On the performance of truss panels with Kagomé cores

The performance characteristics of a truss core sandwich panel design based on the 3D Kagomé has been measured and compared with earlier simulations. Panels have been fabricated by investment casting and tested in compression, shear and bending. The isotropic nature of this core design has been confirmed. The superior performance relative to truss designs based on the tetrahedron has been demonstrated and attributed to the greater resistance to plastic buckling at the equivalent core density.     

Performance enhancement of sandwich panels with honeycomb–corrugation hybrid core

The concept of combining metallic honeycomb with folded thin metallic sheets(corrugation) to construct a novel core type for lightweight sandwich structures is proposed. The honeycomb–corrugation hybrid core is manufactured by filling the interstices of aluminum corrugations with precision-cut trapezoidal aluminum honeycomb blocks, bonded together using epoxy glue. The performance of such hybrid-cored sandwich panels subjected to out-of-plane compression, transverse shear, and three-point bending is investigated, both experimentally and numerically. The strength and energy absorption of the sandwich are dramatically enhanced, compared to those of a sandwich with either empty corrugation or honeycomb core. The enhancement is induced by the beneficial interaction effects of honeycomb blocks and folded panels on improved buckling resistance as well as altered crushing modes at large plastic deformation.The present approach provides an effective method to further improve the mechanical properties of conventional honeycomb-cored sandwich constructions with low relative densities.     

Mechanical Characterization of Biological Membranes with Moiré Techniques and Multi-Point Simulated Annealing

This paper describes an hybrid procedure for mechanical characterization of biological membranes. The in-plane displacement field of a glutaraldehyde treated bovine pericardium patch obtained with an equi-biaxial tension test is measured with intrinsic moiré and then compared with finite element predictions. Preliminary analysis of moiré patterns observed in the experiments justifies the assumption of the constitutive model based on transversely isotropic hyperelasticity. In order to determine the 16 hyperelastic constants included in the constitutive model and the fiber orientation, the difference Ω between displacement values measured with moiré and their counterpart determined numerically is minimized by means of multi-level and multi-point simulated annealing. Results clearly demonstrate the efficiency of the identification procedure presented in this research: in fact, residual difference between experimental data and numerical values of in-plane displacements is less than 2%. In order to validate the entire identification process, another experimental test is conducted by inflating the same specimen. Out-of-plane displacements, now measured with projection moiré, are compared with predictions of a new finite element model reproducing the experimental test. The 16 hyper-elastic constants previously determined are given in input to the inflation test FE model. Remarkably, experimental and numerical results are again in excellent agreement: maximum percent error on w-displacement is less than 3%.     

Elastica of sandwich panels with a transversely flexible core—A high-order theory approach

The elastica behavior of an extensional sandwich panel with a “soft” core when subjected to in-plane compressive loads is presented and it is compared with the response of its extensional equivalent single layer (ESL) with shear deformations model. The field equations along with the appropriate boundary conditions for the sandwich and the ESL panels have been derived through a variational approach following the High-order SAndwich Panel Theory (HSAPT) approach that takes into account the vertical flexibility of the core. The governing equations include the effects of the extension of the mid-surfaces of the face sheets of the sandwich panel or the mid-plane of the ESL model which the classical elastica approach misses. The results of the elastica response of a clamped-simply-supported sandwich panel and its ESL counterpart are presented and compared. They include the response along the panel, deformed shapes and equilibrium curves of in-plane loads versus structural quantities such as displacements and internal stress resultants and stresses. These results reveal that the predicted buckling load of the ESL panel is larger than that of the sandwich panel and that deep in the non-linear range the upper face sheet wrinkles with increasing overall and edge displacements and a release of the load. Hence, the use of an equivalent single layer panel especially when a sandwich panel with a compliant core is considered may lead to unsafe and unreliable predictions when large displacements and large rotations are considered.     

