473 results about "Principal stress" patented technology

In a solar cell module, a solder fillet 19 is formed on an end surface on the shorter length side of a connection tab to be connected to a bus bar electrode 2a, 3a up to the height of the connection tab. The geometry of the solder fillet 19 is adjusted so that an indentation amount is 0-54% of the height or a bulge amount is 0-10% of the height, by which the maximum principal stress generated during the manufacturing process of a solar cell element 4 can be reduced, and therefore occurrences of cracks can be reduced. Also during a laminating process, breaking of the solar cell element or crack generation can be eliminated.

A computational technique to construct a 3-D valve leaflet geometry. The invention pertains to methodology to construct a 3-D heart valve leaflet geometry using finite element analysis (FEA) to simulate the manual assembly process or, in other words, provide a virtual assembly process as an input to a subsequent simulated valve testing step. The simulated valves may be subjected to simulated cyclic valve opening and closings and the stress levels induced therein monitored. Simulated valve designs with lower principal stresses can then be selected for prototyping. Proposed valves can be subjected to cyclic fatigue stress testing under simulated physiologic conditions to study valve durability.

A method for estimating principal stresses of a subterranean formation from seismic data. In one embodiment, rock strength parameters from seismic data of the formation is first determined to calculate the anisotropic elastic properties of the formation. The three principal stresses of the formation: vertical stress, minimum horizontal stress, and maximum horizontal stress, is determined using at least the calculated anisotropic elastic properties and the rock strength parameters of the formation. From the estimated principal stresses, the differential ratio of the maximum and minimum horizontal stresses can be determined to indicate optimal zones for hydraulic fracturing. In another embodiment, a tectonic strain term is introduced to calibrate the estimated principal estimated stress to a known reference point. In yet another embodiment, hoop stress is incorporated to estimate the fracture initiation pressures.

The invention relates to an optimum design method for staged fracturing perforation cluster parameters of a horizontal well of a shale reservoir. The optimum design method includes the following steps of S1, selecting high-fracture-performance fracturing well sections; S2, building a mathematical model for hydrofracture fracture progressing, analyzing an induction stress field model for fracture extension, and analyzing a fracture diverting mechanism; S3, analyzing extending conditions of main fractures, and selecting cluster distances capable of allowing the main fractures to evenly extend forwards; S4, analyzing change conditions of stress fields around the main fractures, selecting the perforation cluster distances with the horizontal principal stress ratios smaller than 1.3, and determining the optimal perforation cluster distances in cooperation with the step S3; S5, further improving the complexity of the fractures through an alternate fracturing principle, and setting the perforation density of perforation clusters in the middle to range from 10 to 16 per m and the perforation density of perforation clusters in the two sides to be larger than 16 per m. By means of the optimum design method, the perforation cluster distances can be optimized, largest fracture transforming sizes can be obtained, the practical effect of reservoir transforming can be improved, and high construction cost and the poor fracturing effect which are caused by aimlessly setting the perforation cluster distances can be avoided.

The present invention relates to a shale gas reservoir crustal stress logging prediction method based on a rock physics model. According to the method, a shale gas reservoir rock physics model which takes kerogen particles into consideration is established, so as to predict a longitudinal and transverse wave velocity of the logging; based on the above, a maximum and minimum horizontal principal stress and a fracture pressure of the reservoir are calculated; and an accurate stress assessment of a shale gas reservoir is carried out while a transverse wave logging is not provided. The beneficial effects of the invention are that: the rock physics model in line with characteristics of the shale gas reservoir is established to improve precision of the prediction velocity; and based on the rock physical model, the maximum and minimum horizontal principal stress and the fracture pressure are obtained, so that while the measured transverse wave logging data are not provided, the underground stress can be predicted on the basis of a conventional logging curve, and the prediction result is high in accuracy.

