Search

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Aimed at the calculation of elements' weight coefficients in the checkerboard pattern filtering technique, a previous checkerboard pattern suppression method was improved, and a more generalized weight coefficient formula with more specific physical meanings was proposed. The topological optimization model, in which the material elasto-plastic deformation was considered, was established under stress constraint conditions, and the improved checkerboard pattern suppression method was employed in the structural topological optimization process with the ESO method. Two numerical examples were implemented. The results show that the improved checkerboard pattern suppression method has better suppression effects than the previous one, and is applicable to the topological optimization of not only linear-material structures, but also nonlinear-material structures. [ABSTRACT FROM AUTHOR]

Based on the high-order deformation theory, the in-plane stiffness and bending stiffness of both surface layer and core layer of the sandwich plate were considered to derive the transverse shearing stiffnesses of all the layers. The transverse stress function was given according to the transverse strain distribution, and the differential equations for the sandwich plate were deduced with the generalized principle of virtual displacement. The bending deformation of simply supported rectangular sandwich plates with different core-to-surface thickness ratios were detailedly studied under transverse loading, and the calculation results were compared with those from the 1st-order deformation theory to give a bigger relative deformation difference at a smaller thickness ratio. The distribution of transverse strain along the thickness direction makes a half sine curve, and the center-plane normal line distortion culminates at the surface height. [ABSTRACT FROM AUTHOR]

By using finite element software ANSYS, the stress of the annular sector semicircular cross section vessel, which is made up of an annular sector plate, two semicircular plates and a semi-cylindrical with the thicknesses of 20 mm, is analyzed. The analysis results show that the maximum equivalent stress of the annular sector plate appears in the middle of the plate, and the maximum equivalent stresses of the semicircular plate and the semi-cylindrical appear in the inner surface connection place. The equivalent stress distribution trends of the annular sector plate, semicircular plates and the semi-cylindrical are obtained. Meanwhile, the equivalent stresses and the sizes of the high stress areas and stress-stable areas in the annular sector plate and semi-cylindrical inner and outer surface areas are obtained. The research result provides a reference for the design of annular sector semicircular cross section vessel. [ABSTRACT FROM AUTHOR]

Experimental research on compressive property of ultra high toughness cementitious composites (UHTCC) at different ages with three cylinder and cube specimens in each group was carried out. The influences of different fiber type, ages and specimen shape on compressive performance of UHTCC were studied, and the axial compressive stress-strain full curves and performance rule of different specimens were obtained. The results show that the peak strain of cylinder specimen at 28 d age is 0. 015, which is higher than that of normal concrete ( it is 0. 002). The ultimate strain is 0. 034, which is 10 times higher than concrete. And the axial compressive stress-strain full curves of UHTCC with 7 d age have a slowly decreasing process when the stress reaches the peak value, which shows that UHTCC has good compressive toughness then. Deformation performance of UHTCC reduces and compressive strength increases along with the growth of the age. The deformation performance of specimens with ordinary high-strength PVA fiber is lower than that of specimens with K-II REC15 PVA fiber, but the compressive strength of the former is higher than that of latter. The cube compressive strength of specimens is generally higher than that of cylinder specimens with the same age, which indicates that the compressive strength is influenced by the size and shape of specimens. [ABSTRACT FROM AUTHOR]

Eccentric loading experiments of 13 steel tube-reinforced concrete columns (STRC), whose slenderness ratio was 4.67, were completed. Through testing the distribution of strain and stress of every part ( including core steel pipes, concrete inside and outside of pipes, longitudinal reinforcements) in the whole loading process, the bearing mechanism and failure feature of STRC were studied. Furthermore, using numerical nonlinear analysis, the influences of position coefficient, eccentricity and longitudinal reinforcement ratio upon bearing capacity were obtained. The study shows following conclusions. STRC columns subjected to eccentric compression are similar to reinforced concrete columns (RC), and the failure types are divided into large eccentric failure, small eccentric failure and limitation failure where the demarcation criterion is that the edge strain of concrete compression reaches the ultimate compressive strain as soon as the tensile steel yields. And its N-M curve is parabolic. STRC adheres to plane cross section assumption and its compressive reinforcements can always yield before the columns' failure without reference to its eccentricity. The bearing capacity of STRC is enhanced with the increase of position coefficient, but not by much, so the steel pipe can be selected only by considering its cross-sectional area and for the convenience of joints construction. Based on the test results, limit equilibrium theory can be used to deduce the normal section capacity formula of STRC columns by referring to that for RC columns. [ABSTRACT FROM AUTHOR]

