Search

We demonstrate the bias-selectable mid- or long-wave infrared detectors composed by back-to-back pin-nip diodes with “M” barrier inserted in two diodes to suppress the dark current. Mid-wave infrared (MWIR) and long-wave infrared (LWIR) active region (π layer) are composed by 8 ML/8 ML and 12.5 ML/7 ML InAs/GaSb superlattices. The cutoff wavelength is 4.8 μm under forward bias called MWIR channel and expands to 10 μm under reverse bias called LWIR channels. The responsivities are 0.27 A/W at 4.2 μm at forward 300 mV bias, while 0.31 A/W at 9 μm at reverse 400 mV bias at 77 K. The dependence of the response on the bias is due to the competition of the built-in electric field from the two junctions. The current–voltage curve and the quantum efficiency were measured at 77 K. The dark current densities are 22.7×10−5 A/cm2 and 4.51×10−2 A/cm2 for two channels under different bias. The peak detectivity of MWIR diode is calculated to 2.0×1012 cm·Hz1/2/W at 4.2 μm and 1.0×1010 cm·Hz1/2/W at 9 μm for LWIR channel.

We compared the photoluminescence (PL) properties of AlInAsSb digital alloy samples with different periods grown on GaSb (001) substrates by molecular beam epitaxy. Temperature-dependent S-shape behavior is observed and explained using a thermally activated redistribution model within a Gaussian distribution of localized states. There are two different mechanisms for the origin of the PL intensity quenching for the AlInAsSb digital alloy. The high-temperature activation energy E 1 is positively correlated with the interface thickness, whereas the low-temperature activation energy E 2 is negatively correlated with the interface thickness. A quantitative high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) study shows that the interface quality improves as the interface thickness increases. Our results confirm that E 1 comes from carrier trapping at a state in the InSb interface layer, while E 2 originates from the exciton binding energy due to the roughness of the AlAs interface layer.

Here we report the 1.3-μm electrical injection lasers based on the InAs/GaAs quantum dot (QD) grown on GaAs substrate, which can steadily work at 110℃ without visible degradation. The QD structure is designed by applying the Stranski-Krastanow growth mode of solid source molecular beam epitaxy. The density of InAs quantum dots in the active region is increased from 3.8×1010 cm -2 to 5.9×1010 cm -2. For lasers performance, the maximum output power of devices with low density quantum dots as active region is 650mW at room temperature, and that of devices with high density is 1030mW. Meanwhile the output power of high density device is 131 mW under the injection current of 4 A at 110℃.

By optimizing the V/III beam-equivalent pressure ratio, a high-quality InAs/GaSb type-II superlattice material for the long-wavelength infrared (LWIR) range is achieved by molecular beam epitaxy (MBE). High-resolution x-ray diffraction (HRXRD), atomic force microscopy (AFM), and Fourier transform infrared (FTIR) spectrometer are used to characterize the material growth quality. The results show that the full width at half maximum (FWHM) of the superlattice zero-order diffraction peak, the mismatching of the superlattice zero-order diffraction peak between the substrate diffraction peaks, and the surface roughness get the best results when the beam-equivalent pressure (BEP) ratio reaches the optimal value, which are 28 arcsec, 13 arcsec, and 1.63 Å, respectively. The intensity of the zero-order diffraction peak is strongest at the optimal value. The relative spectral response of the LWIR detector shows that it exhibits a 100% cut-off wavelength of 12.6 μm at 77 K. High-quality epitaxial materials have laid a good foundation for preparing high-performance LWIR detector.

The etching and passivation processes of very long wavelength infrared (VLWIR) detector based on the InAs/GaSb/AlSb type-II superlattice have been studied. By studying the effect of each component in the citric acid solution (citric acid, phosphoric acid, hydrogen peroxide, deionized water), the best solution ratio is obtained. After comparing different passivation materials such as sulfide + SiO2, Al2O3, Si3N4 and SU8, it is found that SU8 passivation can reduce the dark current of the device to a greater degree. Combining this wet etching and SU8 passivation, the R 0 A of VLWIR detector with a mesa diameter of 500 μm is about 3.6 Ω⋅cm2 at 77 K.

