Computational micromechanical analysis of the representative volume element of bituminous composite materials

Micromechanical computational modeling is used in this study to determine the smallest domain, or Representative Volume Element (RVE), that can be used to characterize the effective properties of composite materials such as Asphalt Concrete (AC). Computational Finite Element (FE) micromechanical modeling was coupled with digital image analysis of surface scans of AC specimens. Three mixtures with varying Nominal Maximum Aggregate Size (NMAS) of 4.75 mm, 12.5 mm, and 25 mm, were prepared for digital image analysis and computational micromechanical modeling. The effects of window size and phase modulus mismatch on the apparent viscoelastic response of the composite were numerically examined. A good agreement was observed in the RVE size predictions based on micromechanical computational modeling and image analysis. Micromechanical results indicated that a degradation in the matrix stiffness increases the corresponding RVE size. Statistical homogeneity was observed for window sizes equal to two to three times the NMAS. A model was presented for relating the degree of statistical homogeneity associated with each window size for materials with varying inclusion dimensions.     

Structural and Magnetic Properties of Nanostructured Pr0.75 Y 0.25Co5 Powders Obtained by Mechanical Milling and Subsequent Annealing

Pr_0.75 Y _0.25Co₅-based as-cast alloys were processed by high-energy ball milling to obtain nanostructured powders with high coercivity. The powders obtained after 4 h of milling exhibited nearly amorphous behavior in X-ray diffraction patterns. DSC scans of the as-milled powders indicated a process of crystallization by broad, exothermic transition peak at 503 °C. Annealing of the milled powders at 850 °C for 2.5 min in high vacuum produced fine grains of size ranging 15–30 nm with optimal microstructure and hard magnetic properties. Magnetic measurements of the annealed powders evaluated a high intrinsic coercivity, _i H _c of 9.3 kOe, and a remanence ratio, M _r/ M _max of 0.72. The magnetic hardening was attributed to higher anisotropy field of the powders and microstructural uniformity achieved by the processing methodologies.     

Mechanics based model for predicting structure-induced rolling resistance (SRR) of the tire-pavement system

The structure-induced rolling resistance of pavements, and its impact on vehicle fuel consumption, is investigated in this study. The structural response of pavement causes additional rolling resistance and fuel consumption of vehicles through deformation of pavement and various dissipation mechanisms associated with inelastic material properties and damping. Accurate and computationally efficient models are required to capture these mechanisms and obtain realistic estimates of changes in vehicle fuel consumption. Two mechanistic-based approaches are currently used to calculate vehicle fuel consumption as related to structural rolling resistance: dissipation-induced and deflection-induced methods. The deflection-induced approach is adopted in this study, and realistic representation of pavement–vehicle interactions (PVIs) is incorporated. In addition to considering viscoelastic behavior of asphalt concrete layers, the realistic representation of PVIs in this study includes non-uniform three-dimensional tire contact stresses and dynamic analysis in pavement simulations. The effects of analysis type, tire contact stresses, pavement viscoelastic properties, pavement damping coefficients, vehicle speed, and pavement temperature are then investigated.     

Characteristics of Tableted Roselle (Hibiscus sabdariffa Linn.) with Addition of Sodium Starch Glycolate

The focus of this research is to study the characteristics of tablets produced from the binary powder mixture of Roselle (Hibiscus sabdariffa Linn.) and sodium starch glycolate (SSG) powders. The experimental parameters studied were the compaction pressure and the mass composition. The findings indicated that the increase of compaction pressure increased the tensile strength of tablets until a limiting value was reached. On the other hand, as the compaction pressure increased, the porosity of tablets decreased to a minimum value. The elastic recovery of tablets slightly decreased in some results. The increase in compaction pressure also increased the dissolution time of tablets up to a maximum value. The increase of SSG composition decreased the tensile strength of tablets to a certain amount. The dissolution time of tablets also reduced when the percentage of SSG increased. Subsequently, under the same compaction conditions, the increase of SSG composition increased the porosity and the elastic recovery of tablets until the limiting values were achieved.     

Effect of Particle Size on Direct Compaction of Urea Fertilizer

The effect of particle size on compaction properties and characteristics of urea tablets manufactured from available urea granules (TG tablets) and ground urea powders (TP tablets) was investigated. The compaction properties, namely, plastic work, elastic work, friction work, and maximum ejection pressure were analyzed from the force-displacement profile of the compaction process. Five applied pressures ranging between 37.67 MPa and 188.35 MPa were used to compact the materials using a universal testing machine. Characteristics of the tablets tested were mechanical strength and the release of ammonium ion through dissolution test. The results demonstrated that TG tablets underwent high plastic work and elastic work but low friction work compared to the TP tablets. TG tablets released lower amount of ammonium ion compared to the TP tablets at almost all applied pressures, except at 75.34 MPa. This study provides a valuable data for evaluating the behavior of urea in the form of granules and powders during the compaction process as well as the suitability in choosing the form of raw material for the production of urea tablets.     

