Effect Of Biaxial Stress Research Articles

Electronic and optical properties in ZnO:Ga thin films induced by substrate stress

The effects of biaxial stress in ZnO:Ga thin films on different substrates, e.g., sapphire(0001), quartz, Si(001), and glass have been investigated by X-ray diffraction, atomic force microscopy, and electrical transport and ellipsometric measurements. A strong dependence of orientation, crystallite size, transport, and electronic properties upon the substrate-induced stress has been found. The structural properties indicate that a tensile stress exists in epitaxial ZnO:Ga films grown on sapphire, Si, and quartz, while a compressive stress appears in films grown on glass. The resistivity of the films decreased with increasing biaxial stress, which is inversely proportional to the product of the carrier concentration and Hall mobility. The refractive index n was found to decrease with increasing biaxial stress, while the optical band gap E0 increased with stress. These behaviors are attributed to lattice contraction and the increase in the carrier concentration that is induced by the stress. Our experimental data suggest that the mechanism of substrate-induced stress is important for understanding the properties of ZnO:Ga thin films and for the fabrication of devices which use these materials.

Photoluminescence spectra and biaxial stress effects of yellow 1S excitons in Cu2O thin films recrystallized epitaxially between paired MgO plates

We investigated biaxial stress effects on the yellow 1S ortho excitons in Cu2O thin films recrystallized between paired MgO plates by measuring photoluminescence spectra, X-ray diffraction and polarization microscope images. On the MgO (001) surface, we found two kinds of epitaxial growth modes of the Cu2O thin films. In such thin films, the yellow 1S ortho exciton states split into two or three levels depending on the respective epitaxial growth modes due to the different biaxial stresses owing to the lattice mismatches between Cu2O and MgO. By using effective Hamiltonians including such biaxial stress effects, we estimated the strengths of the biaxial stresses from the energy splittings of the 1S ortho excitons and confirmed the two kinds of epitaxial growth modes in our Cu2O thin films.

Band gap bowing parameter in pseudomorphic AlxGa1−xN/GaN high electron mobility transistor structures

A method for evaluation of aluminium composition in pseudomorphic AlxGa1−xN layer from the measured photoluminescence (PL) peak energy is presented here. The layers were grown by metalorganic chemical vapor deposition and characterized by high resolution X-ray diffraction (HRXRD), PL, cathodoluminescence, and atomic force microscopy. We estimated the value of biaxial stress in pseudomorphic AlxGa1−xN layers grown on sapphire and silicon carbide substrates using HRXRD scans. The effect of biaxial stress on the room temperature band edge luminescence in pseudomorphic AlxGa1−xN/GaN layers for various aluminium compositions in the range of 0.2 < x < 0.3 was determined. The value of pressure coefficient of band gap was also estimated. The stress corrected bowing parameter in AlxGa1−xN was determined as 0.50 ± 0.06 eV. Our values match well with the theoretically obtained value of bowing parameter from the density functional theory.

A High Power Stress-Gradient Resilient RF MEMS Capacitive Switch

A high power-handling radio frequency (RF) microelectromechanical systems capacitive switch with low sensitivity to both in-plane stress and stress gradients is presented. The novel switch consists of four cantilever beams, which are tied together using an optimized center joint to minimize the effects of biaxial stress and stress gradients. Dimples with a thickness of 0.3 μm are used to result in an air dielectric in the down-state position, which greatly improves the reliability, while still maintaining a measured capacitance ratio of 5. The switch is capable of handling an RF power >12 W under hot switching conditions, as well as having low sensitivity to temperature variations (~20 mV/°C for V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> ). Application areas are in high power reconfigurable filters, matching networks, and tunable antennas for modern communication systems.

