3-dimensional transient wave response in a cracked elastic solid

The three-dimensional transient wave response problem is presented for an infinite elastic medium weakened by a plane crack of infinite length and finite width. Tractions are applied suddenly to the crack, which simulates the case of impact loading. The integral transforms are utilized to reduce the problem to a standard Fredholm integral equation in the Laplace transform variable and sequentially invert the Laplace transforms of the stress components by numerical inversion method. The dynamic mode I stress intensity factors at the crack tip are obtained and some numerical results are presented in graphical form.

Crack growth by grain boundary cavitation in the transient and extensive creep regimes

Crack growth due to cavity growth and coalescence along grain boundaries is analyzed under transient and extensive creep conditions in a compact tension specimen. Account is taken of the finite geometry changes accompanying crack tip blunting. The material is characterized as an elastic-power law creeping solid with an additional contribution to the creep rate arising from a given density of cavitating grain boundary facets. All voids are assumed present from the outset and distributed on a given density of cavitating grain boundary facets. The evolution of the stress fields with crack growth under three load histories is described in some detail for a relatively ductile material. The full-field plane strain finite element calculations show the competing effects of stress relaxation due to constrained creep, diffusion and crack tip blunting. and of stress increase due to the instantaneous elastic response to crack growth. At very high crack growth rates the Hui-Riedel fields dominate the crack tip region. However. the high growth rates are not sustained for any length of time in the compact tension geometry analyzed. The region of dominance of the Hui-Riedel field shrinks rapidly so that the near-tip fields are controlled by the HRR-type field shortly after the onset of crack growth. Crack growth rates under various conditions of loading and spanning the range of times from small scale creep to extensive creep are obtained. We show that there is a strong similarity between crack growth history and the behaviour of the C(t) and C(t) parameters. so that crack growth rates correlate rather well with C(t) and C(t). A relatively brittle material is also considered that has a very different near-tip stress field and crack growth history.

The piston model for coronal transient with forerunner

The observational data show that large scale loop or bubble-like coronal transients frequently associate with forerunners. The forerunner should be related to the rapid motion of the transient behind it, and they are controlled by the same dynamic process. In the present paper, the gasdynamic model with a spherical piston moving at certain speed in the solar gravitational field is devoted to studying the coronal transient with a forerunner. In comparison with observations, the theoretical results show that the piston model may, reasonably explain the configuration, kinetic and dynamic features in the regions of both forerunner and high-speed transient behind it.

The dynamical process of a coronal transient associated with an eruptive prominence .1. Basic mechanism

The statistical correlation between an eruptive prominence and the coronal transient associated with this prominence implies that there should be a relationship between these two kinds of dynamical processes. This paper analyzes the dynamical effect of a plasma

The dynamical process of a coronal transient associated with an eruptive prominence .2. Analytical solutions in finite regions

piston

Numerical Simulation of Heat Transfer and Kinetics in the Bulk Growth of Silicon Carbide

The growth process of 2-inch silicon carbide (SiC) single crystals by the physical vapor transport method (or modified Lely method) has been modeled and simulated. The comprehensive process model incorporates the calculations of radio frequency (RF) induction heating, heat and mass transfer and growth kinetics. The transport equations for electromagnetic field, heat transfer, and species transport are solved using a finite volume-based numerical scheme called MASTRAPP (Multizone Adaptive Scheme for Transport and Phase Change Process). Temperature distribution for a 2-inch growth system is calculated, and the effects of induction heating frequency and current on the temperature distribution and growth rate are investigated. The predicted results have been compared with the experimental data.

Transient Flows in Low Permeability Porous Media with Composite Start-Up Pressure Gradient

A new mathematical model for the transient flow in the composite low permeability is established. It is solved by FEM with different boundary conditions such as infinite, circular closed and constant pressure boundary conditions. The typical curves for transient wellbore pressure have been presented. It is shown that the pressure and pressure derivative curves with composite start-up pressure gradients have different slopes which are depended on the start-up pressure gradients and the mobility radios in different regions. The boundary effects are the same as the normal reservoirs without start-up pressure gradients. The study provides a new tool to analyze the transient pressure test data in the low permeability reservoir.

Transient Temperature Distribution in a Sheet Metal by Low-Energy Laser Scanning

Low-energy laser-heating techniques are widely used in engineering applications such as, thinfilm deposition, surface treatment, metal forming and micro-structural pattern formation. In this paper,under the conditions of ignoring the thermo-mechanical coupling, a numerical simulation on the spatialand temporal temperature distribution in a sheet metal produced by the laser beam scanning in virtue of thefinite element method is presented. Both the three-dimensional transient temperature field and thetemperature evolution as a function of heat penetrating depth in the metal sheet are calculated. Thetemperature dependence of material properties was taken into account. It was shown that, after taking thetemperature dependence of the material absorbance effect into consideration, the temperature change ratealong the scanning direction and the temperature maximum were both increased.

Numeric Calculation for Transient Thermal Stress Field in Wall-Shape Metal Part During Laser Direct Forming

In order to investigate the transient thermal stress field in wall-shape metal part during laser direct forming, a FEM model basing on ANSYS is established, and its algorithm is also dealt with. Calculation results show that while the wall-shape metal part is being deposited, in X direction, the thermal stress in the top layer of the wall-shape metal part is tensile stress and in the inner of the wall-shape metal part is compressive stress. The reason causing above-mentioned thermal stress status in the wall-shape metal part is illustrated, and the influence of the time and the processing parameters on the thermal stress field in wall-shape metal part is also studied. The calculation results are consistent with experimental results in tendency.

Numerical Solution for Polymer Transient Flows in a Circle Bounded Composite Formation

A new numerical model for transient flows of polymer solution in a circular bounded composite formation is presented in this paper. Typical curves of the wellbore transient pressure are yielded by FEM. The effects of non-Newtonian power-law index, mobility and boundary distance have been considered. It is found that for the mobility ratio larger than 1, which is favorable for the polymer flooding, the pressure derivative curve in log-log form rises up without any hollow. On the other hand, if the pressure derivative curve has a hollow and then is raised up, we say that the polymer flooding fails. Finally, the new model has been extended to more complicated boundary case.

2D Kinetics and Forced Dissociation of Selectin-ligand Bindings

Cell adhesion is crucial to many pathophysiological processes, such as inflammatory reaction and tumor metastasis. It is mediated by specific interactions between receptors and ligands, and provides the physical linkages among cells. For example, interactions between selectins and glycoconjugate ligands mediate leukocyte initially tethering to and subsequently rolling on vascular surfaces in sites of inflammation or injury, which is determined by their fast kinetic rates. To mediate cell adhesion, the interacting receptors and ligands must anchor to apposing surfaces of two cells or a cell and the substratum, i.e. , the so-called two-dimensional (2D) binding, which differs from interactions in the fluid phase, i.e. , the three-dimensional (3D) binding. How structural variations and surface environments of interacting molecules affect their 2D kinetics, and how external forces manipulate their dissociation has little been known quantitatively, and nowadays attracts more and more attentions.