Deformation mechanism of roadways in deep soft rock at Hegang Xing’an Coal Mine

Engineering geomechanics characteristics of roadways in deep soft rock at Hegang Xing'an Coal Mine were studied and the nature of clay minerals of roadway surrounding rock was analyzed. This paper is to solve the technical problems of high stress and the difficulty in supporting the coal mine, and provide a rule for the support design. Results show that mechanical deformation mechanisms of deep soft rock roadway at Xing'an Coal Mine is of ⅠABⅡABCⅢABCD type, consisting of molecular water absorption (the ⅠAB -type), the tectonic stress type + gravity deformation type + hydraulic type (the ⅡABC -type), and the ⅢABCD -type with fault, weak intercalation and bedding formation. According to the compound mechanical deformation mechanisms, the corresponding mechanical control measures and conversion technologies were proposed, and these technologies have been successfully applied in roadway supporting practice in deep soft rock at Xing'an Coal Mine with good effect. Xing'an Coal Mine has the deepest burial depth in China, with its overburden ranging from Mesozoic Jurassic coal-forming to now. The results of the research can be used as guidance in the design of roadway support in soft rock.

Mechanical behavior and damage constitutive model of sandstone under hydro-mechanical (H-M) coupling

Underground engineering often passes through water-rich fractured rock masses, which are prone to fracture and instability under the long-term coupling of in-situ stress field and pore water(P-W) pressure, ultimately threatening the stability of underground structures. In order to explore the mechanical properties of rocks under H-M coupling, the corresponding damage constitutive(D-C) model has become the focus of attention. Considering the inadequacy of the current research on rock strength parameters,energy evolution characteristics and D-C model under H-M coupling, the mechanical properties of typical sandstone samples are discussed based on laboratory tests. The results show that the variation of characteristic stresses of sandstone under H-M coupling conforms to the normalized attenuation equation and Mohr-Coulomb(M-C) criterion. The P-W pressure mechanism of sandstone exhibits a dynamic change from softening effect to H-M fracturing effect. The closure stress is mainly provided by cohesive strength, while the initiation stress, damage stress, and peak stress are jointly dominated by cohesive strength and friction strength. In addition, residual stress is attributed to the friction strength formed by the bite of the fracture surface. Subsequently, the energy evolution characteristics of sandstone under H-M coupling were studied, and it was found that P-W pressure weakened the energy storage capacity and energy dissipation capacity of sandstone, and H-M fracturing was an important factor in reducing its energy storage efficiency. Finally, combined with energy dissipation theory and statistical damage theory, two types of D-C models considering P-W pressure are proposed accordingly, and the model parameters can be determined by four methods. The application results indicate that the proposed and modified D-C models have high reliability, and can characterize the mechanical behavior of sandstone under H-M coupling, overcome the inconvenience of existing D-C models due to excessive mechanical parameters,and can be applied to the full-range stress–strain process. The results are conducive to revealing the deformation and damage mechanisms of rocks under H-M coupling, and can provide theoretical guidance for related engineering problems.

NEW THEORY IN TUNNEL STABLILITY CONTROL OF SOFT ROCK──MECHANICS OF SOFT ROCK ENGINEERING

Tunnel stability control is a world-wide difficult problem. For the sake of solving it,the new theory of soft rock engineering mechanics has been estabilished. Some key points,such as the definition and classification of soft rock, mechanical deformation mechanism of a soft rock tunnel, the critical support technique of soft rock tunnel and the new theory of the soft rock tunnel stability control are proposed in this paper.

Structural Synthesis of a Class of 2R2T Hybrid Mechanisms

Conventional overconstrained parallel manipulators have been widely studied both in industry and academia,however the structural synthesis of hybrid mechanisms with additional constraints is seldom studied,especially for the four degrees of freedom（DOF） hybrid mechanisms.In order to develop a manipulator with additional constraints,a class of important spatial mechanisms with coupling chains（CCs） whose motion type is two rotations and two translations（2R2T） is presented.Based on screw theory,the combination of different types of limbs which are used to construct parallel mechanisms and coupling chains is proposed.The basic types of the general parallel mechanisms and geometric conditions of the kinematic chains are given using constraint synthesis method.Moreover,the 2R2T motion pattern hybrid mechanisms which are derived by adding coupling chains between different serial kinematic chains（SKCs） of the corresponding parallel mechanisms are presented.According to the constraint analysis of the mechanisms,the movement relationship of the moving platform and the kinematic chains is derived by disassembling the coupling chains.At last,fourteen novel hybrid mechanisms with two or three serial kinematic chains are presented.The proposed novel hybrid mechanisms and construction method enrich the family of the spatial mechanisms and provide an instruction to design more complex hybrid mechanisms.