The present invention provides a joining structure capable of greatly improving the proof stress and the fatigue property by alleviating the stress concentration and residual stress caused by welding heat at one or both ends of a tabular member.In the present invention, one or both ends 4 of a tabular member 3 such as a reinforcing rib, fixed to the surface of a structural member 1 in the direction of the principal stress of the structural member 1 so as to protrude in the shape of T, is / are bent in a direction deviating from the direction of the principal stress and, by this, the rigidity at the end(s) 4 of the tabular member 3 decreases and the stress concentration is alleviated. It is preferable to bend one or both ends of a tabular member 3 in the shape of an gradual curve and to the extent that each bent end is formed at a right angle to the direction of the principal stress. The tabular member may have the shape of a flat plate, or it may be bent so that it has the shape of U or V as a whole. Further, the tabular member may be welded to a structural member or formed as an integral part of a structural member.

A method for optimizing hydraulic fracturing simulates the geomechanical interaction between regional stress and natural fractures in a reservoir. An equivalent fracture model is created from data on the natural fracture density, regional stress and geomechanical properties of the reservoir, so that points in the reservoir are assigned a fracture length and fracture orientation. The horizontal differential stress and maximum principal stress direction at points in the reservoir are then estimated by meshless particle-based geomechanical simulation using the equivalent fracture model as an input. The meshless particle-based geomechanical simulator uses the derived initial geomechanical condition to simulate the sequence of hydraulic fracturing and derive the resulting strain and J integral that can be used to estimate the asymmetric half fracture lengths and initial propped permeability needed by hydraulic fracturing design and reservoir simulation software to optimize wellbore and completion stage positions.

A method for spacing heater wells for an in situ conversion process includes the steps of determining a direction along which thermal energy will travel most efficiently through a subsurface formation, and completing a plurality of heater wells in the subsurface formation, with the heater wells being spaced farther apart in the determined direction than in a direction transverse to the determined direction. In one aspect, the step of determining a direction along which thermal energy will travel most efficiently is performed based upon a review of geological data pertaining to the subsurface formation. The geological data may comprise the direction of least horizontal principal stress in the subsurface formation. Alternatively, the geological data may comprise the direction of bedding in the subsurface formation, the tilt of the subsurface formation relative to the surface topography, the organic carbon content of the kerogen, the initial formation permeability, and other factors.

A method for spacing heater wells for an in situ conversion process is provided. The method includes the steps of determining a direction along which thermal energy will travel most efficiently through a subsurface formation, and completing a plurality of heater wells in the subsurface formation, with the heater wells being spaced farther apart in the determined direction than in a direction transverse to the determined direction. In one aspect, the step of determining a direction along which thermal energy will travel most efficiently is performed based upon a review of geological data pertaining to the subsurface formation. The geological data may comprise the direction of least horizontal principal stress in the subsurface formation. Alternatively, the geological data may comprise the direction of bedding in the subsurface formation, the tilt of the subsurface formation relative to the surface topography, the organic carbon content of the kerogen, the initial formation permeability, and other factors.

A method for optimizing hydraulic fracturing and refracturing simulates the geomechanical interaction between regional stress and natural fractures in a reservoir. An equivalent fracture model is created from data on the natural fracture density, regional stress and elastic properties of the reservoir, so that points in the reservoir are assigned a fracture length and fracture orientation. The horizontal differential stress and maximum principal stress direction at points in the reservoir are then estimated by meshless particle-based geomechanical simulation using the equivalent fracture model as an input. Regions in the reservoir having low differential stress based on the simulation can then be selected for initial hydraulic fracturing. Regions in the reservoir having high differential stress based on the simulation can then be selected for refracturing.

