Process planning strategies for solid freeform fabrication of metal parts

Process planning of additive manufacturing of metals is a research interest because of the applications of solid freeform fabrication of metal parts in industry. The strategy is to transform the model of the part into the combinations of 2D layers that will be deposited using different fabrication methods. Process planning for metal deposition in this paper consists of three major modules: spatial decomposition, slicing of the part, and toolpath generation for every slicing layer. Algorithmic improvements are proposed and implemented for these major modules. For spatial decomposition, 3D part decomposition based on modular boundary models and centroidal axis extraction methods are combined to decompose parts more robustly and reliably. For generating slicing layers, a planning process for building non-uniform layers is investigated to greatly increase the variety of the parts that can be manufactured without the need of support structure. For toolpath generation methods, optimization of the generated toolpath is studied especially for complex thin-wall structures to ensure the deposition quality. Experiments were carried out to evaluate the improvements of the major modules of process planning strategies for rapid manufacturing.     

Numerical simulation of flows past periodic arrays of cylinders

We present a detailed numerical investigation of three unsteady incompressible flow problems involving periodic arrays of staggered cylinders. The first problem is a uniperiodic flow with two cylinders in each cell of periodicity. The second problem is a biperiodic flow with two cylinders in each cell, and the last problem is a uniperiodic flow with ten cylinders. Both uniperiodic flows are periodic in the direction perpendicular to the main flow direction. In all three cases, the Reynolds number based on the cylinder diameter is 100, and initially the flow field has local symmetries with respect to the axes of the cylinders parallel to the main flow direction. Later on, these symmetries break, vortex shedding is initiated, and gradually the scale of the shedding increases until a temporally periodic flow field is reached.We furnish extensive flow data, including the vorticity and stream function fields at various instants during the temporal evolution of the flow field, time histories of the drag and lift coefficients, Strouhal number, initial and mean drag coefficients, amplitude of the drag and lift coefficient oscillations, and the phase relationships between the drag and lift oscillations associated with each cylinder. Our data confirms that, at this Reynolds number, there are no stable steady-state solutions with local symmetries. Of course, one can obtain such unphysical solutions by assuming symmetry conditions along the axes of the cylinders parallel to the main flow direction and taking half of the computational domain needed normally. In such cases, the steady-state flow fields obtained would be identical to the flow fields observed at the initial stages of our computations. However, we show that such flow fields do not represent the temporally periodic flow fields even in a time-averaged sense, because, in all three cases, the initial drag coefficients are different from the mean drag coefficients. Therefore, we conclude that stability studies involving periodic arrays of cylinders should be carried out, as it is done in this work, with the true implementation of the spatial periodicity.     

“782”速凝剂在基岩帷幕灌浆中的试验应用

通过工程实践,提出了“782”速凝剂在不同裂隙情况下的合理掺量、可灌性和使用效果,以及灌浆施工中应注意的问题。实践证明,在宽大裂隙的帷幕灌浆中,将“782”和氯化钙联合使用,与常规方法比,能缩短灌浆时间,节约灌浆材料,降低工程造价,且工艺简单,灌浆效果良好。     

Origin of Kern's arc

With the aid of computer-simulated halo patterns, we show that Kern's arc, as seen on the latitude of the circumzenithal arc and on the other side of the zenith, is produced by double-plate ice crystals with a vertical principal axis. Light rays that contribute to Kern's arc are demonstrated by geometric ray tracing. We also discuss the condition under which an arc that is opposite a circumhorizontal arc can appear.     

Preparation and properties of polyimide–clay nanocomposite materials for anticorrosion application

A series of polymer–clay nanocomposite (PCN) materials that consist of organosoluble polyimide and layered montmorillonite clay were prepared by the solution dispersion technique. The organosoluble polyimide containing non‐coplanar moiety in diamine monomer and flexible bridging linkages in dianhydride monomer was synthesized by chemical imidization. The as‐synthesized PCN materials were characterized by infrared spectroscopy, wide‐angle powder X‐ray diffraction, and transmission electron microscopy. The organosoluble polyimide showed better corrosion resistance compared to polyaniline, poly(o‐ethoxyaniline) and poly(methyl methacrylate) by using a series of standard electrochemical corrosion measurements of corrosion potential, polarization resistance, and corrosion current in 5 wt % aqueous NaCl electrolyte. Polyimide–clay nanocomposite materials incorporated with low loading of clay were found to further improve corrosion inhibition over pure polyimide. Effects of the material composition on the O₂/H₂O molecular permeability, optical clarity, and thermal properties of polyimide–clay nanocomposite materials were studied by molecular permeability analysis, UV–visible transmission spectra, thermogravimetric analysis, and differential scanning calorimetry, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3573–3582, 2004     

Ozone Yields from Oxygen Irradiated at 193 nm

The use of ArF laser radiation at wavelength 193 nm to generate ozone from various pressures of oxygen gases was investigated. Kinetic results were interpreted from molecular spectroscopy and dynamics points of view. The 193 nm radiation can dissociate both oxygen molecules and ozone to produce oxygen atoms. This is an essential process in ozone generation. In this investigation, we focused on the mechanisms that ozone dissociates into three oxygen atoms or vibrationally excited oxygen molecules. The above mechanisms imply a potential process to improve the efficiency of ozone generation.     

