Modeling mode i fracture of bitumen films

The fracture behavior of thin films of bitumen in double cantilever beam (DCB) specimens was investigated over a wide range of temperature and loading rate conditions using finite-element analysis. The model includes a phenomenological model for the mechanical behavior of bitumen, implemented into a special-purpose finite-element user material subroutine, combined with a cohesive zone model (CZM) for simulating the fracture process. The finite-element model is validated against experimental results from laboratory tests of DCB specimens by comparing measured and predicted load-line deflection histories and fracture energy release rates. Computer simulation results agreed well with experimental data of DCB joints containing bitumen films in terms of peak stress, fracture toughness, and stress-strain history response. The predicted "normalized toughness," G=2h, was found to increase in a power-law manner with effective temperaturecompensated strain rate in the ductile region as previously observed experimentally. In the brittle regime, G=2h is virtually constant. The model successfully captured the ductile and brittle failure behavior of bitumen films in opening mode (tension) for stable crack growth conditions. © 2013 American Society of Civil Engineers.

Isothermal crystallization kinetics of PEO in poly(ethylene terephthalate)-poly(ethylene oxide) segmented copolymers. I. Effect of the sofi-block length

The isothermal crystallization kinetics of poly(ethylene oxide) (PEO) block in two poly(ethylene terephthalate) (PET)-PEO segmented copolymers was studied with differential scanning calorimetry. The Avrami equation failed to describe the overall crystallization process, but a modified Avrami equation, the Q equation, did. The crystallizability of the PET block and the different lengths of the PEO block exerted strong influences on the crystallization process, the crystallinity, and time final morphology of the PEO block. The mechanism of nucleation and the growth dimension of the PEG block were different because of the crystallizability of time PET block and the compositional heterogeneity. The crystallization of the PEO block was physically constrained by the microstructure of time PET crystalline phase, which resulted in a lower crystallization rate. However, this influence became weak with the increase in the soft-block length. (C) 2000 John Wiley & Sons, Inc.

Studies on the alkylation of isobutane with butene over WO3/ZrO2 strong solid acid (I) - Effect of preparation, load of WO3 and calcination temperature

A series of WO3/ZrO2 strong solid acid prepared under different conditions were studied. Their crystal structures, surface properties and acidities were determined by means of XRD, DTA-TG, H-2- TPR, Laser Raman and acidity measurements. The results revealed that ZrO2 in WO3/ZrO2 existed mainly in tetragonal phase, the addition of WO3 plays an important role to stabilize tetragonal phase of ZrO2 and thus the catalyst had a considerable surface area. WO3 in WO3/ZrO2 was dispersed and crystalized in WO3 crystalite on ZrO2 surface and partly reacted with ZrO2 to form the bond of Zr-O-W, which acts as the strong solid acid site. The catalytic properties of WO3/ZrO2 strong solid acid for alkylation of iso-butane with butene under the different conditions were investigated. They had a better reaction performance than other strong solid acids, a parallel relationship could be drawn between the catalytic activity and the amount of acid sites as well as the acidic strength of the catalysts.

Isobutane/butene alkylation over supported heteropoly acid catalysts: I. Influence of the structure of silica

Catalysts consisting of heteropoly acids (HPAs) supported on different silica and mesoporous molecular sieves have been prepared by impregnation and the sol-gel method, respectively, and their catalytic behavior in fixed-bed alkylation of isobutane with butene has been investigated. The activity, selectivity and stability of the supported-HPA catalysts could be correlated with the surface acidity of the catalysts, the structure of supports as well as the time on stream (TOS). In the fixed-bed reactor, the acidity of the heteropoly acid is favorable to the formation of dimerization products (C-8(=)); especially, the pore size of supports was seen to have an important effect on activity and product distribution of the catalysts. Contrary to the traditional solid-acid catalysts, the supported-HPA catalysts own an excellent stability for alkylation, which makes it possible for these supported catalysts to replace the liquid-acid catalysts used in industry.

THE CRYSTALLIZATION BEHAVIOUR OF BLOCK COPOLYMER/HOMOPOLYMER BLENDS I. INFLUENCE OF NONSPHERICAL MICELLE ON CRYSTALLIZATION BEHAVIOUR IN DILUTE SOLID SOLUTIONS

The effect of micelle on crystallization behaviour of dilute poly(methyl methacrylate-b-tetrahydrofuran) diblock copolymer/tetrahydrofuran homopolymer, dilute poly (ethylene-b-styrene-b-ethylene) triblock copolymer/ethylene homopolymer solutions has been studied. The results show that with the structural teansitions from spherical to nonspherical micelle in the blends, great changes in the nucleation and spherulite morphologies take place.