Mechanics Unloading Analysis and Experimentation of a New Type of Parallel Biomimetic Shoulder Complex

The structure design for high ratio of carrying capacity to deadweight is one of the challenges for the bionic mechanism,while the problem concerning high carrying capacity has not yet be solved for the existing shoulder complex.A new type biomimetic shoulder complex,which adopts 3-PSS/S（P for prismatic pair,S for spherical pair） spherical parallel mechanism（SPM）,is proposed.The static equilibrium equations of each component are established by using the vector method and the equations for constrain forces with certain load are solved.Then the constrain force on the middle limb and that on the side limbs are compared in order to verify the unloading performance of the mechanism.In addition,the prototype mechanism of the shoulder complex is developed,and the force feedback experiment is conducted to verify the static analysis,which indicates that the middle limb suffers most of the external force and the effect of mechanics unloading is achieved.The 3-PSS/S spherical parallel mechanism is presented for the shoulder complex,and the realization of mechanics unloading is benefit for the improvement of the carrying capacity of the shoulder complex.

Formation Mechanism of NiAl/TiB_2 Nanocomposite by Mechanical Alloying Elemental Powders

A NiAl/TiB2 nanocomposite is synthesized by mechanical alloying elemental powders. Upon milling for a certain time, an abrupt exothermic reaction occurs and a large amount of NiAl and TiB2 compounds form simultaneously. It is suggested that two separate chemical reactions,i.e. Ni+Al →NiAl and Ti+2B→TiB2, are involved during the exothermic reaction. Additionof Ti and B to Ni-Al system impedes the structural evolution of Ni and Al powders and delays the abrupt reaction. The final products are equilibrium phases without any metastable phases formed. This type of reaction is suggested to be suitable for alloy systems with two large heatrelease reactions.

Influence of intermediate principal stress on failure mechanism of hard rock with a pre-existing circular opening

Based on particle flow theory, the influences of the magnitude and direction of the intermediate principal stress on failure mechanism of hard rock with a pre-existing circular opening were studied by carrying out true triaxial tests on siltstone specimen. It is shown that peak strength of siltstone specimen increases firstly and subsequently decreases with the increase of the intermediate principal stress. And its turning point is related to the minimum principal stress and the direction of the intermediate principal stress. Failure characteristic(brittleness or ductility) of siltstone is determined by the minimum principal stress and the difference between the intermediate and minimum principal stress. The intermediate principal stress has a significant effect on the types and distributions of microcracks. The failure modes of the specimen are determined by the magnitude and direction of the intermediate principal stress, and related to weakening effect of the opening and inhibition effect of confining pressure in essence: when weakening effect of the opening is greater than inhibition effect of confining pressure, the failure surface is parallel to the x axis(such as σ2=σ3=0 MPa); conversely, the failure surface is parallel to the z axis(such as σ2=20 MPa, σ3=0 MPa).

Mechanical mechanism and support design analysis on bolt-beam-net support in soft rock roadway in Qigou Coal Mine

The deformation and failure mechanical mechanism in soft rock roadway is related to the stability of supported tunnels, which is important to coal mine production and construction. By physical mechanics experiments and X-ray diffraction （XRD） tests, the engineering mechanical properties of soft rock, as well as main mineral composition of the surrounding soft rock of Qigou Coal Mine, were obtained. Based on analysis results, a method using bolt-beam-net combination to support was put forward. Mechanical analysis of the support form was done by using the calculation software FLAC3D. Results show that clay minerals of this mine are kaolinite and illite mixed layer, of which the water absorption is relatively obvious and presented mudding characteristic after absorbing water, with the plasticity index of 0.35, with small expansibility, which is weakly consolidated colloid with strong connected force in unit cell. The rock blocks have the characteristics of moisture absorption softening, and the deformation mechanical mechanism of which is with the coexistence of molecular expansive mechanism, colloid expansive mechanism, and weak layer trend type. The calculation results show that the bolt-beam-net support structure makes the bolt, beam, and roof deform compatibly. The beams make the force in the bolt relatively homogeneous, which restricts the displacement of the tunnel roof as well. Finally, using in situ monitoring, the numerical results were verified.