The effects of thermally-induced biaxial stress on the structural, electrical, and optical properties of Cu2O thin films

The effects of biaxial stress in Cu2O thin films grown by rf magnetron sputtering at different growth temperatures were investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), electrical transport, and ellipsometric measurements. A predominant diffraction peak in the XRD patterns corresponds to the (111) plane direction of the Cu2O phase. Biaxial tensile stress was induced by thermal mismatch between the film and substrate and increased with increasing growth temperature. As the growth temperature and biaxial stress increased, the electrical resistivity decreased, while the carrier concentration and Hall mobility both increased. The ellipsometric data were fit using an optical dispersion model, and the decrease in refractive index was attributed to contraction of the lattice parameter with increasing biaxial stress. The optical absorption peaks shifted slightly toward higher energy with increasing stress. Our experimental data suggest that the mechanisms of stress are important for understanding the properties of Cu2O thin films and for the fabrication of devices using them.

Investigation of the response of an aluminium plate subjected to repeated low velocity impact using a continuum damage mechanics approach

AbstractExperimental investigation of repeated impacts on aluminium plates is performed using drop weights impacting from either constant or variable heights. In repeated impacts of constant and variable heights, the effect of plasticity is noticeable on the specimens in the very first impact. The effect of strain hardening is observed at higher impact numbers. Stiffness of plates is decreased by initiation and propagation of cracks in the specimens. Finally, perforation and penetration occur at the ultimate consecutive impacts. Numerical simulations of repeated impacts are also conducted using continuum damage mechanics by Abaqus software. Lemaitre's model is used as the damage model, and the code is written in Vumat subroutine. The effect of initial uniaxial and biaxial tensile stress on the plates is considered in repeated impacts, and it is concluded that plates with initial tensile uniaxial stress at transverse edges have maximum values of contact force and absorbed energy.

An analytical study on cracking directions and damage in thermal fatigue crazing subjected to variable amplitude loadings

In this paper, the effects of biaxial mean stress, mainly contributed by the weld residual stress, and thermal loading conditions on cracking directions and damage in high cycle thermal fatigue crazing subjected to variable amplitude loadings are investigated by a combined analytical and computational approach. The cracking directions are related to the orientation of the critical plane defined by the maximum damage. Analytical solutions of the critical plane orientation under constant amplitude biaxial tension/compression loadings are first derived and then employed to study the effects of biaxial mean stress on the critical plane orientation. The critical plane orientation appears to strongly depend on the dominant direction defined by the larger maximum stress. The developed analytical solution of the critical plane orientation and the analytical solution of the thermal stress from the literature are employed to study the effects of thermal loading conditions on the critical plane orientation. The critical plane orientation does not seem to significantly depend on the frequency, the amplitude and the mean value of the fluid temperature fluctuations, and the heat transfer film coefficient between the fluid and the pipe wall. The critical plane orientation under variable amplitude loadings is also studied, and an approximate solution is proposed for convenient engineering applications. The critical plane orientations are used to partially explain the observed cracking directions in the high cycle thermal fatigue crazing in the old residual heat removal system of a nuclear power plant. Finally, the effects of biaxial mean stress and thermal loading conditions on the fatigue crack initiation life are discussed.

Effects of biaxial mean stress on the critical plane orientation under biaxial tension/compression fatigue loading conditions

In this paper, the effects of biaxial mean stress on the orientation of the critical plane defined by maximum damage under biaxial tension/compression fatigue loading conditions are investigated by analytical and computational approaches. The analytical solutions of the critical plane orientation using the Matake’s and Fatemi–Socie’s criteria are first derived and validated by computational results. For the linear loading path of the applied biaxial stress in this study, the critical plane orientation strongly depends on the dominant direction defined by the larger maximum stress. The critical plane, or the crack initiation plane, is parallel to the less dominant direction. For the special case of equal biaxial stress, many possible critical planes or crack initiation planes exist. The critical plane orientations using the Matake’s and Fatemi–Socie’s criteria also depend on the ratio of the mean stress to the stress amplitude and the maximum stress in the dominant direction, respectively. The critical plane orientations are used to partially explain the observed cracking directions of the thermal fatigue crazing in the old residual heat removal system (RHRS) of the nuclear power plant. A Monte-Carlo study on the cracking directions of the thermal fatigue crazing is conducted in a plate which represents the inner surface of the pipe wall. Finally, the effects of material fatigue properties on the critical plane orientation are discussed.