Techniques and Applications of the Simulated Pattern Adaptation of Wilkinson’s Method for Advanced Microstructure Analysis and Characterization of Plastic Deformation

Electron Backscatter Diffraction (EBSD) based Orientation Imaging Microscopy (OIM) is used routinely at ~500 materials laboratories worldwide for the characterization and development of diverse crystalline materials. Statistically significant data sets (~10⁷ individual EBSD measurements) can be collected and analyzed within time periods of acceptable beam stability (~10⁵s). However, limitations in angular and spatial resolution have motivated a continued search for more robust EBSD-based methods. Herein is a gathered presentation of advanced techniques in use, intended as a guide to researchers in selecting the most appropriate method for their work. Wilkinson’s method has been shown to increase angular resolution nearly two orders of magnitude to ±0.006°, facilitating measurement of elastic strain, lattice curvature, and dislocation density. A simulated pattern adaptation of Wilkinson’s method extends these measurement capabilities to polycrystalline materials, by avoiding the need for an experimental strain free reference pattern. The angular resolution limit obtained is ~0.04°. Accurate pattern center calibration, essential to the high resolution methods, is accomplished by parallelization of band edges projected onto a sphere centered at the interaction volume. FFT powered cross-correlation functions improve the spatial resolution near grain boundaries and correct for measurement inaccuracies induced by overlapping patterns. To corroborate these claims, exemplary results taken from a wedge-indented nickel single crystal, cold-worked copper polycrystal, and rolled nickel polycrystal are shown.     

Structural and transport properties of Sn–Mg alloys

In this work, the structural and transport properties of Mg-doped Sn-based alloys have been investigated. The temperature-dependent transport and structural properties of Sn–Mg alloys were investigated for five different samples (Pure Sn, Sn-1.0 wt% Mg, Sn-2.0 wt% Mg, Sn-6.0 wt% Mg and Pure Mg). Scanning electron microscopy (SEM), X-ray diffraction and energy dispersive X-ray analysis measurements were carried out in order to clarify the structural properties of the samples. It was found that the samples had tetragonal crystal symmetry, except for pure Mg which had hexagonal crystal symmetry. We also found that the cell parameters changed slightly with the addition of Mg element. The SEM micrographs of the samples showed that they had smooth surfaces with a clear grain boundary. The electrical and thermal conductivity of the samples were measured by four-point probe and the radial heat flow method, respectively. The electrical resistivity of the samples increased almost linearly with the increasing temperature. The thermal conductivity values ranged between 0.60 and 1.00 W/Km, while they decreased slightly with temperature and increased with Mg composition. The thermal conductivity values of the alloys were in between the values of pure Sn and Mg. The thermal conductivity results of the alloys were compared with other available results, and a good agreement was seen between the results. In addition, the temperature coefficients of electrical resistivity and thermal conductivity were determined; these were independent of the composition of the alloying elements.     

The moiré method and the evaluation of principal-moment and stress directions

This paper discusses, in relation to the moiré method as used for the solution of plate bending and two-dimensional stress problems, two graphical techniques for the determination of the directions of principal moments and stresses.The so-called isoclinic method and the point method are described.The application of these new techniques on three different models—a circular disk under diametrically opposite loads and two different circular plates subjected to a lateral load—are fully discussed.The graphically determined principal-stress and moment directions show excellent agreement with analytically determined comparable values.Paper was presented at 1963 SESA Annual Meeting held in Boston, Mass., on November 6–8.     

Lamé problem for a weakly anisotropic body with cubic symmetry of elastic properties

The Lamé problem is solved for a body with cubic symmetry of elastic properties and the elastic anisotropy parameter is determined. In the case of plane deformation, the stresses in a ring are found to terms of the first order in the small anisotropic parameter. Stresses in a ring of KCl under internal pressure are calculated.     

Painlevé analysis and invariant solutions of generalized fifth-order nonlinear integrable equation

In present work, new form of generalized fifth-order nonlinear integrable equation has been investigated by locating movable critical points with aid of Painlevé analysis and it has been found that this equation passes Painlevé test for \(\alpha =\beta \) which implies affirmation toward the complete integrability. Lie symmetry analysis is implemented to obtain the infinitesimals of the group of transformations of underlying equation, which has been further pre-owned to furnish reduced ordinary differential equations. These are then used to establish new abundant exact group-invariant solutions involving various arbitrary constants in a uniform manner.     

Structure of turbulent bubbly jets—I. Methods and centerline properties

The structure of dilute bubbly turbulent round jets, injected vertically upward in still water, was studied both theoretically and experimentally. All measurements were nonintrusive, including mean and fluctuating phase velocities, bubble number intensities, bubble-size distributions and calibration of the motion of individual bubbles. Predictions from three analyses were compared with measurements: (1) locally homogeneous flow analysis, where velocity differences between the phases were neglected; (2) deterministic separated flow analysis, where relative velocity was considered but bubble/turbulence interactions were ignored; and (3) stochasic separated flow analysis, where both relative velocity and bubble/turbulence interactions were considered using random-walk methods. This paper describes theoretical and experimental methods, flow structure near the source and mean properties along the jet axis. Effects of relative velocity were important almost everywhere in the flow; therefore, only the separated flow models yielded satisfactory predictions of bubble velocities along the axis. A companion paper treats mean and fluctuating properties in other regions of the flow.     

