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Nonlocal continuum damage, localization instability and convergence
26A 891204 Comparison of various models for strain-softening Pijaudier-Cabot, G; Bazant, Z P; Tabbara, M Engng Comput II5, N2, June 1988. P141-150
space under prescribed time dependent stress distribution, and an underground explosion in a layered soil medium. Results are compared with those of other methods and the accuracy and applicability of the proposed method established.
A comparison of various models for strain softening due to damage such as cracking or void growth is presented. Wave propagation in strain-softening materials, a structural approach, time independent continuum model, rate-dependent continuum model, localization limiters and differential approximation of non-local damage are considered.
891209 Mechanical modeling of material damage Murakami, S J Appi Mech (Trans ASME Set E) V55, N2, June 1988, P280-286
891205 Effects of voids and volume changes on the behaviour of frictional materials Lade, P V int J Num Anal MetA Geomech VI2, N4, July-Aug 1988, P351-370 Constitutive models for frictional materials are often based on elasticity and work hardening plasticity theory, developed for metals. The most important characteristics of frictional materials are briefly reviewed. Frictional materials behave differently to metals, two of the main factors contributing to this difference being the presence of voids and the tendency to change volume during compression or shear of frictional materials. These essential differences must be recognised if realistic constitutive models for geologic materials are to be developed. 891206 Variational principle for granular materials Chandler, H W lnt J Num Anal Meth Geomech VI2, N4, July-Aug 1988, P371-378 A development of a theory of plasticity which makes use of the mathematical theory of envelopes is used to construct a variational principle for granular materials which is valid even when frictional dissipation occurs. Both stresses and strains can be varied. The displacement field must obey the prescribed displacement rates at the boundary, and derived stresses must obey the prescribed tractions at the boundary. The principle is straightforward to apply. 891207 Bifurcation analysis of deep boreholes: !. Surface instabilities Vardoulakis, I G; Papanastasiou, P C Int J Num Anal Metk Geomech VI2, N4, July-Aug 1988, P379-399 A borehole in a deep rock layer is considered. Breakout will arise from surface instabilities which tend to open surface parallel microcracks, or if these instabilities are not possible, by shear failure. Stability is studied using a linear bifurcation theory. A complete solution for stress and strain fields is first obtained. The inhomogeneous bifurcation problem is formulated, and solved by finite element analysis. Results are used to establish a simplified breakout analysis which combines Blot's hodograph method with surface stability analysis. 891208 Dynamic stress analysis of a class of geomechanics problems by the boundary element method Ahmad, S lnt J Num Anal Meek Geomech VI2, N4, July-Aug 1988, P401-417 An advanced BEM for dynamic stress analysis is presented. The boundary element formulation is described, and its numerical implementation illustrated with applications to a rigid strip footing on inhomogeneous viscoelastic soil, a half
A systematic theory to describe anisotropic damage states of materials, and a consistent definition of effective stress tensors are developed within the framework of continuum damage mechanics. It is postulated that material damage can be characterised mainly by fall in load carrying effective area due to development of microscopic cracks and cavities. It is extended to analyse the stress path dependency of cracked elastic-brittle materials under combined hydrostatic stress and shear. 891210 Nonlocal continuum damage, localization instability and convergence Bazant, Z P; Pijaudier-Cabot, G J Appl Mech (Trans ASME Set E) V55, N2, June 1988, P287-293 Prediction of failure of brittle heterogeneous materials such as rocks requires realistic description of strain softening behaviour. Attempts to describe this using local inelastic continuum theories such as plasticity or continuum damage mechanics prove unsatisfactory, as strain localization cannot be captured objectively. These models incorrectly predict energy dissipated at failure to be zero, and finite element solutions produce meaningless results as mesh is refined. A nonlocal formulation for strain softening is proposed, whose main attribute is that strain as a kinematic variable should be described as local. Various aspects are explored: static strainlocalization instability; influence of various types of spatial averaging; and convergence at mesh refinement. 891211 Constitutive model for non-cohesive soils (In French) Cambou, B; Jafari, K Rev Fr Geotech N44, 1988, P43-55 A constitutive model for granular soils, which describes behaviour under complex loading, such as cyclic loading with rotation of principal stress axes, is presented. The general thermodynamic framework of the model is defined, and isotropic and deviatoric plastic deformation mechanisms developed. These are coupled using a kinematic condition. Calibration of the model is described, and its predictions are compared to experimental results. 891212 How should one-dimensionni laboratory equations be cast into three-dimensional form? Fossum, A F; Callahan, G D; Van Sambeek, L L; Senseny, P E Key Questions in Rock Mechanics: Proc 29tk US Symposium, Minneapolis, 13-15 June 1988 P35-41. Publ Rotterdam: A A Balkema, 1988 One-dimensional constitutive laws based on laboratory tests provide no information on how materials deform when all 3 principal stresses are unique. Thermodynamics principles are used to derive a three-dimensional generalisation consistent with laboratory stress and strain measures. The multiaxial
© 1989 Pergamon Press plc. Reproduction not permitted
space under prescribed time dependent stress distribution, and an underground explosion in a layered soil medium. Results are compared with those of other methods and the accuracy and applicability of the proposed method established.
