Orientation-Dependent Developments in Misorientation and Residual Stress in Rolled Aluminum: The Defining Role of Dislocation Interactions

Orientation-dependent developments in misorientation and residual stress, in rolled aluminum, were quantified experimentally and simulated numerically. The latter involved analysis using a crystal plasticity finite element model, accounting for anisotropies in slip system hardening but neglecting near-neighbor interactions, and discrete dislocation dynamics of the single crystals. Both were successful in capturing the experimental patterns of orientation dependence. Numerical simulations, without slip transfer across the neighboring grains, thus established the defining role of dislocation interactions in establishing orientation-sensitive microstructural evolution.     

Simulation of lattice strain due to a CNT-metal interface

We report an atomistic molecular statics study of strains in single wall carbon nanotubes (SWCNTs) interfaced with a planar nickel surface. We calculate axial and radial strain distributions along the SWCNT axis. We demonstrate axial strains of up to 2% extending over a distance of ～ 10 nm away from the interface along the CNT axis. In addition to the effect of strains on the thermal and mechanical properties of a CNT-metal contact, our results suggest a significant contribution to the contact electrical resistance via local strain-induced modification in the SWCNT electron energy band structure.     

A probabilistic method to determine the minimum leakage vector for combinational designs in the presence of random PVT variations

The control of leakage power consumption is a growing design challenge for current and future CMOS circuits. Among existing techniques, ‘parking’ a circuit in a minimum leakage state during its standby mode of operation requires minimal circuit modification and results in significant leakage reduction. In this paper we present a heuristic approach (referred to as MLVC) to determine the input vector which minimizes leakage for a combinational design. This approach utilizes approximate signal probabilities of internal nodes to aid in finding the minimum leakage vector. We utilize a probabilistic heuristic to select the next gate to be processed as well as to select the best state of the selected gate. A fast SAT solver is employed to ensure the consistency of the assignments that are made in this process. A variant of MLVC, referred to as MLVC-VAR, is also presented. MLVC-VAR includes the effect of random variations in leakage values due to process, voltage and temperature (PVT) variations. Including the effect of PVT variations for determining minimum leakage vector is crucial because leakage currents have an exponential dependence on power supply, threshold voltage and temperature. To the best of the authors’ knowledge, no other minimum leakage vector determination work has to date included the effect of PVT variations. Experimental results indicate that our MLVC method has very low runtimes, with excellent accuracy compared to existing approaches. Further, the comparison of the mean and standard deviation of the circuit leakage values for MLVC with MLVC-VAR and an existing random vector generating approach proves the need for considering these variations while determining the minimum leakage vector. MLVC-VAR reports, on average, about 9.69% improvement over MLVC with similar runtimes and 5.98% improvement over the random vector generation approach with significantly lower runtimes.     

Materials informatics: Facilitating the integration of data-driven materials research with education

Materials informatics integrated into undergraduate and graduate materials education is a key component and critical issue to address the nation’s shortage of well-trained, future scientists. A.C. Powell is with OpenInnovation     

Temperature dependence of thermal conductivity and thermal diffusivity of some composites using the transient plane source technique

The recently developed transient plane source (TPS) technique has been applied for the simultaneous measurement of thermal conductivity and thermal diffusivity of two composite materials namely, marble and magnesium oxychloride cement in the range of temperatures from 30 to 150°C. The experimental results of these samples show that there is very slight variation in thermal conductivity and thermal diffusivity of these materials in this range of temperature. An effort has been made to express this variation of thermal conductivity and diffusivity with temperature by a linear relation, in these materials.     

Green's Function for Multilayers with Interfacial Membrane and Flexural Rigidities¹

A three-dimensional Green's function for a material system consisting of anisotropic and linearly elastic planar multilayers with interfacial membrane and flexural rigidities has been derived. The Stroh formalism and two-dimensional Fourier transforms are applied to derive the general solution for each homogeneous layer. The Green's function for the multilayers is then solved by imposing the surface boundary condition, the interfacial displacement continuity condition, and the interfacial traction discontinuity condition. The last condition is given by the membrane and bending equilibrium equations of the interphases modeled as Kirchhoff plates. Numerical results that demonstrate the validity and efficiency of the formulation are presented for the case of a stack of silicon thin films embedded in epoxy.     

Reducing the Hardness of Mine Water Using Transformed Fly Ash

In the Jharia Coalfields, Dhanbad, India, huge quantities of water are pumped out of underground mines to make mining possible. The water contains high concentrations of total hardness, which makes it unsuitable for domestic use. Waste fly ash generated nearby from burning the coal in thermal power plants can be converted into a zeolitic mineral, and used to treat the mine water. The fly ash zeolite was determined to be effective in removing total hardness from the mine water. At a 40 g/L dose of fly ash zeolite, approximately 72% of the hardness was removed from the mine water. However, the mine water still requires additional treatment to further reduce total dissolved solids to make the mine water potable.     

Microstructure,mechanical properties and corrosion performance of a few TMT rebars

The present work aims to study the evaluation of the microstructure, tensile properties, hardness, corrosion behaviour of the various grades of rebars. The microstructures of all rebar samples comprise an outer tempered martensite ring with an inner core of ferrite-pearlite in between a narrow bainitic transition zone. Maximum hardness is achieved at the periphery which gradually decreases towards the centre. Chinese grade has a similarity with the Fe 600 rebar in terms of strength and % elongation, whereas Fe 500D and Fe 500 have lower strength but higher ductility. The EDS analyses of corrosion products obtained after immersion test in 5% NaCl solution for a period of 7 days apparently indicate the occurrences of iron oxy-hydroxides and iron oxides. X-ray diffraction and FTIR studies of the corrosion products formed on all thermo-mechanically treated (TMT) rebar surfaces after the aforesaid immersion test primarily indicate the presence of Lepidocrocite (γ-FeOOH), Goethite (α-FeOOH), Magnetite (Fe₃O₄) and Maghemite (γ-Fe₂O₃). Fe 500 (12?mm) and Chinese rebars have lower corrosion resistance as compared to the other rebars in 5% NaCl solution. Nevertheless, all the TMT rebars are corrosion resistant and can be satisfactorily used for construction purposes.     

A Semicontinuum Model for Si_<i>x</i>Ge_{<i>1 - x</i>} Alloys: Calculation of Their Elastic Characteristics and the Strain Field at the Free Surface of a Semi-Infinite Alloy

A semicontiuum Green's-function-based model is proposed for analysis of averaged mechanical characteristics of Si_xGe_{1 - x}. The atomistic forces in the model are distributed at discrete lattice sites, but the Green's function is approximated by the continuum GF in the far field and by the averaged lattice GF in the near field. Averaging is achieved by replacing Si and Ge atoms by identical hypothetical atoms that are x fraction Si and (1-x) fraction Ge. The parameters of the model are derived using the atomistic model from the interatomic potential between the hypothetical atoms. The interatomic potential is obtained from the radial embedded atom model proposed in an earlier paper. The parameters of the model potential are estimated partly by interpolation and partly by fitting the calculated and measured values of the cohesive energy and the lattice constant of Si_xGe_{1 - x} as functions of x. The model is applied to calculate the elastic constants of Si_xGe_{1 - x} and the displacement and the strain field at the free surface of a semi-infinite alloy for different values of x due to a buried point defect. The elastic constants predicted by the model are used to calculate the curvature of a single crystal of Si with a 49 nm epitaxial film of Si(0.846)Ge(0.154). The calculated value (312.8 m) of the radius of curvature is in excellent agreement with the recently measured value (314.5 m) at our laboratory.