Constitutive equations of a tensorial model for ductile damage of metals

Larichkin

2017

Z. Angew. Math. Mech.

A new phenomenological model of cyclic creep, which is suitable for applications involving finite creep deformations of the material, is proposed. The model accounts for the effect of the transient increase of the creep strain rate upon the load reversal. In order to extend the applicability range of the model, the creep process is fully coupled to the classical Kachanov-Rabotnov damage evolution. As a result, the proposed model describes all the three stages of creep. Large strain kinematics is described in a geometrically exact manner using the assumption of a nested multiplicative split, originally proposed by Lion for finite strain plasticity. The model is thermodynamically admissible, objective, and w-invariant. The implicit time integration of the proposed evolution equations is discussed. The corresponding numerical algorithm is implemented into the commercial FEM code MSC.Marc. The model is validated using this code; the validation is based on real experimental data on cyclic torsion of a thick-walled tubular specimen made of the D16T aluminium alloy. The numerically computed stress distribution exhibits a "skeletal point" within the specimen, which simplifies the analysis of test data.

mentioning

confidence: 99%

“…For simplicity we assume here that the bulk modulus and the shear modulus deteriorate with the same rate. In a more general case one may introduce two different rates[50] or even two different damage variables[55,56] 6. The maximum positive eigenvalue is obtained as R → ∞.…”

mentioning

confidence: 99%

Modelling of cyclic creep in the finite strain range using a nested split of the deformation gradient

Larichkin

2017

Z. Angew. Math. Mech.

“…Different approaches to anisotropic damage can be found inMurakami and Ohno (1980);Kachanov (1986);Chaboche (1993);Krajcinovic (1996);Brünig (2001Brünig ( , 2003;Zapara et al (2010Zapara et al ( , 2012;Voyiadjis et al (2012);Tutyshkin et al (2014).…”

mentioning

confidence: 99%

Ductile damage model for metal forming simulations including refined description of void nucleation

International Journal of Plasticity

Silbermann

Ihlemann

2015

We address the prediction of ductile damage and material anisotropy accumulated during plastic deformation of metals. A new model of phenomenological metal plasticity is proposed which is suitable for applications involving large deformations of workpiece material. The model takes combined nonlinear isotropic/kinematic hardening, strain-driven damage and rate-dependence of the stress response into account. Within this model, the work hardening and the damage evolution are fully coupled. The description of the kinematics is based on the double multiplicative decomposition of the deformation gradient proposed by Lion. An additional multiplicative decomposition is introduced in order to account for the damage-induced volume increase of the material. The model is formulated in a thermodynamically admissible manner. Within a simple example of the proposed framework, the material porosity is adopted as a rough measure of damage.A new simple void nucleation rule is formulated based on the consideration of various nucleation mechanisms. In particular, this rule is suitable for materials which exhibit a higher void nucleation rate under torsion than in case of tension.The material model is implemented into the FEM code Abaqus and a simulation of a deep drawing process is presented. The robustness of the algorithm and the performance of the formulation is demonstrated.

“…Understanding the mechanisms of damage growth and healing under plastic deformation of metals is still an urgent problem. In order to solve it a theoretical framework for anisotropic ductile damage based on a physically motivated concept for changes in the void volume and shape was recently developed [6]. Strain-induced damage was experimentally determined during uniaxial compression of cylindrical metallic specimens with artificial voids represented by fully-trough drilled holes.…”

mentioning

confidence: 99%

Growth and Closure of Voids in Metals at Negative Stress Triaxialities

Zapara

Tutyshkin

Müller³

2013

KEM

Self Cite

Damage of metals subjected to large plastic deformations typical for forming processes is mainly governed by void nucleation, growth and coalescence. An opposite process may occur in deformation processes with negative stress triaxialities: the closure of strain-induced defects under large hydrostatic pressure. Understanding the mechanisms of damage growth and healing under plastic deformation of metals is still an urgent problem. In order to solve it a theoretical framework for anisotropic ductile damage based on a physically motivated concept for changes in the void volume and shape was recently developed [6]. Strain-induced damage was experimentally determined during uniaxial compression of cylindrical metallic specimens with artificial voids represented by fully-trough drilled holes. It was revealed that the governing physical mechanism of failure is a change in void shapes due to compressive stresses at low negative stress triaxialities in contrast to the growth of voids volume due to high positive stress triaxialities in the processes with dominating tensile stresses. The tensorial model presented in [6] proved to be able to describe kinetics of ductile damage, failure as the ultimate damage, and the closure of voids at negative stress triaxialities.