Heat-induced Internal Strain Relaxation and its Effect on the Microstructure of Polyacrylonitrile-based Carbon Fiber

The transformation of the internal strain and its effect on the microstructure of polyacrylonitrile-based carbon fiber during the high-temperature graphitization were investigated. The internal compressive strain within the carbon turbostratic structure was confirmed through a careful analysis by wide-angle X-ray diffraction and Raman spectroscopy. Heat-induced strain/stress relaxation along the fiber axis was observed and was found to have a profound effect on the structure of both the crystallites and microvoids. The results indicated that, the relaxation of residual strain changed the graphite layers from a wrinkled and distorted morphology to a straight and smooth one, and consequently led the crystallites to stack closely and orderly with increasing stack height. The strain relaxation also changed the morphology of crystallites and microvoids, resulting in an anisotropic growth for the latters.

Suppressed Internal Intrinsic Stress Engineering in High-Performance Ni-Rich Cathode Via Multi layered In Situ Coating Structure

LiNi_(x)Co_(y)Al_(z)O_(2)(NCA)cathode materials are drawing widespread attention,but the huge gap between the ideal and present cyclic stability still hinders their further commercial application,especially for the Ni-rich LiNi_(x)Co_(y)Al_(z)O_(2)(x>0.8,x+y+z=1)cathode material,which is owing to the structural degradation and particles'intrinsic fracture.To tackle the problems,Li_(0.5)La_(2)Al_(0.5)O_(4)in situ coated and Mn compensating doped multilayer LiNi_(0.82)Co_(0.14)Al_(0.04)O_(2)was prepared.XRD refinement indicates that La-Mn co-modifying could realize appropriate Li/Ni disorder degree.Calculated results and in situ XRD patterns reveal that the LLAO coating layer could effectively restrain crack in secondary particles benefited from the suppressed internal strain.AFM further improves as NCA-LM2 has superior mechanical property.The SEM,TEM,XPS tests indicate that the cycled cathode with LLAO-Mn modification displays a more complete morphology and less side reaction with electrolyte.DEMS was used to further investigate cathode-electrolyte interface which was reflected by gas evolution.NCA-LM2 releases less CO_(2)than NCA-P indexing on a more stable surface.The modified material presents outstanding capacity retention of 96.2%after 100 cycles in the voltage range of 3.0-4.4 V at 1C,13%higher than that of the pristine and 80.8%at 1 C after 300 cycles.This excellent electrochemical performance could be attributed to the fact that the high chemically stable coating layer of Li_(0.5)La_(2)Al_(0.5)O_(4)(LLAO)could enhance the interface and the Mn doping layer could suppress the influence of the lattice mismatch and distortion.We believe that it can be a useful strategy for the modification of Ni-rich cathode material and other advanced functional material.

GEOMETRICALLY NONLINEAR ANALYSIS OF MINDLIN PLATEUSING THE INCOMPATIBLE BENDING ELEMENTSWITH INTERNAL SHEAR STRAIN

An approach of the incompatible elements with additional internal shear strain is,in the presem paper,suggested and applied to geometrically nonlinear analysis of Mi-ndlin plate bending problem.It provides a quite covenient way to avoid the whear loc-king troubles.An energy consistency condition for this kind of C°elements is offered.The nonlinear element formulations and some numerical results are presented.

Effects of Internal Relaxation under Inplane Strain on the Structural,Electronic and Optical Properties of Perovskite BaZrO3

We present the specific ab-initio calculations that detail the variations of perovskite BaZrO3 caused by in-plane strain. Specifically, the internal relaxation, which was not captured in the widely used biaxial strain model, was included in a complementary manner to lattice relaxation. Density functional theory as well as a hybrid functional method based on a plane wave basis set was employed to calculate the lattice structure, elastic constants, electronic properties and optical properties of perovskite BaZrO3. The lattice parameter c exhibited a clear linear dependence on the imposed in-plane strain, but the Poisson＇s ratio caused by internal relaxation was smaller than the elastic deformation, indicating an ＂inelastic＂ or ＂plastic＂ relaxation manner caused by the introduction of internal relaxation. As a result, the related electronic and optical properties of perovskite BaZrO3 were also strongly affected by the in-plane strain, which revealed an effective way to adjust the properties of perovskite BaZrO3 via internal relaxation.

Dependence of Nanocrystalline Phase Formation and Magnetic Properties in Fe_(25)Ni_(75) on Ball Milling Time

Nanocrystalline Fe 25 Ni 75 powders were prepared by the mechanical alloying process . They were investigated by X ray diffraction and magnetic measurements .The ball milling time dependence of grain size, internal strain and magnetic properties has been discussed. The results show that the formation of Fe 25 Ni 75 alloy phase is almost completed after milling for 30 hours. The reduction of grain size accompanied by the growth of internal strain was observed after extended milling. An average grain size about 10-20 nm of alloyed powders has been determined by Sherrer formula estimation. The saturation magnetisation Ms has a slight increase when the average grain size continues to decrease by intensive milling. This fine size of mechanically alloyed powders (10-20 nm) results in a single domain magnetic structure and the formation of superparamagnetic phase.

Limit Analysis of Defect-Free Pipe Elbow Under Internal Pressure With Mean Yield Criterion

With mean yield（MY）criterion,an analytical solution of the collapse load for a defect-free pipe elbow under internal pressure is first obtained.It is a function of ratio of thickness to radius t0/r0,strain hardening exponent n,curvature influence factor mand ultimate tensile strength.The collapse load increases with the increase of m,and it is the same as the burst pressure of straight pipe if m=1is assumed.The MY-based solution is compared with those based on Tresca,Mises and twin shear stress（TSS）yield criteria,and the comparison indicates that Tresca and twin shear stress yield criteria predict a lower bound and an upper bound to the collapse load respectively.However,the MY-based solution lies just between the TSS and Tresca solutions,and almost has the same precision with the Mises solution.