짧은 보 압축 시험법을 이용한 암석의 모드 II 파괴 인성 측정

전단응력에 의한 전단강도 및 모드 II 파괴인성은 이산화탄소 지중저장에서의 덮개암 및 주입층의 안정성 평가에 활용되는 중요한 인자들이다. 본 연구에서는 짧은 보 압축시험을 이용하여 코코니노 사암의 전단강도 및 모드 II 파괴인성을 측정하였다. 측정된 평균 전단강도는 23.53 MPa이며, 모드 II 파괴인성은 1.58 MPa<TEX>${\surd}$</TEX>m이다. 응력확대계수(stress intensity factor)는 변위외삽법(displacement extrapolation method)을 이용한 유한요소법으로 결정하였다. 또한 이축응력(biaxial stress)과 수분포화(water saturation)가 모드 II 파괴인성에 미치는 영향을 분석하였다. 그 결과 이축응력이 증가할수록 파괴인성도 증가하였고, 완전포화된 시험편의 파괴인성은 건조상태의 파괴인성보다 대략 11.4% 감소하였다. The mode II fracture toughness and strength due to shear stress are important parameters in the stability of caprock and injection zone with application to geological sequestration of carbon dioxide. In this research, a short beam compression test has been used to determine the shear strength and the mode II fracture toughness for Coconino sandstone. The average value of the shear strength and mode II fracture toughness are estimated to be 23.53 MPa and 1.58 MPa<TEX>${\surd}$</TEX>m respectively. The stress intensity factor is suggested by finite element analysis using the displacement extrapolation method. The effect of biaxial stress and water saturation on the fracture toughness has also been investigated. The fracture toughness increases with confining stresses, but decreases by 11.4% in fully saturated condition.

Experimental Study on Bond Behavior of Deformed Bars Embedded in Concrete Subjected to Biaxial Lateral Tensile Compressive Stresses

AbstractThe bond behavior of deformed reinforcing bars, which is important to the assessment and design of reinforced concrete structures, is greatly influenced by the stress state in concrete. Because the effect of biaxial lateral tensile-compressive stresses on the bond behavior of deformed bars is seldom studied, an experimental investigation is presented in this paper. A total of 252 pull-out specimens with different strengths of concrete, bar diameters, and combinations of lateral tensile-compressive stresses were included in the test. The results show that the failure mode of specimens with deformed bars is influenced by the strength of concrete, ratio of the cover depth to bar diameter c/D, and the coupling effect of lateral stresses ζ(=pt/ft+pc/fcu). The bond strength and the slip at the peak bond stress decrease by increasing ζ, whereas the deteriorating ratio depends on the strength of concrete and c/D for specimens failed by pull-out and splitting, respectively. Regardless of ζ, the ratio of th...

Optical gain of germanium infrared lasers on different crystal orientations

We investigate the effects of biaxial tensile stress and n-type doping on the direct-transition optical gain in germanium infrared lasers, in which three differently oriented systems of (0 0 1), (1 1 0) and (1 1 1) Ge are analysed. We show our theoretical model for the strain tensor, strained electronic band structure, carrier occupation, optical gain and free-carrier absorption to evaluate the net optical gain under different strain and n-doping levels. Our analysis shows that for a large strain, (0 0 1) Ge can produce a larger optical gain than the others due to its clear direct-bandgap behaviour for mid-infrared lasers. For a moderate strain combined with the use of n-type doping, (1 1 1) Ge can generate a larger net optical gain than the others for near-infrared lasers. Our modelling results provide an insight into the improvement of optical emission in Ge for lasers.

Estimation of low cycle fatigue life of elbows considering bi-axial stress effect

Estimation of low cycle fatigue life of elbows considering bi-axial stress effect

Effects of biaxial oscillatory shear stress on endothelial cell proliferation and morphology

