There are various methods to determine the compressive and tensile strength of asphalt concrete under static loading conditions and most studies on asphalt strength and fracture have been conducted under such loading conditions. However, pavement materials also have to withstand a wide variety of loading and temperature conditions which may vary from quasi-static to high-strain rate impact, and pavement breakdown may occur due to fracture and/or fatigue failure. In the present study, a bituminous mix with 30% RAP has been characterized under quasi-static (10?3–10?4 strain/s) and high-strain rate (200–700 strain/s) regimes. The experimental studies have been performed to better understand the compressive, tensile and fracture response of bituminous mixes. Split Hopkinson pressure bar (SHPB) and its modifications were used for high-strain rate characterization of this bituminous mixture. It was observed that the mechanical properties of the hot mix asphalt (HMA) changed significantly under high-strain rate testing. Also, the failure mechanisms observed under the high-strain rate loading were found to be considerably different from those obtained in static testing, where failure of binder was a predominant mechanism. It was observed that high-strain rate loading caused trans-aggregate failures in the specimens; in addition to failure of the binder. 相似文献
The direct α‐Csp2 H functionalization and thiomethylation of α‐oxoketene dithioacetals (DTAs) has been accomplished with dimethyl sulfoxide (DMSO) in the presence of iodine and a copper(I) salt for the first time. A prerequisite is the in situ iodination of the α‐Csp2 atom of dithioacetals that could offer other reaction channels. The operationally simple one‐pot protocol includes region‐defined consecutive iodination and sulfenylation of the challenging α‐Csp2 H bond of dithioacetals employing cheap and readily available reagents. DMSO here plays a dual role as thiomethyl source and solvent.
Binder evolution information generated using thermal analysis techniques is used along with microstructural information to define a thermal cycle for debinderizing injection-molded articles. In addition, the roles of binder chemistry, powder morphology, binder loading, article size, heating rate, and environmental conditions in determining a satisfactory thermal cycle are investigated. Major binder evolution events and types of defects generated are identified. An improved binder removal cycle is developed from this evaluation for organics elimination of a honeycomb structure. 相似文献
When the water table rises in a granular soil mass, a large additional settlement of footing resting on such a soil mass is commonly expected. Laboratory model tests show that when the water table rises to the footing level, there can be an additional 400 to 500% of the settlements compared to when the soil is dry. To understand the mechanics of the additional settlements of footings resting on the granular soil masses caused by water table rise, an investigation into the change in the Young's modulus of soil was therefore made using oedometer tests. A relation between the saturated and the dry Young's moduli of the granular soils is presented for use in the elastic analysis of footing settlements. The findings of the investigation were then used to predict the additional settlements of a model footing when subjected to a water table rise, using elastic analysis. The theoretical predictions of the additional settlements are lower than the actual additional settlements observed in the settlement tests conducted in the laboratory using model tests. The model tests show that the additional settlements are larger in loose sands than in dense sands. 相似文献
The paper presents the nonlinear flexural response of laminated composite plates. The mathematical formulation of the actual physical problem of the laminated composite plate subjected to mechanical loading is presented utilizing higher order shear deformation theory and von-Karman nonlinear kinematics. These nonlinear governing differential equations of equilibrium are linearized using quadratic extrapolation technique. A meshfree technique based on multiquadric RBFs is used for analysis of the problems. Isotropic, orthotropic and laminated composite plates with immovable simply supported and clamped edges are analyzed. 相似文献
Fuel cell-based automobiles have gained attention in the last few years due to growing public concern about urban air pollution
and consequent environmental problems. From an analysis of the power and energy requirements of a modern car, it is estimated
that a base sustainable power ofca. 50 kW supplemented with short bursts up to 80 kW will suffice in most driving requirements. The energy demand depends greatly
on driving characteristics but under normal usage is expected to be 200 Wh/km. The advantages and disadvantages of candidate
fuel-cell systems and various fuels are considered together with the issue of whether the fuel should be converted directly
in the fuel cell or should be reformed to hydrogen onboard the vehicle. For fuel cell vehicles to compete successfully with
conventional internal-combustion engine vehicles, it appears that direct conversion fuel cells using probably hydrogen, but
possibly methanol, are the only realistic contenders for road transportation applications. Among the available fuel cell technologies,
polymer-electrolyte fuel cells directly fueled with hydrogen appear to be the best option for powering fuel cell vehicles
as there is every prospect that these will exceed the performance of the internal-combustion engine vehicles but for their
first cost. A target cost of $ 50/kW would be mandatory to make polymer-electrolyte fuel cells competitive with the internal
combustion engines and can only be achieved with design changes that would substantially reduce the quantity of materials
used. At present, prominent car manufacturers are deploying important research and development efforts to develop fuel cell
vehicles and are projecting to start production by 2005. 相似文献
Journal of Materials Science - This paper presents an investigation aimed at understanding the shock wave propagation response of oriented α-quartz single crystals by using molecular dynamics... 相似文献
Nowadays, several research groups are extensively trying to develop by synthesizing and characterizing single/co-doped single-phase bismuth ferrite (BFO) in order to get a highly efficient eco-friendly multifunctional devices. In this process, this report is an attempt to provide the detailed studies of structural, dielectric, impedance and ferroelectric properties of Bi(Fe0.85Dy0.15)O3 ceramic fabricated via the solid-state reaction method. Analysis of X-ray diffraction (XRD) data confirms a single phase of orthorhombic symmetry. The average crystallite (particle) size is found to be in the order of?~?41 nm. The field emission scanning electron microscopy (FE-SEM) spectrum shows a homogeneous grain distribution of the sample. The elemental composition examined by means of energy dispersive X-ray spectroscopy (EDXS) shows the existence of constituent elements of the sample. The electrical measurements and analysis, carried out using a computer-controlled phase sensitive multimeter (PSM) in a frequency range of 1 kHz–1 MHz at different sets of temperature (25–325 °C), provide many interesting features to explain further conduction mechanism. The dielectric analysis exhibits high value of dielectric constant (?r) and small value of dielectric loss (tanδ). Due to the effect of electronic and space charge polarization, the ?r value falls with an increasing frequency. The frequency–temperature dependence of impedance and electrical modulus analysis reveals the presence of semiconductor nature and non-Debye type of relaxation process in the sample. The analysis of ac-conductivity (σac) with respect to frequency and temperature obeys the universal Jonscher’s power law. The electric polarization study shows an enhancement in ferroelectric property of the material. Hence, based on the significant enhancement in electrical and ferroelectric properties of the Bi(Fe0.85Dy0.15)O3 material, the material may be considered for some applications.
Thermal history of droplets associated with gas atomization of melt has been investigated. A mathematical model, based on
classical theory of heterogeneous nucleation and volume separation of nucleants among droplets size distribution, is described
to predict undercooling of droplets. Newtonian heat flow condition coupled with velocity dependent heat transfer coefficient
is used to obtain cooling rate before and after nucleation of droplets. The results indicate that temperature profile of droplets
in the spray during recalescence, segregated and eutectic solidification regimes is dependent on their size and related undercooling.
The interface temperature during solidification of undercooled droplets rapidly approaches the liquidus temperature of the
alloy with a subsequent decrease in solid-liquid interface velocity. A comparison in cooling rates of atomized powder particles
estimated from secondary dendrite arm spacing measurements are observed to be closer to those predicted from the model during
segregated solidification regime of large size droplets. 相似文献