不同加载条件下含预制单裂隙岩石强度和变形特性研究

为揭示不同加载条件下含预制单裂隙岩石强度和变形特性,配制相似材料,分别预制裂隙倾角α为0°、15°、30°、45°、60°、75°、90°,设置侧压为0,5,10 MPa,在常规压缩、循环加卸载条件下开展试验。试验结果表明:循环加卸载对岩样有弱化作用,其峰值强度小于同条件下常规加载的岩样。试验中一共观察到9种贯通模式。常规加载时,当α≥45°时,贯通模式以张性贯通为主;当α<15°时,贯通模式以剪性贯通为主;当α为15°、30°时,贯通模式以张剪性贯通为主。循环加卸载时,更容易发生剪性贯通。岩样变形过程中,由PIV粒子成像测速系统导出的流场可知,产生裂纹的区域位移方向线都发生显著变化,但并非所有位移发生变化的区域都会形成裂纹,只有当位移矢量差达到一定值时裂纹才会产生。     

Real-time detection of hyperosmotic stress response in optically trapped single yeast cells using Raman microspectroscopy

Living cells survive environmentally stressful conditions by initiating a stress response. We monitored changes in the Raman spectra of optically trapped Saccharomyces cerevisiae yeast cell under normal, heat-treated, and hyperosmotic stress conditions. It is shown that when glucose was used to exert hyperosmotic stress, two chemical substances-glycerol and ethanol-can be monitored in real time in a single cell.     

Empirical correlation for viscoelastic and viscoplastic deformation of structural planes under different normal stress conditions

Mechanics of Time-Dependent Materials - The creep behavior of rock mass, including structural plane creep and rock creep, is different from that of intact rock. It is generally recognized that the...     

Effect of annealing temperature on void coalescence in 5086 aluminium alloy formed under different stress conditions

In this paper, the influence of annealing temperature on formability, fracture behavior, void nucleation, its growth, and coalescence are studied. The voids and fracture behavior are studied as a function of various void parameters, namely δd-factor (ligament thickness between consecutive voids), d factor (ratio of δd and radius of the void), void area fraction (V_a) and L/W ratio (ratio of length to width of the void). The L/W ratio of the oblate or prolate voids at fracture is correlated with the mechanical properties, microstructure, minor strain at fracture (ε₂), Mohr’s circle shear strains, stress, and strain triaxiality factors. The Lode factor (θ) is determined and correlated with the Stress triaxiality factor (T), which is the ratio of mean stress (σ_m) to effective stress (σ_e). In addition, the Void area fraction (V_a), which is the ratio of void area to the representative sample area, is determined correlated with the Strain triaxiality factor (T_o). It is found that the sheets annealed at 300°C, possesses better formability due to lower d-factor, higher and -values, greater void area fraction and lower L/W ratio of void accommodating more plastic deformation.     

High resolution imaging of actin filaments in living cells under physilogically relevant conditions using apertureless near-field microscopy

Living cells were used to demonstrate the potential biological applications of the apertureless SNOM when operating under fluid. An oral epithelial squamous cell carcinoma cell line (H357) was imaged under physiological-like conditions using apertureless SNOM following staining with FITC-Phalloidin which preferentially stains intracellular actin filaments of the cytoskeleton. Compared with simultaneously obtained AFM topographic image, the apertureless SNOM data provides greater detail on these cellular structures and the spatial resolution of the apertureless SNOM fluorescence image appears to be about 100 nm.     

Mathematical model and boundary conditions in stress analysis relating to steam turbine rotors,under transient operating conditions

An appropriate mathematical model for calculation of thermoelastic stress in steam turbine rotors, under transient operating conditions, is developed in the framework of so called uncoupled quasi-static theory. The numerical analysis has been carried out by means of the finite element code ANGUS, the accuracy of which has been evaluated by comparing it with an analytical solution given by one of the authors in Reference 2. It has been shown that, with an appropriate choice of thermal and elastic boundary conditions, it is possible to carry out stress transient analysis considering only a segment of the hottest zone of high or intermediate pressure body of rotors. The paper includes a comparison study of the influence of two types of thermal boundary conditions in the labyrinth glands.     

