Locally refined p-FEM modeling of patch repaired plates

An accurate and practical modeling technique is proposed to analyze cracked metal plates with patch repair. In the single-model approach, a p-convergent high-precision element is developed with three-dimensional elasticity theory. Whereas, in the mixed-model approach, a p-convergent transition element is developed to connect the p-convergent high-precision elements for threedimensional response and p-convergent ESL (equivalent single layer) elements for two-dimensional response. For the developed elements, two- and three-dimensional virtual crack closure techniques based on linear elastic fracture mechanics are modified to estimate the stress intensity factor. Modeling simplicity and calculation efficiency of the mixed-model approach using the p-convergent transition elements is shown for the analysis of patch repaired plates. Some results of present analysis are verified by comparison with published results. Also, performance of analysis using the proposed technique with simplicity and efficacy of modeling is investigated for patch repaired plates with respect to a number of parameters such as thicknesses of patch and adhesive, patch size, single-sided patch vs. double-sided patch.     

Reaction mechanisms of polyacrylonitrile on thermal treatment

A high-temperature radical scavenger, 2,2-diphenyl-l-picryl hydrazyl (DPPH), has been used to study the reaction mechanisms of polyacrylonitrile (PAN) on thermal treatment. The effect of DPPH on the cyclization reaction of PAN in both air and nitrogen, investigated by differential scanning calorimetry (DSC), helped to verify the proposed reaction mechanisms, i.e., the free radical and the ionic ones. For PAN homopolymer, the peak temperature of the reaction exotherm shifted to higher temperatures and the heat of reaction was decreased with increasing DPPH concentration. For PAN copolymer with methylacrylate and itaconic acid, however, the effects of DPPH on DSC thermograms were insignificant. The effects of IPPH suggest that the reaction of the nitrile groups proceeds by free radicals for the homopolymer while by ions for the copolymer. The activation energies for the thermal reactions of PAN in both air and nitrogen were also estimated by the dynamic DSC method, and they proved to be highly dependent on reaction mechanism, environment of thermal treatment, and DPPH concentration.     

Precision surface grinding of Mn–Zn ferrite with in-process electro-discharge dressing (IEDD)

Ferrite is widely used as a material for hard disk magnetic heads, but is difficult to grind because of its high hardness and brittleness. Therefore, a superabrasive (diamond) wheel is used for precision surface grinding of this material. But the conventional dressing method cannot be applied to the diamond wheel. This study describes a newly proposed method for carrying out effective in-process electro-discharge dressing (IEDD) of a diamond wheel. Using IEDD, the surface roughness of Mn–Zn ferrite was improved and the grinding force was reduced. IEDD is a good method to obtain efficient grinding and surface grinding of ferrite.     

Microstructural evolution during reactive spray forming of dispersion strengthened Cu alloy

Dispersion strengthened Cu alloy was fabricated by injecting Cu-B alloy powders into the spray of Cu-Ti droplets. The microstructures of over-sprayed powders and spray deposited billet were observed by optical microscopy, scanning electron microscopy, and transmission electron microscopy. The over-sprayed powders were composed of not only Cu-B and Cu-Ti alloy powders but also small amounts of Cu-B alloy powders surrounded by Cu-Ti droplets. Fine dispersoids of TiB were observed in the Cu-B powders surrounded by Cu-Ti, indicating that very rapid reaction of Ti and B had occurred during the flight of the droplets. TiB dispersoids of ∼10 nm having an orientational relationship with the Cu matrix were distributed in the Cu-B alloy powder region and coarser TiB dispersoids of ∼50 nm were observed in the circumferencial Cu-Ti region. The spray deposited billet consisted of the regions showing a fine microstructure of round shape, presumably originating from the injected Cu-B alloy powders, and a relatively coarse cellular microstructure. TiB2 and TiB of ∼200 nm were observed along the grain and cell boundaries. Fine TiB dispersoids of ∼10 nm having an orientational relationship with the Cu matrix were observed in both regions. The solidification behavior, with special interest in (he formation of dispersoids, was examined based on this observation.     

