Void Content Minimization in Vacuum Infusion (VI) via Effective Degassing

This paper addresses the major concern which component porosity represents in Vacuum Infusion (VI) manufacturing due to resin gelation at pressures close to absolute vacuum. Degassing is a fundamental step to minimize or even avoid resin outgassing and enhance dissolution of voids created during preform impregnation. The efficacy of different degassing procedures based on vacuum degassing, and assisted by adding a nucleation medium, High Speed (HS) resin stirring and/or later pressurization during different time intervals have been analyzed in terms of final void content is studied. Through a rigorous and careful design of the manufacturing process, outgassing effects on final void content were isolated from the rest of porosity causes and specimens with two clearly identifiable regions in terms of porosity were manufactured to facilitate its analysis. Maximum void content was kept under 4% and porous area size was reduced by 72% with respect to conventional vacuum degassing when resin was stirred at HS; therefore, highlighting the importance of enhancing bubble formation during degassing.

Effect of the manufacturing parameters on the pore size and porosity of closed-cell hybrid aluminum foams

Over the recent years metallic foams have become a popular material due to their unique characteristics like low density coupled with beneficial mechanical properties such as good energy absorption, heat resistance, flame resistance, etc. However, their production processes (foaming) is highly stochastic which results in an inhomogeneous foam structure. Hybrid aluminum foam with closed-cell has been manufactured using direct foaming method coupled with the Taguchi Design of Experiments (DOE). Image analysis has been carried out to determine the average porous area and pore size. The influence of the production parameters (amount of foaming agent added, mixing speed and temperature) on the pore size and the porous area has been analyzed using the statistical Taguchi technique. From the experiments it was seen that the most important control factor for both the pore size and the porous area is the amount of the foaming agent added, followed by temperature and stirring speed. Furthermore, the statistical significance of these manufacturing parameters on the response was also investigated by performing analysis of variance (ANOVA) statistical method.

THE STUDY OF CROSS SECTION OF MULTYLAYER CARDBOARD WITH USE OF ION BEAM CUTTING TECH-NOLOGY

This scientific article contains results of research the two layers cardboard`s cross-section produced by ion beam cutting technology with converting of cross-section image by computer programs. The cross-section of two layers cardboard`s which produced by traditional wet method and aerodynamic forming method was presented to compare. The bottom layer was obtained by the traditional wet method from old corrugated cardboard recovered paper and the top layer was obtained by aerodynamic forming method from print recovered paper. The boundary layers, cut fibers, fibrils, additives, porous area, and lines of contact fibers for the each layer and the contact line of the fiber walls were determined with converting and analyzing of cross-section image by computer programs. The developed method made it possible to separate lines of contact fibers which determine the emergence of inter fiber bonds from the contact line of the fiber walls. The comparison of the results allowed explaining in a new way the decrease in mechanical parameters of cardboard during dry preparation of recovered paper. The ion beam cutting technology with converting of cross-section image by computer programs allowed determining cut fibers area and porous area. This made it possible to quantify the effect of fiber distribution factors on the mechanical property of cardboard. The content of the additive (calcium carbonate) and its distribution in layers is estimated by the spectrum of the elemental composition.

Influência da atmosfera de sinterização na densificação de uma liga Monel 400

Resumo O presente estudo compara a densificação de amostras de uma liga de níquel Monel 400 sinterizadas em duas diferentes atmosferas, sendo uma atmosfera inerte de gás argônio e outra um sólido composto de coque de petróleo. Três pares de amostra foram feitos, cada uma delas compactadas em diferentes pressões de 665 MPa, 1350 MPa e 2000 MPa; nos pares de mesma pressão, uma amostra foi sinterizada no meio gasoso, e a outra amostra sinterizada no meio sólido a uma temperatura de 1100°C por um tempo de 180 minutos. Diversas imagens metalográficas foram obtidas e analisadas por meio de software, para descobrir a porcentagem de área porosa superficial. Verificou-se que as amostras que tiveram maior pressão de compactação obtiveram uma menor área porosa, assim como as sinterizadas, em meio sólido, também obtiveram uma maior densificação, em relação às amostras sinterizadas em meio gasoso. Palavras-chave: Densificação. Sinterização. Atmosferas de sinterização. Abstract The present study compares the densification of samples of a sintered Monel 400 nickel alloy in two different atmospheres, one being an inert atmosphere of argon gas and other a solid medium composed of petroleum coke. Three sample pairs were made, each compressed at different pressures of 665 MPa, 1350 MPa and 2000 MPa; in the same pressure pairs, one sample was sintered in the gaseous environment, and the other sample sintered in the solid environment at a temperature of 1100 ° C for a time of 180 minutes. Several metallographic images were obtained and analyzed by software to find the percentage of porous surface area. It was found that the samples that had higher compaction pressure had a smaller porous area, as well as the sintered ones, in solid medium, also had a higher densification, compared to the sintered samples in gas medium. Keywords: Densification. Sintering. Sintering atmospheres.