Experimental study on rheological and thermophysical properties of seawater with surfactant additive—part I: rheological properties

The rheological properties of seawater with the addition of surfactant additive (cetyltrimethyl ammonium chloride (CTAC)/sodium salicylate (NaSal)) are measured at different temperatures, including shear viscosity and first normal stress difference (N₁). The effects of the temperature, the salts, and CTAC/NaSal concentration on the rheological properties of test solutions are investigated, and the corresponding influence mechanisms are analyzed. It shows that the addition of salt can decrease the shear viscosities of the solutions, and also decrease N₁ and even eliminate the sharp augment of N₁ above a certain shear rate. The growing elasticity can be characterized by the increase of the initial shear rate for shear-thickening inception. High temperature can also remove the sharp increase of N₁ with salt. Nevertheless, the increase of CTAC/NaSal concentration can withstand the elimination of the sharp augment of N₁.     

Preparation and Li^＋ storage properties of hierarchical hollow porous carbon spheres

Hollow ordered porous carbon spheres （HOPCS） with a hierarchical structure were prepared by templating with hollow ordered mesoporous silica spheres （HOMSS）. Scanning electron microscopy （SEM） and transmission electron microscopy （TEM） showed that HOPCS exhibited a spherical hollow morphology. High-resolution TEM, small angle X-ray diffraction （SAXRD） and N2 sorption measurements confirmed that HOPCS inversely replicated the unconnected hexagonal-stacked pore structure of HOMSS, and possessed ordered porosity. HOPCS exhibited a higher storage capacity for Li^＋ ion battery （LIB） of 527.6 mA h/g, and good cycling performance. A large capacity loss during the first discharge-charge cycle was found attributed to the high content of micropores. The cycling performance was derived from the hierarchical structure.     

Ground-based measurements of aerosol optical properties and radiative forcing in North China

In order to gain an insight into the aerosol properties and their climatic effect over the continental source regions of China, it is of significance to carry out long-term ground-based measurements of aerosol optical properties and radiative forcing. A couple of temporary and permanent Aerosol Robotic Network （AERONET） sites and three comprehensive radiative sites were established in China as a result of international cooperation in recent years. Heavy aerosol loading and significant temporal and spatial variation over North China are revealed by the AERONET data. Aerosol-induced reductions in surface radiation budget are examined on the basis of collocated observations by sun photometers and pyranometers. 2007 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V.     

Isothermal viscoelastic properties of PMMA and LDPE over 11 decades of frequency and time: a test of time–temperature superposition

Many instruments used to measure viscoelastic properties are only capable of subjecting a sample to a limited range of loading frequencies. For thermorheologically simple materials, it is assumed that a change in temperature is equivalent to a shift of the viscoelastic behavior on the log frequency or time axis. For many materials, time–temperature superposition appears to work well for modulus or compliance curves over three decades of time or frequency, but some deviations are known if the window is expanded to five or six decades. To apply a more stringent test of the validity of time–temperature superposition, broadband viscoelastic spectroscopy is used to isothermally study polymethylmethacrylate and low-density polyethylene at several temperatures in the glassy region. Shear modulus and damping (tan δ) are measured isothermally over a wide range (up to 11 decades) of time and frequency. Results indicate that, while modulus curves can be approximately superimposed, the damping (tan δ) curves change in height and shape with temperature.     

Accuracy of the Sampling Moiré Method and its Application to Deflection Measurements of Large-Scale Structures

Measuring accurate displacement distributions for large-scale structures is an important issue and a very challenging task. Recently, a simple and accurate phase measurement technique called sampling moiré method [Exp Mech 50–4:501–508, (2010)] has been developed for small-displacement distribution measurements. In this method, the phase distribution of moiré fringes can be analyzed from a single grating image by simultaneously performing down-sampling image processing and intensity-interpolation to generate multiple phase-shifted moiré fringe images. In addition, the phase of the original grating can also be obtained from the phase of the moiré fringe by adding the phase of the sampling grating. In this study, the measurement accuracy of the sampling moiré method was analyzed through computer simulations and a displacement measurement experiment. Four factors of the sampling moiré method were investigated, including the sampling pitch, the order of the intensity-interpolation, random noise, and the form of grating. The results show that determining the optimal sampling pitch is an important factor for obtaining better results but it is not critical. In addition, a practical application of the sampling moiré method is presented that involves a deflection measurement on a 10-meter-long crane. The experimental results demonstrate that submillimeter deflections of the crane can be successfully detected.     