Effect of processing conditions and reactive compatibilizer on the morphology of injection molded modified poly(phenylene oxide)/polyamide‐6 blends

The effect of injection molding conditions and reactive compatibilization on the morphology of maleic anhydryde‐modified poly(phenylene oxide)/polyamide‐6 blends was investigated. The injection flow rate primarily influenced the position of the subskin layer, and the injection temperature affected the aspect ratio of the dispersed phase. A reduction of the sue of the dispersed phase occured during the converging flow in the barrel‐to‐sprue zone. The reactive compatibilization reduced the flow induced deformation, the coalescence and the breakup of particles and improved the dispersion of the minor phase.     

Binary blends of nylons with ethylene vinyl alcohol copolymers: Morphological,thermal, rheological,and mechanical behavior

Binary blends of ethylene vinyl alcohol copolymers, containing 62 (EVOH-62) and 71 (EVOH-71) mole percent vinyl alcohols, with nylons (nylon-6, nylon-6/12, and nylon-12) have been prepared from melt mixing in a twin screw compounding machine. Morphological, thermal, rheological, and mechanical properties were determined. EVOH-62/nylon-6 and EVOH-71/nylon-6 blends showed homogeneous phase morphologies in the nylon-6-rich region, and fine phase separations (c.a. 2 × 10^?7 m) in the EVOH-rich region. Melting point depression, positive deviations in viscosity and flexural modulus, and negative deviation in impact strength from the simple additive rule were generally observed. And the results were possibly interpreted in terms of compatibility and increased nylon/EVOH interactions over the nylon/nylon interactions. On the contrary, clean phase separations in large domains were observed from EVOH-71/nylon-6/12 and EVOH-71 /nylon-12 blends. Fibrillation was also obtained from EVOH rich blends. Probably due to the incompatible nature of these blends, yield at low rate of shear and a mechanical property drop were also observed.     

Fluorescent chemosensor for metal ions using a polymer having pendant pyridylbenzoxazole groups

Summary A polymer having fluorescent pyridylbenzoxazole groups has been prepared for the purpose of detecting of metal ions. Metal ions such as Co²⁺, Ni²⁺, Cu²⁺ and Fe²⁺ were found to coordinate with the bipyridyl-like fluorescent benzoxazole chromophores. Among the metal ions investigated, the Fe²⁺ ion was shown to be the most effective in terms of its fluorescence quenching ability. The addition of a metal scavenger 2,2'-dipyridyl to the metal ion-quenched polymer solution resulted in the recovery of the fluorescence. Received: 2 November 1999/Revised version: 19 December 1999/Accepted: 22 December 1999     

Control of molecular weight distribution in propylene polymerization with Ziegler–Natta/metallocene catalyst mixtures

Propylene polymerization was investigated with a sequential addition of Ziegler–Natta and metallocene catalysts. From the fact that the molecular weights of polypropylene (PP) produced with Ziegler–Natta and with metallocene catalysts differ, it was possible to control the molecular weight distribution (MWD) of PP with a sequential addition of methylaluminoxane and rac-ethylenebis(indenyl)zirconium dichloride followed by triethylaluminum and magnesium dichloride-supported titanium tetrachloride catalyst. The obtained PP exhibited a wide MWD curve with shoulder peak. The position and height of each peak was controlled with the variation of polymerization time for each catalyst as well as the amount of each catalyst. The MWD of PP prepared with sequential addition of catalysts was much wider than that of PP obtained from each catalyst. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:2213–2222, 1998     

Application of optimal temperature trajectory to batch PMMA polymerization reactor

A mathematical model is developed for the polymerization of methyl methacrylate (MMA) in a batch reactor. The model includes chain transfers to the monomer and solvent and termination by both combination and disproportionation and also takes into account the density change of the reactor contents and the gel effect. The usual pseudo-steady-state assumption is relaxed here. The validity of the proposed model is tested by an isothermal experiment of batch PMMA polymerization. Indeed, the experimental results show that the proposed model can describe the real polymerization system very well in view of both monomer conversion and average molecular weights. The optimal control theory is applied together with Pontryagin's minimum principle to calculate the optimal temperature trajectory for a batch polymerization reactor system which would lead to a polymer product having the desired properties set a priori. The performance index of the control system is composed of three factors—the desired monomer conversion and number- and weight-average molecular weights. The desired values of number- and weight-average molecular weights are obtained at a specified monomer conversion within acceptable error ranges. Control experiments are conducted to track the optimal temperature trajectory obtained from the model and the results are found to be in good agreement with the desired values. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 59–68, 1998