Mathematical Simulation of Drying Process of Fibrous Material

The article describes mathematical simulation of flowing air through porous zone and water vaporisation from mentioned porous area which actually represents dried fibrous material - cotton towel. Simulation is based on finite volume method. Wet towel is placed in pipe and hot air flow through the towel. Water from towel is evaporated. Simulation of airflow through porous element is described first. Eulerian multiphase model is then used for simulation of water vaporisation from porous medium. Results of simulation are compared with experiment. Ansys Fluent 13.0 was used for calculation.

Preparation and Sintering Effect in Quartz-Barium Titanate Porous Ceramics and Permeability Modulation Using an Implanted Electrode

Barium titanate and quartz mixed in different proportions were used to create porous piezoelectric ceramics. Three different sintering temperatures were used for the ceramics preparation; a nichrome wire was used as internal electrode in porous ceramics. Characteristics as porous area, porosity, and its relationship with quartz percentage and sintering temperatures were studied. Porous ceramics with an implanted electrode were created, by applying an alternating voltage in the internal electrode that controlled the liquid permeability coefficient, calculated by the Darcy Law.

Modified Polylactide Microfiber Scaffolds for Tissue Engineering

ABSTRACTPhysical properties of porous membranes made of biocompatible and biodegradable polymers have been studied. The membranes are intended to be used as scaffolds for the regeneration of soft and hard tissues. Polylactides, polycaprolactone and some of their derivates are biocompatible as well as biodegradable materials, and are used for the preparation of nanofibers and nanoporous membranes. These membranes also have comparative advantages as cellular scaffolds for tissue engineering since they can be prepared to mimic the morphology of the extra cellular matrix.Chemical, physical, and biological properties of microfibers and scaffolds of polylactic acid (PLLA), as well as PLLA modified with hydroxyapatite nanoparticles and collagen (Col) are reported in this paper. The microfibers and the scaffolds were prepared by electrospinning. Morphology, diameter and porosity of the scaffold were determined by scanning electron microscopy and an image analyzer program. The microfibers are semicrystalline showing a shell of crystalline nanofibrils. The diameter of the fibers varied between 100 and 800 nm and the porous area of the membrane is between 60 and 80%. The mechanical properties of the microfibers and scaffolds were evaluated by microtensile tests and their behavior was simulated by using an original multiscale asymptotic homogenization model. Cultures of mesenchymal stem cells were used to evaluate their biological activity. Cell adhesion was observed in the modified PLLA scaffolds with grafted hydroxyapatite.

Sharpening Mechanism Using Composite Electro-Plating In-Process Sharpening Technique

The in-process sharpening mechanism of the grinder during the grinding process of a CVD diamond film surface is investigated using the composite electro-plating in-process sharpening (CEPIS) technique. The bath concentration is employed to investigate the variation of coating structure deposited on the grinder. Results show that the land area ratio increases with increasing nickel chloride concentrations (NiCl2．6H2O) of the plating bath from 10 to 30 g/L, and the coating structure becomes very smooth without porous area at the nickel chloride concentration of 75 g/L. Therefore the coating structure becomes compact to hold the diamond particles rigidly. Consequently, the grinding ability of the grinder can be significantly improved, where the mirror-like surface of the CVD diamond film can be achieved.