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Numerical modelling of bifurcation and localisation in cohesive-frictional materials
40A 931298 Simple double-hardening model for geomateriais Banerjee, S; Davis, R O; Sribalaskandarajah, K J Geotech Engng Div ,4SCE Vl18, N6, June 1992, P889-901 A relatively simple approach for nonassociative elastoplastic modelling of soils is presented. The model has distinct mechanisms for volumetric and distortional yielding, plastic flow functions similar to those of the original Cam-Clay model, yield stresses given by single state variables, and hardening moduli controlled by the evolution of a state variable. Many complex features of behaviour of granular soil in triaxial loading, as reported in the literature, can be reproduced by the model, including mean stress and path dependent dilatancy, strain hardening and softening in drained shear, and densitydependent undrained shear response. 931299 Deformation of rock: a pressure-sensitive, dilatant material Ord, A Pure ,4ppl Geophys V137, N4, 1991, P337-366 A model is presented for plastic deformation of rock in the brittle regime, based on Mohr-Coulomb behaviour in which cohesion, friction angle,and dilatancy angle follow hardening or softening laws in both plastic deformation and increase in confining pressure. The physical basis is a series of triaxial compression tests on Gosford sandstone and Carrera marble over a large range of confining pressures. Both materials are pressure sensitive and dilatant. A set of material parameters is derived to describe material behaviour in terms of a non-associated Mohr-Coulomb constitutive model in the brittle-ductile regime. Its predictions are tested against laboratory data using the finite difference code FLAC. 931300 Numerical modelling of bifurcation and Iocalisation in cohesive-frictional materials de Borst, R Pure ,4ppi Geophys V137, N4, 1991, P367-390 Many engineering materials exhibit strain localisation. Methods for numerically analysing the phenomenon are reviewed and fundamental shortcomings identified. The emphasis is then placed on a proper numerical modelling of localisation phenomena. The main purpose is to achieve a mesh-objective numerical simulation in which on mesh refinement a finite width of the localisation zone is computed. The model developed, a v o n Mises yield function formulated in a Cosserat continuum, is limited in that it cannot model pressure-sensitive behaviour, but transfer to more complicated constitutive models which better describe geological materials is possible. 931301 Tensile response of quasi-brittle materials Karihaloo, B L; Huang, X Pare ,4ppi Geophys V137, N4, 1991, P461-487 Rocks are amongst materials exhibiting nonlinear behaviour in tension or flexure. Strain softening as a result of Iocalisation of damage is observed after attainment of ultimate strength. Existing flaws grow and new ones are generated. A general micromechanical description of the various stages in the tensile response of quasi-brittle materials is presented. Pre-peak strain hardening is described by a damage mechanics approach and post-peak behaviour by a combination of damage mechanics and fracture mechanics. Enhanced fracture toughness and the size effect on brittle-ductile behaviour seen in quasi-brittle materials are discussed.
931302 Modified stress tensors for anisotropic behaviour of granular materials Tobita, Y; Yanagisawa, E Soils Found V32, NI, March 1992, P85-99 Effects of inherent and induced anisotropy on the mechanical behaviour of granular materials are well known. Variables describing fabric anisotropy must be introduced into the constitutive equations to allow complete description of the deformation features. Modified stress tensors as a result of fabric anisotropy are proposed and discussed. It is demonstrated that the classical isotropic, kinematic, and combined hardening models are special cases of the proposed method. The effectiveness of the method is illustrated with its incorporation into the non-associated flow model with a Drucker-Prager yield criterion. 931303 Back analysis procedure for establishing load parameters and Young's moduli from stress and displacement measurements Akutagawa, S; Brown, E T; Meek, J L Proc 7th I S R M International Congress on Rock Mechanics, Aachen, 16-20 September 1991 VI, P665-669. Publ Rotterdam: A ,4 Balkema, 1991 The Double Back Analysis of Material and Load Parameters (DBML) is an iterative procedure developed to simultaneously determine unknown applied load and material properties (Young's modulus) parameters from measurements of stress components and relative displacements during application of a load. The method is based on the combination of two independent numerical modules used to estimate load parameters and Young's modulus respectively. Advantages and limitations of the DBML are examined using numerical examples, and its computational performance is compared to that of Baye's method. 