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1.
Jaka Dujc Boštjan Brank Adnan Ibrahimbegovic 《Computer Methods in Applied Mechanics and Engineering》2010,199(21-22):1371-1385
In this work we present a new modelling paradigm for computing the complete failure of metal frames by combining the stress-resultant beam model and the shell model. The shell model is used to compute the material parameters that are needed by an inelastic stress-resultant beam model; therefore, we consider the shell model as the meso-scale model and the beam model as the macro-scale model. The shell model takes into account elastoplasticity with strain-hardening and strain-softening, as well as geometrical nonlinearity (including local buckling of a part of a beam). By using results of the shell model, the stress-resultant inelastic beam model is derived that takes into account elastoplasticity with hardening, as well as softening effects (of material and geometric type). The beam softening effects are numerically modelled in a localized failure point by using beam finite element with embedded discontinuity. The original feature of the proposed multi-scale (i.e. shell-beam) computational model is its ability to incorporate both material and geometrical instability contributions into the stress-resultant beam model softening response. Several representative numerical simulations are presented to illustrate a very satisfying performance of the proposed approach. 相似文献
2.
Christophe Kassiotis Adnan Ibrahimbegovic Hermann G. Matthies Bostjan Brank 《Computer Methods in Applied Mechanics and Engineering》2010,199(21-22):1254-1264
An efficient implementation of the operator split procedure for boundary value solution with plastic flow computation is presented for a general form of associated plasticity model. We start with the general form of phenomenological model of plasticity where the yield criterion is not restricted to a simple (quadratic) form, and the elasticity tensor does not have constant entries. We then turn to the multi-scale model of plasticity which employs the fine scale representation of the plastic deformation along with the homogenization procedure for stress computation. We also visit the plasticity model with rate sensitive plastic response where plastic flow computation is carried out at fine scale in time. We proved herein the sufficient and necessary conditions for the proposed operator split procedure to converge, for any such general form of associated plasticity. Moreover, we presented a systematic manner for constructing the main ingredients for the plastic flow computation and the global Newton’s iteration, such as the consistent elastoplastic tangent. 相似文献
3.
Combined continuum damage‐embedded discontinuity model for explicit dynamic fracture analyses of quasi‐brittle materials
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Timo Saksala Delphine Brancherie Isaac Harari Adnan Ibrahimbegovic 《International journal for numerical methods in engineering》2015,101(3):230-250
In this paper, a novel constitutive model combining continuum damage with embedded discontinuity is developed for explicit dynamic analyses of quasi‐brittle failure phenomena. The model is capable of describing the rate‐dependent behavior in dynamics and the three phases in failure of quasi‐brittle materials. The first phase is always linear elastic, followed by the second phase corresponding to fracture‐process zone creation, represented with rate‐dependent continuum damage with isotropic hardening formulated by utilizing consistency approach. The third and final phase, involving nonlinear softening, is formulated by using an embedded displacement discontinuity model with constant displacement jumps both in normal and tangential directions. The proposed model is capable of describing the rate‐dependent ductile to brittle transition typical of cohesive materials (e.g., rocks and ice). The model is implemented in the finite element setting by using the CST elements. The displacement jump vector is solved for implicitly at the local (finite element) level along with a viscoplastic return mapping algorithm, whereas the global equations of motion are solved with explicit time‐stepping scheme. The model performance is illustrated by several numerical simulations, including both material point and structural tests. The final validation example concerns the dynamic Brazilian disc test on rock material under plane stress assumption. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
4.
Brittle and ductile failure of rocks: Embedded discontinuity approach for representing mode I and mode II failure mechanisms
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M. Nikolic A. Ibrahimbegovic P. Miscevic 《International journal for numerical methods in engineering》2015,102(8):1507-1526
In this work, we present a discrete beam lattice model with embedded discontinuities capable of simulating rock failure as a result of propagating cracks through rock mass. The developed model is a two‐dimensional (plane strain) microscale representation of rocks as a two‐phase heterogeneous material. Phase I is chosen for intact rock part, while phase II stands for pre‐existing microcracks and other defects. The proposed model relies on Timoshenko beam elements enhanced with additional kinematics to describe localized failure mechanisms. The model can properly take into account the fracture process zone with pre‐existing microcracks coalescence, along with localized failure modes, mode I of tensile opening and mode II of shear sliding. Furthermore, we give the very detailed presentation for two different approaches to capturing the evolution of modes I and II, and their interaction and combination. The first approach is to deal with modes I and II separately, where mode II can be activated but compression force may still be transferred through rock mass which is not yet completely damaged. The second approach is to represent both modes I and II being activated simultaneously at a point where complete failure is reached. A novel numerical procedure for dealing with two modes failure within framework of method of incompatible modes is presented in detail and validated by a set of numerical examples. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
5.