Maximum and minimum horizontal stresses, and horizontal to overburden stress ratio, are estimated using radial profiles of shear moduli. Inversion enables estimation of maximum and minimum horizontal stresses using radial profiles of three shear moduli associated with an orthogonal set of axes defined by the three principal stress directions. Differences in the far-field shear moduli are inverted together with two difference equations obtained from the radial profiles of the dipole shear moduli C44 and C55, and borehole stresses in the near-wellbore region. The horizontal to overburden stress ratio is estimated using differences in the compressional, dipole shear, and Stoneley shear slownesses at two depths in the same lithology interval where the formation exhibits azimuthal isotropy in cross-dipole dispersions, implying that horizontal stresses are nearly the same at all azimuths. The overburden to horizontal stress ratio in a formation with axial heterogeneity may also be estimated using the far-field Stoneley shear modulus C66 and dipole shear modulus C55 together with the radial variation of the dipole shear modulus C55 caused by near-wellbore stress concentrations.

The invention establishes a prediction method for the multi-axial high-cycle fatigue life of a plastic metal material based on a critical plane approach. According to the invention, a fatigue failure mode of the plastic metal material under the condition of combined loading of tension and torsion is taken into consideration, influence of a stress amplitude ratio and phase difference on the multi-axial high-cycle fatigue life under the condition of multi-axial loading is also considered, a fatigue life prediction model for prediction of the multi-axial high-cycle fatigue life is established by using linear combination of a maximum principal stress peak value and a maximum shear stress range on the basis of critical plane criteria of multi-axial fatigue and used for predicating the life of the plastic metal material bearing multi-axial high-cycle fatigue load, and the prediction method for the multi-axial high-cycle fatigue life of the plastic metal material based on the critical plane approach is eventually brought forward. The model established in the invention is based on the critical plane criteria capable of revealing damage of a physical mechanism multi-axial fatigue and takes influence of the stress amplitude ratio and phase difference on multi-axial high-cycle fatigue failure under the condition of multi-axial loading into consideration, and small dispersity and high accuracy of prediction results of the model are realized.

Fracture- and stress-induced sonic anisotropy is distinguished using a combination of image and sonic logs. Borehole image and sonic logs are acquired via known techniques. Analysis of sonic data from monopole P- and S-waves, monopole Stoneley and cross-dipole shear sonic data in an anisotropic formation are used to estimate at least one compressional and two shear moduli, and the dipole fast shear direction. Fracture analysis of image logs enables determination of fracture types and geometrical properties. Geological and geomechanical analysis from image logs provide a priori discrimination of natural fractures and stress-induced fractures. A forward quantitative model of natural fracture- and stress-induced sonic anisotropy based on the knowledge of fracture properties interpreted from image logs allows the computation of the fast-shear azimuth and the difference in slowness between the fast- and slow-shear. The misfit between predicted and observed sonic measurements (i.e. fast-shear azimuth and slownesses) is then optimized in order to discriminate depth zones with an elastic medium as being influenced by the presence of open natural fractures, closed natural fractures and fractures induced by non-equal principal stress effects.

The invention provides an automobile body-in-white light weighting analysis method. The method comprises following steps: setting each optimization size of automobile body-in-white as a design variable and setting the modal frequency value of each stage, bending rigidity value, torsional rigidity value and maximum principal stress at all extreme work conditions of the automobile body-in-white as target functions; performing experiment design and simulation calculation on each design variables to obtain response function values corresponding to each design variable and according to the response function values, establishing a simulation model; based on the simulation model, performing multiple discipline and multi-target optimization on the design variables to obtain Pareto solution set of the variables. According to the automobile body-in-white light weighting analysis method of the invention, through selecting proper design variables, analysis methods and technical routes, the light weighting of automobile body-in-white is realized and at the same time, on the basis of satisfying multiple discipline and multi-target, the optimized size parameters of the automobile body-in-white among all performances can be found.

