Multiscale Evaluation of Mechanical Properties for Metal-Coated Lattice Structures

With the combination of 3D printing and electroplating technique,metal-coated resin lattice is a viable way to achieve lightweight design with desirable responses.However,due to high structural complexity,mechanical analysis of the macroscopic lattice structure demands high experimental or numerical costs.To efficiently investigate the mechanical behaviors of such structure,in this paper a multiscale numerical method is proposed to study the effective properties of the metal-coated Body-Centered-Cubic(BCC)lattices.Unlike studies of a similar kind in which the effective parameters can be predicted from a single unit cell model,it is noticed that the size effect of representative volume element(RVE)is severe and an insensitive prediction can be only obtained from models containing multiple-unit-cells.To this end,the paper determines the minimum number of unit cells in single RVE.Based on the proposed method that is validated through the experimental comparison,parametric studies are conducted to estimate the impact of strut diameter and coating film thickness on structural responses.It is shown that the increase of volume fraction may improve the elastic modulus and specific modulus remarkably.In contrast,the increase of thickness of coating film only leads to monotonously increased elastic modulus.For this reason,there should be an optimal coating film thickness for the specific modulus of the lattice structure.This work provides an effective method for evaluating structural mechanical properties via the mesoscopic model.

Dynamic stretching–electroplating metal-coated textile for a flexible and stretchable zinc–air battery

A metal electrode is a significant component of a zinc–air battery(ZAB),but the metal material is usually not elastic,which severely restricts the application of flexible and stretchable ZABs in the field of wearable electronic devices.Herein,we report a flexible and stretchable metal-coated textile prepared by a dynamic stretching–electroplating based on a wavy spandex textile substrate.Benefiting from the unique woven and wavy structure,the metal-coated textile shows a high stretchability of 100%and stable conductivity.In situ scanning electron microscope observation during stretching showed that the tensile strain of the metal-coated textile is mainly attributed to the deformation of the microfiber network at the bottom position of the wave structure.In addition,a sodium carboxymethyl cellulose–polyacrylic acid–potassium hydroxide composite hydrogel has been used as the electrolyte.This hydrogel shows excellent ionic conductivity,mechanical properties,and water retention properties,which makes it suitable for the semi-open system of ZAB.Furthermore,a flexible and stretchable sandwich-structure ZAB,assembled using the above-mentioned electrodes and electrolyte,operates stably even under rapid stretching/releasing cycle deformation.Because of its facile preparation and low cost,this flexible and stretchable ZAB is suitable for fabrication of large-area batteries to obtain higher output current and power to drive wearable electronic devices.

Ray-optics model for optical force and torque on a spherical metal-coated Janus microparticle

In this paper, we develop a theoretical method based on ray optics to calculate the optical force and torque on a metallo-dielectric Janus particle in an optical trap made from a tightly focused Gaussian beam. The Janus particle is a 2.8 μm diameter polystyrene sphere half-coated with gold thin film several nanometers in thickness. The calculation result shows that the focused beam will push the Janus particle away from the center of the trap,and the equilibrium position of the Janus particle, where the optical force and torque are both zero, is located in a circular orbit surrounding the laser beam axis. The theoretical results are in good agreement qualitatively and quantitatively with our experimental observation. As the ray-optics model is simple in principle, user friendly in formalism, and cost effective in terms of computation resources and time compared with other usual rigorous electromagnetics approaches, the developed theoretical method can become an invaluable tool for understanding and designing ways to control the mechanical motion of complicated microscopic particles in various optical tweezers.

Electroless Nickel Plating and Electroplating on FBG Temperature Sensor

Metal-coated fiber Bragg grating（FBG）temperature sensors were prepared via electroless nickel（EN）plating and tin electroplating methods on the surface of normal bare FBG.The surface morphologies of the metal-coated layers were observed under a metallographic microscope.The effects of pretreatment sequence,pH value of EN plating solution and current density of electroplating on the performance of the metal-coated layers were analyzed.Meanwhile, the Bragg wavelength shift induced by temperature was monitored by an optical spectrum analyzer.Sensitivity of the metal-coated FBG（MFBG）sensor was almost two times that of normal bare FBG sensor.The measuring temperature of the MFBG sensor could be up to 280℃,which was much better than that of conventional FBG sensor.

Fabrication of Ni-, Co- and NiCo-coated Graphite Microspheres by Heterogeneous Precipitation

The precursors with NiCO3.2Ni（OH）2.2H2O, Co2（OH）2CO3, or both NiCO3.2Ni（OH）2.2H2O and Co2（OH）2CO3 coated graphite microspheres were prepared respectively by the aqueous heterogeneous precipitation using nickel sulfate, cobalt nitrate, sodium carbonate, ammonium bicarbonate and graphite microspheres as the main starting materials. Subsequently, Ni-, Co- and NiCo-coated graphite microspheres were successfully obtained by thermal reduction of the as-prepared precursors at 500 ℃ for 2 h, respectively. These metal-coated graphite microspheres were characterized with a smooth, cohesive surface consisting of fine metallic particles. Optimized precipitation processing parameters of the concentration of graphite microspheres （10 g/L）, the rate of adding reactants （3 mL/min） and pH value （8.0） were determined by a trial and error method. The thermal analysis of the precursors was investigated by TG. Powders of the precursors and the resultant metal-（Ni, Co and NiCo alloy） coated graphite microspheres were characterized by scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS） and X-ray diffraction （XRD）.

Structural and geochemical features of coal‑bearing sediments and sources of rare element impurities in coals of the Rakovka depression,Primorsky Krai,Russia

There are known brown coal deposits in Primorsky Krai(Russian Federation),where coals contain rare elements(Ge,U,REE,etc.)up to industrial concentrations.One of the known metalliferous coals is the Rakovka coal-bearing depression,located on the southern edge of the Khanka(Prikhankaiskaya)Lowland,with an area of about 70 km2.Rare-metal granites with a developed weathering crust are spread in its basement and flanks.The structural conditions forming the depression were studied using measurements of orientations of structural elements(layering,contacts,veins,and dikes)with regard to kinematic conditions of faulting.The coal and host rocks were sampled in sections in the cross strike of the coal seam.Granites and dikes cutting them were sampled by separate rock chip samples.The chemical composition and element content were determined for all samples.It was found that the adjacent rocks played a major role in the formation of the Rakovka rare-metal-coal deposit.The rare-elements enrichment is not associated with active tectonics,faults,and hydrothermal sources,as was previously assumed.Rather,it was caused by the hydrogenic and clastogenic removal of these metals from the weathering crust of granites of the depression's flanks and argillated basite dikes cutting the granites.The hydrogenic nature of the anomalous accumulation of U in sorbed form on organic matter of coals is confirmed by the predominant enrichment of low-ash beds.Rare earth elements entered coal seams both in mineral and dissolved forms.A model of REE and uranium input into the coal-bearing sediments of the Rakovka depression was proposed.