Thermal transport in composition graded silicene/germanene heterostructures

Through equilibrium and non-equilibrium molecular dynamics simulations,we have demonstrated the inhibitory effect of composition graded interface on thermal transport behavior in lateral heterostructures.Specifically,we investigated the influence of composition gradient length and heterogeneous particles at the silicene/germanene(SIL/GER)heterostructure interface on heat conduction.Our results indicate that composition graded interface at the interface diminishes the thermal conductivity of the heterostructure,with a further reduction observed as the length increases,while the effect of the heterogeneous particles can be considered negligible.To unveil the influence of composition graded interface on thermal transport,we conducted phonon analysis and identified the presence of phonon localization within the interface composition graded region.Through these analyses,we have determined that the decrease in thermal conductivity is correlated with phonon localization within the heterostructure,where a stronger degree of phonon localization signifies poorer thermal conductivity in the material.Our research findings not only contribute to understanding the impact of interface gradient-induced phonon localization on thermal transport but also offer insights into the modulation of thermal conductivity in heterostructures.

A Broadband Long-Wavelength Superluminescent Diode Based on Graded Composition Bulk InGaAs

A novel unselective regrowth buried heterostructure long-wavelength superluminescent diode （SLD） with a graded composition bulk InGaAs active region is developed by metalorganic vapor phase epitaxy （MOVPE）. At a 150mA injection current, the full width at half maximum of the emission spectrum of the SLD is about 72nm, ranging from 1602 to 1674nm. The emission spectrum is smooth and flat. The ripple of the spectrum is less than 0.3dB at any wavelength from 1550 to 1700nm. An output power of 4.3mW is obtained at a 200mA injection current under continuous-wave operation at room temperature. This device is suitable for the applications of light sources for gas detectors and L-band optical fiber communications.

Graded composition and doping p-i-n Al_(x)Ga_(1−x)As/GaAs detector for unbiased voltage operation

p-i-n Al_(x)Ga_(1−x)As/GaAs detectors with graded compositions and graded doping were grown and prepared.From the current-voltage and capacitance-voltage measurement results,the devices had good p-n junction diode characteristics,and the electric field strength under an unbiased voltage was 1.7×10^(5) Vcm^(-1).The full width at half maximum and charge collection efficiency of the detectors obtained from energy spectrum measurements of 5.48-MeV alpha particles were 3.04 and approximately 93%,respectively.In this study,we created the most advanced and promising state-of-the-art unbiased detector reported to date.

Thermoelectric properties of p-type Bi-Sb-Te compositionally graded thermoelectric materials with different barriers

In order to find more suitable materials as barriers and to improve the thermoelectric properties, p-type (Bi1-xSbx) 2Te3 (x = 0.85, 0.9) two segments compositionally graded thermoelectric materials (CGTM) with different barriers were fabricated by conventional hot pressure method. Metals Fe, Co, Cu and Al were used as barriers between two segments. The effects of different barriers on thermoelectric properties of CGTM were investigated. The results show that metal Fe is more stable and suitable as the barrier.

Development of functionally graded aluminium composites using centrifugal casting and influence of reinforcements on mechanical and wear properties

Functionally graded Al/B_4C, Al/Si C, Al/Al_2O_3 and Al/TiB_2 composites with constant 12%(mass fraction) of reinforcement were fabricated by centrifugal casting and hollow cylindrical components were obtained. Microstructural characteristics were investigated at outer surface of all composites and segregation of reinforcement particles was observed. Graded property of the composites with different reinforcements was investigated through hardness and tensile measurements. Results revealed that the outer peripheries of all composites exhibit higher hardness except in Al/B_4C composite and the outer zones of all composites show higher tensile strength. Abrasive wear test was conducted on the outer peripheries of all composites and Al/TiB_2 composite exhibits less wear rate.

Nonlinear vibration of functionally graded graphene platelet-reinforced composite truncated conical shell using first-order shear deformation theory

In this study,the first-order shear deformation theory(FSDT)is used to establish a nonlinear dynamic model for a conical shell truncated by a functionally graded graphene platelet-reinforced composite(FG-GPLRC).The vibration analyses of the FG-GPLRC truncated conical shell are presented.Considering the graphene platelets(GPLs)of the FG-GPLRC truncated conical shell with three different distribution patterns,the modified Halpin-Tsai model is used to calculate the effective Young’s modulus.Hamilton’s principle,the FSDT,and the von-Karman type nonlinear geometric relationships are used to derive a system of partial differential governing equations of the FG-GPLRC truncated conical shell.The Galerkin method is used to obtain the ordinary differential equations of the truncated conical shell.Then,the analytical nonlinear frequencies of the FG-GPLRC truncated conical shell are solved by the harmonic balance method.The effects of the weight fraction and distribution pattern of the GPLs,the ratio of the length to the radius as well as the ratio of the radius to the thickness of the FG-GPLRC truncated conical shell on the nonlinear natural frequency characteristics are discussed.This study culminates in the discovery of the periodic motion and chaotic motion of the FG-GPLRC truncated conical shell.