Analysis of fracture limit curves and void coalescence in high strength interstitial free steel sheets formed under different stress conditions

Void formation, which is a statistical event, depends on inhomogeneities present in the microstructure. The analysis on void nucleation, their growth and coalescence during the fracture of high strength interstitial free steel sheets of different thicknesses is presented in this article. The analysis shows that the criterion of void coalescence depends on the d-factor, which is the ratio of relative spacing of the ligaments (δd) present between the two consecutive voids to the radius of the voids. The computation of hydrostatic stress (σ_m), the dominant factor in depicting the evolution of void nucleation, growth and coalescence and the dimensional analysis of three different types of voids namely oblate, prolate and spherical type, have been carried out. The ratio of the length to the width (L/W) of the oblate or prolate voids at fracture is correlated with the mechanical properties, microstructure, strains at fracture, Mohr’s circle shear strains and Triaxiality factors. The Lode angle (θ) is determined and correlated with the stress triaxiality factor (T), ratio of mean stress (σ_m) to effective stress (σ_e). In addition, the Void area fraction (V _a), which is the ratio of void area to the representative area, is determined and correlated with the strain triaxiality factor (T_o).     

Remote Raman spectroscopic detection of minerals and organics under illuminated conditions from a distance of 10 m using a single 532 nm laser pulse

Raman spectra of several minerals and organics were obtained from a small portable instrument at a distance of 10 m in a well-illuminated laboratory with a single 532 nm laser pulse with energy of 35 mJ/pulse. Remote Raman spectra of common minerals (dolomite, calcite, marble, barite, gypsum, quartz, anatase, fluorapatite, etc.) obtained in a short period of time (1.1 mus) clearly show Raman features that can be used as fingerprints for mineral identification. Raman features of organics (benzene, cyclohexane, 2-propanol, naphthalene, etc.) and other chemicals such as oxides, silicates, sulfates, nitrates, phosphates, and carbonates were also easily detected. The ability to identify minerals from their Raman spectra obtained from a single laser pulse has promise for future space missions where power consumption is critical. Such a system could be reduced in size by minimizing the cooling requirements for the laser unit. The remote Raman system is also capable of performing time-resolved measurements. Data indicate that further improvement in the performance of the system is possible by reducing the gate width of the detector (ICCD) from 1.1 mus to approximately 20 ns, which would significantly reduce the background signal from daylight or a well-illuminated laboratory. The 1.1 mus signal gating was effective in removing nearly all background fluorescence with 532 nm excitation, indicating that the fluorescence in most minerals is probably from long-lifetime inorganic phosphorescence.     

Laser-induced breakdown spectroscopy for determination of the organic oxygen content in anthracite coal under atmospheric conditions

Laser-induced breakdown spectroscopy has been used to measure the organic oxygen content in pulverized anthracite coal under atmospheric conditions. Special spectral processing including the optimal O(I) emission-line selection by comparing the spectral correlation coefficients with the N(I) line, internal normalization with the N(I) line, and temperature correction are proposed and employed to satisfy the multi-line analysis method and yield the most accurate quantitative results. The calibration method for determining the organic oxygen content of coal is presented, with an accuracy of 1.15-1.37% and an average relative error of 19.39% being evaluated through an experiment performed on six anthracite coal samples. The relative measurement error distribution has also been studied.     

Calibration of the thermoelastic stress analysis technique under sinusoidal and random loading conditions

For the past five years the National Engineering Laboratory (NEL) has been engaged in a research programme investigating the applications of thermoelastic stress analysis to engineering structures. This paper discusses the use of a uniformly stressed component for the calibration of SPATE (Stress Pattern Analysis by Thermal Emission). Experimental results for sinusoidal loading on a carbon steel are compared with a theoretical prediction based upon material properties and instrument characteristics. A calibration technique which is suitable for the measurement of quantitative stresses under random loading, including modal behaviour, is also described.     

Intracellular uptake, trafficking and subcellular distribution of folate conjugated single walled carbon nanotubes within living cells

Herein we studied the uptake, trafficking and distribution of folate conjugated single walled carbon nanotubes (SWNTs) within living cells. SWNTs were noncovalently functionalized with chitosan and then linked with folate acid and fluorescence dye Alexa Fluor 488 (denoted FA-SWNTs). Hep G2 cells were cultured in vitro and incubated with FA-SWNTs at different levels. The FA-SWNTs exhibited a concentration-dependent uptake within Hep G2 cells, and Hep G2 cells were able to internalize FA-SWNTs via a folate receptor-mediated pathway. The distribution of nanotubes inside cells demonstrated that the FA-SWNTs only locate in the cytoplasm and not in nuclei, indicating the failure of transporting through the nuclear envelope. Transmission electron microscope (TEM) results showed the presence of FA-SWNTs in lysosomes and the discharge to extracellular space after incubation with nanotubes for 5?h. No obvious cellular death rate was observed when the concentration of nanotubes was below 50?μg?ml(-1). However, cells with FA-SWNT uptake showed a concentration-dependent apoptosis. These discoveries might be helpful for understanding the interaction of SWNTs and living cells.     

