To study the distribution law of circumferential residual stress after casing expansion, using the finite element explicit dynamic analysis method analyzed the expansion process of expandable casings under different expansion rates. The analysis obtained key technical parameters of circumferential residual stress, average circumferential residual stress and elastic recovery along the wall thickness direction after casing expansion. It is recognized that the maximum residual tensile stress after casing expansion locates in the middle part of the casing thickness direction. The maximum residual compressive stress locates in the outer wall of the casing. When the expansion rate exceeds 18%, the increase in expansion rate will not lead to an increase in circumferential residual stress after casing expansion. The elastic recovery after casing expansion will reduce the circumferential stress during the expansion process. Considering collapse strength and the influence of elastic recovery on casing patch sealing performance after casing expansion, 23% is the most suitable expansion rate, which can effectively reduce the circumferential residual stress and improve the casing collapse strength. The analysis in this paper can provide bases for the calculation of casing collapse strength after expansion.
This paper 2 briefly reviews key European and American vehicle emission models including NAEI, COPERT, HBEFA, ARTEMIS and MOBILE. Their databases, modelling approaches, strengths, shortcomings and their relevance to New Zealand are discussed. The classification and application of vehicle emission models are also summarised. Some traffic situation models, especially the recently-released ARTEMIS model, seem to have some advantages as they can simulate driving dynamics in a more reliable but relatively simple way. The ARTEMIS database is probably the most comprehensive one developed to date. Two New Zealand models are also reviewed: the Ministry of Transport’s VFEM dating from 1998 and the Auckland Regional Council’s more recent VEPM. It is believed that these NZ models have significant room for improvement, especially as to the accuracy of emission factors for the unique NZ vehicle fleet. The paper identifies the issues associated with the NZ models and recommends possible ways for improving them. Furthermore, emission data for heavy-duty vehicles are especially scarce for the New Zealand fleet and collection of these data should be given priority.
The production of high-performance, low-cost warm mix additives (WMa) for matrix asphalt remains a challenge. The pyrolysis method was employed to prepare wax-based WMa using waste polypropylene plastic (WPP) as the raw material in this study. Penetration, softening point, ductility, rotational viscosity, and dynamic shear rheological tests were performed to determine the physical and rheological properties of the modified asphalt. The adhesion properties were characterized using the surface free energy (SFE) method. We proved that the pyrolysis temperature and pressure play a synergistic role in the production of wax-based WMa from WPPs. The product prepared at 380 °C and 1.0 MPa (380-1.0) can improve the penetration of matrix asphalt by 61% and reduce the viscosity (135 °C) of matrix asphalt by 48.6%. Furthermore, the modified asphalt shows favorable elasticity, rutting resistance, and adhesion properties; thus, it serves as a promising WMa for asphalt binders.
Additive manufacturing has the potential to produce novel high-performance electrical machines enabling direct printing of complex shapes and simultaneous processing of multiple feedstocks in a single build. We report properties and functional performance of Fe-3wt.%Si material that is printed by selective laser melting, machined down to thin laminates, and stacked to form a stator core of a prototype brushless permanent-magnet electrical motor. Big Area Additive Manufacturing (BAAM) of Nd2Fe14B (NdFeB)-polyphenylene (PPS) sulfide bonded magnets are magnetized and used for the rotor. The magnetic, mechanical, and electrical properties of the as-printed and various heat-treated thin laminates and the back electromotive force (emf) of the electrical motors at different rotational speeds are measured. The thin laminates exhibit a maximum relative permeability of 7,494 at an applied field of 0.8 Oe, and a core loss of about 44 W/kg at 60 Hz with the maximum induction of 15 kG. In addition to demonstration of AM printing, motor assembly and complete characterization of printed Fe-3wt.%Si, this report highlights the areas of improvement needed in printing technologies to achieve wholly AM built electrical motors and need of isotropic microstructures refinements to make the laminates appropriates for high mechanical strength and low loss rotational electrical devices.
The knowledge of adsorption behaviors and mechanism of CO2/CH4 in organic matter is of great importance for CO2 geological sequestration with enhanced gas recovery in shale reservoirs. In this study, the adsorption behaviors and confinement effects of CO2/CH4 in realistic kerogen nanopores have been investigated by using the grand canonical Monte Carlo method. To represent realistic nanopores in the kerogen matrix, the inkbottle-shaped and slit-like nanopores were developed. The effects of temperature, pressure, and pore size on competitive adsorption behaviors and adsorption mechanism of CO2/CH4 were explored. Simulation results indicate that the adsorption capacity of CH4 is lower than that of CO2 in the kerogen matrix with/without kerogen nanopores. A higher pressure and lower temperature are favorable for the adsorption capacities of CO2 and CH4. The gas adsorption capacities have been enhanced in both the inkbottle-shaped and slit-like nanopores. Meanwhile, the existence of inkbottle-shaped micropores is favorable for improving the selectivity of CO2/CH4 in shale organic matter. A higher CO2 injection pressure could improve its adsorption capacity but lower the adsorption selectivity of CO2 over CH4. Furthermore, confinement effects were observed in inkbottle-shaped and slit-like kerogen micropores and small mesopores. Two major factors, including the supercritical state of gas and microscale pores, could enhance the confinement effects. In addition to monolayer adsorption, micropore filling was observed in inkbottle-shaped and slit-like kerogen nanopores because of the confinement effects. It is expected that these results could help in understanding the microscopic adsorption mechanism and provide fundamental information for shale gas exploitation and CO2 sequestration.
Many scholars are concerned about the effect of nano-MgO as an expansion agent on the performance of cement-based materials at an early age, but over a long period less attention is paid to expansion stability and mechanical properties. This article examines the influence of nano-MgO on the long-term consistency, fluidity, expansion stability, hydration, and mechanical properties of 30% fly ash cement-based materials and improves research into nano-MgO as an expansion agent. Expansion performance, flexural and compressive strength, and stability after boiling and autoclave treatment were tested for specimens mixed with a 2, 4, 6, 8 and 10% cementitious material mass of nano-MgO. X-ray diffraction (XRD) and scanning electronic microscopy (SEM) were employed to study their hydration process and microstructure. The results showed that nano-MgO had an obvious effect on the consistency, fluidity and expansion performance of cement paste. After curing in water for 365 days and autoclaving thereafter, the hydration of nano-MgO was relatively complete. The volumetric expansion pressure of the magnesium hydroxide (Mg(OH)2) crystals and the crystallization pressure generated after their continuous precipitation were the main reasons for the expansion of the slurry. Nano-MgO improved the microstructure of cement paste and significantly enhanced its long-term flexural strength and compressive strength. When the content of nano-MgO was less than 10%, the cement with 30% fly ash had good long-term stability with the potential to compensate for the shrinkage of large-volume concrete.
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