The invention relates to a shale reservoir compressibility evaluation method based on a support vector machine technology. The method comprises the following steps: (1) mineral composition quantitative analysis and uniaxial compressive test are firstly carried out; (2) logging characteristic parameters for recognizing a crack are extracted; (3) maximum and minimum horizontal principal stress in different layers is calculated through a combined spring model, and a stress sensitivity degree is then calculated; (4) a compressibility evaluation model is built; and (5) discrete layer stratum compressibility evaluation sample space is then built, and a relationship between a compressibility evaluation result and different response logging curves is subjected to correlation analysis. The shale reservoir compressibility evaluation method based on the support vector machine technology has the beneficial effects that compressibility influencing factors are considered perfectly, the shale gas reservoir compressibility model is built from three aspects of a brittleness index, a natural crack development degree and the stress sensitivity, insufficient consideration on the factors by the existing evaluation method is remedied, and the comprehensive ability of the shale to form a complex crack network during volume cracking can be better reflected.

The invention provides a method for extracting gas from a bedding level fractured well of a ground coal seam roof, orderly comprising the following steps: selecting a coal storage layer with the gas content more than 8 m<3> / t; determining fissure zone position generated by extracting the coal layer, taking the rock formation at 3-7 m of the middle lower part of the fissure zone as the level construction layer; determining positions of the well opening and kickoff points according to landing points of the level segment; and realizing large curvature radius increased slanting, wherein the drilling position is parallel to a gate road at a coal stope working surface or vertical to the largest principal stress direction, and the length of the level segment is less than or equal to the strike length of the working surface; the well structure adopts a three-part structure; the level segment can be an uncased hole or a lower sleeve tube which is an emission hole; the level segment is constructed in the selected rock layer; the level segment uses an open hole packer or a sleeve tube packer for performing hydraulic fracture in segments; a drainage and extracting apparatus is arranged for extracting the ground gas by a virtual storage layer; and the negative pressure extracting is exchanged between the middle and last phase, thereby realizing multiple functions of the well. The method in the invention improves the extracting efficiency of the ground drilling well, realizes area outburst elimination, and reduces the gas disasters to the maximum limit.

The invention discloses a three-dimensional space stress-strain measurement method based on a fiber bragg grating sensor. The method comprises the following steps: arranging six fiber bragg grating strain sub-sensors on the three principal axes of a space coordinate system and the axes of angular bisectors between every two adjacent principal axes respectively; arranging a temperature sub-sensor on the axis k in the body diagonal direction of a cube; working out the strain in the directions of the six fiber bragg grating strain sub-sensors through a decoupling equation set of the fiber bragg grating sensor based on wavelength, wherein the wavelength is measured by the six fiber bragg grating strain sub-sensors and the temperature sub-sensor; obtaining the values of epsilon x, epsilon y, epsilon z, gama xy, gama yz and gama zx through the plane strain relationship formula of the mechanics of materials; substituting the six quantities into a cubic space principal strain equation to obtain the values of the principal strain epsilon 1, epsilon 2 and epsilon 3; obtaining the values of the principal stress sigma 1, sigma 2 and sigma 3 through a physical equation of the elastic mechanics; obtaining the directions of the principal strain and the principal stress through a space strain relationship equation set of the elastic mechanics and a direction cosine relational expression; obtaining the maximum value taw maximum of shear stress through the maximum shear stress formula; obtaining the direction of the maximum shear stress through the relationship between the principal stress and principal shear stress.

The invention provides a three dimensional earth pressure testing device based on general earth pressure cells and a rhombic dodecahedron. According to the device, six general earth pressure cells are fixed onto six surfaces, of which the normal vector quantities are uncorrelated, of the rhombic dodecahedron, so that the three dimensional earth pressure testing device is formed; grooves used for accommodating earth pressure cells are arranged on the surfaces of the rhombic dodecahedron with uncorrelated normal direction vector quantities; a conducting wire hole leading to the centroid of the rhombic dodecahedron is formed in the center of each groove; a conducting wire converging hole leading to the centroid is formed in each surface center of the rhombic dodecahedron except the grooves, so that six conducting wire holes and the converging holes converge at the centroid; meanwhile, a method for assembly and compute the three dimensional earth pressure testing device is provided. The invention has the effect that the three dimensional earth pressure testing device obtain, through testing, three principal stress of the earth pressure in the principal directions with measuring accuracy of 1.22 Rho, the measuring accuracy of three shearing stress is 0.71 Rho, the average measuring accuracy is 0.965 Rho, the safety storage of the engineering construction is improved, and the health condition of the engineering in later period can be effectively evaluated.