6.
On a consistent field transfer in non linear inelastic analysis and ultimate load computation 总被引:1,自引:1,他引:0
In this work we propose a field transfer operator for remeshing carried out in the course of incremental analysis of a non
linear inelastic behavior. The proposed procedure is geared towards the ultimate load computation of a complex structure,
where we choose the appropriate mesh grading for each different phase of computations, starting with a coarse mesh for the
initial linear response and going towards a more refined mesh for highly nonlinear inelastic response. The proposed projection
operator is developed on the basis of diffuse approximation method. The key feature of such an operator is to guarantee the
conservation of relevant mechanics quantities which ensures a superior performance of the proposed field transfer with respect
to the standard remeshing procedure. We present the illustrative results both for an isotropic damage model and standard plasticity
model, indicating very satisfying performance. 相似文献
7.
8.
In this work we discuss the finite element model using the embedded discontinuity of the strain and displacement field, for
dealing with a problem of localized failure in heterogeneous materials by using a structured finite element mesh. On the chosen
1D model problem we develop all the pertinent details of such a finite element approximation. We demonstrate the presented
model capabilities for representing not only failure states typical of a slender structure, with crack-induced failure in
an elastic structure, but also the failure state of a massive structure, with combined diffuse (process zone) and localized
cracking. A robust operator split solution procedure is developed for the present model taking into account the subtle difference
between the types of discontinuities, where the strain discontinuity iteration is handled within global loop for computing
the nodal displacement, while the displacement discontinuity iteration is carried out within a local, element-wise computation,
carried out in parallel with the Gauss-point computations of the plastic strains and hardening variables. The robust performance
of the proposed solution procedure is illustrated by a couple of numerical examples. Concluding remarks are stated regarding
the class of problems where embedded discontinuity finite element method (ED-FEM) can be used as a favorite choice with respect
to extended FEM (X-FEM). 相似文献
9.
In this work we develop a geometrically nonlinear version of the method of incompatible modes, suitable for quasi-incompressible
finite deformation hyperelasticity. The proposed method is featuring the principal axis representation of the theory, facilitating
the choice of the strain energy function (in terms of the principal stretches) and simplifying the stress computation. The
choice of the spatial Cauchy-Green strain measure, leading to a very sparse structure of the strain-displacement operators,
and the operator split solution of equilibrium equations, leading to reduced secondary storage requirements, further increase
the computational efficiency. A set of numerical examples is used to illustrate a robust performance of the constructed plane
strain element with a single incompatible mode in quasi-incompressible deformation patterns.
Received 14 December 1998 相似文献
10.
Damijan Markovic K. C. Park Adnan Ibrahimbegovic 《International journal for numerical methods in engineering》2007,70(2):163-180
A flexibility‐based component mode synthesis (CMS) is proposed for reduced‐order modelling of dynamic behaviour of large structures. The approach employs partitioning via the localized Lagrange multiplier method. The use of the localized Lagrange multipliers leads to, unlike the classical Lagrange multipliers, a linearly independent set of interface forces without any redundancies at multiply connected interface nodes. The flexibility‐based CMS method has shown significant advantages over the classical Craig–Bampton method. A key feature of the method is its substructural mode selection criterion that is independent of loading conditions. Unlike the majority of available CMS approaches, where one retains the full dimension of partition boundary degrees of freedom (DOFs), the flexibility‐based method allows to reduce significantly the interface DOFs. The reduction of interface DOFs represents the major contribution of the present communication. The efficiency of the proposed approach is demonstrated on an analysis of a simple plate partitioned and of a more complex 3D structure, both partitioned into several substructures. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献