Mechanical Engineering

Purpose -The paper's aim is to show the development of materials and methods which allow freeform fabrication of macroscopic Zn-air electrochemical batteries. Freedom of geometric design may allow for new possibilities in performance optimization. Design/methodology/approach -The authors have formulated battery materials which are compatible with solid freeform fabrication (SFF) while retaining electrochemical functionality. Using SFF processes, they have fabricated six Zn-air cylindrical batteries and quantitatively characterized them and comparable commercial batteries. They analyze their performance in light of models from the literature and they also present SFF of a flexible twocell battery of unusual geometry.

This work is focused on the freeform fabrication of complete zinc-air batteries. This method of production gives great freedom in the geometry and construction of the battery, allowing tailoring of the output characteristics, and the possibility of embedding a customized battery within a larger integrated freeform fabricated device. Our batteries utilize a gelling agent to prevent phase separation in the zinc anode and catalyst layers, permitting the use of nozzles down to 1.3mm in diameter. Polyvinyl alcohol is utilized for the separator layer, which replaces the unprintable paper separator used in commercial batteries. With various freeform batteries we have achieved a specific capacity of 60mAh/g of zinc, an average power 7.25mW, and continuous service life of 63h, all with a load of 100 ohms. The specific capacity of our freeform batteries is about 1 order of magnitude lower than that of commercial zinc-air batteries, although under different test conditions. We have investigated the effect of cell active surface area on performance for a cylindrical cell-geometry, and have produced a flexible, two-cell battery with unusual geometry. The tailoring of performance and geometry possible with freeform fabrication will be of great value in the design of optimized smart devices with unusual geometry, portable electronics, and prototypes.

Influence of different grain sizes on deformation behavior of Mg-3Al-Zn magnesium alloy was investigated by in-situ observation with scanning electron microscopic under uniaxial tensile loadings. The results indicate that there are the different deformation behaviors between coarse grains and finedgrains magnesium alloy by the two-step equal channel angular extruded (ECAE) technology. Why the elongation to be well improved and simultaneously why the yield stress to be slightly decreased are explained based on the different surface plastic deformed types and cavity evolution processes.

Carbon nanotubes (CNTs) were grown from the surface of glass fibers by chemical vapor deposition, and these hybrid fibers were individually dispersed in an epoxy matrix to investigate the local composite structure and properties near the fiber surface. High-resolution transmission electron microscopy revealed the influence of infiltration and curing of a liquid epoxy precursor on the morphology of the CNT ''forest'' region, or region of high CNT density near the fiber surface. Subsequent image analysis highlighted the importance of spatially dependent volume fractions of CNTs in the matrix as a function of distance from the fiber surface, and nanoindentation was used to probe local mechanical properties in the CNT forest region, showing strong correlations between local stiffness and volume fraction. This work represents the first in situ measurements of local mechanical properties of the nano-structured matrix region in hybrid fiber-reinforced composites, providing a means of quantifying the reinforcement provided by the grafted nanofillers.

In this paper, we investigate the enhancement mechanism of the mechanical properties for hard-soft block copolymers by using molecular dynamics simulations at various temperatures. A coarse-grained approach is adopted to study sufficiently generic models. Our numerical experiments demonstrate that the nonbond potential plays a more significant role in mechanical properties compared to the bond potential. This finding serves as a cornerstone to understand the hard-soft materials. To explore the effect of hard segments, four copolymers with different concentrations and energy factors that describe the interaction between hard beads are conducted. Simulation results show that the mechanical performances of the system with large attractive force and small concentration of hard segments could be improved dramatically in conjunction with a moderate increment of the glass transition temperature. In particular, the energy factor shows a substantial influence in determining the microphase separation as well as the morphology of hard domains. These observations are believed to provide design guidelines for polymeric materials in engineering practice.