Thermal barrier coating systems (TBCs) are widely used in turbines. However, premature failures have impaired the use of TBCs and cut down their lifetime. The thermally grown oxide layer (TGO) thickening and the material thermal expansion misfit under thermal cyclic loading significantly affect the interfacial stress field and stability of TBCs. In this study, the stability evaluation method of TBCs under thermal cyclic loading based on energy is established using the visco-elastoplastic and shakedown theorem. The semicircular shape interface is used to simplify the complicated interfacial undulations in FEA model. And actual TGO thickness obtained from experiment is used to simulate the bond coat oxidation. Then the effect of TGO thickening on the stability and stress field of TBCs under thermal cyclic loading is analyzed through the numerical simulation. It is concluded that estimating from the stress-strain evolution behavior, the local stability of the TBCs decreases with the TGO thickening, and assessing from energy, TBCs shows instable with TGO thickening.

Unintentionally doped GaSb films grown by Molecular Beam Epitaxy (MBE) on GaAs (001) substrates were annealed under different temperatures and time. It was found that the rapid thermal annealing (RTA) process can improve the optical properties. By changing annealing temperature and time, the optimized annealing temperature and times are found to be 650°C and 30s, respectively. Point defects and dislocations are two major kinds of defect in undoped GaSb thin films grown by MBE on GaAs (001) substrates.

A model of gear contact has been established based on Hertz theory in this thesis, Analysis of non-standard gear contact fatigue life test process . For ha* take 1,1.15,1.25 and c* take 0.25,0.5 respectively ,the gear generates contact fatigue failure, then calculate the meshing ratio under different tooth high coefficients, and gear pairs state with fatigue testing time by the finite element method and orthogonal test. These data are compared with the results of specific experiments verified. They description that tooth height coefficients and headspace coefficients change have a great impact on gear contact fatigue life.

Pre-bulging effect on the sheet hydroforming process of irregular box with unequal height and flat bottom was investigated by means of numerical simulation and experiment. The influences of pre-bulging height and pre-bulging pressure on the forming were discussed respectively. The pressure loading path was optimized. The results show that pre-bulging has important influences on the forming results. Too high pre-bulging height causes the crack and obvious crease at the punch nose near the lowest corner. Too low pre-bulging height causes fracture at the punch nose of the highest corner. Pre-bulging pressure has a smaller effect on the fracture at the punch nose of the highest corner when the pre-bulging height is reasonable. But over high pre-bulging pressure causes crack and obvious crease at the punch nose near the lowest corner. Failure can be avoided by using reasonable pre-bulging height and pre-bulging pressure.

An finite element model of orthogonal dry cutting with separate line is established according to the constitutive relation of large thermo-elastic-plastic displacement and the principle of virtual work in metal plastic deformation process,. The influence of cutting depth on residual stress was simulated for materials GH4169 with high speed. The residual stresses are analyzed on the machined surface and subsurface. The result shows that tensile residual stress of the machined surface is minimum value when the cutting depth is 0.2mm. the deeper is the depth of cut, the large the augmentation of compressive stress on the subsurface, which proves foundation for cutting process of dry-machined difficult-to-machine material with high speed and make it more efficiently to control the integrity of the machined surface.

This paper adopts finite-element method to analyze and test the factors which influence the brake shimmy. Based on the prototype of a particular heavy truck, finite element model of the brake shimmy about drum brake is developed upon the mechanism analysis of drum brake. The reasons that drum brake has oscillation phenomenon during braking process is analyzed by simulation and calculation the transient response in this process. Tests indicate that results of finite element analysis are consistent with the conclusion of real vehicle road test.

The wear resistance of coated tool can be predicted widely by experiments and theoretical analysis. In the paper, an unique method is adopted to analyze influence of high speed on key stresses of the coated tool .First, through the cutting process simulation with different high cutting speeds, contact stress, shear stress and temperature distribution of the surface of the coated tool can be obtained when the cutting process is steady. Then the stresses and temperature are applied to the coated tool to analyze the key stresses in the tool. The result shows the potential failure of coated tool can be predicted by Finite element analysis correctly. Crack between coating and substrate may occur at the same position with different cutting speeds.

Grinding induces residual stresses, which can play an important role on the fatigue of the component. In general, residual stresses in a ground surface are primarily generated due to three effects: thermal expansion and contraction during grinding, plastic deformation caused by the abrasive grains of the wheel and phase transformations due to high grinding temperature. It was found that thermal expansion and plastic deformation in the grinding process were the major causes of residual stresses. In this paper, an analysis model for the calculation of residual stresses induced by a surface grinding process on an ultrahigh-strength steel (Aermet100) workpiece is presented. Firstly, the stress distribution induces by thermal expansion was obtained base on the transient heat conduction equation and the thermal properties of Aermet100. All the calculations were based on the moving heat source solution which was modeled as a uniformly distributed, 2D heat source moving across the surface of a half-space, found in Carslaw and Jaeger. The results show that the near surface residual stress is predominantly tensile and that the magnitude of this stress increases with increasing heat flux values. Secondly, the plastic deformation caused by the abrasive grains of the wheel was simulated base on the grain-workpiece interaction. The chip formation process and the material removal mechanisms can be examined using the micro-scale approach. The results show that the residual stress induced by the grinding force itself is generally compressive which is smaller than the residual tensile stress induced by thermal stress. Therefore, the residual stress brought about by grinding operation is generally a tensile stress. This paper offers an insight into the mechanism understanding of thermal and mechanical residual stresses induced by surface grinding. Key words: grinding, residual stress, grain