Polyacrylamide–clay nanocomposite materials prepared by photopolymerization with acrylamide as an intercalating agent

A series of nanocomposite materials consisting of water‐soluble polyacrylamide (PAA) and layered montmorillonite (MMT) clay platelets were prepared by the effective dispersion of the inorganic nanolayers of the MMT clay in the organic PAA matrix via in situ ultraviolet‐radiation polymerization. The acrylamide monomers functioned as both the intercalating agent and the reacting monomers. As a representative procedure for the preparation of the nanocomposites, organic acrylamide monomers were first intercalated into the interlayer regions of acrylamide‐treated organophilic clay hosts, and this was followed by one‐step ultraviolet‐radiation free‐radical polymerization with benzil as a photoinitiator. The as‐prepared polyacrylamide–clay nanocomposite (PCN) materials were subsequently characterized by Fourier transform infrared spectroscopy, wide‐angle powder X‐ray diffraction, and transmission electron microscopy. The effects of the material composition on the thermal stability, optical clarity, and gas‐barrier properties of pristine PAA and PCN materials, in the forms of fine powders and membranes, were also studied by differential scanning calorimetry, thermogravimetric analysis, ultraviolet–visible transmission spectroscopy, and gas permeability analysis. The molecular weights of PAA extracted from PCN materials and pristine PAA were determined by gel permeation chromatography with tetrahydrofuran as an eluant. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3489–3496, 2004     

Pervaporation separation of a water–ethanol mixture by PSF–PEG membrane

For dehydrating a water–ethanol mixture by pervaporation, a polysulfone–And poly(ethylene glycol)(PSF–PEG) membrane was prepared. The separation performance of water and ethanol was found to strongly depend on the diffusion selectivity of permeates. On the other hand, the solubility selectivity of water to ethanol showed only minor change with an increasing PEG composition of the PSF–PEG membrane. This study found that the PEG content in a PSF–PEG membrane showed mobility enhancement of pervaporation properties and that the diffusion difference of permeates increased with increasing PEG content. The effect of PEG content on separation performance was a result of the improvement of the permeate diffusion properties of the PSF/PEG membrane. The diffusion difference in the membrane, not the solubility of water–ethanol in the membrane, was the dominant factor for the separation. Suitable PEG content in PSF/PEG membranes can prepare a high‐performance pervaporation membrane. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2158–2164, 2003     

Curing and pyrolysis of cresol novolac epoxy resins containing BABODOPN

This work investigates the curing kinetics, thermal stability, flammability, and decomposition kinetics of cresol novolac epoxy (CNE) cured with two curing agents, [1,4‐bis(3‐aminobenzoyloxy)‐2‐(6‐oxido‐6h‐dibenz(c,e)(1,2) oxaphosphorin‐6‐yl)‐naphthalene] (BABODOPN) and diamino diphenyl methane (DDM). The DSC curing study shows that the activation energy (E_a) can be estimated by Kissinger's method and the E_a of CNE/DDM, 54.3 KJ/mole, is one‐half that of CNE/BABODOPN, 112.6 KJ/mole; also, the glass transition temperature (T_g) of the latter, 479.5 K, is substantially higher than that, 383 K, of the former. Both increases are attributed to the incorporation of phosphorus‐containing a bulky pendant aromatic group into the BABODOPN molecule, which inhibits its mobility. In comparison with the conventional DDM system, the phosphorus‐nitrogen synergistic effect of BABODOPN improves the limiting oxygen index (LOI) from 26 to 47, and increases the char yield from 30.4% to 38.3%. Moreover, the CNE/BABODOPN system even exhibits better flame retardancy than the excellent CNE/ODOPN system, developed by the authors previously, because of the synergistic effect. Finally, the investigation of thermal gravimetric analysis (TGA) decomposition in N₂ by Ozawa's method demonstrates that the mean E_a declines as the phosphorus content increases, because the ease of decomposition of the phosphorus in the initiation stage facilitates the formation of an insulating layer. POLYM. ENG. SCI., 45:478–486, 2005. © 2005 Society of Plastics Engineers     

Mediating Effect between Supportive Culture and Job Satisfaction in Administrative Services at Higher Education Institutions

The purpose of this article is to examine halo effect and organizational commitment in relation to employees' job satisfaction and organizational supportive culture at universities in Taiwan. The study used a questionnaire to collect data from 210 female faculty members of Taiwanese universities. The conceptual model was tested mediating the effect of structural equation modeling with maximum likelihood estimation. This study not only found the mediating role of halo effect and organizational commitment between supportive culture and job satisfaction, but also proved that a supportive culture in universities is directly and positively related to job satisfaction and that emotional and identification‐oriented organizational commitment may affect job satisfaction in a positive way among female faculty members. © 2012 Wiley Periodicals, Inc.