Results in the literature demonstrate that substantial improvements in the mechanical behavior of polymers have been attained through the addition of small amounts of carbon nanotubes as a reinforcing phase. This suggests the possibility of new, extremely lightweight carbon nanotube-reinforced polymers with mechanical properties comparable to those of traditional carbon-fiber composites. Motivated by micrographs showing that embedded nanotubes often exhibit significant curvature within the polymer, we have developed a model combining finite element results and micromechanical methods to determine the effective reinforcing modulus of a wavy embedded nanotube. This effective reinforcing modulus (ERM) is then used within a multiphase micromechanics model to predict the effective modulus of a polymer reinforced with a distribution of wavy nanotubes. We found that even slight nanotube curvature significantly reduces the effective reinforcement when compared to straight nanotubes. These results suggest that nanotube waviness may be an additional mechanism limiting the modulus enhancement of nanotube-reinforced polymers. #

Polymer-based composites were heralded in the 1960s as a new paradigm for materials. By dispersing strong, highly stiff fibres in a polymer matrix, high-performance lightweight composites could be developed and tailored to individual applications 1 . Today we stand at a similar threshold in the realm of polymer nanocomposites with the promise of strong, durable, multifunctional materials with low nanofiller content 2-11 . However, the cost of nanoparticles, their availability and the challenges that remain to achieve good dispersion pose significant obstacles to these goals. Here, we report the creation of polymer nanocomposites with functionalized graphene sheets, which overcome these obstacles and provide superb polymer-particle interactions. An unprecedented shift in glass transition temperature of over 40 8 8 8 8 8C is obtained for poly(acrylonitrile) at 1 wt% functionalized graphene sheet, and with only 0.05 wt% functionalized graphene sheet in poly(methyl methacrylate) there is an improvement of nearly 30 8 8 8 8 8C. Modulus, ultimate strength and thermal stability follow a similar trend, with values for functionalized graphene sheetpoly(methyl methacrylate) rivaling those for single-walled carbon nanotube -poly(methyl methacrylate) composites.

A one-dimensional constitutive model for the thermomechanical behavior of shape memory alloys is developed based on previous work by Liang and Tanaka. An internal variable approach is used to derive a comprehensive constitutive law for shape memory alloy materials from first principles without the assumption of constant material functions. This constitutive law is of such a form that it is well suited to further practical engineering applications and calculations.

The present paper studies multi-objective design of lightweight thermoelastic structure composed of homogeneous porous material. The concurrent optimization model is applied to design the topologies of light weight structures and of the material microstructure. The multiobjective optimization formulation attempts to find minimum structural compliance under only mechanical loads and minimum thermal expansion of the surfaces we are interested in under only thermo loads. The proposed optimization model is applied to a sandwich elliptically curved shell structure, an axisymmetric structure and a 3D structure. The advantage of the concurrent optimization model to single scale topology optimization model in improving the multi-objective performances of the thermoelastic structures is investigated. The influences of available material volume fraction and weighting coefficients are also discussed. Numerical examples demonstrate that the porous material is conducive to enhance the multi-objective performance of the thermoelastic structures in some cases, especially when lightweight structure is emphasized. An "optimal" material volume fraction is observed in some numerical examples.

A scale invariant model of statistical mechanics is applied to derive invariant forms of conservation equations. A modified form of Cauchy stress tensor for fluid is presented that leads to modified Stokes assumption thus a finite coefficient of bulk viscosity. The phenomenon of Brownian motion is described as the state of equilibrium between suspended particles and molecular clusters that themselves possess Brownian motion. Physical space or Casimir vacuum is identified as a tachyonic fluid that is "stochastic ether" of Dirac or "hidden thermostat" of de Broglie, and is compressible in accordance with Planck's compressible ether. The stochastic definitions of Planck h and Boltzmann k constants are shown to respectively relate to the spatial and the temporal aspects of vacuum fluctuations. Hence, a modified definition of thermodynamic temperature is introduced that leads to predicted velocity of sound in agreement with observations. Also, a modified value of Joule-Mayer mechanical equivalent of heat is identified as the universal gas constant and is called De Pretto number 8338 which occurred in his mass-energy equivalence equation. Applying Boltzmann's combinatoric methods, invariant forms of Boltzmann, Planck, and Maxwell-Boltzmann distribution functions for equilibrium statistical fields including that of isotropic stationary turbulence are derived. The latter is shown to lead to the definitions of (electron, photon, neutrino) as the most-probable equilibrium sizes of (photon, neutrino, tachyon) clusters, respectively. The physical basis for the coincidence of normalized spacings between zeros of Riemann zeta function and the normalized Maxwell-Boltzmann distribution and its connections to Riemann Hypothesis are examined. The zeros of Riemann zeta function are related to the zeros of particle velocities or "stationary states" through Euler's golden key thus providing a physical explanation for the location of the critical line. It is argued that because the energy spectrum of Casimir vacuum will be governed by Schrödinger equation of quantum mechanics, in view of Heisenberg matrix mechanics physical space should be described by noncommutative spectral geometry of Connes. Invariant forms of transport coefficients suggesting finite values of gravitational viscosity as well as hierarchies of vacua and absolute zero temperatures are described. Some of the implications of the results to the problem of thermodynamic irreversibility and Poincaré recurrence theorem are addressed. Invariant modified form of the first law of thermodynamics is derived and a modified definition of entropy is introduced that closes the gap between radiation and gas theory. Finally, new paradigms for hydrodynamic foundations of both Schrödinger as well as Dirac wave equations and transitions between Bohr stationary states in quantum mechanics are discussed. 2 p c = molar specific heat at constant pressure v c = molar specific heat at constant volume Figure1. A scale invariant view of statistical mechanics from cosmic to tachyon scales.

