13 results about "Yield surface" patented technology

The invention provides an elastic-plastic unified description method and system for nonlinear characteristics of surrounding rock considering medium-principal stress, and belongs to the technical field of computer aided design. The method comprises the following steps: carrying out a true triaxial mechanical property test on surrounding rock to obtain a surrounding rock total stress-strain curve, extracting characteristic stress points of the stress-strain curve, and carrying out stage division on the stress-strain curve; constructing a characteristic yield surface in the stress space based on the characteristic stress points; based on the staged characteristics of the stress-strain curve, plastic deformation capacity characterization functions of different stages are constructed respectively, and the plastic deformation capacity characterization functions are used for describing the plastic deformation capacity of the stress-strain curve; and constructing a nonlinear hardening-softening equation to describe evolution characteristics of the characteristic yield surface. According to the scheme, the nonlinear characteristics of the stress-strain curve can be more comprehensively and accurately described under different minimum principal stresses and medium principal stresses.

The invention relates to a novel method for constructing a soil constitutive model based on a stress test, which comprises the following steps of: performing the stress test on a soil sample by adopting a discrete element method, and analyzing the strain response of the soil under the action of stress increment in different directions; deriving key composition elements of the constitutive model based on the response envelope obtained by the stress test, including a yield surface, a plastic flow direction, a shear expansion coefficient and a plastic modulus; establishing a state-related constitutive model in combination with a critical state theory; and verifying the prediction capability of the constitutive model through a DEM heuristic test and a triaxial loading test. The method has the beneficial effects that the incremental behaviors of the soil body under different stress paths can be accurately captured through a stress tentative test, and the simulation precision of the model is remarkably improved.

The present invention discloses a method for predicting the bending springback of metal pipes taking into account non-isothermal thermal field loading. For the bending modes of half-circle heating of the outer arch of the bending section, half-circle heating of the inner arch, and full-circle heating, the temperature field of the bending process is regarded as a thermal equilibrium state, and the temperature distribution of the pipe cross section under different heating methods is evaluated; according to the material constitutive properties of the metal pipe at high temperature, based on the force balance conditions of the bending outer arch and the bending inner arch, the offset of the neutral layer on the pipe cross section and the asymmetry of the yield surface distribution in the elastic-plastic zone are taken into account, so as to accurately calculate the elastic-plastic bending moment and improve the prediction accuracy of the springback angle. The present invention can be used for the preliminary and rapid calculation of the springback angle after hot bending of pipes under different position mold heating conditions, and has a guiding role in the design of the temperature field of hot bending of pipes and the selection of forming parameters.

The application relates to a constitutive calculation method and device for improving a GTN model, equipment and a medium, comprising the following steps: obtaining initial porosity of a target material at a current increment step in a finite element implicit calculation process; judging whether the initial porosity is greater than a preset minimum porosity threshold; if the initial porosity is greater than the preset minimum porosity threshold, completing constitutive calculation of the target material at the current increment step based on a preset improved GTN yield criterion. The preset improved GTN yield criterion is used to calculate constitutive material parameters of the target material. In the increment step of the finite element implicit calculation, the application first carries out minimum threshold validity checking on the initial porosity, and only when the porosity meets the physical rationality requirement, the improved GTN yield criterion is used to carry out material constitutive calculation, so that the yield surface shape continuously changes when the porosity changes from a positive value to a negative value in the iteration process, and the technical problem that the traditional GTN model cannot converge due to the numerical iteration divergence caused by the negative porosity is solved.

