Calibration of an elastoplastic model of sand liquefaction using the swarm intelligence with a multi-objective function

According to post-seismic observations,spectacular examples of engineering failures can be ascribed to the occurrence of sand liquefaction,where a sandy soil stratum could undergo a transient loss of shear strength and even behave as a“liquid”.Therefore,correct simulation of liquefaction response has become a challenging issue in geotechnical engineering field.In advanced elastoplastic models of sand liquefaction,certain fitting parameters have a remarkable effect on the computed results.However,the identification of these parameters,based on the experimental data,is usually intractable and sometimes follows a subjective trial-and-error procedure.For this,this paper presented a novel calibration methodology based on an optimization algorithm(particle swarm optimization(PSO))for an advanced elastoplastic constitutive model.A multi-objective function was designed to adjust the global quality for both monotonic and cyclic triaxial simulations.To overcome computational problem probably appearing in simulation of the cyclic triaxial test,two interrupt mechanisms were designed to prevent the particles from wasting time in searching the unreasonable space of candidate solutions.The Dafalias model has been used as an example to demonstrate the main programme.With the calibrated parameters for the HN31 sand,the computed results were highly consistent with the laboratory experiments(including monotonic triaxial tests under different confining pressures and cyclic triaxial tests in two loading modes).Finally,an extension example is given for Ottawa sand F65,suggesting that the proposed platform is versatile and can be easily customized to meet different practical needs.

Unified elastoplastic finite difference and its application

Two elastoplastic constitutive models based on the unified strength the- ory （UST） are established and implemented in an explicit finite difference code, fast Lagrangian analysis of continua （FLAC/FLAC3D）, which includes an associated/non- associated flow rule, strain-hardening/softening, and solutions of singularities. Those two constitutive models are appropriate for metallic and strength-different （SD） materials, respectively. Two verification examples are used to compare the computation results and test data using the two-dimensional finite difference code FLAC and the finite element code ANSYS, and the two constitutive models proposed in this paper are verified. Two application examples, the large deformation of a prismatic bar and the strain-softening be- havior of soft rock under a complex stress state, are analyzed using the three-dimensional code FLAC3D. The two new elastoplastic constitutive models proposed in this paper can be used in bearing capacity evaluation or stability analysis of structures built of metallic or SD materials. The effect of the intermediate principal stress on metallic or SD mate- rial structures under complex stress states, including large deformation, three-dimensional and non-association problems, can be analyzed easily using the two constitutive models proposed in this paper.

Application and comparison of different elastoplastic constitutive models for springback simulation of aluminum sheet forming

Springback is considered to be one of the most important problems in aluminum sheet stamp forming, leading to deviation from the designed target shape and assembly defects. In this study, a springback simulation model based on the benchmark of a Jaguar Land Rover aluminum panel is established. We embed several elastoplastic constitutive models （ Barlat＇ s 89, Barlat＇ s YLD2000, Yoshida-Uemori （YU） ＋ Barlat＇ s 89, and YU ＋ Barlat＇ s YLD2000） in the finite element model,in order to discuss the influence of the constitutive model selection on springback prediction in aluminum sheet forming.

Predictive Elastoplastic Damage Constitutive Law: Establishment of Equivalence Relation between Intrinsic and Extrinsic Material Parameters

The purpose of the current work is the development and application of a new identification method of material parameters of elastoplastic damage constitutive model under large strains. A relationship relating the intrinsic and extrinsic parameters of a reference material is built and transformed in equivalence relation. Extrinsic parameters concern the shape of their experimental tensile force/elongation curve, however, intrinsic parameters deal with Swift hardening law coupled with an isotropic damage variable. The relationship is carried out from a statistical characterization of a material reference (standard-steel E24). It based on multiple linear regression of a data set obtained according to a full factor design of numerical simulations of mechanical tensile tests. All materials satisfying this equivalence relation belong to the same equivalence class. This is motivated by observing that gathered materials must behave somewhat like the reference material. The material parameters can be immediately identified by only one task by running the found relationship. The current method facilitates the identification procedure and offers a substantial savings in CPU time. However it just needs only one simulation for the identification of similar behavior instead of the few hundred required when using other methods.

Formulation of thermo-hydro-mechanical coupling behavior of unsaturated soils based on hybrid mixture theory

Thermo-Hydro-Mechanical （THM） coupling pro- cesses in unsaturated soils are very important in both theoretical researches and engineering applications. A coupled formulation based on hybrid mixture theory is derived to model the THM coupling behavior of unsaturated soils. The free-energy and dissipative functions for different phases are derived from Taylor＇s series expansions. Constitutive relations for THM coupled behaviors of unsaturated soils, which include deformation, entropy change, fluid flow, heat conduction, and dynamic compatibility conditions on the interfaces, are then established. The number of field equations is shown to be equal to the number of unknown variables; thus, a closure of this coupling problem is established. In addition to modifications of the physical conservation equations with coupling effect terms, the constitutive equations, which consider the coupling between elastoplastic deformation of the soil skeleton, fluid flow, and heat transfer, are also derived.

THE CONSTITUTIVE EQUATION RESEMBLANCE OF ELASTIC-PLASTIC MULTIPHASE SOLID

Based on composite materials, the equivalent elastic-plastic constitutive equations of multiphase solid are researched. According to the suggested definition of. constitutive equivalence it is demonstrated that the multiphase solid, composed of several kinds of homogeneous elastic-plastic media that conform to the generalized normality rule, has the same type of constitutive equations as its constituents have that also conform to the generalized normality rule.