The influence of inter-particle friction and the intermediate stress ratio on soil response under generalised stress conditions

Previous research studies have used either physical experiments or discrete element method (DEM) simulations to explore, independently, the influence of the coefficient of inter-particle friction (μ) and the intermediate stress ratio (b) on the behaviour of granular materials. DEM simulations and experiments using photoelasticity have shown that when an anisotropic stress condition is applied to a granular material, strong force chains or columns of contacting particles transmitting relatively large forces, form parallel to the major principal stress orientation. The combined effects of friction and the intermediate stress ratio upon the resistance of these strong force chains to collapse (buckling failure) are considered here using data from an extensive set of DEM simulations including triaxial and true triaxial compression tests. For all tests both?μ and b affected the macro- and micro-scale response, however the mechanisms whereby the force chain stability was improved differ. While friction clearly enhances the inherent stability of the strong force chains, the intermediate stress ratio affects the contact density and distribution of orthogonal contacts that provide lateral support to the force chains.     

Service life and fracture of solid bodies under the conditions of cyclic contact interaction

A numerical-analytic model is formulated for the investigation of fracture processes and evaluation of the residual service life of solid bodies under the conditions of cyclic contact interaction. The model is based on the criteria of fracture of materials in the process of growth of fatigue cracks and the algorithms of step-by-step construction of the paths crack propagation developed by the method of singular integral equations for two-dimensional contact problems of the theory of elasticity for bodies with curvilinear cracks. The model is realized for contact interactions of rolling and fretting fatigue. The causes and specific features of the formation of typical defects in rolling bodies of revolution, such as pitting, spalling, squat defects, and cracking are analyzed depending on the operating parameters of a rolling couple. It is shown that, both in the case of rolling and under the conditions of fretting fatigue, the character of fracture of the contact surface and the sizes of debris particles are strongly affected by the value of the friction coefficient, the distribution of tangential forces between contacting bodies, the characteristics of cyclic crack-growth resistance of the material, and the service or random products in the contact zone (water, lubricants, powder fretting products, etc.). We present examples of evaluation of the residual service life of rail (RSB12) and roller (9KhF and GH) steels. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 6, pp. 5–25, November–December, 2005.     

Microscopic studies on the mechanisms of wear of NR,SBR and HNBR vulcanizates under different conditions

Microscopic investigations, undertaken to understand the mechanism of wear of natural rubber (NR), styrene-butadiene rubber (SBR) and hydrogenated nitrile rubber (HNBR) vulcanizates abraded against hard rock, a knurled aluminium disc and a silicone carbide abrader under different conditions, are reported. The wear of NR and SBR vulcanizates against hard rock at low normal load (6 kPa) takes place by a fatigue wear mechanism and it switches over to frictional wear at high normal load (above 18 kPa). In HNBR vulcanizates the wear takes place by an abrasive wear mechanism. Ridges are observed on worn surface of swollen N R and SBR vulcanizates at low normal load, but at higher normal load the wear takes place by catastrophic fracture and extensive plough marks along the direction of abrasion are observed. The wear of NR and SBR vulcanizates proceeds by frictional wear, even at elevated temperatures. In HNBR vulcanizates, the mechanism changes from abrasive wear at 25C to frictional wear above 50C. Above 50C, ridges are observed and the spacing between adjacent ridges increases with rise of temperature.     

Estimation of the cyclic life of 15KhMl and 20KhMl steels under nonisothermal conditions

The effect of nonisothermal loading on the deformation and fracture of structural steels was studied. The fracture mode of the material was shown to be determined by the peak and mean cycle stresses under isothermal conditions and by the cycle asymmetry under nonisothermal conditions. Institute for Problems of Strength, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 3, pp. 22–27, May–June, 1998.