The invention discloses a volume alternating fracturing method of a horizontal well in an experimental shale reservoir. The method comprises the following steps: collecting the stratum parameter, the natural fracture parameter and the hydraulic fracture basic parameter of a reservoir; establishing stretching, shearing and pass through failure criterions of a natural fracture when a hydraulic fracture and the natural fracture are interacted, and quantitatively analyzing the influence on the natural fracture failure by a horizontal principal stress difference; establishing a hydraulic fracture induced stress calculation model, and computing the influence on the induced stress of a middle perforation cluster fracture elongated area by gaps among different perforation cluster fractures and fracture extended lengths; optimally selecting a shale reservoir horizontal well volume fracturing perforation cluster gap and perforation cluster extended lengths at the two ends, so as to promote a middle perforation cluster hydraulic fracturing fracture to be extended and interactively produce stretching, shearing and pass through failure modes with the natural fracture at the same time to form a complex fracture. According to the method, induced stress field produced through the extension of the hydraulic fracture, perforation gaps within the same fracturing section and the extended fracture lengths are organically combined, and the horizontal well volume fracturing technology is properly perfected.

The invention relates to an indoor rock mechanics testing device, in particular to a rock hollow cylinder torsion shear apparatus capable of realizing complex stress path, and belongs to the technical field of geotechnical engineering techniques. The torsion shear apparatus comprises a base, a sleeve, a lower pressure head, an upper pressure head, a piston, an upper seat, a head cover, a connecting rod and a torsion device. The rock hollow cylinder torsion shear apparatus disclosed by the invention has the advantages that the puzzle that the stress path of the rock indoor testing device is single is solved; axial force, inner confining pressure, outer confining pressure and torque can be loaded on a rock sample separately or together; the defect that the four external forces interfere with one another during loading is overcome; the magnitude variation of principal stress or the rotating stress path of the principal axis of stress can be simulated; the rock hollow cylinder torsion shear apparatus is reasonable in structure, easy to manufacture, easy to operate, accurate in measuring system and high in automation degree and can be used for indoor tests of rock complex loading paths.

The invention relates to the field of numerical simulation technology and discloses a rock material true triaxial test numerical simulation method considering an intermediate principal stress effect to truly reflect strength characteristics and failure modes of rock materials under a true triaxial stress condition. The method comprises the steps that a finite difference increment iterative computing format based on Mogi-Coulomb failure criteria is subjected to secondary development in FLAC3D numerical simulation software, and a Mogi-Coulomb constitutive model is obtained; and a numerical model of the rock materials under the true triaxial stress condition is established, basic physical mechanical parameters are assigned to the numerical model, and the Mogi-Coulomb constitutive model is loaded and called to perform simulation operation to obtain a corresponding numerical simulation computing result. According to the method, influences of intermediate principal stress on rock strength and the failure modes are fully considered during numerical analysis of the failure characteristics of the rock materials under the true triaxial stress condition, so that the simulation result is truer and more reliable.

The invention discloses a preparation method of a bio-ceramic coating titanium-wire sintering porous titanium artificial bone, belonging to the biomedical engineering field. In the invention, a three-dimensional weaving method is utilized, a titanium metal fiber wire is constructed into a controllable structure model, a random structure model and a bionic structure model which can stimulate the bone trabecula and principal stress line of a human bone, and then is prepared into the porous titanium artificial bone through prepressing molding and vacuum sintering, after that, a sol-gel method is utilized to manufacture a gradient coating or a complex coating on the surface of the porous titanium artificial bone, so that the gradient coating transiting from titanium dioxide to bio-ceramics or the bio-ceramics-titanium dioxide complex coating is formed on the surface of the porous titanium artificial bone to obtain the bio-ceramic coating titanium-wire sintering porous titanium artificial bone. The preparation method not only can protect the titanium metal skeleton and prevent titanium ions from dissociating to enter a human body, but also can ensure that the titanium metal skeleton the surface of which is coated with the bio-ceramics has the biological characteristics, therefore, the bio-ceramic coating titanium-wire sintering porous titanium artificial bone can be applied to repairing clinical segmental defect of long bones.