Characterization of aluminum based functionally graded composites developed via friction stir processing

Al/SiC functionally graded material(FGM) was developed through a novel multi-step friction stir processing(FSP) method. Si C particles with a mean size of 27.5 μm were embedded in the groove on the 6082-Al plate. To create a graded structure over a predefined value, FSP was carried out with three tools with different pin lengths and with varying volume fractions of SiC particles. The structure was formed by passing tools with 1-3 passes with a constant rotational and traveling speeds of 900 r/min and 20 mm/min, respectively. The experiments were conducted at room temperature. Microstructural features of functionally graded(FG) samples were examined by using scanning electron microscopy(SEM) and 3D light microscopy. Mechanical properties in terms of wear resistance and microhardness were thoroughly assessed. The results indicate that the increase in FSP pass number causes more uniform SiC particle dispersion. The microhardness values were impacted by the number of passes and improved by 51.54% for Pass 3 when compared to as-received 6082-Al. Wear resistance of Al/SiC FG samples was found to increase as a result of the addition of SiC particles.

Co-electrodeposition and properties evaluation of functionally gradient nickel coated ZrO_2 composite coating

For the first time,functionally electroless nickel plated ZrO2(NCZ)graded Ni-NCZ composite coating has been successfully co-electrodeposited from a bath with gradually increasing of stirring rate.Studies showed that co-electrodeposition in a bath with stirring rate of250r/min results in the maximum co-electrodeposited particle content and the best particle distribution.To produce NCZ graded Ni-NCZ composite coating,the stirring rate was continuously increased from0to250r/min.The electroplated coating had a continuous gradient increasing of co-electrodeposited NCZ content from substrate towards the surface.The results showed that with increasing the co-electrodeposited NCZ particles content in Ni matrix,microhardness increases from interface towards the surface of the coating.Little crystallite size of Ni matrix and higher co-electrodeposited hard particles content were recognized as the reasons of microhardness increasing.Bend test revealed that the functionally graded composite coating shows more excellent adhesion to the substrate compared with the ordinary distributed Ni-NCZ on the same substrate.This result is attributed to lower mechanical mismatch between coating and substrate in the functionally graded composite coating with respect to the uniformly distributed one.The results of wear resistance measurements reveal that wear resistance of functionally graded Ni-NCZ is higher than that of ordinary distributed composite coating.

Love Waves in Layered Graded Composite Structures with Imperfectly Bonded Interface

Theoretical analysis and numerical calculations of Love wave propagation in layered graded composites with imperfectly bonded interface are described in this paper. On the basis of WKB method, the approximate analytic solutions for Love waves are obtained. By the interface shear spring model, the dispersion relations for Love waves in layered graded composite structures with rigid, slip, and imperfectly bonded interfaces are given, and the effects of the interface conditions on the phase velocities of Love waves in SiC/Al layered graded composites are discussed. Numerical analysis shows that the phase velocity decreases when the defined flexibility parameter is greater. For the general imperfectly bonded interface, the phase velocity changes in the range of the velocities for the rigid and slip interface conditions.

In-Situ Synthesis and Characteristics of TiC-Fe Cermet Graded Composite Coating on a Steel Substrate

By means of an inherent elevated-temperature of poured liquid steel,a Ti-C-30wt%Fe preform,which was pre-placed in a mould cavity,was directly ignited and a combustion synthesis reaction took place.As a result,a TiC-Fe cermet coating with a thickness of about 10mm was simultaneously synthesized on the solidified steel matrix.The synthesized coating exhibits a feature of graded composite structure,in which both the amount and size of TiC particles decrease gradually with an increasing distance from the furface of the coating.Moreover,by a proper casting technique,the pores formed during the combustion synthesis of the preform could be centrally distributed in 2-3mm in outer layer of the coating.When this outer porous layer was worn off,the rest coating with a thickness of about 8mm possesses a dense structure and a high abrasive wear resistance.