A comparison of various models for strain softening due to damage such as cracking or void growth is presented. Wave propagation in strain-softening materials, a structural approach, time independent continuum model, rate-dependent continuum model, localization limiters and differential approximation of non-local damage are considered.
891209 Mechanical modeling of material damage Murakami, S J Appi Mech (Trans ASME Set E) V55, N2, June 1988, P280-286
891205 Effects of voids and volume changes on the behaviour of frictional materials Lade, P V int J Num Anal MetA Geomech VI2, N4, July-Aug 1988, P351-370 Constitutive models for frictional materials are often based on elasticity and work hardening plasticity theory, developed for metals. The most important characteristics of frictional materials are briefly reviewed. Frictional materials behave differently to metals, two of the main factors contributing to this difference being the presence of voids and the tendency to change volume during compression or shear of frictional materials. These essential differences must be recognised if realistic constitutive models for geologic materials are to be developed. 891206 Variational principle for granular materials Chandler, H W lnt J Num Anal Meth Geomech VI2, N4, July-Aug 1988, P371-378 A development of a theory of plasticity which makes use of the mathematical theory of envelopes is used to construct a variational principle for granular materials which is valid even when frictional dissipation occurs. Both stresses and strains can be varied. The displacement field must obey the prescribed displacement rates at the boundary, and derived stresses must obey the prescribed tractions at the boundary. The principle is straightforward to apply. 891207 Bifurcation analysis of deep boreholes: !. Surface instabilities Vardoulakis, I G; Papanastasiou, P C Int J Num Anal Metk Geomech VI2, N4, July-Aug 1988, P379-399 A borehole in a deep rock layer is considered. Breakout will arise from surface instabilities which tend to open surface parallel microcracks, or if these instabilities are not possible, by shear failure. Stability is studied using a linear bifurcation theory. A complete solution for stress and strain fields is first obtained. The inhomogeneous bifurcation problem is formulated, and solved by finite element analysis. Results are used to establish a simplified breakout analysis which combines Blot's hodograph method with surface stability analysis. 891208 Dynamic stress analysis of a class of geomechanics problems by the boundary element method Ahmad, S lnt J Num Anal Meek Geomech VI2, N4, July-Aug 1988, P401-417 An advanced BEM for dynamic stress analysis is presented. The boundary element formulation is described, and its numerical implementation illustrated with applications to a rigid strip footing on inhomogeneous viscoelastic soil, a half
A systematic theory to describe anisotropic damage states of materials, and a consistent definition of effective stress tensors are developed within the framework of continuum damage mechanics. It is postulated that material damage can be characterised mainly by fall in load carrying effective area due to development of microscopic cracks and cavities. It is extended to analyse the stress path dependency of cracked elastic-brittle materials under combined hydrostatic stress and shear. 891210 Nonlocal continuum damage, localization instability and convergence Bazant, Z P; Pijaudier-Cabot, G J Appl Mech (Trans ASME Set E) V55, N2, June 1988, P287-293 Prediction of failure of brittle heterogeneous materials such as rocks requires realistic description of strain softening behaviour. Attempts to describe this using local inelastic continuum theories such as plasticity or continuum damage mechanics prove unsatisfactory, as strain localization cannot be captured objectively. These models incorrectly predict energy dissipated at failure to be zero, and finite element solutions produce meaningless results as mesh is refined. A nonlocal formulation for strain softening is proposed, whose main attribute is that strain as a kinematic variable should be described as local. Various aspects are explored: static strainlocalization instability; influence of various types of spatial averaging; and convergence at mesh refinement. 891211 Constitutive model for non-cohesive soils (In French) Cambou, B; Jafari, K Rev Fr Geotech N44, 1988, P43-55 A constitutive model for granular soils, which describes behaviour under complex loading, such as cyclic loading with rotation of principal stress axes, is presented. The general thermodynamic framework of the model is defined, and isotropic and deviatoric plastic deformation mechanisms developed. These are coupled using a kinematic condition. Calibration of the model is described, and its predictions are compared to experimental results. 891212 How should one-dimensionni laboratory equations be cast into three-dimensional form? Fossum, A F; Callahan, G D; Van Sambeek, L L; Senseny, P E Key Questions in Rock Mechanics: Proc 29tk US Symposium, Minneapolis, 13-15 June 1988 P35-41. Publ Rotterdam: A A Balkema, 1988 One-dimensional constitutive laws based on laboratory tests provide no information on how materials deform when all 3 principal stresses are unique. Thermodynamics principles are used to derive a three-dimensional generalisation consistent with laboratory stress and strain measures. The multiaxial
© 1989 Pergamon Press plc. Reproduction not permitted