Hydrothermal synthesis of Mn-Zn ferrites from spent alkaline Zn-Mn batteries

Nanocrystalline Mn-Zn ferrites （Mno.GZno.4Fe204） with particle size of 12 nm were synthesized hydrotherreally using spent alkaline Zn-Mn batteries, and accompanied by a study of the influencing factors. The nanocrystals were examined by powder X-ray diffraction （XRD） for crystalline phase identification, and scanning electron microscopy （SEM） for grain morphology. The relationship between concentration of Fe（II）, Mn（II）, and Zn（II） and pH value was obtained through thermodynamic analysis of the Fe（II）-Mn（II）-Zn（II）-NaOH-H2O system. The results showed that all ions were precipitated completely at a pH value of 10-11. The optimal preparation conditions are： co-precipitation pH of 10.5, temperature of 200 ℃ and time of 9 h.     

The effects of the interphase and strain gradients on the elasticity of layer by layer (LBL) polymer/clay nanocomposites

A synergistic stiffening effect observed in the elastic mechanical properties of LBL assembled polymer/clay nanocomposites is studied via two continuum mechanics approaches. The nanostructure of the representative volume element (RVE) includes an effective interphase layer that is assumed to be perfectly bonded to the particle and matrix phases. An inverse method to determine the effective thickness and stiffness of the interphase layer using finite element (FE) simulations and experimental data previously published in Kaushik et al. (2009), is first illustrated. Next, a size-dependent strain gradient Mori–Tanaka (M–T) model (SGMT) is developed by applying strain gradient elasticity to the classical M–T method. Both approaches are applied to LBL-assembled polyurethane–montmorillonite (PU–MTM) clay nanocomposites. Both two-dimensional (2D) and three-dimensional (3D) FE models used in the first approach are shown to be able to accurately predict the stiffness of the PU–MTM specimens with various volume fractions. The SGMT model also accurately predicts the experimentally observed increase in stiffness of the PU–MTM nanocomposite with increasing volume fraction of clay. An analogy between the strain gradient effect and the role of an interphase in accounting for the synergistic elastic stiffening in nanocomposites is provided.     

Comparison of different implementation algorithms for HiSS constitutive models in fem

Relative accuracy, stability and efficiency of four popular algorithms to implement elasto-plastic constitutive models in non-linear finite element procedures have been compared. Elastic Predictor–Plastic Corrector (EP–PC) method, Plastic Predictor–Plastic Corrector (PP–PC) method, Implicit Integration (Implicit) method and Modified Euler (ME) method wereused to implement Hierarchical Single Surface (HiSS) δ₀1 model into the general purpose finite element program ABAQUS. First, these algorithms were used outside the finite element program to simulate various triaxial stress paths. After that, they were used in ABAQUS to simulate two strip footings: (a) displacement controlled rigid footing and (b) load controlled flexible footing. The effect of the sub-strain increment size on the accuracy, stability and efficiency of each algorithm during these simulations have been compared. Implicit Method and ME performed well for some problems but performed poorly on others. EP–PC and PP–PC methods performed equally well for all the problems. This also showed the importance of testing algorithms under various stress paths and boundary value problems to assess their relative performance.     

Development of New Strain Gage for High-Pressure Hydrogen Gas Use

The output changes of two conventional strain gages (Cu–Ni and Ni–Cr) and a newly-selected strain gage for high-pressure hydrogen gas use (Fe–Cr–Al) in 90 MPa hydrogen and nitrogen gases were measured under unloading conditions to find a high-performance strain gage for high-pressure hydrogen gas use. The changes in the outputs of the Cu–Ni and Ni–Cr gages in hydrogen gas were much larger than those in nitrogen gas, and the Fe–Cr–Al gage showed almost the same output changes in both gases. These results imply that the Fe–Cr–Al gage is superior to the others as a strain gage for high-pressure hydrogen gas use. A large amount of hydrogen entered the Cu–Ni and Ni–Cr foils, and the electrical resistances of these foils were significantly changed by hydrogen exposure, whereas almost no hydrogen entered the Fe–Cr–Al foil, and its electrical resistance was not changed. These resistance changes of the foils as a result of hydrogen entry were consistent with the gage output changes in hydrogen gas.     

Shock wave refraction patterns at interfaces

Interactions of shock waves with gas–gas and gas–liquid interfaces (under both slow–fast and fast–slow configurations) are studied using the recently developed Adaptive Characteristics-based Matching (aCBM) method for capturing interfaces in compressible multi-fluid media. First, we verify our approach for the gas–gas case; a class of problems for which a substantial body of knowledge already exists. Then, we consider slow–fast, gas–liquid interfaces under weak shocks, and fast–slow, liquid–gas interfaces under strong shocks. The very high acoustic impedance mismatch situation here creates significant numerical (simulation) and experimental (visualization) difficulties, and the literature for it is meager and sporadic. Compared to gas–gas interfaces we note both similarities and differences. We discuss the sources for these differences, as well as potential implications of generalizing and embedding such results in multi-dimensional simulation schemes towards improving their front-capturing performance.     

