such products could be viewed and conducted as a quasi-FOAT, an early stage of FOAT that adequately replicates the initial non-destructive segment of the previously conducted comprehensive 'full-scale' FOAT. © 2015 IEEE. Source

Amel B.A.,Institute of Technological Research | Paridah M.T.,University Putra Malaysia | Rahim S.,Malaysian Forest Research Institute | Osman Z.,Institute of Technological Research | And 2 more authors.
Journal of Tropical Forest Science | Year: 2014

The compatibility between cement and kenaf bast fibre and its improvement with various types of accelerators were investigated by observation and analysis on hydration behaviour in terms of hydration characteristics, namely, maximum hydration temperature and required time to reach maximum temperature. Five extraction methods (crude, water retting, decortication, NaOH retting and benzoate retting), four accelerators (CaCl2, AlCl3, Na2SO4, CaO), three concentrations (2, 4 and 6%) and three particle sizes (0.5, 0.8 and 4.0 mm) were used. The hydration behaviour of mixtures demonstrated that NaOH and benzoate were unsuitable with cement. Meanwhile, CaCl2 and CaO were found to be effective accelerators for restraining inhibitory influences. In addition, 2% accelerator was available and acceptable for quick-curing cement. Particle sizes of 0.5 and 0.8 mm required addition of accelerators to reach maximum cement setting. © Forest Research Institute Malaysia. Source

Discover hidden collaborations