The invention relates to the field of exploration and development of oil and gas fields, in particular to a method for forecasting the opening pressure, the opening sequence and the water injection pressure of a reservoir fissure. According to the method, a geomechanical model is determined through geological data, physical experiments and the like, and on the basis of paleo-stress-field numerical simulation, by means of the rock fracturing criterion and the ancient-and-modern rock-mechanics layer evolution characteristics, the present occurrence of different group fissures is forecasted; on the basis of present-stress-field numerical simulation, the work-area rock-mechanics layer distribution regularities are combined, principal-stress vertical gradients of different nodes are obtained with the rock-mechanics layer-top-bottom-face point searching method, ground stress information and fissure information are synthesized, inversion forecast of the opening pressure, the opening sequence and the water injection pressure of the fissure is achieved. The method is composed of strict mathematical algorithm derivation, after corresponding geological information is digitized, the corresponding calculation procedure can be developed with computer programming languages, forecast cost is low, and operability is high.

Fracture- and stress-induced sonic anisotropy is distinguished using a combination of image and sonic logs. Borehole image and sonic logs are acquired via known techniques. Analysis of sonic data from monopole P- and S-waves, monopole Stoneley and cross-dipole shear sonic data in an anisotropic formation are used to estimate at least one compressional and two shear moduli, and the dipole fast shear direction. Fracture analysis of image logs enables determination of fracture types and geometrical properties. Geological and geomechanical analysis from image logs provide a priori discrimination of natural fractures and stress-induced fractures. A forward quantitative model of natural fracture- and stress-induced sonic anisotropy based on the knowledge of fracture properties interpreted from image logs allows the computation of the fast-shear azimuth and the difference in slowness between the fast- and slow-shear. The misfit between predicted and observed sonic measurements (i.e. fast-shear azimuth and slownesses) is then optimized in order to discriminate depth zones with an elastic medium as being influenced by the presence of open natural fractures, closed natural fractures and fractures induced by non-equal principal stress effects.

The invention discloses a method for preparing an integral turbine blade disc based on a SiC fiber ceramic matrix composite material, which is used for solving the technical problem of the poor practicability of the existing integral turbine blade disc preparation method. The technical scheme is as follows. Firstly, a plane polar coordinate weaving method is adopted to prepare a turbine blade discprefabricated body unit layer, so that continuous SiC fibers are arranged in two principal stress directions in the warp direction and the weft direction. Then Z-direction puncture, sewing and die pressing are adopted to finish the shaping of the prefabricated body. A BN interface layer is prepared on the surface of the SiC fiber of the prefabricated body by utilizing a chemical vapor infiltration method. The prefabricated body of the turbine disc is pre-densified by adopting a chemical vapor infiltration process. The turbine disc blade is processed by adopting a cubic boron nitride or diamond special cutter on a multi-axis numerical control machine tool. Finally, an anti-oxidation coating is prepared. As the prefabricated body is provided with the continuous SiC fibers in two main principal directions in the warp direction and the weft direction, the bearing performance of the integral turbine blade disc is improved, the preparation period of the integral turbine blade disc is shortened, and the practicability is good.

