LDEF fiber-composite materials characterization

Degradation of a number of fiber/polymer composites located on the leading and trailing surfaces of LDEF where the atomic oxygen (AO) fluences ranged from 10(exp 22) to 10(exp 4) atoms/cm(sup 2), respectively, was observed and compared. While matrices of the composites on the leading edge generally exhibited considerable degradation and erosion-induced fragmentation, this 'asking' process was confined to the near surface regions because these degraded structures acted as a 'protective blanket' for deeper-lying regions. This finding leads to the conclusion that simple surface coatings can significantly retard AO and other combinations of degrading phenomena in low-Earth orbit. Micrometeoroid and debris particle impacts were not a prominent feature on the fiber composites studied and apparently do not contribute in a significant way to their degradation or alteration in low-Earth orbit

Nanotailoring Stereolithography Resins for Unique Applications using Carbon Nanotubes

Nanostructured materials and exploiting their properties in stereolithography (SL) may open new markets for unique rapidly manufactured functional devices. Controlled amounts of multiwalled carbon nanotubes (MWCNTs) were successfully dispersed in SL epoxy-based resins and complex three-dimensional (3D) parts were successfully fabricated by means of a multi-material SL setup. The effect of the nanosized filler was evaluated using mechanical testing. Small dispersions of MWCNTs resulted in significant effects on the physical properties of the polymerized resin. A MWCNT concentration of .05 wt% (w/v) in DSM Somos® WaterShed™ 11120 resin increased the ultimate tensile stress and fracture stress an average of 17% and 37%, respectively. Electron microscopy was used to examine the morphology of the nanocomposite and results showed affinity between the MWCNTs and SL resin and identified buckled nanotubes that illustrated strong interfacial bonding. These improved physical properties may provide opportunities for using nanocomposite SL resins in end-use applications. Varying types and concentrations of nanomaterials can be used to tailor existing SL resins for particular applications.Mechanical Engineerin

On the Geometry of Surface Stress

We present a fully general derivation of the Laplace--Young formula and discuss the interplay between the intrinsic surface geometry and the extrinsic one ensuing from the immersion of the surface in the ordinary euclidean three-dimensional space. We prove that the (reversible) work done in a general surface deformation can be expressed in terms of the surface stress tensor and the variation of the intrinsic surface metric

Estudo da cinética da secagem de tomate cereja.

Edição de Resumos expandidos e palestras do 43. Congresso Brasileiro de Olericultura, Recife, jul. 2003. Publicado também o resumo em: Horticultura Brasileira, Brasília, v. 21, n. 2, p. 394, jul. 2003. Suplemento 1

Influence of drying process variables on fresh and osmotically pre-treated mushrooms.

The aim of this work was to study the drying of fresh and osmotically dehydrated mushrooms and evaluate their qualities. The osmotic treatment was carried out at 20 °C with a 10% w.w?1 salt solution, 80 rpm agitation and 60 min immersion time. The mushrooms were dried in a vertical bed dryer with forced air-flow. An experimental design was applied to evaluate the influence of the temperature and air velocity on the drying constant, obtained according to an exponential model and on the colour difference between the dried and fresh samples. Using Response Surface Methodology, a condition was chosen to obtain the largest drying constants and smallest colour differences. The optimum conditions for the drying process were 70 °C and 2.0 m/s, and 80 °C and 2.5 m/s for fresh and osmotically dehydrated mushrooms, respectively. The dried mushrooms aresented â-glucan content values of 6.14 ± 0.55 and 6.77 ± 0.47 g.100 g?1 d.b under the optimised drying conditions. Osmotically dehydrated samples showed a slower re-hydration rate and smaller water activity than samples without pre-treatment

Evidence of Low-Temperature Superparamagnetism in Mn3O_{3}O_{4}$ Nanoparticle Ensembles

Please refer to the abstract within the main body of the paper

Influence of osmotic pretreatment on dried cashew apple acceptability.

Resumo P2.1.10

Estudo da desidratação osmótica de abóbora utilizando metodologia de superfície de resposta.

Suplemento 1. Edição dos Resumos do 43 Congresso Brasileiro de Olericultura, Recife, jul. 2003

Avaliação do efeito da concentração e da temperatura na desidratação osmótica de abóbora utilizando metodologia de superfície de resposta.

O objetivo deste estudo foi avaliar o efeito da temperatura (12 a 33°C) e da concentração de cloreto de sódio (3 a 17% p/p) na perda de água (PA) e no ganho de sólidos (GS) durante a desidratação osmótica de abóbora. Observou-se que, na faixa estudada, quanto maior a temperatura e a concentração maior foi a PA e o GS e a concentração de NaCl mostrou ser a variável de maior influência no processo

Effect of Build Parameters and Build Geometries on Residual Microstructures and Mechanical Properties of Ti-6Al-4V Components Built by Electron Beam Melting (EBM)

In this study, involving additive manufacturing (AM) using electron beam melting (EBM), we have examined build defects which result from beam tripping, porosities (including unmelted or unsintered zones) due to excursions from optimal build parameters (especially variations in melt scan beam current and scan speed), and gas bubbles trapped in atomized Ti-6Al-4V starting powder as well as recycled powder, and retained in the build. At optimized build conditions we have also examined microstructure-mechanical property (hardness, tensile strength, and elongation) variations for multiple rake building and multiple melt scans using optical metallography and scanning and transmission electron microscopy (SEM and TEM). These build variances cause cooling rate variances which promote α-phase growth and variations in dislocation density, as well as α-to-α' (martensite) phase changes, all of which produce some degree of mechanical property variations. These features (especially α-to-α' phase changes) are notable on comparing solid builds in comparison with a variety of mesh arrays where strut dimension and build-element complexities alter the cooling rates in a significant way. We illustrate these microstructure variations with corresponding variations in microindentation hardness measurements made directly on fine mesh (strut) structures. Finally, we have examined Ti-6Al-4V powder chemistries and solid build chemistries which for single-pass melt scans at optimized build conditions are shown to be relatively constant up to 40 cycles of powder reuse with the exception of Al content which was reduced by 10 to 15% in solid builds at optimized conditions. However, Al loss in solid builds approached 25% for multiple (2 and 3) melt scans, while no changes in Ar gas-bubble density were observed with changes in α-phase (grain) width which increased from 3 µm for a single melt scan to 4.5 and 6 µm for 2 and 3 melt scans, respectively. Corresponding Rockwell C-scale (HRC) hardness varied from 37, 36, and 35, respectively; with ultimate tensile strengths exceeding 1.2 GPa at elongations of 12% or higher for this melt scan sequence.Mechanical Engineerin