The effect of aggregate gradation on creep and moisture susceptibility performance of warm mix asphalt

It is clear that the purpose of mixture design is to select optimum asphalt content for a desired aggregate structure to meet the prescribed criteria. Aggregate makes up high proportion of volume and mass of mixtures; hence, it is considered as an important constituent of asphalt concrete. This study postulates that the gradation is an important characteristic of the aggregate in adoption of the optimum mixture. One aggregate source, three gradations and different percentages of Sasobit^® was used to manufacture hot mix asphalt and warm mix asphalt. The test results indicated that the aggregate gradation affects the rutting resistance and especially the moisture susceptibility of the introduced mixtures, differently. Rutting resistance was evaluated using the flow number parameter, and in order to determine the moisture sensitivity mechanism, a mechanical and visual inspection tests were carried out. At the end, it is concluded that the optimum aggregate gradation for these two types of mixtures is different.     

Synthesis and antibacterial activity of stable bio-conjugated nanoparticles mediated by walnut (Juglans regia) green husk extract

Nanoparticles have gained significant attention in recent years due to their numerous applications in various aspects of human life. A variety of methods have been investigated for synthesis of nanoparticles among which, biogenic approaches are considered as both simple and eco-friendly. Here, a new single-step biological approach was employed for synthesis of silver chloride nanoparticles (AgCl-NPs) at room temperature, using walnut green husk extract. Macromolecules present in the plant extract, which might act as bio-reductants and/or stabilisers of nanoparticles were characterised by Fourier transform Infrared spectroscopy. X-ray diffraction pattern and transmission electron microscopy revealed that 1 mM of AgNO3 produced mostly spherical nanoparticles in a range of 4–30 nm in diameter with an average of 16 nm. Interestingly, the synthesised nanoparticles showed significant inhibitory effects against Escherichia coli and Staphylococcus aureus clinical isolates. Altogether, these data suggest a new encouraging application of a medicinal plant bound with synthesised AgCl nanoparticles.     

Phonon engineering in carbon nanotubes by controlling defect concentration

Outstanding thermal transport properties of carbon nanotubes (CNTs) qualify them as possible candidates to be used as thermal management units in electronic devices. However, significant variations in the thermal conductivity (κ) measurements of individual CNTs restrict their utilizations for this purpose. In order to address the possible sources of this large deviation and to propose a route to solve this discrepancy, we systematically investigate the effects of varying concentrations of randomly distributed multiple defects (single and double vacancies, Stone-Wales defects) on the phonon transport properties of armchair and zigzag CNTs with lengths ranging between a few hundred nanometers to several micrometers, using both nonequilibrium molecular dynamics and atomistic Green's function methods. Our results show that, for both armchair and zigzag CNTs, κ converges nearly to the same values with different types of defects, at all lengths considered in this study. On the basis of the detailed mean free path analysis, this behavior is explained with the fact that intermediate and high frequency phonons are filtered out by defect scattering, while low frequency phonons are transmitted quasi-ballistically even for several micrometer long CNTs. Furthermore, an analysis of variances in κ for different defect concentrations indicates that defect scattering at low defect concentrations could be the source of large experimental variances, and by taking advantage of the possibility to create a controlled concentration of defects by electron or ion irradiation, it is possible to standardize κ with minimizing the variance. Our results imply the possibility of phonon engineering in nanostructured graphene based materials by controlling the defect concentration.     

Wavelet filtration of noisy images

Methods of noisy image filtration using wavelet transforms with real and complex basis sets have been compared. It is shown that the use of a complex wavelet transform provides more effective filtration and admits automatic optimization of the filter parameters. Optimized choice of the threshold level during filtration based on a complex wavelet transform significantly decreases the error of image reconstruction as compared to that achieved with a standard method of discrete wavelet transform employing basis sets of the Daubechies wavelet family.

     

Synthesis of carbon nanotube,graphene, CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript>, and NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> polypyrrole nanocomposites and study their microwave absorption

In this experimental work, different conductive polymer nanocomposites were synthesized using polypyrrole as conductive polymer and CoFe₂O₄, NiFe₂O₄, CNT and graphene as fillers. X-ray diffraction pattern was used to study the crystallinity of the products and it was found CoFe₂O₄, NiFe₂O₄, CNT, and graphene were successfully embedded in the polymer matrix. To further approve the synthesis of the nanocomposites, energy dispersive X-ray spectroscopy was served. Surface groups of the synthesized nanocomposites were studied by Fourier transform infrared and Raman spectroscopy. The morphology of the products was examined by scanning electron microscopy and transmission electron microscopy. It was found the fillers were successfully embedded in the polymer matrix and they were in nanometer scales. To investigate the magnetic properties and conductivity of the polymer nanocomposites, alternating gradient force magnetometer and four-point probe were used, respectively. Finally, the microwave absorption properties of the polymer nanocomposites were studied and it was found the fillers have different effects on the polymer microwave absorption value.