Couple stress-based nonlinear primary resonant dynamics of FGM composite truncated conical microshells integrated with magnetostrictive layers

The size-dependent geometrically nonlinear harmonically soft excited oscillation of composite truncated conical microshells(CTCMs)made of functionally graded materials(FGMs)integrated with magnetostrictive layers is analyzed.It is supposed that the FGM CTCMs are subjected to mechanical soft excitations together with external magnetic fields.An analytical framework is created by a microstructuredependent shell model having the 3rd-order distribution of shear deformation based on the modified couple stress(MCS)continuum elasticity.With the aid of the discretized form of differential operators developed via the generalized differential quadrature technique,a numerical solution methodology is introduced for obtaining the couple stress-based amplitude and frequency responses related to the primary resonant dynamics of the FGM CTCMs.Jump phenomena due to the loss of the first stability branch and falling down to the lower stable branch can be seen in the nonlinear primary resonance of the FGM CTCMs.It is demonstrated that the hardening type of nonlinearity results in bending the frequency response to the right side,and the MCS type of size effect weakens this pattern.Moreover,for higher material gradient indexes,the hardening type of nonlinearity is enhanced,and the MCS-based frequency response bends more considerably to the right side.

Effective Dielectric Response of Composites with Graded Material

The effective dielectric response of linear composites containing graded material is investigated under an applied electric field E_0.For the cylindrical inclusion with gradient dielectric function,ει(r)=b+cr,randomly embedded in a host with dielectric constant εm,we have obtained the exact solution of local electric potential of the composite media regions,which obeys a linear constitutive relation D=εE,using hypergeometric function.In dilute limit,we have derived the effective dielectric response of the linear composite media.Furthermore,for larger volume fraction,the formulas of effective dielectric response of the graded composite media are given.

Electric field distribution and effective nonlinear AC and DC responses of graded cylindrical composites

The perturbation method is used to study the localization of electric field distribution and the effective nonlinear response of graded composites under an external alternating-current（AC） and direct-current（DC） electric field E app = E 0（1 ＋ sin ωt）.The dielectric profile of the cylindrical inclusions is modeled by function ε i（r） = C k r k（r ≤ a）,where r is the radius of the cylindrical inclusion,and C k,k,a are parameters.In the dilute limit,the local potentials and the effective nonlinear responses at all harmonics are derived.Meanwhile,the general effective nonlinear responses are also derived and compared with the effective nonlinear responses at harmonics under the AC and DC external field.It is found that the effective nonlinear AC and DC responses at harmonics can be calculated by those of the general effective nonlinear of the graded composites under the external DC electric field.Moreover,the obtained local electrical fields show that the electrical field distribution in the cylindrical inclusions is controllable,and the maximum of the electric field inside the cylinder is at its center.

Isogeometric nonlocal strain gradient quasi-three-dimensional plate model for thermal postbuckling of porous functionally graded microplates with central cutout with different shapes

This study presents the size-dependent nonlinear thermal postbuckling characteristics of a porous functionally graded material(PFGM) microplate with a central cutout with various shapes using isogeometric numerical technique incorporating nonuniform rational B-splines. To construct the proposed non-classical plate model, the nonlocal strain gradient continuum elasticity is adopted on the basis of a hybrid quasithree-dimensional(3D) plate theory under through-thickness deformation conditions by only four variables. By taking a refined power-law function into account in conjunction with the Touloukian scheme, the temperature-porosity-dependent material properties are extracted. With the aid of the assembled isogeometric-based finite element formulations,nonlocal strain gradient thermal postbuckling curves are acquired for various boundary conditions as well as geometrical and material parameters. It is portrayed that for both size dependency types, by going deeper in the thermal postbuckling domain, gaps among equilibrium curves associated with various small scale parameter values get lower, which indicates that the pronounce of size effects reduces by going deeper in the thermal postbuckling regime. Moreover, we observe that the central cutout effect on the temperature rise associated with the thermal postbuckling behavior in the presence of the effect of strain gradient size and absence of nonlocality is stronger compared with the case including nonlocality in absence of the strain gradient small scale effect.

On Co-precipation Fabrication of Continuously Graded Composites

The manner by which the particles settle in the laminar flow region is first described and the characteristics of co sedimentation of two species particles are summarized.The subsequent introduction is focused on the fabrication process of continuously graded composites using co sedimentation technique.Finally,the authors point out the key problem that should be solved immediately,based on their current work.

