1,599 research outputs found
Electrostatic fluidized bed deposition of a high performance polymeric powder on metallic substrates
The electrostatic fluidized bed deposition of a single-layer PPA 571 coating onto low carbon steel rods is reported. A full factorial experimental design was developed in order to study the influence of several operative variables on the effectiveness of the coating process and on the coating thickness and uniformity. The operative variables included exposure time, air flow, the applied voltage, attitude, and the radial and vertical location of the work-piece in the fluid bed. After the experimentation, several process maps were developed as a support to identify the best way to lead the coating process. Finally, by using a statistical approach, the reliability and repeatability of the coating process was also established. Experimental trends were consistent with theoretical expectation. A significant growth in achievable coating thickness was obtained by increasing voltage and air flow. Furthermore, at higher values of exposure time and applied voltage, relevant back ionization phenomena occurred, which simultaneously caused a top limit in coating thickness and a worsening of surface finishing. Process characteristics, leading mechanisms, and some practical aspects are also discussed in detail. (c) 2005 Elsevier B.V. All rights reserved
The Brera Multi-scale Wavelet (BMW) ROSAT HRI source catalog. I: the algorithm
We present a new detection algorithm based on the wavelet transform for the
analysis of high energy astronomical images. The wavelet transform, due to its
multi-scale structure, is suited for the optimal detection of point-like as
well as extended sources, regardless of any loss of resolution with the
off-axis angle. Sources are detected as significant enhancements in the wavelet
space, after the subtraction of the non-flat components of the background.
Detection thresholds are computed through Monte Carlo simulations in order to
establish the expected number of spurious sources per field. The source
characterization is performed through a multi-source fitting in the wavelet
space. The procedure is designed to correctly deal with very crowded fields,
allowing for the simultaneous characterization of nearby sources. To obtain a
fast and reliable estimate of the source parameters and related errors, we
apply a novel decimation technique which, taking into account the correlation
properties of the wavelet transform, extracts a subset of almost independent
coefficients. We test the performance of this algorithm on synthetic fields,
analyzing with particular care the characterization of sources in poor
background situations, where the assumption of Gaussian statistics does not
hold. For these cases, where standard wavelet algorithms generally provide
underestimated errors, we infer errors through a procedure which relies on
robust basic statistics. Our algorithm is well suited for the analysis of
images taken with the new generation of X-ray instruments equipped with CCD
technology which will produce images with very low background and/or high
source density.Comment: 8 pages, 6 figures, ApJ in pres
Design and mechanical characterization of voronoi structures manufactured by indirect additive manufacturing
Additive manufacturing (AM) is a production process for the fabrication of three-dimensional items characterized by complex geometries. Several technologies employ a localized melting of metal dust through the application of focused energy sources, such as lasers or electron beams, on a powder bed. Despite the high potential of AM, numerous burdens afflict this production technology; for example, the few materials available, thermal stress due to the focused thermal source, low surface finishing, anisotropic properties, and the high cost of raw materials and the manufacturing process. In this paper, the combination by AM of meltable resins with metal casting for an indirect additive manufacturing (I-AM) is proposed. The process is applied to the production of open cells metal foams, similar in shape to the products available in commerce. However, their cellular structure features were designed and optimized by graphical editor Grasshopper®. The metal foams produced by AM were cast with a lost wax process and compared with commercial metal foams by means of compression tests
FIMEC Test to evaluate thewater uptake of coated and uncoated CFRP composites
This study focuses on the application of the FIMEC (flat-top cylinder indenter for mechanical characterization) indentation test to evaluate the effect of water uptake on the mechanical properties of high-performance materials, in particular CFRP (carbon fibre reinforced polymer) composites. Coated and uncoated samples were analyzed. Silicon-based and siloxane coatings were formulated and applied to CFRP to reduce the moisture absorption of the material. The FIMEC test was adopted to study the reduction of the stiffness of CFRP plates for different ageing in water. The evolution of mechanical properties is reported as a function of the water uptake. IR analyses and weight variation measures were used as supporting data. Experimental results show that the FIMEC test is suitable to assess the stiffness reduction due to the aging in water and to identify coatings able to minimize the water uptake
Improvement of the mechanical and thermal characteristics of open cell aluminum foams by the electrodeposition of Cu
Abstract Recently aluminum foaming has been of much interest due to its characteristics properties of light weight structure. Metallic foams are highly porous materials which present complex structure of three-dimensional open cells. This aspect causes strong limitations in mass transport due to electro-deposition technology. In this work, the electro-deposition of copper on aluminum open-cell foams substrates was developed, in order to enhance the thermal and mechanical properties of these cellular materials. The mechanical and thermal characterization of the produced samples was lead through compression and conductivity tests. On the basis of the experimental results, analytical models are proposed to predict the quantity and the quality characteristics of the coating
Drilling polymeric matrix composites
This chapter presents the basics of drilling of polymeric matrix composites
(PMCs). PMCs are becoming widely used in the manufacturing of products where
a high mechanical strength must be accompanied by a low weight. However, the
machining of PMCs implies coping with problems that are not encountered when
machining other materials. Drilling is a particularly critical operation for PMCs
laminates because the large concentrated forces generated can lead to widespread
damage. This damage causes aesthetic problems but, more importantly, may compromise
the mechanical properties of the finished part
- …