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• A comparative study on finite elements for capturing strong discontinuities: E-FEM vs X-FEM

  J. Oliver, A. Huespe, P. Sánchez

  Computer Methods in Applied Mechanics and Engineering (2006). Vol. 195 (37-40), pp. 4732-4752

  
  

  Abstract

  A comparative study on finite elements for capturing strong discontinuities by means of elemental (E-FEM) or nodal enrichments (X-FEM) is presented. Based on the same constitutive model (continuum damage) and linear elements (triangles and tetrahedra) optimized implementations of both types of enrichments in the same non-linear code are tested for a representative set of 2D and 3D crack propagation examples. It is shown that both methods provide the same qualitative and quantitative results for enough refined meshes. For the performed tests, E-FEM exhibited, in general, a higher accuracy, mostly for coarse meshes, whereas, convergence rate with mesh refinement, which is super-linear, showed slightly higher for X-FEM. As for the computational costs for single crack modelling X-FEM showed, depending on the case, from 1.1 to about 2.5 times more expensive than E-FEM. For multiple cracks, the computational cost of E-FEM keeps constant, whereas the cost associated to X-FEM increases linearly with the number of modelled cracks

  Abstract
  A comparative study on finite elements for capturing strong discontinuities by means of elemental (E-FEM) or nodal enrichments (X-FEM) is presented. Based on the same constitutive [...]

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• On the fracture models determined by the continuum-strong discontinuity approach

  A. Huespe, J. Oliver, M. Gómez, S. Blanco, D. Linero

  International Journal of fracture (2006). Vol. 137 (1-4), pp. 211-229

  
  

  Abstract

  The paper focuses on the Continuum Strong Discontinuity Approach (CSDA) to fracture mechanics, and the traction-separation cohesive laws induced from continuum dissipative models as their projections onto the failure interface. They are compared with the cohesive laws commonly used for the fracture simulation in quasi-brittle materials, typically concrete. Emphasis is placed in the analysis of the mechanical stress-strain states induced by the CSDA into the fracture process zone: first when the damage mechanism is initiated and, after, when the cohesive model determines the crack response. The influence of the material parameters, particularly the fracture energy and the initial continuum softening modulus, in the obtained phenomenological responses is also analyzed. Representative numerical solutions of fracture problems are finally presented

  Abstract
  The paper focuses on the Continuum Strong Discontinuity Approach (CSDA) to fracture mechanics, and the traction-separation cohesive laws induced from continuum dissipative [...]

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• On numerical simulation of powder compaction process: powder transfer modelling and characterisation

  J. Cante, J. Oliver, C. González, J. Calero, F. Benítez

  Powder Metallurgy (2005). Vol. 45 (1), pp.85-92

  
  

  Abstract

  A numerical model for the powder transfer stage in powder metallurgy cold compaction processes, and the corresponding material characterisation procedure, are proposed. They have been designed on the basis of the following requirements: robust and consistent computational mechanics ingredients, reliability of the obtained results for practical processes in powder metallurgy and industrial viability in the sense that characterisation of any mixture doesn't require either much effort or much time of the enduser. The starting point is a previously developed numerical model for powder compaction, formulated in terms of the large plastic deformation theory, which requires calibration of four parameters controlling the evolution of the yield surface. This calibration, which had been successfully carried out in the past in a range of moderate to high densities, is now extended to very low densities in order to make numerical simulations able to deal with compaction processes involving relevant powder transfer stages. To circumvent the difficulties inherent to direct measurements of very low powder densities, a simple apparatus, which allows studying the powder motion in the chamber, has been designed to provide an indirect way of calibration. On this basis, a set of calibration experiments is proposed. The proposed methodology appears to be simple and industrially viable. Although in the work it is applied to the specific constitutive model used by the authors, it also appears available for other families of constitutive models for powder compaction. As a relevant result, this would allow the same constitutive model to be used, via only the appropriated material characterisation, for simulation of densification in powder transfer stages as well as in pure compaction stages

  Abstract
  A numerical model for the powder transfer stage in powder metallurgy cold compaction processes, and the corresponding material characterisation procedure, are proposed. They [...]

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• Theoretical and computational issues in modelling material failure in strong discontinuity scenarios

  J. Oliver, A. Huespe

  Computer Methods in Applied Mechanics and Engineering (2004). Vol. 193 (27-29), pp. 2987-3014

  
  

  Abstract

  The paper deals with several aspects related to numerical modelling of material failure in strong discontinuity settings: (a) the onset and development of local material failure in terms of continuum constitutive models equipped with strain softening. Closed forms formulas for the solutions of the discontinuous material bifurcation problem are given for a class of those models; (b) finite elements with embedded discontinuities: nodal and elemental enrichments families are formulated in the continuum strong discontinuity approach (CSDA); (c) instability treatment: a discrete viscous perturbation method at the failure surfaces is presented as a way to substantially improve the robustness of the numerical simulations

  Abstract
  The paper deals with several aspects related to numerical modelling of material failure in strong discontinuity settings: (a) the onset and development of local material failure [...]

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• Continuum approach to material failure in strong discontinuity settings

  J. Oliver, A. Huespe

  Computer Methods in Applied Mechanics and Engineering (2004). Vol. 193 (30-32), pp. 3195-3220

  
  

  Abstract

  The paper focuses the numerical modelling of material failure in a strong discontinuity setting using a continuum format. Displacement discontinuities, like fractures, cracks, slip lines, etc., are modelled in a strong discontinuity approach, enriched by a transition from weak to strong discontinuities to get an appropriate representation of the fracture process zone. The introduction of the strong discontinuity kinematics automatically projects any standard dissipative constitutive model, equipped with strain softening, into a discrete traction–separation law that is fulfilled at the discontinuity interface. Numerical issues like a global discontinuity tracking algorithm via a heat conduction-like problem are also presented. Some representative numerical simulations illustrate the performance of the presented approach

  Abstract
  The paper focuses the numerical modelling of material failure in a strong discontinuity setting using a continuum format. Displacement discontinuities, like fractures, cracks, [...]