An analytical model based on multilayer structure with thermal expansion mismatch caused by temperature gradients was established to predict the residual stress in the system. The solution obtained from the model is independent of the number of layers. Three simplified models: bi-layer structure, coating system and film system with great compatibility are developed considering different engineering application. And the bilayer structure is verified by Stoney’s equation under the same conditions. Tri-layer coating system ZrO2/ Al2O3/1Cr18Ni9Ti is established in order to research the effect of temperature variations on the residual stress between different layers. The results suggested the stress has obvious mutation in coating interface with different temperature variation. And the residual stress with different temperature variation in different layers is larger than that with identical temperature variation. Key words: multilayer structures; residual stress; analytical model; thermal expansion mismatch; temperature variation

The most commonly used Micro tubular solid oxide fuel cell (MT-SOFC) anode material is a two phase nickel and yttria stabilized zirconia (Ni/YSZ) cermet. And the mechanical stability of anode support layer, in anode-supported electrolyte designs, is very important for large scale applications. During the assembly of stack and normal operation, MT-SOFC is easy to crack under the residual stress induced by manufacture and thermal stress due to multi-physics coupling. In this work, MT-SOFC model was founded on the background of MT-SOFC stack of electric vehicle and was analyzed by finite element method, based on theories of multi-physical field coupling. In order to find out which is the main reason for cracking, the residual stress due to manufacture and work were investigated separately. Thermal stress based on residual stresses of operating are studied for further research of life of MT-SOFC. It concluded that the failure of the MT-SOFC occurs mainly because of the residual stress due to the mismatch between the coefficients of thermal expansion of the materials of the electrode assembly, thermal stress will increase the mismatch in some partial areas. The results are important for studying the life and final spallation of MT-SOFC of electric vehicle.

Shakedown analysis of gear contact is very important. Local coordinates are constructed on different meshing points because curvature of gear profile is not constant and then distributions of residual stresses and strains are given. Upper and lower bounds for the shakedown limits have been obtained. The steady-state residual stresses of gear under repeat meshing are calculated and relations between shakedown limits and frictional coefficient/meshing position are given. The results are useful information for the strength design of gear.

The most commonly used Micro tubular solid oxide fuel cell (MT-SOFC) anode material is a two phase nickel and yttria stabilized zirconia (Ni/YSZ) cermet. And the mechanical stability of anode support layer, in anode-supported electrolyte designs, is very important for large scale applications. During the assembly of stack and normal operation, MT-SOFC is easy to crack under the fuel pressure and thermal loading due to various mechanical properties. In this study, MT-SOFC model was founded on the background of MT-SOFC stack of electric vehicle and was analyzed by finite element method, based on theories of elasto-plasticity, thermo-mechanical coupling. The effect of thermal load was investigated. It concluded that the failure of the micro-tubular cell occurs mainly because of the residual stress due to the mismatch between the coefficients of thermal expansion of the materials of the electrode assembly. The results are important for studying the life and final spallation of MT-SOFC of electric vehicle.

Contact fatigue is the primary failure form in the closed and well lubricated gear driving. Residual stress is an important factor influenced the fatigue. In this paper a relationship between the compressive residual stress and the gear contact fatigue strength was established basis on static shakedown analysis with elastic-plastic contact theory. The contact stress was obtained by hertz theory, and the residual stress induced by the gear meshing was simulated though finite element method. Base on the residual stress distribution obtained in previous step, three different pressures according to James theory was loaded into the contact zone. It was shown that the gear plastic deformation was unchanged if the secondary loading was no more than the initial load. The results suggest that residual compressive stress could improve the contact fatigue strength.

Drum brake is a braking part which is widely used on heavy truck. The distribution and dimension of contacting pressure and contacting area between friction linings and brake drum have important influence on braking performance. Entire contact theory in this article was found based on the conditions that the outside radius of linings was equal to the inside radius of drum. The relation between the corresponding points on contact surface and the angle which lining rotated around support pin axis was calculated based on entire contact theory. The radial deformation, pressure distribution, contact area of linings and the brake performance were analyzed in the condition of entire contact theory.