The present application relates to a method for establishing a constitutive model of soil based on a prototype test and a test device used by the method, the method comprising the following steps: placing a sealed bag in a soil column test hole, injecting fluid into the sealed bag to load the soil, measuring the lateral displacement of the deep soil, calculating the yield cylindrical surface radius of the soil, the radial compressive stress at yield, and the principal stress state of the soil unit according to the circular hole expansion theory and the Lame equation, establishing the yield criterion, the subsequent yield surface, and the failure criterion, dividing the soil in the plastic deformation area into multiple concentric soil cylinders according to the graded loading, calculating the size and radial displacement of each soil cylinder from outside to inside, combining the test hole sidewall radial displacement test value, calculating the elastic parameters required by the incremental method in the elastic-plastic mechanics according to the test loading grade, establishing the constitutive model, assuming that the yield surface is a plane and the intermediate principal stress is ignored, degrading the yield criterion into the Mole-Coulomb criterion, and verifying the constitutive model through a prototype test.

The application discloses a construction method of a constitutive model considering particle crushing of rock-soil granular material under a three-dimensional stress state, and the method comprises the following steps: according to an internal friction angle φ of the rock-soil granular material to be researched, quantifying influence of a shear stress under the three-dimensional stress state, and obtaining a quantified value of the influence of the shear stress under the three-dimensional stress state; according to a particle crushing degree B, a critical stress ratio M and a critical crushing energy E C of the rock-soil granular material, a current state particle crushing energy E B , the quantified value of the influence of the shear stress under the three-dimensional stress state and a static water pressure p under a current stress state, calculating a yield surface function Y; judging a stress-strain development stage according to a value of the yield surface function Y, and calculating a stiffness tensor D ep corresponding to the stress-strain development stage; and according to the stiffness tensor D ep , calculating a strain tensor ε, a strain increment tensor dε, a stress σ under a current state of a stress path and a stress increment tensor dσ. The method can predict mechanical responses of the rock-soil granular material under complex working conditions.

The invention discloses a concrete elastic-plastic damage model valuing method considering a constraint effect. The concrete elastic-plastic damage model valuing method comprises the following steps: acquiring stress-strain curves of concrete in different constraint states; secondly, calculating the constraint stress of the concrete based on the yield surface in an equivalent pseudo-triaxial stress state; converting a stress-strain curve of the concrete based on the yield surface in a constraint state into a stress-strain curve in a uniaxial stress state; then plastic flow correction is carried out on the concrete based on the plastic potential function in a constraint state; and finally performing material unit test verification and component numerical simulation calculation. On the basis of the constitutive model yield surface, a constraint stress calculation method and a curve conversion process are deduced, and stress-strain curve integration is achieved; and meanwhile, a plastic expansion angle correction formula is deduced, so that numerical simulation better fits a test result, the strength and ductility improvement of the concrete under a constraint effect can be accurately simulated, and the accuracy of numerical simulation of a complex structure is improved.

The application provides a kind of automobile deep drawing steel yield surface determination method and system, it is related to the technical field of mechanics test yield surface determination, it aims at solving the defects that traditional uniaxial tensile test cannot reflect the anisotropic yield behavior of deep drawing steel.The method adopts the technical scheme of uniaxial tensile test combined with cross-shaped biaxial tensile test: prepare uniaxial tensile test sample in rolling direction and perpendicular to rolling direction and cross-shaped biaxial tensile test sample; obtain real stress-real plastic strain curve and plastic work under different plastic strain by uniaxial tensile test; load different proportion of biaxial tensile test on cross-shaped test sample, obtain biaxial stress-strain data; based on the principle of equivalent plastic work per unit volume, back-calculate the stress value corresponding to each loading proportion, draw yield locus curve.Precisely characterize the yield surface evolution law and anisotropic deformation behavior of deep drawing steel under complex stress state.The automobile deep drawing steel yield surface determination system is applied to the automobile deep drawing steel yield surface determination method.