Wall shear stress (WSS) on anchored cells affects their responses, including cell proliferation and morphology. In this study, the effects of the directionality of pulsatile WSS on endothelial cell proliferation and morphology were investigated for cells grown in a Petri dish orbiting on a shaker platform. Time and location dependent WSS was determined by computational fluid dynamics (CFD). At low orbital speed (50 rpm), WSS was shown to be uniform (0-1 dyne/cm(2)) across the bottom of the dish, while at higher orbital speed (100 and 150 rpm), WSS remained fairly uniform near the center and fluctuated significantly (0-9 dyne/cm(2)) near the side walls of the dish. Since WSS on the bottom of the dish is two-dimensional, a new directional oscillatory shear index (DOSI) was developed to quantify the directionality of oscillating shear. DOSI approached zero for biaxial oscillatory shear of equal magnitudes near the center and approached one for uniaxial pulsatile shear near the wall, where large tangential WSS dominated a much smaller radial component. Near the center (low DOSI), more, smaller and less elongated cells grew, whereas larger cells with greater elongation were observed in the more uniaxial oscillatory shear (high DOSI) near the periphery of the dish. Further, cells aligned with the direction of the largest component of shear but were randomly oriented in low magnitude biaxial shear. Statistical analyses of the individual and interacting effects of multiple factors (DOSI, shear magnitudes and orbital speeds) showed that DOSI significantly affected all the responses, indicating that directionality is an important determinant of cellular responses.

Biaxial stress effects on estimating J under combined mechanical and thermal stresses

In this paper, the applicability to bi-axial stress states of a simple approximation proposed in our previous work for quantifying the elastic–plastic J under combined primary and secondary stresses is investigated.To produce the bi-axial stress states, circumferential cracked pipes under combined pressure, axial tension (or compression) and thermal stresses are considered. The results suggest that the proposed approximation can be applied to bi-axial stress states, and is slightly more conservative for bi-axial mechanical stresses than for uni-axial ones. The degree of conservatism decreases with increasing strain hardening exponent and with increasing relative magnitude of secondary stress.

OS0707 エルボ配管の低サイクル疲労に関する研究 : 二軸応力の影響(OS7-2 解析・評価・き裂I,OS-7 多軸応力下における疲労損傷および疲労き裂進展1)

OS0707 エルボ配管の低サイクル疲労に関する研究 : 二軸応力の影響(OS7-2 解析・評価・き裂I,OS-7 多軸応力下における疲労損傷および疲労き裂進展1)

Correlation between film thickness and zinc defect distribution along the growth direction in an isotopic multilayer ZnO thin film grown by pulsed laser deposition analyzed using the internal diffusion method

Zinc self-diffusion along the growth direction was analyzed for the isotopic multilayer ZnO thin film (( 64ZnO/ 68ZnO) 6 64ZnO) deposited by pulsed laser deposition. The isotopic distribution was measured using a secondary ion mass spectrometry. The amplitude of the 64Zn abundance in the depth profile was reduced by annealing at 993 K for several hours due to interdiffusion between the 64ZnO and 68ZnO layers. The diffusion profiles at the isotopic interfaces were analyzed using a periodic equation. The obtained zinc self-diffusion coefficients at several isotopic interfaces along the growth direction showed that the self-diffusion coefficients increased towards the film/substrate interface. A similar trend was also found in the lateral direction. The variation among the self-diffusion coefficients was related to the film thicknesses at the analysis positions. Since zinc self-diffusion is controlled by a vacancy-mediated mechanism, the variation in zinc diffusivity along the growth direction can be attributed to the effect of compressive biaxial stress. These findings are useful for producing high-quality ZnO devices.

Evaluation of Stress Effects on Electrical Characteristics of N-Type MOSFETs: Variations of DC Characteristics During the Resin-Molding Process

Stress-induced changes in the electrical characteristics of a semiconductor device become a major concern in the production of semiconductor packages because the electrical characteristics are adversely affected by packaging (residual) stresses. The objective of our project is to evaluate the effects of stress on semiconductor devices. In this study, the shift of the DC characteristics of nMOSFETs during the resin-molding process was investigated experimentally. After a silicon chip including the n-type metal oxide semiconductor field effect transistors (nMOSFETs) was encapsulated in a quad flat package, the drain current variations and the transconductance shifts were measured. The drain current decreased during the resin-molding process while no significant shift in threshold voltage was observed. The experimental results were estimated adequately from the residual stress predicted by numerical and experimental analyses and from the stress-sensitivity of the nMOSFETs measured by the four-point bending method. Also, we tested the validity of an electron-mobility model that included the effect of stress. The electron-mobility model takes into account the variation in the relative occupancy of the electrons in each conduction-band energy valley. It was found that the effect of biaxial stress on the variation in electron-mobility can be qualitatively evaluated by the electron-mobility model but are quantitatively different from the experimental results. Several needed improvements to the electron-mobility model are proposed in this article.