In-situ fabrication of Al(Zn)-Al_2O_3 graded composite using the aluminothermic reaction during hot pressing

In INs study, the fabrication of multilayer AI（Zn）-A1203 with different volume fractions of A1203 was investigated. A1 and ZnO powders were milled by a plaaetaxy ball mill, after which five-layer functionally graded samples were produced flarough hot pressing at 580~C and 90 MPa pressure for 30 min. Formation of reinforcing A1203 particles occurred in the aluminum matrix via the aluminolkermic reaction. Determination of the ignition temperature of the aluminolkennic reaction was accomplished using differential lkermal and lkermo- gravimelric amlyses. Scaaming electron microscopy, energy dispersive spectroscopy, and X-ray diffractometery amlyses were utilized to characterize the specimens. The lkermal amlysis results showed that the ignition temperatures for the aluminolkennic reaction of layers with the highest and lowest ZnO contents were 667 and 670~C, respectively. Microslxuctural observation and chemical amlysis confirmed the fa- brication of AI（Zn）-A1203 functionally graded materials composites with precipitation of additional Zn in the matrix. Moreover, nearly dense functionally graded samples demonstrated minimum and maximum hacdness values of HV 75 and HV 130, respectively.

Dielectric responses of graded composites having generalized gradation profiles

Under an external uniform electric field, the dielectric response of graded cylindrical composites having generalized dielectric profile inclusions is investigated. The generalized dielectric profile of graded cylindrical inclusion is expressed in the form, εi（r） = c（b ＋ r）^keβr where r is the radial variable of the cylindrical inclusions and c, b, k and β are parameters. The local potential solution of generalized dielectric profile graded composites is derived by means of the power series method and the effective dielectric response is predicted in the dilute limit. Moreover, from the result of generalized profile, the analytical solutions of local potentials and the effective responses of graded composites having three cases of dielectric profiles, i.e., the exponential profile εi（r） = ce^βr, the general power law profile εi（r） = c（b ＋ r）^k and the profile εi（r） = cr^keβr, are sorted out, respectively. In the dilute limit, our exact results are used to test the validity of differential effective dipole approximation （DEDA） for estimating the effective response of graded cylindrical composites, and it is shown that the DEDA is in excellent agreement with the exact result.

Enhanced optical nonlinear absorption of graded Au-TiO_2 composite films

This paper reports that single-layer and graded Au-TiO2 granular composite films with Au atom content 15%- 66% were prepared by using reactive co-sputtering technique. The third-order optical nonlinearity of single-layer and graded composite films was investigated by using s- and p-polarized Z-scans in femtosecond time scale. The nonlinear absorption coefficient βeff of single-layer Au-TiO2 films is measured to be -2.3×10^3-0.76×10^3 cm/GW with Au atom content 15%-66%. The βeff value of the 10-layer Au-TiO2 graded film is enhanced to be -2.1×10^4cm/GW calculated from p-polarized Z-scans, which is about ten times the maximum βeff of single-layer films. Broadened response in the wavelength region 730-860 nm of the enhanced optical nonlinearity of graded Au-TiO2 composite films was also investigated.

Vibration characteristics of piezoelectric functionally graded carbon nanotube-reinforced composite doubly-curved shells

This paper presents an analytical solution for the free vibration behavior of functionally graded carbon nanotube-reinforced composite(FG-CNTRC) doubly curved shallow shells with integrated piezoelectric layers. Here, the linear distribution of electric potential across the thickness of the piezoelectric layer and five different types of carbon nanotube(CNT) distributions through the thickness direction are considered. Based on the four-variable shear deformation refined shell theory, governing equations are obtained by applying Hamilton's principle. Navier's solution for the shell panels with the simply supported boundary condition at all four edges is derived. Several numerical examples validate the accuracy of the presented solution. New parametric studies regarding the effects of different material properties, shell geometric parameters, and electrical boundary conditions on the free vibration responses of the hybrid panels are investigated and discussed in detail.

The effect of initial geometric imperfection on the nonlinear resonance of functionally graded carbon nanotube-reinforced composite rectangular plates

The purpose of the present study is to examine the impact of initial geometric imperfection on the nonlinear dynamical characteristics of functionally graded carbon nanotube-reinforced composite(FG-CNTRC) rectangular plates under a harmonic excitation transverse load. The considered plate is assumed to be made of matrix and single-walled carbon nanotubes(SWCNTs). The rule of mixture is employed to calculate the effective material properties of the plate. Within the framework of the parabolic shear deformation plate theory with taking the influence of transverse shear deformation and rotary inertia into account, Hamilton’s principle is utilized to derive the geometrically nonlinear mathematical formulation including the governing equations and corresponding boundary conditions of initially imperfect FG-CNTRC plates. Afterwards, with the aid of an efficient multistep numerical solution methodology, the frequency-amplitude and forcing-amplitude curves of initially imperfect FG-CNTRC rectangular plates with various edge conditions are provided, demonstrating the influence of initial imperfection,geometrical parameters, and edge conditions. It is displayed that an increase in the initial geometric imperfection intensifies the softening-type behavior of system, while no softening behavior can be found in the frequency-amplitude curve of a perfect plate.