Six reinforced concrete columns subjected to monotonic horizontal loading under different axial compressive ratios were tested to investigate the size effect on flexural behavior of columns. Axial compressive ratio and section size of specimen were different, while the shear span ratio and reinforcement ratio remained constant. The flexural behavior of specimens was analyzed, including nominal ultimate flexural moment, ductility, location of neutral axis and length of plastic hinge, etc. The analysis results show that the size effect of nominal ultimate flexural moment, compressive strain of concrete at peak loading, ductility, location of neutral axis and length of plastic hinge is apparent, which decrease as the specimen size increases; when axial compressive ratio is big, nominal ultimate flexural moment and compressive strain of concrete at peak loading show more significant size effect; when axial compressive ratio is small, the size effect of displacement ductility coefficient is more apparent. Then on the basis of experiment, a practical calculation model of flexural strength of reinforced concrete column considering section size effect coefficient was proposed. The safety coefficient of large size specimen is consistent with results of small size specimen. [ABSTRACT FROM AUTHOR]

The cracks in the material are in varied forms, such as bend, cross and branch. The numerical and experimental methods were applied to study the fracture problem of the branch crack under compression, considered the influence of different branch crack inclination and length to the stress intensity factors and the wing crack propagation. The results show that the increase of the crack inclination stress intensity factor K1 decreases, and the stress intensity factors increase with the crack length increases, the branch crack with a large length may inhibit the smaller one. The sandstone specimens containing open branch cracks or kink cracks subjected by uniaxial compressive loads were used to analysis the wing crack propagation, the experimental results find that the forms of the destruction of the sandstone specimen are mainly type I wing cracks, and its distance from the crack tip decreases with the increase of branch crack inclination; the bigger branch crack inclination, the smaller wing crack initial angle but the bigger wing crack initial load. The comparison was also made between open and closed cracks, wing crack initial angle of the open crack is greater than the closed one's, but its wing crack initial load is just the opposite. [ABSTRACT FROM AUTHOR]

Use the FLAC3D and the COMSOL Multiphysics numerical simulation software to analy rockmass stress field in high gas coal seam driving roadway surround, energy field distribution characteristics, gas accumulation process rule under different support. The studies show that the bolt prestress form integrally compressive stress structure in roadway section,in advance ahead of tunneling, the bolt prestress of the rear support area form a continuous distribution compressive stress zone, lead to the prestress diffusion into the empty top area. The prestress is larger, the spread is wider, which play an important role in the inhibition of surround rock broken and weathered. High prestress strength rock bolting can reduce the energy concentration of coal and rockmass, and does not produce gas accumulation analysis thinks coal and gas outburst danger can be reduced on some extent under high prestress rock bolting. [ABSTRACT FROM AUTHOR]

Using hollow inclusion method measure the in-situ stress of Kailuan mining area. In-situ stress field types, interaction behavior and the relationship between regional structure was systematically analyzed. Based on this, the inner relationship between in-situ stress field and coal and gas outburst, rockburst, water inrush and other coal and rock dynamic disaster was analyzed. Studies show that in-situ stress field in Kailuan mining area belongs to the Earth dynamical field, the horizontal tectonic stress is dominant, and it belongs to the high stress zone. In-situ stress magnitude and orientation is controlled by Kaiping syncline. Stress value is the highest in Kaiping synclinal axis section. As far away from the axis, the stress value decreases gradually. The maximum principal stress orientation and axis trend of Kaiping synclinal is approximate vertical. At the same time tectonic stress field controls coal structure, coal gas parameters,permeability and so on. In the Kailuan mining area, coal and gas outburst and rock burst occurred in synclinal axis section of Kaiping where stress value is highest, water inrush occurred in the Kaiping syncline wing where stress value is the lowest. Coal and rock dynamic disaster in Kailuan mining area is in the unified tectonic stress environ- ment. [ABSTRACT FROM AUTHOR]

In order to analyze the creep properties of cemented body used in backfilling mining, triaxial creep experiments were conducted. Based on these, the damage evolution equation considering time and stress was deduced, and damage variable was brought in modified Nishihara model, and the new constitutive model was established and the 3D creep equation of backfilling cemented body was deduced. The creep model parameters were integrated based on the experiment data, and the comparative analysis of creep curves in theory and on experiment was conducted. The findings show that backfilling cemented body is viscosity elastic-plastic material and has obvious rheological characteristics, there are only decay creep and steady-state creep when deviatoric stress is small, when it is big, there is accelerated creep. Creep amount increases with the increasing of stress, but increase rate is weakened. It shows that the modified Nishihara model considering damage can better reflect the creep law of backfilling cemented body. [ABSTRACT FROM AUTHOR]