The invention discloses a rock core clamp holder capable of simulating complex migration process of formation fluid and a using method of the rock core clamp holder. The clamp holder is a closed combined body formed by an axial compression plunger, a clamp holder barrel body and a pressure-resistant hose embedded in a rock core, wherein the tested rock core is processed to be of a hollow cylindrical shape, the pressure-resistant hose penetrates into a pore passage inside the rock core, the axial compression plunger is arranged at two ends of the rock core, three metering pumps are respectively arranged to be communicated with the axial compression plunger to apply the maximum principal stress to the rock core, are communicated with an inner annular pressure cavity of the clamp holder barrel to apply intermediate principal stress to the rock core, and are communicated with the pressure-resistant hose to apply the minimum principal stress to the inner pore of the rock core; one metering pump is additionally arranged to be communicated with the pore passage deviating from the axis of the plunger to inject the fluid into the rock core; the pressure and the flow rate of pressure transmitting fluid in the liquid chambers are controlled to realize the functions of controlling the stress and the deformation of the rock core. The rock core clamp holder provided by the invention can realize gas / liquid seepage of pores of the rock core under a triaxial stress state and also can meet the rock core deformation and the permeability test during stress relieving.

A limited entry perforating phased gun system and method for accurate perforation in a deviated / horizontal wellbore is disclosed. The system / method includes a gun string assembly (GSA) deployed in a wellbore with shaped charge clusters. The charges are spaced and angled such that, when perforated, they intersect at a preferred fracturing plane. Upon fracturing, the fractures initiate at least principal stress location in a preferred fracturing plane perpendicular to the wellbore from an upward and downward location of the wellbore. Thereafter, the fractures connect radially about the wellbore in the preferred fracturing plane. The fracture treatment in the preferred fracturing plane creates minimal tortuosity paths for longer extension of fractures that enables efficient oil and gas flow rates during production.

The invention provides a determination method of a mine fault influence area, and belongs to the technical field of mine safe mining. By the adoption of the determination method, a precursor influence area of a fault zone is determined according to geological exploration and roadway tunneling and revealing conditions; weakened zones of an upper set and a lower set of the fault are determined according to mechanical experiments of a coal rock layer near the fault zone; distribution characteristics of ground stress is inverted according to a three-dimensional fine numerical value model, and a maximum principal stress influence area is calculated in theory; finally, by the union of the precursor influence area, the weakened zones and the maximum principal stress influence area, a space influence area of the fault zone is scientifically determined; in this way, a new determination method is provided for the fault influence area, and a new thought and method are provided for division of a dangerous area where a coal rock dynamic disaster is induced by a fault tectonic zone.

Disclosed is a rock true triaxial pressure chamber. Four self-balance pistons which are arranged crosswise are disposed on a wall of the chamber. Each piston has a pressure cavity and a backpressure cavity, wherein the pressure cavity is attached to the pressure chamber through an external oil-way provided with a one-way valve; and the backpressure cavity is respectively attached to the atmosphere and a hand pump for transposition through a pipeline and the one-way valve. The self-balance pistons are provided with a pressure control system which reliefs pressure of the external oil-way of the piston's pressure cavity through the hand pump. An EDC controller receives feedback signals of a pressure transducer and a force transducer and outputs a control command to a Moog servo valve. According to the command, the servo valve controls the external oil-way for oil supply of an actuator and adjusts the pressure on the pistons. The advantage of original two-hardness one-softness true triaxial pressure chamber is maintained in the invention. On this basis, a self-balance to non-self-balance transition function is added in the true triaxial pressure chamber provided by the invention, thus making up the insufficiency that the original true triaxial pressure chamber can only unload hydrostatic pressure and realizing unloading of complete stress path.

A glass plate has a thickness of from 1.5 to 3 mm, and it has a peripheral region having a predetermined width along the edge line of the plate and having its principal stress difference of compressive properties, an intermediate region having a predetermined width adjacent to an inner periphery of the peripheral region and having its principal stress difference of tensile properties and a central region occupying an inner peripheral side of the intermediate region wherein the central region has an averaged surface compression stress of from 15 to 35 MPa, and the peripheral region has a width of from 5 to 20 mm; the maximum value of the principal stress difference averaged in a thickness direction of the plate along its center line is from 20 to 40 MPa, and the minimum value of the principal stress difference averaged in a thickness direction along the center line is from 8 to 25 MPa.