Determination of Ti-6242 α and β slip properties using micro-pillar test and computational crystal plasticity

The properties and behaviour of an α−β colony Ti-6242 alloy have been investigated at 20 °C utilising coupled micro-pillar stress relaxation tests and computational crystal plasticity. The β-phase slip strength and intrinsic slip system strain rate sensitivity have been determined, and the β-phase shown to have stronger rate sensitivity than that for the α phase. Close agreement of experimental observations and crystal plasticity predictions of micro-pillar elastic-plastic response, stress relaxation, slip activation in both α and β-phases, and strain localisation within the α−β pillars with differing test strain rate, β morphology, and crystal orientations is achieved, supporting the validity of the properties extracted. The β-lath thickness is found to affect slip transfer across the α−β−α colony, but not to significantly change the nature of the slip localisation when compared to pure α-phase pillars with the same crystallographic orientation. These results are considered in relation to rate-dependent deformation, such as dwell fatigue, in complex multiphase titanium alloys.     

A Modified Poincaré Method for the Persistence of Periodic Orbits and Applications

This paper is devoted to the persistence of periodic orbits under perturbations in dynamical systems generated by evolutionary equations, which are not smoothing in finite time, but only asymptotically smoothing. When the periodic orbit of the unperturbed system is non-degenerate, we show the existence and uniqueness of a periodic orbit (with a minimal period near the minimal period of the unperturbed problem) by using “modified” Poincaré methods. Examples of applications, including the perturbed hyperbolic Navier–Stokes equations, systems of damped wave equations and the system of second grade fluids, are given.     

Phase behavior and effects of microstructure on viscoelastic properties of a series of polylactides and polylactide/poly(ε-caprolactone) copolymers

Dynamic viscoelastic measurements were combined with differential scanning calorimetry (DSC) and atomic force microscopy (AFM) analysis to investigate the rheology, phase structure, and morphology of poly(l-lactide) (PLLA), poly(ε-caprolactone) (PCL), poly(d,l-lactide) (PDLLA) with molar composition l-LA/d-LA?=?53:47, and poly(l-lactide-co-ε-caprolactone) (PLAcoCL) with molar composition l-LA/CL?=?67:33. After melt conformation, both copolymers PDLLA and PLAcoCL were found to be amorphous whereas PLLA and PCL presented partial crystallinity. The copolymers and PCL were considered as thermorheologically simple according to the rheological methods employed. Therefore, data from different temperatures could be overlapped by a simple horizontal shift (a _T) on elastic modulus, G′, and loss modulus, G′, versus frequency graph, generating the corresponding master curves. Moreover, these master curves showed a dependency of G″≈ω and G′≈ω ² at low frequencies, which is a characteristic of homogeneous melts. For the first time, fundamental viscoelastic parameters, such as entanglement modulus G _N ⁰ and reptation time τ _d, of a PLAcoCL copolymer were obtained and correlated to chain microstructure. PLLA, by contrast, was unexpectedly revealed as a thermorheologically complex liquid according to the failure observed in the superposition of the phase angle (δ) versus the complex modulus (G*); this result suggests that the narrow window for rheological measurements, chosen to be close to the melting point centered at 180 °C thus avoiding thermal degradation, was not sufficient to assure an homogeneous behavior of PLLA melts. The understanding of the melt rheology related to the chain microstructural aspects will help in the understanding of the complex phase structures present in medical devices.     

Microstructural and mechanical properties of thermal barrier coating at 1400°C treatment

The mechanical properties of plasma-sprayed thermal barrier coating (TBC) play a vital role in governing their lifetime and performance. This work investigated the microstructural and mechanical properties of TBC with high temperature treatment at 1400°C by scanning electron microscopy and indentation. We calculated elastic modulus and hardness through the application of Weibull statistics analysis. The results indicate that the microstructure of ceramic coating will change continuously at high temperature, and accordingly the porosity decreases due to the grain growths and crack closes. In addition, the elastic modulus and hardness nonlinearly go up with the heat treatment time and go down with increasing porosity. This demonstrates that the microstructural evolution and porosity of TBC are caused by high temperature treatment, and as a result its mechanical properties are influenced.