Applications of a reduction method for reanalysis to nonlinear dynamic analysis of framed structures

 This paper is concerned with the nonlinear dynamic analysis of framed structures using a reduction method recently proposed by the authors. The reduction method is originally devised for structural static reanalysis and has been applied in optimal design of structures to speed up the design process. For nonlinear dynamic analysis of framed structures, the incremental or iterative equations of motion can be transformed into an algebraic system of equations if appropriate integration methods such as Newmark's method are used to integrate the equations of motion. The resulting algebraic system, referred to as the effective system in this paper, changes during the simulation for a nonlinear dynamic problem. Therefore, from the point of view of solving systems of equations, a nonlinear dynamic problem is very similar to an optimal design problem in that the system of equations changes for both types of problems. Hence, any reanalysis technique can be readily applied to carry out a nonlinear dynamic analysis of structures. As demonstrated from the presented numerical examples, the response obtained by the adopted reduction method is as accurate as that obtained by the Cholesky method, and as estimated from the operation counts involved in the method, it is more efficient than the Cholesky method when the half-band width is greater than about 50. Received 23 March 2000     

Processability‐enhanced bimodal high‐density polyethylene with comb‐branched high‐density polyethylene

Two solution reactors in series were utilized to synthesize comb‐branched high‐density polyethylene (HDPE), cbHDPE, where the first reactor prepares vinyl‐terminated HDPE macromers catalyzed by an organometallic catalyst favoring beta hydride transfer and the second reactor copolymerizes HDPE macromers with ethylene using a different organometallic catalyst capable of incorporating macromers. A bimodal HDPE, biHDPE with bimodalities in molecular weight, and hexene content of the desired composition distribution was also prepared in a gas phase reactor using silica supported dual organometallic catalysts. By blending 3% solution‐made cbHDPE into the gas‐phase biHDPE, the resulting trimodal HDPE preserves the excellent stiffness and toughness of the bimodal HDPE while having exceptional melt strength and processability. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45755.     

Polyester-based green renewable eco-composites by solar energy tube processing: characterization and assessment of properties

A solar energy tube was used for the processing of banana fiber (BF), which is employed as filler in polycaprolactone-based green composites. The composite was made by melt-blending acrylic acid-grafted polycaprolactone (PCL-g-AA) with a coupling agent-treated banana fiber (TBF). To improve the interface adhesion of the PCL/BF composites, acrylic acid was used as a stabilizer for the blending of PCL and TBF. The water resistance of PCL-g-AA/TBF was greater than that of PCL/BF and a cytocompatibility evaluation with human foreskin fibroblasts (FBs) indicated that both materials were nontoxic. The results from the FB proliferation assays indicated a higher cytocompatibility of the PCL/BF composites than of the PCL-g-AA/TBF composites. The cell-cycle test of FBs on PCL/BF and PCL-g-AA/TBF composites were not affected by the DNA content related to damage. Moreover, both BF and TBF enhanced the polysaccharide content and antioxidant properties of the composites, demonstrating the potential of PCL/BF and PCL-g-AA/TBF composites for biomedical material applications.     

Studies on the electrospun Nylon 6 nanofibers from polyelectrolyte solutions: 1. Effects of solution concentration and temperature

Polyelectrolyte solutions of Nylon 6 in 99 vol% formic acid were electrospun, and the effect of polymer concentration was studied. Using a laser device to locally heat the needle spinneret, the solution temperature was feasibly elevated up to 66 °C, and its effect on electrospinning was investigated as well. The microstructure of the as-spun products was characterized by several analytical techniques, including electron diffraction, differential scanning calorimetry (DSC) and wide-angle X-ray diffraction. Based on the solution rheology, the entanglement concentration (c_e) was determined to be 1 wt%. To prepare bead-free fibers, the minimum polymer concentration was 8 c_e, which was much higher than that (1.75-2.0 c_e) required for conventional neutral solutions. Increasing the polymer concentration and/or solution temperature led to a gradual change of electrospun products from round fibers with major γ form crystals to ribbon-like fibers in possession of exclusive α form ones. For intermediate concentrations, nanowebs made of nanofibrils with diameters of 20-40 nm were seen. Thin ribbon-like fibers (ca. 40 nm thick) with nanowebs became the dominant products obtained from the 15 wt% solutions at high temperatures. The dramatic variations in morphological features and crystal modification could be thoroughly explained on the basis of the interplay between solvent evaporation at the jet surface and solvent diffusion in the liquid jet. DSC heating traces on the ribbon-like fibers exhibited an unusually high melting temperature of ∼235 °C, which is higher than the equilibrium melting temperature of Nylon 6 crystals of 232 °C.     