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• Computational modeling of cracking of concrete in strong discontinuity settings

  J. Oliver, A. Huespe, M. Gómez, S. Blanco

  Computers and Concrete (2004). Vol. 1 (1), pp. 61-76

  
  

  Abstract

  The paper is devoted to present the Continuum Strong Discontinuity Approach (CSDA) and to examine its capabilities for modeling cracking of concrete. After introducing the main ingredients of the CSDA, an isotropic continuum damage model, which distinguishes tension and compression states, is used to implicitly induce a projected traction separation-law that rules the cracking phenomena. Criteria for onset and propagation of material failure and specific finite elements with embedded discontinuities are also briefly sketched. Finally, some representative numerical simulations of cracking, in plain and reinforced concrete specimens, using the CSDA are presented.

  Abstract
  The paper is devoted to present the Continuum Strong Discontinuity Approach (CSDA) and to examine its capabilities for modeling cracking of concrete. After introducing the [...]

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• On the strong discontinuity approach in finite deformation settings

  J. Oliver, A. Huespe, M. Valentín, E. Samaniego

  International Journal for Numerical Methods in Engineering (2003). Vol. 56 (7), pp. 1051-1082

  
  

  Abstract

  Taking the strong discontinuity approach as a framework for modelling displacement discontinuities and strain localization phenomena, this work extends previous results in infinitesimal strain settings to finite deformation scenarios. By means of the strong discontinuity analysis, and taking isotropic damage models as target continuum (stress–strain) constitutive equation, projected discrete (tractions–displacement jumps) constitutive models are derived, together with the strong discontinuity conditions that restrict the stress states at the discontinuous regime. A variable bandwidth model, to automatically induce those strong discontinuity conditions, and a discontinuous bifurcation procedure, to determine the initiation and propagation of the discontinuity, are briefly sketched. The large strain counterpart of a non-symmetric finite element with embedded discontinuities, frequently considered in the strong discontinuity approach for infinitesimal strains, is then presented. Finally, some numerical experiments display the theoretical issues, and emphasize the role of the large strain kinematics in the obtained results

  Abstract
  Taking the strong discontinuity approach as a framework for modelling displacement discontinuities and strain localization phenomena, this work extends previous results in [...]

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• A study on finite elements for capturing strong discontinuities

  J. Oliver, A. Huespe, E. Samaniego

  International Journal for Numerical Methods in Engineering (2003). Vol. 56 (14), pp. 2135-2161

  
  

  Abstract

  The work focuses on the presently existing families of finite elements with embedded discontinuities and explores the possibilities of obtaining symmetric statically consistent finite elements that alleviate the stress-locking problem. For this purpose, mixed (reduced integration) and assumed enhanced strain techniques are applied to the basic symmetric four-noded element. Numerical simulations show the effectiveness of the proposed measures.

  Abstract
  The work focuses on the presently existing families of finite elements with embedded discontinuities and explores the possibilities of obtaining symmetric statically consistent [...]

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• From continuum mechanics to fracture mechanics: the strong discontinuity approach

  J. Oliver, A. Huespe, M. Pullido, E. Chaves

  Engineering Fracture Mechanics (2002). Vol. 69 (2), pp. 113-136

  
  

  Abstract

  The paper deals with the strong discontinuity approach and shows the links with the decohesive fracture mechanics provided by that approach. On the basis of 1D continuum damage models it is shown that, by introducing some few ingredients like the strong discontinuity kinematics, discrete constitutive models (traction vs. displacement jumps) are automatically induced. For the general 2D–3D cases it is shown that the weak discontinuity concept is an additional ingredient, necessary in order to fulfill the strong discontinuity conditions, which allows to establish additional links with the fracture process zone concept. Also classical fracture mechanics properties as the fracture energy are related to the continuum model properties in a straightforward manner

  Abstract
  The paper deals with the strong discontinuity approach and shows the links with the decohesive fracture mechanics provided by that approach. On the basis of 1D continuum damage [...]

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• On the discrete constitutive models induced by strong discontinuity kinematics and continuum constitutive equations

  J. Oliver

  International Journal of Solids and Structures (2000). Vol. 37 (48-50), pp. 7207-7229

  
  

  Abstract

  On the basis of continuum constitutive models (stress vs. strain), the introduction of strong discontinuity kinematics (considering jumps in the displacement fields across a discontinuity interface) induces projected discrete constitutive models (traction-displacement jumps) in a consistent manner. Therefore, this projection provides possible links between the classical continuum strain-localization analysis and the non-linear (decohesive) fracture mechanics techniques. The strong discontinuity analysis shows that (bandwidth based) regularization of the hardening/softening parameter is the crucial modification to be done on the continuum model to achieve such a projection, and it also provides the strong discontinuity conditions that set restrictions on the stress state compatible with bifurcations in a strong discontinuity format. The methodology is illustrated on the basis of two classical families of non-linear constitutive models (scalar continuum damage and elasto-plasticity) for which the corresponding discrete constitutive models and the strong discontinuity conditions are derived

  Abstract
  On the basis of continuum constitutive models (stress vs. strain), the introduction of strong discontinuity kinematics (considering jumps in the displacement fields across [...]

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