Fracture analysis for 3-dimensional bodies with a surface crack

This paper deals with fracture analyses in 3-dimensional bodies containing a surface crack. A general solution of stress-strain fields at crack tip is proposed. Based on the stress-strain fields obtained, a high-order 3-dimensional special element is established to calculate the stress intensity factors in a plate with a surface crack. The variation of stress intensity factors with geometric parameters is investigated.

Numerical Simulation of Pulsed Laser Transformation Hardening

A novel pulsed laser surface processing technology is introduced, which can make use of the spatial and temporal profile of laser pulse to obtain ideal hardening parameters. The intensity distribution of laser pulse is spatially and temporally controlled by using laser shape transformation technology. A 3D numerical model including multi-phase transformations is established to explore material microstructure evolution induced by temperature field evolution. The influences of laser spatial-temporal profiles on hardening parameters are investigated. Different from the continuous laser processing technology, results indicate that spatial and temporal profiles are important factors in determining processing quality during pulsed laser processing method.

Depth dependence of structural quality in InN grown by metalorganic chemical vapor deposition

Rutherford backscattering and channeling is combined with X-ray diffraction to study the depth dependence of crystalline quality in InN layers grown by metalorganic chemical vapor deposition on sapphire substrate. The poorest crystalline quality in InN layer is produced at the intermediate region over 100 nm away from the InN/sapphire interface. With increasing layer thickness the crystalline quality improves to a certain degree dependent on the growth temperature. The InN sample grown at 450 degrees C is found to be more homogeneous than the sample grown at 550 degrees C. The difference in the defect profile is explained by the temperature-dependent growth modes. The inhomogeneity of structural quality and related properties such as carrier concentration and strain field is possibly the reason to observe a high energy wing in PL spectrum of the InN sample grown at 550 degrees C. (c) 2006 Elsevier B.V All rights reserved.

Spatial distribution of deep level defects in crack-free AlGaN grown on GaN with a high-temperature AlN interlayer

The deep level luminescence of crack-free Al0.25Ga0.75N layers grown on a GaN template with a high-temperature grown AlN interlayer has been studied using spatially resolved cathodoluminescence (CL) spectroscopy. The CL spectra of Al0.25Ga0.75N grown on a thin AlN interlayer present a deep level aquamarine luminescence (DLAL) band at about 2.6 eV and a deep level violet luminescence (DLVL) band at about 3.17 eV. Cross-section line scan CL measurements on a cleaved sample edge clearly reveal different distributions of DLAL-related and DLVL-related defects in AlGaN along the growth direction. The DLAL band of AlGaN is attributed to evolve from the yellow luminescence band of GaN, and therefore has an analogous origin of a radiative transition between a shallow donor and a deep acceptor. The DLVL band is correlated with defects distributed near the GaN/AlN/AlGaN interfaces. Additionally, the lateral distribution of the intensity of the DLAL band shows a domainlike feature which is accompanied by a lateral phase separation of Al composition. Such a distribution of deep level defects is probably caused by the strain field within the domains. (c) 2006 American Institute of Physics.

Structural anisotropy and optical properties of InxGa1-xAs quantum dots on GaAs(001)

InAs and InxGa1-xAs (x = 0.2 and 0.5) self-organized quantum dots (QDs) were fabricated on GaAs(0 0 1) by molecular beam epitaxy (MBE) and characterized by atomic force microscopy (AFM), transmission electron microscopy (TEM), acid photoluminescence polarization spectrum (PLP). Both structural and optical properties of InxGa1-xAs QD layer are apparently different from those of InAs QD layer. AFM shows that InxGa1-xAs QDs tend to be aligned along the [1 (1) over bar 0] direction, while InAs QDs are distributed randomly. TEM demonstrates that there is strain modulation along [1 1 0] in the InxGa1-xAs QD layers. PLP shows that In0.5Ga0.5As islands present optical anisotropy along [1 1 0] and [1 (1) over bar 0] due to structural and strain field anisotropy for the islands. (C) 2001 Elsevier Science B.V. All rights reserved.

Elastic deformation of wafer surfaces in bonding

A model has been proposed for describing elastic deformation of wafer surfaces in bonding. The change of the surface shape is studied on the basis of the distribution of the periodic strain field. With the condition of diminishing periodic strain away from the interface, Airy stress function has been found that satisfies the elastic mechanical equilibrium. The result reveals that the wavy interface elastically deforms a spatial wavelength from the interface. (C) 2000 American Institute of Physics. [S0021-8979(00)04219-5].