Non-Newtonian flow at lowest order,the role of the Reiner–Rivlin stress

In 1963 Giesekus [H. Giesekus, Die simultane Translations- und Rotationsbewegung einer Kugel in einer elastikoviskosen Flüssigkeit, Rheol. Acta 3 (1962) 59–71] showed that a Stokes velocity field also satisfies the equilibrium equation for the flow of a restricted form of the second order fluid. The same result was found by Tanner [R.I. Tanner, Plane creeping flows of incompressible second order fluids, Phys. Fluids 9 (1966) 1246–1247] in 1966 in the context of plane flow for which the restrictions on the second order fluid are not relevant. Tanner [R.I. Tanner, Some extended Giesekus-type theorems for non-Newtonian fluids, Rheol. Acta 28 (1989) 449–452] later showed that the velocity field for the inertialess, plane flow of the generalized Newtonian fluid is also the velocity field for the flow of a special form of the Criminale–Ericksen–Filbey (CEF) stress system [W.O. Criminale Jr., J.L. Ericksen, G.L. Filbey Jr., Steady flow of non-Newtonian fluids, Arch. Rat. Mech. 1 (1958) 410–417]. In this paper it will be shown that the results of Giesekus and Tanner are special cases of a more general theorem in which the velocity field, in any dimension, of the equilibrium Reiner–Rivlin problem also satisfies the corresponding problem for the materially steady stress system (a generalization of the CEF system) provided the coefficients of the Reiner–Rivlin stress [M. Reiner, A mathematical theory of dilatancy, Am. J. Math. 67 (1945) 350–362; R.S. Rivlin, The hydrodynamics of non-Newtonian fluids, Proc. R. Soc. Lond. 193 (1948) 260–281] are derivable from a strain-rate potential. As with the Giesekus–Tanner theorems the new theorem holds generally for velocity boundary conditions, but in some cases, such as the free jet, stress boundary conditions can be imposed.     

Complete kinematics of a serial–parallel manipulator formed by two Tricept parallel manipulators connected in serials

Complete kinematic is an essential and a challenging work for series–parallel manipulators (S–PMs). This paper studied the complete kinematic of a 2(3-SPS+UP) series–parallel manipulator. First, a S–PM formed by two well-known Tricept parallel manipulators (PMs) connected in serial is presented. Second, the forward and inverse displacements are studied using sylvester dialytic elimination method. Third, the forward and inverse Jacobian matrices are established based on integrating the constraint and coupling information of the single PMs into the S–PM. Fourth, simple and compact formulae for the forward and inverse acceleration are derived using vector approach. Finally, the workspace of this S–PM is constructed using CAD variation geometry approach. The results show that the 2(3-SPS+UP) S-PM has multiple forward and inverse position solutions. The existence and uniqueness of the forward, inverse Jacobian matrices and the acceleration formula are shown from their explicit form. The workspace analysis shows that this S–PM has large workspace. The research works provided a theoretical basis for the novel 2(3-SPS+UP) S–PM, as well as a feasible approach for establishing the complete kinematics for S–PMs.     

Numerical simulation of transonic limit cycle oscillations using high-order low-diffusion schemes

This paper simulates the NLR7301 airfoil limit cycle oscillation (LCO) caused by fluid–structure interaction (FSI) using Reynolds averaged Navier–Stokes equations (RANS) coupled with Spalart–Allmaras (S–A) one-equation turbulence model. A low diffusion E-CUSP (LDE) scheme with 5th order weighted essentially nonoscillatory scheme (WENO) is employed to calculate the inviscid fluxes. A fully conservative 4th order central differencing is used for the viscous terms. A fully coupled fluid–structural interaction model is employed. For the case computed in this paper, the predicted LCO frequency, amplitudes, averaged lift and moment, all agree excellently with the experiment performed by Schewe et al. The solutions appear to have bifurcation and are dependent on the initial fields or initial perturbation. The developed computational fluid dynamics (CFD)/computational structure dynamics (CSD) simulation is able to capture the LCO with very small amplitudes measured in the experiment. This is attributed to the high order low diffusion schemes, fully coupled FSI model, and the turbulence model used. This research appears to be the first time that a numerical simulation of LCO matches the experiment. The simulation confirms several observations of the experiment.     

GPU-accelerated smoothed particle hydrodynamics modeling of jet formation and penetration capability of shaped charges

The prediction of the penetration of three-dimensional (3D) shaped charge into steel plates is a challenging task. In this paper, the smoothed particle hydrodynamics (SPH) method is applied to simulate the jet formation generated by the shaped charge detonation and its damage to steel plates. The Jones–Wilkins–Lee (JWL) equation of state (EOS), Tillotson EOS, and elastic–perfectly plastic constitutive model were incorporated into SPH for the modeling of explosive detonation and dynamic behavior of metal material. The compute unified device architecture (CUDA) parallel programming interface has been employed in SPH to improve the computational efficiency of SPH. Firstly, the constitutive models and EOSs are validated by 3D TNT slab detonation and aluminum–aluminum (Al–Al) high velocity impact. Then the jet formation of the shaped charge detonation and its penetration into the steel plates are investigated using the graphics processing unit (GPU)-accelerated SPH methodology. The numerical results of these test cases are compared against the published experimental data or analytical result, which shows that the GPU-accelerated SPH methodology is capable of tackling the 3D shaped charge detonation and penetration involving millions of particles with high computational efficiency.     

A critical review of experimental results and constitutive models for BCC and FCC metals over a wide range of strain rates and temperatures

Four currently utilized constitutive models for metals (i.e. Johnson–Cook, Zerilli–Armstrong, Bodner–Partom and Khan–Huang) are investigated and used to predict the mechanical behaviors of the materials and compared with experimental results. Limitations for each model in describing work-hardening behavior of metals are discussed.