Mechanism Modeling and Simulation Based on Dimensional Deviation

To analyze the effects on motion characteristics of mechanisms of dimensional variations, a study on random dimensional deviation generation techniques for 3D models on the basis of the present mechanical modeling software was carried out, which utilized the redeveloped interfaces provided by the modeling software to develop a random dimensional deviation generation system with certain probability distribution characteristics. This system has been used to perform modeling and simulation of the specific mechanical time delayed mechanism under multiple deviation varieties, simulation results indicate the dynamic characteristics of the mechanism are influenced significantly by the dimensional deviation in the tolerance distribution range, which should be emphasized in the design.

QM/MM Study on Enzymatic Mechanism in Sinigrin Biosynthesis

As the major and abundant type of glucosinolates(GL)in plants,sinigrin has potential functions in promoting health and insect defense.The final step in the biosynthesis of sinigrin core structure is highly representative in GL compounds,which corresponds to the process from 3-methylthiopropyl ds-GL to 3-methylthiopropyl GL catalyzed by sulfotransferase(SOT).However,due to the lack of the crystallographic structure of SOT complexed with the 3-methylthiopropyl GL,little is known about this sulfonation process.Fortunately,the crystal structure of SOT 18 from Arabidopsis thaliana(At SOT18)containing the substance(sinigrin)similar to 3-methylthiopropyl GL has been determined.To understand the enzymatic mechanism,we employed molecular dynamics(MD)simulation and quantum mechanics combined with molecular mechanics(QM/MM)methods to study the conversion from ds-sinigrin to sinigrin catalyzed by AtSOT18.The calculated results demonstrate that the reaction occurs through a concerted dissociative mechanism.Moreover,Lys93,Thr96,Thr97,Tyr130,His155,and two enzyme peptide chains(Pro92-Lys93 and Gln95-Thr96-Thr97)play a role in positioning the substrates and promoting the catalytic reaction by stabilizing the transition state geometry.Particularly,His155 acts as a catalytic base while Lys93 acts as a catalytic acid in the reaction process.The presently proposed concerted dissociative mechanism explains the role of At SOT18 in sinigrin biosynthesis,and could be instructive for the study of GL biosynthesis catalyzed by other SOTs.

LIRR's Project of “Study on Spalling Mechanism Mechanism of Dense Refractory Castables by Rapid Heating-up” Being Obtained the Support from National Natural Natural Science Foundation of China

LIRR＇s Priject of ＂Research on Spalling Mechanism Due to Rapid Heating-up of Dense Refractory Castables＂ declared by Wang Zhanmin,vice-president of LIRR,will gain the fund support from National Natural Science Foundation of China in 2011.

MODELLING OF MECHANICAL MECHANISM OF CHROMATOGRAPHIC SYSTEM AND THEORETICAL EQUATIONS SHOWING DYNAMICAL CHARACTERISTICS OF CHROMATOGRAPHY

A simple model of chromatographic mechanical mechanism is present, and then a scrics of theoretical chromatographic equations and fundamental Formulae are derived. These theoretical equations and formulae not only reserve thermodynamic characteristics in the current fundamental chromatographic formulae, but also introduce one or more kinetic parameter, so it is possible to make the macroscopic-control on the effect of kinetic characteristics on chromatographic system.

Perspective for aggregation-induced delayed fluorescence mechanism:A QM/MM study

To enhance the potential application of thermally activated delayed fluorescence(TADF)molecular materials,new functions are gradually cooperated to the TADF molecules.Aggregation induced emission can effectively solve the fluorescence quenching problem for TADF molecules in solid phase,thus aggregation-induced delayed fluorescence(AIDF)molecules were recently focused.Nevertheless,their luminescent mechanisms are not clear enough.In this work,excited state properties of an AIDF molecule DMF-BP-DMAC[reported in Chemistry-An Asian Journal 14828(2019)]are theoretically studied in tetrahydrofuran(THF)and solid phase.For consideration of surrounding environment,the polarizable continuum method(PCM)and the combined quantum mechanics and molecular mechanics(QM/MM)method were applied for solvent and solid phase,respectively.Due to the increase of the transition dipole moment and decrease of the energy difference between the first single excited state(S1)and the ground state(S0),the radiative rate is increased by about 2 orders of magnitude in solid phase.The energy dissipation of the non-radiative process from S1 to S0 is mainly contributed by low-frequency vibrational modes in solvent,and they can be effectively suppressed in aggregation,which may lead to a slow non-radiation process in solid phase.Both factors would induce enhanced luminescence efficiency of DMF-BP-DMAC in solid phase.Meanwhile,the small energy gap between S1 and triplet excited states results in high reverse intersystem crossing(RISC)rates in both solvent and solid phase.Therefore,TADF is confirmed in both phases.Aggregation significantly influences both the ISC and RISC processes and more RISC channels are involved in solid state.The enhanced delayed fluorescence should be induced by both the enhanced fluorescent efficiency and ISC efficiency.Our calculation provides a reasonable explanation for experimental measurements and helps one to better understand the luminescence mechanism of AIDF molecules.