The modified forms of the equation of motion and the Helmholtz vorticity equation are solved for the classical problem of Stokes flow across a rigid cylinder. For such creeping flows, the modified equation of motion suggests the existence of a closed streamline around the cylinder within which the surface-generated vorticity will be confined. The solution within such closed region is presented that may help in the resolution of the well know Stokes paradox. The problems of laminar flow across and within a cylindrical liquid body are also examined. For the former, an approximate analytical solution is presented and qualitatively compared with the numerical solution of the Navier-Stokes equation. For the latter, parallel to the classical Hill spherical vortex, the solution describing two cylindrical vortex lines is presented.

Scale-invariant form of the Planck law of energy distribution is introduced as belE:first fracɛ_νN_νV=ρ_νdν=frac8π m_β^2k fracν^3dνe^hν/kT-1 that at the chromodynamic scale β = γ for photon gas involves the gravitational mass of photon m_γ = (hk/c^3)^1/2. At a constant T, (1) describes the size spectrum of photon clusters of energy ɛ_cj = N_γ jhν_γ j = N_γ jɛ_γ j where N_γ j is the number of photons in cluster j (energy level j) per unit volume and ɛ_γ j is the energy of photon in cluster j. Similarly, at molecular-dynamic scale, Eq.(1) with m_β = M_β/No = M_βm_γc^2 gives the spectrum of size of molecular clusters acting as composite bosons with energy ɛ_cj = N_mjhν_mj = N_mjɛ_mj and matter wavelength and frequency given by h_β = p_βλ_β = h (de Broglie) and k_β = p_βν_β = k. Particles are suggested to oscillate in two directions (x^+, x^-) such that mm < u^2 > = 2mm < u^2_x^+ > = 3kT leading to calculated rms molecular speeds (1346, 336, 360, 300, 952, 287) m/s that are comparable with the observed velocity of sound (1286, 332, 337, 308, 972, 268) m/s for gases (H_2, O_2, N_2, Ar, He, CO_2) at s.t.p. as initially suspected by Newton.

A scale-invariant model of statistical mechanics is described and applied to derive the invariant Planck law of energy distribution from the invariant Boltzmann distribution function. Also, the invariant Schrödinger equation is derived from the invariant Bernoulli equation for potential incompressible flow. It is shown that a homogeneous isotropic turbulent fluid is composed of a spectrum of eddies (energy levels) each composed of a spectrum of molecular clusters with energy spectra governed by the Planck distribution law and harmonious with the Kolmogorov law. The stability of clusters, de Broglie wave packets, is shown to be due to a potential that acts as Poincaré stress. Atomic transitions between different size clusters (energy levels) are shown to result in emission/absorption of energy in harmony with Bohr's theory of atomic spectra. 5/ 3 − κ Key-Words: -Planck energy distribution. Statistical theory of turbulence. Schrödinger equation. TOE GALACTIC CLUSTER LGD (J + 11/2) UNIVERSE LHD (J + 7/2) LPD (J + 9/2) GALAXY LCD (J + 1/2) LMD (J -1/2) LSD (J -5/2) LED (J + 3/2) LFD (J + 5/2) LAD (J -3/2) LKD (J -7/2) LTD (J -9/2) EDDY FLUID ELEMENT HYDRO-SYSTEM PLANET MOLECULE CLUSTER ATOM SUB-PARTICLE PHOTON ETD (J -5) EGD (J +5) EMD (J -1) EAD (J -2) ESD (J -3) GALACTIC CLUSTER EDDY FLUID ELEMENT HYDRO SYSTEM PLANET GALAXY MOLECULE CLUSTER ATOM SUBPARTICLE PHOTON