Ultrahigh molecular weight polyethylene fibers prepared using conical dies with varying dimensions

Dimensions of conical dies were found to have a significant influence on thermal, morphological, orientation, ultradrawing, and dynamic mechanical properties of the as‐prepared and/or drawn ultrahigh molecular weight polyethylene (UHMWPE) fiber specimens prepared in this study. Many demarcated “micro‐fibrils” were found paralleling to fiber direction of the as‐prepared UHMWPE fiber specimens. The percentage crystallinity, melting temperatures, orientation factor (f_o) and achievable draw ratio (D_ra) values of each as‐prepared UHMWPE fiber specimen prepared at a fixed length of outlet land reach a maximum value, as the entry angles of the conical die approach the optimum value at 75°. The maximum f_o and D_ra values obtained for each F₂₀^75‐y as‐prepared fiber series specimens prepared using the optimum entry angle reach another maximum value as their length of outlet land approach the optimum value of 6.5 mm. The ultimate tensile strengths and moduli of the drawn UHMWPE fibers prepared at the optimum entry angle and length of outlet land are significantly higher than those of fibers prepared at other conditions but stretched to the same draw ratio. Possible reasons accounting for the above interesting properties were discussed in this study. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers     

Influence of Aging on Autohesive Tack of Brominated Isobutylene-co-p-methylstyrene (BIMS) Rubber in the Presence of Phenolic Resin Tackifier

The role of phenolic resin tackifier on autohesive tack of brominated isobutylene-co-p-methylstyrene (BIMS) rubber was studied by a 180° peel test with particular reference to aging. Phenolic resin showed very little effect on the unaged tack of BIMS rubber. The tack strength of the rubber/resin mixture marginally increased at 1 phr resin concentration, beyond which it decreased. Based on the data on the compression creep, maximum tensile stress, and viscoelastic properties of the rubber/resin mixtures, phenolic resin did not enhance the interfacial viscous flow behavior of the rubber/resin mixtures. The results from dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM) confirmed the existence of a phase-separated morphology in the rubber/resin blends even at low resin concentration. Upon aging at 100°C for 36 h, the rubber/resin blend containing 1 phr of phenolic resin showed further increase in tack strength which was attributed to migration of the tackifier to the rubber surface and the changes in the compression creep, viscoelastic behavior, and maximum tensile stress of the rubber/resin mixtures. This is also a function of aging time. Surface energy analysis by contact angle measurement, Fourier Transform Infrared Spectroscopy (FT-IR/ATR) studies, and surface roughness measurement by atomic force microscopy (AFM) elucidate the enrichment of the phenolic resin on the rubber surface upon aging and the mechanism of enhanced tack strength.     

Hemolytic disease of the newborn caused by anti-M antibody

An unusual case of hemolytic disease of the newborn caused by anti-M antibody is presented. Hyperbilirubinemia was noted in a full-term baby boy at 4 days of age. A total of 160 mL of M-positive packed red blood cells from the baby's father were transfused during the next 9 days and the hemolytic process became aggravated. The baby was referred to our hospital at 14 days of age. Maternal anti-M was detected and the baby was transfused with 50 mL of M-negative packed red blood cells. The baby's condition stabilized and he was discharged uneventfully at 18 days of age.     

Characterization study of time- and temperature-dependent mechanical behavior of polyimide materials in electronic packaging applications

The thermo-mechanical testing of the type HPP ST polyimide films with high performance, supplied by Dupont, was realized under different strain rates and temperature effects. Therefore, the rate-temperature-dependent stress-strain behavior of materials was investigated and the dependence of the Young’s modulus on temperature and strain rate was reported. In view of the uncertainty of the Young’s modulus determination, the specimens were tested with the unloading-reloading technique to verify the test results. The constant strain rate uniaxial tensile test and long-time creep test at various temperatures were performed to characterize the time-temperature-dependent mechanical property precisely. The cyclic loading test was also implemented on the specimen to investigate cyclic stress-strain behavior. In addition, the nanoindentation test was carried out at room temperature to validate the elastic modulus derived from the uniaxial tensile test. This research is expected to investigate the time-temperature-dependent mechanical behavior of the polyimide materials for different service regimes including tensile and cyclic mechanical loading under elevated temperature in a systematic manner.