A Modifi ed Molecular Structure Mechanics Method for Analysis of Graphene

Based on molecular mechanics and the deformation characteristics of the atomic lattice structure of graphene, a modifi ed molecular structure mechanics method was developed to improve the original one, that is, the semi-rigid connections were used to model the bond angle variations between the C-Cbonds in graphene. The simulated results show that the equivalent space frame model with semi-rigid connections for graphene proposed in this article is a simple, efficient, and accurate model to evaluate the equivalent elastic properties of graphene. Though the present computational model of the semi-rigid connected space frame is only applied to characterize the mechanical behaviors of the space lattices of graphene, it has more potential applications in the static and dynamic analyses of graphene and other nanomaterials.

Mechanical Properties and Solidified Mechanism of Tailings Mortar with Waste Glass

In order to improve the comprehensive utilization of solid waste such as iron tailings and waste glass and so on,mechanical property test of cement tailings mortar mixed waste glass and curing mechanism research were conducted in the key materials mechanics lab of Liaoning province.The experimental results show that adding waste glass particles can improve the grain size distribution of tailings.The effect is proportional to the content.The compressive strength of tailings mortar has increased significantly.The fineness modulus of tailings mortar mixture adding waste glass powder was gradually reducing with the increase of the dosage of waste glass powder,but the compressive strength of the mixture has gradually enhanced with the increase of the dosage.Microscopic analysis shows that the waste glass particles in the mortar mainly play a role of coarse aggregate and glass powder after grinding fine below a certain size shows strong volcanic activity,which can act hydration with tailings,at the same time glass powder also,plays a role in fine aggregate filling.Therefore,all of glass particles and glass powder can be used as the additive material for improving and optimizing the mechanical property of tailings mortar.

Reaction Mechanism of Actin ATP Hydrolysis Studied by QM/MM Calculations

Actin fibers are an important part of the cytoskeleton,providing vital support for the plasma membrane.This function is driven by its ATPase(ATP:adenosine triphosphate)activity,i.e.,ATP+H_(2)O→ADP+Pi.This seemingly simple reaction has attracted much attention because the hydrolysis of ATP provides energy to support life processes.However,the reaction mechanism of ATP hydrolysis in actin is not clear.In order to gain deep insights into the functions of actin,it is essential to elucidate the reaction mechanism of the actin ATP hydrolysis.In this paper,we have studied the reaction mechanism of the ATP hydrolysis in actin by the combined quantum mechanical and molecular mechanics(QM/MM)calculations.Our results show that 1)bond cleavage of the Pγ—OS of ATP and bond formation between oxygen of the lytic water and Pγatoms take place simultaneously,and this is the rate-limiting step of the hydrolysis;2)the proton on the lytic water transfers to the phosphate to form H_(2)P_(γ)O_(4)−via one bridge water.The energy barrier of the complete reaction is 17.6 kcal/mol(1 kcal=4.184 kJ),which is in high agreement with the experimental value.

