47 results about "Yield surface" patented technology

The invention discloses a method for measuring a yield surface of a metal material. The method utilizes a prestretching-torsion deformation loading path to determinate a later yield surface evolution rule and comprises (1) preparing a stretching-torsion combined test sample according to material mechanical test standards, (2) determining a stretching and torsion stress-strain curve and determining stretching and torsion yield strength values, (3) determining an initial yield surface, (4) determining a prestretching-torsion pre-deformation loading path to realize prestretching-torsion pre-deformation loading, (5) determining a later stretching stress-strain curve and determining stretching yield strength after pre-deformation, and (6) determining a later yield surface. The yield surface determined by the loading path has obvious shape change, shows plastic deformation anisotropic behaviors of the metal material in a complex loading way and is especially suitable for metal materials having strong anisotropic mechanical properties.

The invention discloses a normalization method for fatigue characteristics of an asphalt mixture under different stress states. The strength yield surface of the asphalt mixture based on a yield criterion is established by combining strength and fatigue test at different loading speeds under different stress states with a Desai strength yield surface model, a fatigue characteristic analysis technology based on the yield criterion is provided, and a normalization model for the fatigue characteristics of the asphalt mixture in different stress states is obtained. The fatigue characteristic analysis technology and the normalization model can be used to eliminate a difference between the fatigue test results of the asphalt mixture under different test conditions and make up for the deficiencyof no accurate evaluation of the fatigue performances of the asphalt mixture in traditional S-N fatigue equation; and the method realizes the unified expression of the fatigue performances of the asphalt mixture under different test conditions, and provides a theoretical, technologic and technical basis for realizing the scientific transformation from material fatigue to structural fatigue.

The invention relates to an analysis method for forecasting a periodic lattice-material yield surface. According to the analysis method, the coupling effect of the internal-structure axial force and bending moment when a material is actually stressed is considered, a yield condition of periodic lattice-material representative volume element (RVE) is obtained through theoretical derivation, and then through finite element analysis software, mass total calculation is achieved through programming. In post-processing, the calculating result is obtained in the mode that a yield point is automatically identified and extracted, the calculating result and the theoretical result are jointly visualized, and are compared mutually and verified, the accuracy of the result is guaranteed, and therefore forecasting of the strength performance of the periodic lattice material is achieved.

The invention discloses a method for determining a yielding surface by crossed pre-stretching deformation and loading. The method mainly comprises the following steps: determining an initial yielding surface and a subsequent yielding surface; determining the yielding surface by adopting a loading path of carrying out pre-stretching deformation in one direction and then carrying out stretching deformation in the other direction. In the step of determining the initial yielding surface, firstly, a crossed stretching test sample is stretched to selected different stress points along one direction to keep load and then is stretched until the test sample is broken from the other direction; the initial yielding surface is drawn according to obtained yielding strength value; in the step of determining the subsequent yielding surface, firstly, the crossed stretching test sample is stretched to a selected pre-stretching point along a rolling direction and then is unloaded to zero or is unloaded to the selected different stress points; then the next step of a loading manner is selected according to different unloading manners to obtain the corresponding yielding strength value for drawing the subsequent yielding surface. The method disclosed by the invention can be used for reflecting an evolution law of the yielding surface in biaxial loading of a sheet material very well and can be used for effectively characterizing anisotropic mechanical behaviors of plastic deformation of a metal material.

Methods and systems using a numerical model to describe polymeric material properties are disclosed. FEM model of a product is defined. FEM model includes one or more solid elements of polymeric material. In a time-marching simulation of the product under loads, stress state of the solid elements is calculated from deformation gradient tensors. Stress state incorporates the Mullins effect and strain hardening effect, also includes elastic stress, viscoelastic stress and back stress. A yield surface is defined to determine whether the elements are under plastic deformation. Plastic strain is obtained to update the deformation gradient tensor, which is then used to recalculate the stress state. Calculations continue until updated stress state is within a tolerance of the yield surface, at which time the results of polymeric material elements are obtained. The numerical model takes into account all characteristics of a polymeric material.

The invention provides a numerical simulation method for generating a three-dimensional damaged pattern. The method comprises the steps of establishing a three-dimensional geometric model for an object described in a three-dimensional damaged pattern, dissecting mesoscopic grids, setting a boundary condition, an initial condition and material parameters for the numerical simulation, selecting a yield surface with angular points, considering a strength-softening constitutive relationship and a non-associated flow rule, conducting the numerical simulation on the geometric model based on the finite-element dynamic relaxation method to get a solution, and outputting a three-dimensional damaged pattern. In this way, the three-dimensional damaged pattern can be generated directly based on a mechanical equation without the need of pre-assuming any physical mechanism. The above method provided in the invention is used for directly generating three-dimensional damaged patterns. Three-dimensional damaged patterns, generated based on the above method, can better reflect the actual damage situations of materials. Therefore, the mechanical performances of materials can be reflected more intuitively and more truly.

The invention discloses a method for representing fatigue characteristic temperature correlation of an asphalt mixture in a three-dimensional stress state, and particularly relates to the field of road engineering. The method concretely comprises the following steps of: S1, establishing a strength yield surface model based on a three-dimensional stress state; S2, establishing a response function of the yield surface of the asphalt mixture; S3, determining fatigue stress paths in different stress states; S4, providing a novel fatigue characteristic analysis method based on a yield criterion idea. The method redefines the fatigue equation from the three-dimensional angle, and represents the fatigue life by using the temperature in combination with the influence of the temperature on the fatigue life. The fatigue life equation determined by the method is more scientific and more practical, and can play a guiding role in the design of asphalt pavements in China.

The invention provides a wood cross grain pressure-bearing constitutive relation model construction method and device based on a wood weak phase structure, and a storage medium. The method comprises the steps that: the stress-strain relation of wood in the elastic stage is constructed according to the Hooke law of a transverse isotropic material; according to stress characteristics of wood cross grain pressure bearing, equivalent stress causing wood volume deformation in a wood cross grain plane and deviating stress causing wood shear deformation are separated, and a yield surface equation of an elastic-plastic stage in the wood cross grain plane based on the equivalent stress and the deviating stress is constructed; according to a non-correlation flow rule, a plastic flow equation in a wood cross grain plane is constructed; according to the evolutionary relationship of the yield stress along with strain during unidirectional compression of the wood and the relationship between the yield stress during unidirectional compression of the wood and the yield stress during bidirectional compression of the wood, a hardening equation in a wood cross grain plane is constructed; and a stress-strain relationship in a wood rift-grain plane is constructed. The invention can better simulate the compression deformation of the volume when the cross grain of the wood is pressed.

Methods and apparatus for thermally altering the near surface characteristics of a material are described. In particular, a repetitively pulsed ion beam system comprising a high energy pulsed power source and an ion beam generator are described which are capable of producing single species high voltage ion beams (0.25-2.5 MeV) at 1-1000 kW average power and over extended operating cycles (108). Irradiating materials with such high energy, repetitively pulsed ion beams can yield surface treatments including localized high temperature anneals to melting, both followed by rapid thermal quenching to ambient temperatures to achieve both novel and heretofore commercially unachievable physical characteristics in a near surface layer of material.