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Investigation of hole quality in drilled Ti/CFRP/Ti laminates using CO2 laser
No full textThe machinability of titanium (Ti) and carbon fiber reinforced plastic (CFRP) (Ti/CFRP/Ti) laminates using CO2 laser is presented in this work. The effect of line energy and laser frequency on output responses such as heat affected zone (HAZ), taper angle (TA), metal composite interface (MCI) damage, surface roughness, dross height, and circularity were investigated. Line energy - the most influential parameter - demonstrated a threshold behavior; no drilling was observed below a certain line energy. Scanning acoustic microscopy (SAM), scanning electron microscopy (SEM), micro-computed tomography (μ-CT), and other imaging techniques were used to establish a correlation between laser parameters and CO2 laser machined damage in Ti/CFRP/Ti laminates. The results show that using a higher frequency and lower line energy can significantly improve the hole quality. However, dross free holes with minimum taper can be obtained using higher line energy. © 2020 Elsevier Lt
A nonequilibrium thermodynamic model for viscoplasticity coupled with damage for BCC metals
No full textWe present a physically enhanced ductile damage model applicable for body centered cubic (BCC) metals. The current proposition extends the authors� recent work on thermo-viscoplasticity based on two-temperature thermodynamics and physics of disparate types of dislocation densities. The description of the thermodynamic system involves primarily two types of variables (or degrees of freedom, DOFs) representing several micro/meso-scopic processes occurring in two separable time-scales during ductile damage. Processes of rearrangement and movement of defects, namely dislocations, voids, micro-cracks, take place in a time scale much slower than that of the vibration of atoms about their equilibrium positions in the lattice. Consequently, they appear in the thermodynamic theory in terms of slow configurational DOFs and the fast kinetic vibrational DOFs respectively. While we consider physics based internal variables, e.g., mobile and forest dislocation densities, for modeling viscoplasticity alone, material degradation due to ductile damage is treated in a phenomenological fashion taking recourse to the framework of continuum damage mechanics. In order to assess the performance of our proposal, numerical experiments on boundary value problems of viscoplasticity with or without damage are carried out and validated against available experimental evidence
Iron-Carbon Hybrid Magnetic Nanosheets for Adsorption-Removal of Organic Dyes and 4-Nitrophenol from Aqueous Solution
No full textHere, we report a nonprecious mesoporous adsorbent obtained from the carbonization of bagasse. The material shows an impressive pH-dependent adsorbent property for cationic, anionic, and commercially used dyes along with an organic contaminant (4-nitrophenol) in water. The adsorbent shows specific surface area of �462 m2 g-1 and the porous layered structure as confirmed by gas adsorption and microscopic techniques, respectively. Further, pH triggered adsorption of methylene blue (MB, cationic dye), Congo red (CR, anionic dye), and commercial hair dye were studied. The results show >96 adsorption for CR and MB within 24 min at pH 2 and pH 8, respectively. Moreover, fast adsorption response, 92.6 in 20 min, was obtained for a commercially used hair dye and demonstrates the practical applicability of the material for wastewater remediation. Under experimental conditions, adsorbent shows ultrafast adsorption kinetics (4 min to achieve equilibrium state with 99.5 adsorption) for 4-nitrophenol from water. Notably, the adsorbent shows structural stability, easily separable with an external magnetic field, and recyclability with �85 efficiency even after the fifth cycle
Phase & morphology engineered surface reducibility of MnO2 nano-heterostructures: Implications on catalytic activity towards CO oxidation
No full textAn understanding of the surface reducibility of a catalytically active oxide support is a pre-requisite to understanding its catalytic behavior. In this work, we report that through a stringent control over the phase and morphology of catalytically active MnO2 supports, a control over the surface reducibility can be achieved. Through temperature-programmed reduction (TPR), we prove a higher availability of lattice oxygen for the alpha-MnO2 phase, compared to that of beta-MnO2. Furthermore, by modifying the synthesis method, we could engineer the morphology of the alpha-phase into nanoflowers which in turn leads to a higher surface area, further enhancing the activity. On the engineered support, decoration of Pt nanoparticles can lower the full conversion temperature for CO oxidation at a considerably low temperature
Heat and mass transfer from a system of closely packed capillaries - Possible choice for wicks
No full textEvaporation characteristics of a radiatively heated (similar to 1000 W/m(2) of incident heat flux) unconventional porous medium consisting of closely packed vertical capillaries have been investigated. Three stages of mass loss from a conventional porous medium, consisting of spheres, are well known; high evaporation rate in stage 1 is sustained by capillary liquid films, which transport liquid from lower regions of a porous medium to its exposed top surface. We show that in a bundle of capillaries, stage 1 is sustained by near-zero radii (NZR) of contacts, formed throughout the contact line of two or more touching capillaries, which can theoretically lead to infinite height rise. Some of the evaporative features of these NZR of contacts were recently (Kumar and Arakeri, 2018b) explored. With closely packed capillaries, along with the existence of the NZR of contacts (as in rods' case), we get an additional advantage of having inner diameter, which we show act as a reservoir for the nearby NZR of contacts. We report extremely high (time) duration of high rates of evaporation from a bundle of capillaries, which is seemingly impossible to achieve in the conventional systems. In passive systems like loop heat pipes and capillary pumped loops, an additional reservoir is not needed in case a wick consisting of closely packed capillaries are used