Deformation characteristics and instability mechanism of transportation hub under downward traversal conditions of the double-track super-large diameter shield tunnel

To investigate the deformation characteristics and instability mechanism of the transportation hub underdownward traversal conditions of the double-track super-large diameter shield tunnel, take the example of BeijingEast Sixth Ring Road into the ground reconstruction project. Using the field experimental monitoring method andnumerical simulation method, after verifying the accuracy of the model, this manuscript begins to unfold theanalysis. The results show that, without any deformation prevention and control measures, The basement raft ofthe underground structure of the transportation hub will produce a deformation difference of 18 mm, and thetensile stress is more than 1.43 MPa, the inhomogeneous deformation and structural cracking will lead tostructural instability and groundwater surges, which seriously affects the safe operation of the transportation hubstation. When control measures are taken, the deformation and stress of the base raft slab of the undergroundstructure of the transportation hub are within the prescribed limits, which can ensure the safe operation of thestation. The displacement of the base slab of the underground structure in the horizontal direction of the crosssection is all pointing to the east, and the overall trend is to shift from the first tunnel to the backward tunnel. Thehorizontal displacement of the base slab in the direction of the tunnel axis all points to the beginning of thecrossing, and the displacement of the slab in the vertical direction is distributed as "rising in the middle andsinking in the surroundings". For a two-lane super-large diameter shield tunnel penetrating an undergroundstructure, there are two mechanical effects: unloading rebound and perimeter rock pressure. The above deformation characteristics are the superposition effect produced by the two, and this fine assessment of the deformation of the raft foundation provides a scientific basis for formulating the deformation control countermeasuresof the crossing project. At the same time, it makes up for the blank of the double-track super-large diameter shieldtunnel down through the transportation hub project.

Effect of chemical modification on the properties of wood/polypropylene composites

Aluminate-based coupling agent was added as a compatibilizer to make the chemical modification of wood powder. The mechanical properties and morphology of wood powder/polypropylene composites were studied. The results showed that the compatibilizer can increase the impact strength of the wood/polypropylene composites, but it has a slightly negative effect on the tensile and flexural strength. For dynamic mechanical properties and Differential Scanning Calorimetry, Aluminate-based coupling agent can slightly increase the storage modulus and loss modulus, and decrease the melt point and the Calorie of Melt. Scanning electron microscopy showed that Aluminate-based coupling agent had a stronger affinity between the wood and polypropylene surfaces. These results suggested that Aluminate-based coupling agent may play a useful role in improving wood powder/polypropylene composites properties.

Effect of extrusion temperature on microstructure and mechanical properties of a low-alloying and ultra-high strength Mg-Zn-Ca-Mn matrix composite containing trace TiC nanoparticles

Mechanical properties of microalloying Mg-2.2Zn-1.8Ca-0.5Mn(wt%)matrix composites reinforced by 0.5 wt%TiC nanoparticles before and after extrusion were investigated based on the detailed microstructural analysis.A uniform distribution of TiC nanoparticles was realized in the nanocomposite by the method of ultrasonic-assisted semisolid stirring.The morphology of eutectic Ca2Mg6Zn3 phases changed from plate-like in the free TiC nanoparticles region to lamellar in the dense TiC nanoparticles region for the as-cast nanocomposite.Both the grain structure and precipitates were obviously refined as the extrusion temperature decreased from 350 to 270℃.The nanocomposite exhibited excellent tensile yield strength(352-428 MPa)which was governed by the extrusion temperature.The grain refinement strengthening with the contribution ratio of^80%to this strength increment was much higher relative to thermal expansion effect,Orowan strengthening and dislocation strengthening.Ultrafine recrystallized grain structure with a substantial of ne precipitates appeared in the nanocomposite extruded at 270℃.The refined grain structure was not only due to dynamic recrystallization,but also the synergistic pinning effect of nano-TiCp,precipitated MgZn2 and α-Mn particles.The tensile toughness value of nanocomposite after extrusion improved with increasing the extrusion temperature.Massive micro-cracks formed along the remnant coarse Ca2Mg6Zn3 led to the structural failure during tension.

Mechanical and damage evolution properties of sandstone under triaxial compression

To study the mechanical and damage evolution properties of sandstone under triaxial compression, we analyzed the stress strain curve characteristics, deformation and strength properties, and failure process and characteristics of sandstone samples under different stress states. The experimental results reveal that peak strength, residual strength, elasticity modulus and deformation modulus increase linearly with confining pressure, and failure models transform from fragile failure under low confining pressure to ductility failure under high confining pressure. Macroscopic failure forms of samples under uniaxial compression were split failure parallel to the axis of samples, while macroscopic failure forms under uniaxial compression were shear failure, the shear failure angle of which decreased linearly with confin- ing pressure. There were significant volume dilatation properties in the loading process of sandstone under different confining pressures, and we analyzed the damage evolution properties of samples based on acoustic emission damage and volumetric dilatation damage, and established damage constitutive model, realizing the real-time Quantitative evaluation of samnles damage state in loading process.