Mechanical property of coating under the micro-contact load such as impact and sliding wear significantly influence the reliability of surface coating. In order to research the influence, a contact model between the rigid multi-asperity surface and coating was found based on the G-W model in the background of Thermal Barrier Coatings(TBCs) used in aircraft engine blade. The distribution of stress in subsurface of the micro-contact process was analyzed based on the theories of contact mechanics and tribology with the elasto-plastic finite element method. The effect of coating thickness, elastic modulus, yield strength on the distribution of residual stress for TBCs was investigated. It conclude that primary reason of coating failure are cumulation of plastic deformation and excessive interfacial stress. The results are significant for studying the life and final spallation of TBC system and other coating.

Transition curve is very important to bending strength and life of gear. In order to improve the bending strength of gear, the shape of three kinds of transition curve (ordinary fillet cutter tip, single circle arc cutter tip and double circle arc cutter tip) was analyzed respectively, the relationship of double circle arc cutter tip parameters was established, the relation model of sensitive part of gear and stress concentration factor ( J and γ) was determined, the effect of different transition curves of gear on bending strength ( ) was explored. The results of analysis show that the bending strength of gear cut by double circle arc cutter tip increases by 10% comparing with that of gear cut by ordinary fillet cutter tip. It provides theories foundation for the design of high bending strength gear.

Grinding induces tensile residual stresses, which can play an adverse role on the fatigue and wear resistance of the component. In this paper, a calculation model of residual stresses induced by a surface grinding process on a ultrahigh-strength steel workpiece (Aermet100) is presented, which includes the transient heat conduction equation、a thermal elastic-plastic constitutive equation and the Von Mises yield condition. The model giving the energy conducted as heat in the workpiece as a function of the grinding wheel speed, the workpiece speed, and the cutting depth is proposed. It is shown that, for such grinding conditions, the simulation leads to tensile residual stresses which increase with the wheel speed and cutting depths increase. The paper offers an insight into the mechanism understanding of thermal residual stresses induced by surface grinding.

Technology of digital mockup is introduced and the application background and practical requirement of tunnel boring machine has been discussed in this paper. One type of EPB tunnel boring machine’s digital mockup is built. The kinematics simulation of working station is disigned base on it. And finite element analysis of some critical componants are operated in CATIA.

Mathematical models of basic parameters, force and thermal parameters of cutting were obtained by applying the thermo-elastic-plastic theory and the heat-balance theory, according to the principle of residual stress generation in cutting process. Based on the 2D finite element model of chip molding with separation surface, the direct way was applied in thermo-mechanical coupling, and residual stress of cutting GH4169 were simulated and analyzed by finite element. The results showed that the residual stresses are changed from tensile to compressive with the development of depth away from the workpiece surface. Also its values are changed according to a certain rule as varying the cutting speed. These provide a foundation for the control of cutting quality of workpiece.

It is found that both methods using either continuous Sb supply or pre-deposition of a very thin Sb layer are efficient for the Sb-assisted molecular beam epitaxy growth of highly strained InGaAs/GaAs quantum wells (QWs). The emission of QWs is extended to long wavelength close to 1.25 mu m with high luminescence efficiency at room temperature. The influence of rapid thermal annealing (RTA) on the photoluminescence intensity critically depends on the annealing temperature and duration for highly strained QWs. A relatively low RTA temperature of 700 degrees C with a short duration of 10 s is suggested for optimizing the annealing effect. (c) 2005 Elsevier B.V. All rights reserved.

Based on the band-anticrossing model, the effect of the strain-compensated layer and the strain-mediated layer on the band structure, the gain, and the differential gain of GaInNAs-GaAs quantum well lasers have been investigated. Different band-filling mechanisms have been illustrated. Compared to the GaInNAs-GaAs single quantum well with the same wavelength, the introduction of the strain-compensated layer and the strain-mediated layer increases the transparency carrier density. However, these multilayer structures help to suppress the degradation of the differential gain.

Effects of SiO 2 encapsulation and rapid thermal annealing (RTA) on the optical properties of GaNAs/GaAs single quantum well (SQW) were studied by low temperature photoluminescence (PL). A blueshift of the PL peak energy for both the SiO 2 -capped region and the bare region was observed. The results were attributed to the nitrogen reorganization in the GaNAs/GaAs SQW. It was also shown that the nitrogen reorganization was obviously enhanced by SiO 2 cap-layer. A simple model [1] was used to describe the SiO 2 -enhanced blueshift of the low temperature PL peak energy.