Torsional Behavior of Concrete-Filled Circular Steel Tube Columns

Concrete-filled tubes (CFTs) are columns commonly used in high-rise building construction due to their structural effectiveness. Past studies on CFT have focused primarily on uniaxial compression, bending, and eccentric compression and a few investigations have studied member behavior under combined compression and torsion. In this paper, the behavior of a circular CFT column under combined torsion and compression was theoretically investigated considering the confinement effect of the steel tube, softening of concrete, and spiral effects. Biaxial stress effects due to diagonal cracking were also considered. By incorporating these factors into the compatibility and equilibrium conditions, a basic equation to describe the torsional behavior of the entire loading history of CFT members was derived.

Assessment Procedure for Multiple Volumetric Flaws in p-M Diagram

Assessment of multiple volumetric flaws is one of the most common problems relating to pressure vessels and piping components. Under the current fitness for service rules, such as ASME, BS, and so on, multiple volumetric flaws are usually recharacterized as an enveloping volumetric flaw (defined as a single larger volumetric flaw) as well as multiple cracklike flaws, following their assessment rules. However, the rules proposed in their codes will not often agree and their justification is unknown. Furthermore, they can provide unrealistic assessment in some cases. In this paper, the interaction between two differently sized nonaligned volumetric flaws such as local thin areas is clarified by applying the body force method. Unlike multiple cracklike flaws, the effect of biaxial stresses on the interaction is evident. Based on the interaction that indicates the magnification and shielding effects and reference stress solutions, a new procedure for multiple volumetric flaws is proposed for assessing the flaws in the p-M (pressure-moment) diagram, which is a simple assessment procedure for vessels with volumetric flaws.

Biaxial Thermomechanical-Fatigue Life Property of a Directionally Solidified Ni-Base Superalloy

High-temperature components in thermal power plants are subjected to creep-fatigue loading where creep cavities initiate and grow on grain boundaries. Development of life assessment methods of high-temperature components in gas turbine for maintenance and operating cost reduction is strongly demanded by Japanese utilities. Especially, first row blades are subjected to complicated thermomechanical-fatigue (TMF) loading during start, steady state, stop cycles. Therefore it is important to clarify the TMF life property of blade materials to develop a life assessment procedure. In this study, tension-torsion biaxial TMF tests have been performed between 450°C and 870°C on a Ni-base directional solidified superalloy. Strain ratio ϕ was defined as shear strain range, Δγ, to normal strain range, Δε, and ϕ varied from 0 to infinity. The “Blade wave form,” which simulated temperature and strain condition of the blade surface, was employed. The biaxial TMF tests were also carried out on coated specimens with CoCrAlY. Fatigue life under the biaxial TMF loading showed strain ratio dependency giving shorter life with increasing ϕ. Considering biaxial stress effect on the failure life, an equivalent shear strain range was derived based on the Γ-plane theory, and the biaxial TMF life was well correlated with the equivalent shear strain range. The biaxial TMF life was reduced by introducing strain hold duration at the maximum temperature. The maximum stress increased by introducing the hold time due to increasing mean stress level in the Blade wave form. It was concluded that creep damage gradually accumulated during cycles resulting in reduction in the TMF life. The nonlinear creep-fatigue damage accumulation model was applied to predict failure life of the hold time tests. As a result, the failure lives were predicted within a factor of 1.5 on the observed life. It was found that the fatigue life of CoCrAlY coated material reduced 1∕2 to 1∕3 from that of the substrate. From observation of the longitudinal section of the coated specimens, many cracks started from the coating surface and penetrated into the substrate. It was concluded that the CoCrAlY coating reduced the biaxial TMF life due to acceleration of crack initiation period in the substrate.