Study of self-assembled InAs quantum dots grown on low temperature GaAs epi-layer

InAs self-organized quantum dots (QDs) grown on annealed low temperature GaAs (LT-GaAs) epi-layer were investigated by transmission electron microscopy (TEM) and photoluminescence (PL) measurement. TEM showed that QDs formed on annealed LT-GaAs epi-layer have a smaller size and a higher density than QDs formed on normal GaAs buffer layer. In addition, the PL spectra analysis showed that the LT-GaAs epi-layer resulted in a blue shift in peak energy, and a narrower linewidth in the PL peak. The differences were attributed to the point defects and As precipitates in annealed LT-GaAs epi-layer for the point defects and As precipitates change the strain field of the surface. The results provide a method to improve the uniformity and change the energy band structure of the QDs by controlling the defects in the LT-GaAs epi-layer.

Quasi-3D Cytoskeletal Dynamics of Osteocytes under Fluid Flow

Osteocytes respond to dynamic fluid shear loading by activating various biochemical pathways, mediating a dynamic process of bone formation and resorption. Whole-cell deformation and regional deformation of the cytoskeleton may be able to directly regulate this process. Attempts to image cellular deformation by conventional microscopy techniques have been hindered by low temporal or spatial resolution. In this study, we developed a quasi-three-dimensional microscopy technique that enabled us to simultaneously visualize an osteocyte's traditional bottom-view profile and a side-view profile at high temporal resolution. Quantitative analysis of the plasma membrane and either the intracellular actin or microtubule (MT) cytoskeletal networks provided characterization of their deformations over time. Although no volumetric dilatation of the whole cell was observed under flow, both the actin and MT networks experienced primarily tensile strains in all measured strain components. Regional heterogeneity in the strain field of normal strains was observed in the actin networks, especially in the leading edge to flow, but not in the MT networks. In contrast, side-view shear strains exhibited similar subcellular distribution patterns in both networks. Disruption of MT networks caused actin normal strains to decrease, whereas actin disruption had little effect on the MT network strains, highlighting the networks' mechanical interactions in osteocytes.

Effective elastic properties of piezoelectric composites with radially polarized cylinders

Effective elastic properties of piezoelectric composites containing an infinitely long, radially polarized cylinder embedded in an isotropic non-piezoelectric matrix are theoretically investigated under an external strain field. Analytical solutions of elastic displacement and electric potentials are exactly derived, and the effective elastic responses are formulated in the dilute limit. Meanwhile, a vanishing piezoelectric response mechanism is revealed in the piezoelectric composite containing radially polarized cylinders. Furthermore, it is shown that the effective elastic properties can be enhanced (or reduced) due to the increase of the piezoelectric (or dielectric) constants of the cylinders. (C) 2009 Elsevier B.V. All rights reserved.

辽河盆地东部凹陷热历史及其与油气关系

This dissertation focuses on the basin geothermal history, tectonothermal evolution and the relationship between geothermal field evolution and hydrocarbon generation. Based on the research of present-day geothermal field, geothermal history of Eastern Subdepression of Liaohe Basin was reconstructed with available data from drillings, loggings, seismic cross-sections, BHTs and thermal indicators. 12 heat flow density values were calculated. Ranging from 45.7 mW/m~2 to 70.0 mW/m~2, the mean value of these determinations exhibits 58.0(±5.83mW/m~22). The heat flow density in the uplift and ramp is greater than that in the sag. The main factors affecting the heat flow density are the morphostructure of basement and thickness of sedimentary cover. The Subdepression experienced a much higher heat flow period from 43 Ma to about 25 Ma. The heat flow increased gradually from Sha3 stage to Dongying stage, and reached the peak at the late of Dongying stage, then cooled down. Structural subsidence analysis shows that the subsidence of Eastern Subdepression can be divided into two phases: earlier (25-43Ma) initial (rift) and late (since 25Ma) thermal subsidence. The lower present-day heat flow and the higher palaeo-heat flow corresponding to structural subsidence stage as well as the typical rift subsidence style in Eastern Subdepression provide with some insights to the tectonic-thermal evolution of the basin. The source rocks of Sha3 member began to generate oil in the Shal stage, and entered oil-window at the late of Dongying stage. The source rocks of Shal began to generate oil at the late of Dongying stage, and being at the stage of lower maturation-maturation now. Most of Dongying source rocks are not mature now. The late of Dongying stage is the critical time for the oil system.