931304 Constitutive modelling of Swedish fine grained soils Axelsson, K; Yu, Y; Runesson, K Proc lOth European Conference on Soil Mechanics and Foundation Engineering, Florence, 26-30 May 1991 V1, P183187. Publ Rotterdam: A A Balkema, 1991 Drained and undrained behaviour of Swedish soft clays and silts is outlined. Constitutive models based on the Cam Clay plasticity model are suggested for these soils. Volumetric and deviatoric hardening are taken into account for the silt, a rotated yield surface with mixed hardening assumed for the clay. Both implicit and explicit methods are used in the integration of the plasticity relations. Constitutive parameters are determined from results of drained and undrained triaxial tests via an optimization algorithm. 931305 Kinematic hardening constitutive model for clays Kavvadas, M Proc lOth European Conference on Soil Mechanics and Foundation Engineering, Florence, 26-30 May 1991 V1, P229232. Publ Rotterdam: ,4 ,4 Balkema, 1991 Development and evaluation of an effective stress constitutive model to describe nonlinear anisotropic behaviour of normally consolidated and lightly overconsolidated clays are described. The ellipsoidal yield surface is initially oriented along the consolidation stress axis and is allowed to expand and rotate continuously to describe volumetric hardening and material anisotropy. Validation is against results of triaxial, plane strain, and simple shear tests on Boston Blue Clay.
© 1993 Pergamon Press Ltd. Reproduction not permitted
931302 Modified stress tensors for anisotropic behaviour of granular materials Tobita, Y; Yanagisawa, E Soils Found V32, NI, March 1992, P85-99 Effects of inherent and induced anisotropy on the mechanical behaviour of granular materials are well known. Variables describing fabric anisotropy must be introduced into the constitutive equations to allow complete description of the deformation features. Modified stress tensors as a result of fabric anisotropy are proposed and discussed. It is demonstrated that the classical isotropic, kinematic, and combined hardening models are special cases of the proposed method. The effectiveness of the method is illustrated with its incorporation into the non-associated flow model with a Drucker-Prager yield criterion. 931303 Back analysis procedure for establishing load parameters and Young's moduli from stress and displacement measurements Akutagawa, S; Brown, E T; Meek, J L Proc 7th I S R M International Congress on Rock Mechanics, Aachen, 16-20 September 1991 VI, P665-669. Publ Rotterdam: A ,4 Balkema, 1991 The Double Back Analysis of Material and Load Parameters (DBML) is an iterative procedure developed to simultaneously determine unknown applied load and material properties (Young's modulus) parameters from measurements of stress components and relative displacements during application of a load. The method is based on the combination of two independent numerical modules used to estimate load parameters and Young's modulus respectively. Advantages and limitations of the DBML are examined using numerical examples, and its computational performance is compared to that of Baye's method. 931304 Constitutive modelling of Swedish fine grained soils Axelsson, K; Yu, Y; Runesson, K Proc lOth European Conference on Soil Mechanics and Foundation Engineering, Florence, 26-30 May 1991 V1, P183187. Publ Rotterdam: A A Balkema, 1991 Drained and undrained behaviour of Swedish soft clays and silts is outlined. Constitutive models based on the Cam Clay plasticity model are suggested for these soils. Volumetric and deviatoric hardening are taken into account for the silt, a rotated yield surface with mixed hardening assumed for the clay. Both implicit and explicit methods are used in the integration of the plasticity relations. Constitutive parameters are determined from results of drained and undrained triaxial tests via an optimization algorithm. 931305 Kinematic hardening constitutive model for clays Kavvadas, M Proc lOth European Conference on Soil Mechanics and Foundation Engineering, Florence, 26-30 May 1991 V1, P229232. Publ Rotterdam: ,4 ,4 Balkema, 1991 Development and evaluation of an effective stress constitutive model to describe nonlinear anisotropic behaviour of normally consolidated and lightly overconsolidated clays are described. The ellipsoidal yield surface is initially oriented along the consolidation stress axis and is allowed to expand and rotate continuously to describe volumetric hardening and material anisotropy. Validation is against results of triaxial, plane strain, and simple shear tests on Boston Blue Clay.
© 1993 Pergamon Press Ltd. Reproduction not permitted