Squareness for the Monopole-Dimer Model
No full textThe monopole-dimer model introduced recently is an exactly solvable signed generalisation of the dimer model. We show that the partition function of the monopole-dimer model on a graph invariant under a fixed-point free involution is a perfect square. We give a combinatorial interpretation of the square root of the partition function for such graphs in terms of a monopole-dimer model on a new kind of graph with two types of edges which we call a dicot. The partition function of the latter can be written as a determinant, this time of a complex adjacency matrix. This formulation generalises Wu�s assignment of imaginary orientation for the grid graph to planar dicots. As an application, we compute the partition function for a family of non-planar dicots with positive weights
On the Growth of the Bergman Metric Near a Point of Infinite Type
No full textWe derive optimal estimates for the Bergman kernel and the Bergman metric for certain model domains in C2 near boundary points that are of infinite type. Being unbounded models, these domains obey certain geometric constraints�some of them necessary for a non-trivial Bergman space. However, these are mild constraints: unlike most earlier works on this subject, we are able to make estimates for non-convex pseudoconvex models as well. In fact, the domains we can analyse range from being mildly infinite-type to very flat at infinite-type boundary points
Surface modification influenced properties of silicon nanowires grown by Ag assisted chemical etching with ECR hydrogen plasma treatment
No full textSilicon nanowires (SiNWs) are fabricated by Ag assisted chemical etching and are treated with hydrogen plasma created by electron cyclotron resonance (ECR) plasma system at 600 watts microwave power for various time durations (0�30 min). The hydrogen plasma exposure on the surface of the SiNWs reduced the surface roughness and increased the crystalline nature. SEM analysis revealed that the diameter of the SiNWs decreased on plasma exposure. The electrical conduction measurements suggested that the hydrogen plasma exposure for 5 min on the SiNW surface enhanced the electrical conductivity when compared to as fabricated SiNW surface. The hydrophobic nature of fabricated SiNWs was transformed to hydrophilic at plasma exposure for lower time duration. On plasma exposure of NWs for 30 min the sample turned hydrophobic. Study of different properties of the SiNWs before and after plasma treatment revealed that there is pronounced effect of plasma on the nature of SiNWs
Local stability of PD controlled bipedal walking robots
No full textWe establish stability results for PD tracking control laws in bipedal walking robots. Stability of PD control laws for continuous robotic systems is an established result, and we extend this for hybrid robotic systems, an alternating sequence of continuous and discrete events. Bipedal robots have the leg-swing as the continuous event, and the foot-strike as the discrete event. In addition, bipeds largely have underactuations due to the interactions between feet and ground. For each continuous event, we establish that the convergence rate of the tracking error can be regulated via appropriate tuning of the PD gains; and for each discrete event, we establish that this convergence rate sufficiently overcomes the nonlinear impacts by assumptions on the hybrid zero dynamics. The main contributions are (1) Extension of the stability results of PD control laws for underactuated robotic systems, and (2) Exponential ultimate boundedness of hybrid periodic orbits under the assumption of exponential stability of their projections to the hybrid zero dynamics. Towards the end, we will validate these results in a 2-link bipedal walker in simulation
Addressing Multiple Ions Using Single Optical Probe: Multi-Color Response via Mutually Independent Sensing Pathways
No full textMultiresponsive smart optical probe based on p-phenylene vinylene backbone is designed for simultaneous sensing of multiple ions, such as Cu2+, Zn2+ and F� at pH 7.4. A rapid color change from colorless to deep yellow is observed upon addition of both Cu2+ and Zn2+ ion. However, under long UV lamp, the green-colored emission of the probe is specifically quenched in the presence of Cu2+, while Zn2+ induces change in the emission color from green to yellow. On the contrary, F�, unlike Cu2+ and Zn2+, does not render any change in visible color, however, an emission quenching, similar to that of Cu2+ addition, was noticed. The binding of metal ions to the central bipyridine core diminishes the �conformational flexibility� and facilitates �ligand to metal ion� charge transfer. On the contrary, addition of fluoride triggers the cleavage of silyl ether groups and results in the photo-induced electron transfer from free hydroxyl groups to the core aromatic unit. Thus, we can detect as well as discriminate these three ions (Cu2+, Zn2+ and F�) simultaneously by comparing the respective output signals. Further, a sustainable strategy has been developed for on-site detection of toxic ions using reusable, low-cost paper strips. Most importantly, the current method is found to be fairly effective in quantifying (as evident by relatively smaller standard deviation values) the presence of toxic metal ions, above permissible levels, in a wide range of natural water samples. Further, estimation of fluoride is achieved in commercially available toothpaste and mouthwash products