Towards An Acoustic Model-Based Poroelastic Imaging Method: I. Theoretical Foundation

The ultrasonic measurement and imaging of tissue elasticity is currently under wide investigation and development as a clinical tool for the assessment of a broad range of diseases, but little account in this field has yet been taken of the fact that soft tissue is porous and contains mobile fluid. The ability to squeeze fluid out of tissue may have implications for conventional elasticity imaging, and may present opportunities for new investigative tools. When a homogeneous, isotropic, fluid-saturated poroelastic material with a linearly elastic solid phase and incompressible solid and fluid constituents is subjected to stress, the behaviour of the induced internal strain field is influenced by three material constants: the Young's modulus (E(s)) and Poisson's ratio (nu(s)) of the solid matrix and the permeability (k) of the solid matrix to the pore fluid. New analytical expressions were derived and used to model the time-dependent behaviour of the strain field inside simulated homogeneous cylindrical samples of such a poroelastic material undergoing sustained unconfined compression. A model-based reconstruction technique was developed to produce images of parameters related to the poroelastic material constants (E(s), nu(s), k) from a comparison of the measured and predicted time-dependent spatially varying radial strain. Tests of the method using simulated noisy strain data showed that it is capable of producing three unique parametric images: an image of the Poisson's ratio of the solid matrix, an image of the axial strain (which was not time-dependent subsequent to the application of the compression) and an image representing the product of the aggregate modulus E(s)(1-nu(s))/(1+nu(s))(1-2nu(s)) of the solid matrix and the permeability of the solid matrix to the pore fluid. The analytical expressions were further used to numerically validate a finite element model and to clarify previous work on poroelastography.

Dynamics of charge-displacement channeling in intense laser-plasma interactions

The dynamics of transient electric fields generated by the interaction of high intensity laser pulses with underdense plasmas has been studied experimentally with the proton projection imaging technique. The formation of a charged channel, the propagation of its front edge and the late electric field evolution have been characterized with high temporal and spatial resolution. Particle-in-cell simulations and an electrostatic, ponderomotive model reproduce the experimental features and trace them back to the ponderomotive expulsion of electrons and the subsequent ion acceleration.

Intralaminar toughness characterisation of unbalanced hybrid plain weave laminates

A numerical and experimental investigation on the mode-I intralaminar toughness of a hybrid plain weave composite laminate manufactured using resin infusion under flexible tooling (RIFT) process is presented in this paper. The pre-cracked geometries consisted of overheight compact tension (OCT), double edge notch (DEN) and centrally cracked four-point-bending (4PBT) test specimens. The position as well as the strain field ahead of the crack tip during the loading stage was determined using a digital speckle photogrammetry system. The limitation on the applicability of the standard data reduction schemes for the determination of intralaminar toughness of composite materials is presented and discussed. A methodology based on the numerical evaluation of the strain energy release rate using the J-integral method is proposed to derive new geometric correction functions for the determination of the stress intensity factor for composites. The method accounts for material anisotropy and finite specimen dimension effects regardless of the geometry. The approach has been validated for alternative non-standard specimen geometries. A comparison between different methods currently available for computing the intralaminar fracture toughness in composite laminates is presented and a good agreement between numerical and experimental results using the proposed methodology was obtained. 

Influence of a Single Grain Boundary on Domain Wall Motion in Ferroelectrics

Epitaxial tetragonal 425 and 611 nm thick Pb(ZrTi)O (PZT) films are deposited by pulsed laser deposition on SrRuO-coated (100) SrTiO 24° tilt angle bicrystal substrates to create a single PZT grain boundary with a well-defined orientation. On either side of the bicrystal boundary, the films show square hysteresis loops and have dielectric permittivities of 456 and 576, with loss tangents of 0.010 and 0.015, respectively. Using piezoresponse force microscopy (PFM), a decrease in the nonlinear piezoelectric response is observed in the vicinity (720-820 nm) of the grain boundary. This region represents the width over which the extrinsic contributions to the piezoelectric response (e.g., those associated with the domain density/configuration and/or the domain wall mobility) are influenced by the presence of the grain boundary. Transmission electron microscope (TEM) images collected near and far from the grain boundary indicate a strong preference for (101)/(1-01) type domain walls at the grain boundary, whereas (011)/(01-1) and (101)/(1-01) are observed away from this region. It is proposed that the elastic strain field at the grain boundary interacts with the ferro-electric/elastic domain structure, stabilizing (101)/(1-01) rather than (011)/(01-1) type domain walls, which inhibits domain wall motion under applied field and decreases non-linearity. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Measurement of fibre fracture toughness using an alternative specimen geometry

This paper presents an experimental and numerical study focused on the tensile fibre fracture toughness characterisation of hybrid plain weave composite laminates using non-standardized Overheight Compact Tension (OCT) specimens. The position as well as the strain field ahead of the crack tip in the specimens was determined using a digital speckle photogrammetry system. The limitation on the applicability of standard data reduction schemes for the determination of the intralaminar fibre fracture toughness of composites is presented and discussed. A methodology based on the numerical evaluation of the strain energy release rate using the J-integral method is proposed to derive new geometric correction functions for the determination of stress intensity factor for alternative composite specimen geometries. A comparison between different methods currently available to compute the intralaminar fracture toughness in composites is also presented and discussed. Good agreement between numerical and experimental results using the proposed methodology was obtained.