Based on Lade-Duncan failure criterion and considering the comprehensive effect of intermediate principal stress, dilatancy property and the real elastic strains in the plastic zone, a formula of rock resistant coefficient was derived. The results show that compared with Mohr-Coulomb failure criterion, Lade-Duncan criterion can increase the rock resistant coefficient and develop the strength potentials of surrounding rock by considering the effect of intermediate principal stress. The effect of dilatancy property on rock resistance coefficient can not be ignored, and if the dilatancy property is not considered, it would overestimate the resistant coefficient of surrounding rock, in that way, the design will be very dangerous. The assumption that elastic strain in plastic zone is constant will also overestimate resistance coefficient of surrounding rock, the error will become more apparent with increasing the dilatancy property. In the practical engineering, the real elastic strains in the plastic zone of surrounding rock should be considered. [ABSTRACT FROM AUTHOR]

An investigation was conducted on the characteristics of surface current induced by coal under uniaxial compression. An interpretation of the mechanisms governing the electrical behavior of the coal structures under uniaxial stress tests was presented in this paper. The experimental results show that the current signal is generated during the deformation and fracture process of coal samples. When the load is applied, the electric current makes its initial appearance and increases rapidly after a considerable time lag at 8C, until after the stress reaches a value δc ≈0.75δmax where δmax is the maximum applied stress before sample fracture. There is a good correlativity between the current and the load, and the correlation coefficient between them can reach up to 0.8 to 0.9. The current peaks occur under sudden loading and unloading. It suggests that the current is closely related to the loading. The status of coal loading level may be determined by the current signal. The intensive study on coal surface current can provide a way for monitoring the stability of coal and rock. [ABSTRACT FROM AUTHOR]

In order to understand the coupling characteristics of stress and permeability in overlying strata, an analog experimental simulation was conducted to study the co-extraction of coal and methane in longwall coal mine. The experiment used a plane strain model and flexible loading to simulate the variation characteristics of stress in overly strata and permeability in advanced coal face. The results show that a partition tendency exists with the coal face advancing, the concentration area of stress inside coal pillar removes away from the gob, the coefficient of concentration deceases, and the permeability and stress demonstrates a direct proportional relationship. The range of stress decrease experiences a tendency of slow in the direction from goaf to high position. In addition, the stress arch expands vertically and horizontally at the same time, while it will recede at a fully extraction phase. [ABSTRACT FROM AUTHOR]

Based on the background geological information at Panyi Coal Mine, a physical simulation on protective seam mining was conducted in this study. The simulation obtained the volumetric strain distribution in the mining area through capturing the locations of the markers in real time and calculating the coordinates of pixels using Matlab software, which can effectively describe the distribution of expansion-compression in the mining area. Furthermore, a comprehensive stress-strain permeability test was carried out with the establishment of coupling equation between volumetric strain and permeability. The study shows that with the advance of working face, the distribution of both volumetric strain and permeability also demonstrates a consistent dynamic distribution process. However, the permeability evolution of upper protective coal seam lags behind that in the protective coal seam. [ABSTRACT FROM AUTHOR]

The compressive experiments from low to high strain rates have been performed on the material test machine and the split Hopkinson pressure bar(SHPB)apparatus at room temperature of 20 °C. The availability of SHPB experimental data is examined, and the true stress-strain curves are obtained in the strain rate range from 1.1 x 10-4 s-1 to 4 x 10³ s-1 The results show that the modified double b propellant behaves significant strain rate dependence. At low strain rate, the true stress-strain curves show initial elastic stage, yield and strain strengthening stage, and descend stage, in which the specimen fractures along the slope of 45° ~ 55°, and the failure stress and failure strain increase with the strain rate. At high strain rate, the true stress-strain curve shows the effect of strain softening instead of strain strengthening. The initial modulus of elasticity and yield stress of modified double base propellant increases with the strain rate, what's more, they increase substantially at high strain rates compared with those in quasi-static. The relationship between yield strength and logarithm of strain rate is bilinear, which shows more strain rate sensitiveness at high strain rate than at low strain rate. [ABSTRACT FROM AUTHOR]

A model was established to analyze and predict effectively the wear life of rod. It is considered in this model: the two main reasons for partial-wear: borehole curving and rod blending under pressure in the down stroke. A calculating formula suggested by ???????? was used to evaluate the increase of abrasion thickness of rod with time, and the failure position and time were estimated in accordance with the increase of stress with the decrease of residual cross-section area at the point where the wear was worst. The comparison between the model result and the spot data was used to prove the reliability of this model. The principle that the revolving wellhead could retard the progress of wear was interpreted through the calculating result made by this model [ABSTRACT FROM AUTHOR]