H. Kuna-Ciskal

Bio: H. Kuna-Ciskal is an academic researcher. The author has contributed to research in topics: Constitutive equation & Fracture (geology). The author has an hindex of 3, co-authored 3 publications receiving 67 citations.

Implementation of a Model of Coupled Elastic-Plastic Unilateral Damage Material to Finite Element Code

Abstract: The continuum damage mechanics-based elasto-plastic damage theory, that extends the total form of Hayakawa and Murakami equations, is developed. Weak elastic-plastic dissipation coupling is assumed by the use of two dissipation potentials, plastic and damage, where only isotropic plasticity and damage hardening is included, whereas kinematic hardening is not accounted for. Unilateral damage condition, based on the concept of generalized projection operators, accounts for a partial damage deactivation, which allows for an influence of negative principal components of the stress tensor on damage evolution. The incremental representation of the elastic-damage constitutive equations is derived. Both elastic-damage and plastic-damage compliance matrices are developed for plane stress condition, and implemented to ABAQUS finite element code by the user-supplied procedure for non-standard material properties. Effective computation algorithm for plastic and damage loading/unloading conditions based on the doubly ...

Anisotropic Elastic-Brittle-Damage and Fracture Models Based on Irreversible Thermodynamics

Abstract: Anisotropic damage evolution and crack propagation in elastic-brittle materials is analyzed by the concepts of Continuum Damage Mechanics (CDM) and Finite Element Method FEM (ABAQUS). The original total formulation of the Murakami-Kamiya (MK) model of elastic-damage material is extended and used for damage anisotropy and fracture prediction in concrete. The incremental formulation of the stress-strain equations is developed by the use of the tangent elastic-damage stiffness. The Helmholtz free energy representation is discussed. The unilateral crack opening/closure effect is incorporated in such a way that the continuity requirement during unloading holds. The general failure criterion is proposed by checking the positive definiteness of the Hessian matrix of the free energy function. The Local Approach to Fracture (LAF) by FEM is applied to both the pre-critical damage evolution that precedes the crack initiation, and the post-critical damage/fracture interaction. Crack is modeled as the assembly of failed finite elements in the mesh, the stiffness of which is reduced to zero when the critical points at stress-strain curves are reached. Another way to model crack consists in releasing of the kinematic constrains in the nodes. The developed constitutive model is capable of capturing anisotropic damage evolution and crack growth in 2D structure subjected to the quasistatic or cyclic mechanical or thermal loadings. Different damage evolution in tension or compression, as well as the corresponding fracture modes may be analysed.

Theoretical Formulation of a Coupled Elastic—Plastic Anisotropic Damage Model for Concrete using the Strain Energy Equivalence Concept

Abstract: An anisotropic damage constitutive model for concrete is developed within the framework of elastoplasticity and continuum damage mechanics. The transformation from the effective (undamaged) to the damaged configuration in the elastic regime is obtained by using the hypothesis of elastic strain energy equivalence. Damage in plasticity is accounted for by developing a new formulation relating the plastic strains rate tensors in the effective and damaged configurations. Two anisotropic damage criteria are introduced to account for the different concrete behavior effects under tensile and compressive loadings. The total stress is decomposed into tensile and compressive components in order to satisfy these damage criteria. The plasticity yield criterion presented in this work accounts for the spectral decomposition of the stress tensor and will be used simultaneously with the damage criteria. The transformation of stresses from the effective to the damaged configuration is achieved by using a fourth order transformation tensor that is based on second order tensile and compressive damage tensors. Expressions are derived for the elastoplastic tangent operator in the effective and damaged configurations. The formulations are derived consistently based on sound thermodynamic principles.

Damage mechanics model for brittle failure of transversely isotropic solids : finite element implementation

Abstract: A new continuum damage model, the wing crack damage (WCD) model, was developed for the analysis of brittle failure of transversely isotropic solids. Special attention was paid to the analysis of axial splitting under compression and tensile cracking under tension. In addition to the WCD model a three-dimensional version of the damage model proposed by Murakami and Kamiya was enhanced and implemented in ABAQUS/Standard FE software. The proposed WCD model is based on the use of the damage vector. The vector represents both the normal direction of the surface of the plane crack and the size of the damaged area. Damaging induces anisotropy in an originally transversely isotropic material. The evolution equations for damage are motivated by the wing crack growth mechanism. The evolution is based on propagation of pre-existing damage. The proposed model enables modelling of pre-existing cracks. The feature can be exploited in studying the effect of orientation and size distribution of pre-existing cracks on the failure of materials. The model was implemented in ABAQUS/Standard FE software as a user subroutine. The unsymmetrical behaviour of cracked materials under tension and compression due to the opening and closure of cracks is taken into account in the proposed model. In the work it was shown that the widely used strain-based crack closure criteria cannot be reliably applied in a two- and three-dimensional stress state. To attain a deformation localisation zone of finite width, a damage rate-dependent damage surface was introduced. The validity of the proposed model was verified by testing it against five basic structures composed of known natural materials (ice, marble and concrete). The numerical simulations revealed the capability of the model in modelling brittle failure modes of transversely isotropic materials.%%%%Tutkimuksessa on esitetty kaksi vauriomekaniikkaan (Continuum damage mechanics) perustuvaa materiaalimallia: Murakami Kamiyan (MK) malli, seka uusi "wing crak damage" -malli (WCD). Molemmat mallit on liitetty ABAQUS-elementtimenetelmaohjelmistoon UMAT-aliohjelmana. Esitetty uusi WCD-malli on tarkoitettu transversaali-isotrooppisten materiaalien haurasmurtuman mallintamiseen. Erityista huomiota on kiinnitetty yksiaksiaalisessa puristuksessa tapahtuvan kuormituksen kanssa yhdensuuntaisen halkeamisen seka yksiaksiaalisessa vedossa tapahtuvan kuormitusta vastaan kohtisuorassa olevan saroytymisen mallintamiseen. Esitetty WCD-malli perustuu "vauriovektorin" kayttoon. Vauriovektori edustaa seka tasomaisen saron normaalin suuntaa etta vaurioituneen alueen kokoa. Vaurioitumisen vuoksi transversaali-isotrooppisesta materiaalista tulee anisotrooppista. Vaurion kasvumekanismi simuloi siipisaron (wing crack) kasvumekanismia. Uusi WCD-malli mahdollistaa materiaalissa ennen kuormitusta olevien alkusarojen mallintamisen. Piirretta voidaan hyodyntaa tutkittaessa alkusarojen suunnan ja suuruuden vaikutusta materiaalin vaurioitumiseen. Halkeilleen materiaalin epasymmetrinen kayttaytyminen vedossa ja puristuksessa…

Implementation of a Model of Coupled Elastic-Plastic Unilateral Damage Material to Finite Element Code

Abstract: The continuum damage mechanics-based elasto-plastic damage theory, that extends the total form of Hayakawa and Murakami equations, is developed. Weak elastic-plastic dissipation coupling is assumed by the use of two dissipation potentials, plastic and damage, where only isotropic plasticity and damage hardening is included, whereas kinematic hardening is not accounted for. Unilateral damage condition, based on the concept of generalized projection operators, accounts for a partial damage deactivation, which allows for an influence of negative principal components of the stress tensor on damage evolution. The incremental representation of the elastic-damage constitutive equations is derived. Both elastic-damage and plastic-damage compliance matrices are developed for plane stress condition, and implemented to ABAQUS finite element code by the user-supplied procedure for non-standard material properties. Effective computation algorithm for plastic and damage loading/unloading conditions based on the doubly ...