The present invention discloses a method for analyzing the stability of soil slopes based on the precise finite element method, which includes establishing a two-dimensional slope model and dividing the grid; using the modified hyperbolic circularized Mohr-Coulomb yield constitutive model to determine whether the soil mass yields. If yielding occurs, an accurate explicit Euler algorithm will be used for stress redistribution, and the stress point will always be ensured to be on or within the yield surface through stress back-pulling; for the solution of the non-linear equations, Newton-Raphson iteration is used for solution; the strength reduction method is introduced, and a failure criterion with sufficient accuracy requirements is adopted. The safety factor of the slope is obtained through iterative search, and data such as the displacement and plastic zone of the slope can also be obtained through post-processing of the results. The present invention is reasonable and accurate for the stability analysis of slopes, can give a high-precision slope safety factor, and at the same time, based on the data such as the slope displacement and plastic zone calculated, it can provide a reasonable basis or suggestion for the implementation of slope engineering prevention and control measures.

This invention discloses a method for constructing a multi-scale fracture assessment index for rocks under true three-dimensional stress, comprising the following steps: S1, establishing a yield function F based on the Mogi-Coulomb three-dimensional strength criterion; S2, constructing a formula for assessing the degree of multi-scale fracture of rocks based on the strength envelope of the three-dimensional strength criterion and the geometric relationship between the yield surface and the stress point; S3, assessing the degree of rock mass fracture based on the range of the multi-scale fracture assessment index. This invention proposes a method for constructing a multi-scale fracture assessment index for rocks, providing a theoretical basis for safety evaluation and stability analysis of high-stress deep rock engineering.

The invention discloses a method for constructing a true triaxial time-dependent damage mechanics model of rock, that is: using viscoplastic strain and time-dependent damage to characterize the non-linear rheological behavior of rock, and using the time-dependent damage factor to reflect the progressive equilibrium movement process during the creep of rock; considering the crack azimuth angle, using the damage variable to control and drive the yield surface, proposing a true three-dimensional yield function of rock, and establishing a true triaxial time-dependent damage mechanics model of rock; finally, using an explicit non-linear numerical integration algorithm to accurately calculate the evolution of the time-dependent damage factor during the creep process. The true triaxial time-dependent damage mechanics model of rock proposed by the invention can accurately describe the true triaxial instantaneous and creep mechanical responses of rock, provide a theoretical basis for the long-term stability study of deep rock mass excavation projects, and ensure the safety and stability of deep rock engineering construction.

The application provides an elastoplastic unified description method and system considering the nonlinear characteristics of surrounding rock of intermediate principal stress, and belongs to the technical field of computer-aided design. Through the true triaxial mechanical property test of surrounding rock, the full stress-strain curve of surrounding rock is obtained, the characteristic stress points of the stress-strain curve are extracted, and the stress-strain curve is divided into stages; based on the characteristic stress points, the characteristic yield surface in the stress space is constructed; based on the stage characteristics of the stress-strain curve, the plastic deformation capacity representation functions of different stages are respectively constructed, and the plastic deformation capacity representation functions are used for describing the plastic deformation capacity of the stress-strain curve; and the nonlinear hardening-softening equation is constructed to describe the evolution characteristics of the characteristic yield surface. The scheme can more comprehensively and accurately describe the nonlinear characteristics of the stress-strain curve under different minimum principal stresses and intermediate principal stresses.

The invention discloses a method and system for constructing a critical state constitutive model of over-consolidated gas-bearing clay, and the method comprises the following steps: 1, dispersing the gas-bearing clay into two phases of a saturated soil matrix and a gas cavity according to a composite material theory, and obtaining a stress-strain relationship; step 2, establishing a local drainage equation of pore water flowing into the gas cavity; step 3, constructing a teardrop type yield surface function with an adjustable shape; 4, weakening parameters are introduced, weakening items are obtained, and a hardening law with a weakening effect is obtained; 5, according to the stress and strain relation, the local drainage equation, the yield surface function and the hardening law, a critical state elastic-plastic constitutive model of the over-consolidated gas-containing clay is obtained; and 6, according to the test data of the gas-containing kaolin, reversely calibrating parameters and weakening parameters for modifying the shape of the yield surface. The method aims at obtaining the constitutive model capable of accurately describing the mechanical response of the high-precision over-consolidated gas-containing clay in the complex stress state.