Two mechanisms of ductile fracture: void by void growth versus multiple void interaction

Tvergaard, Viggo; Hutchinson, John W.

doi:10.1016/s0020-7683(02)00168-3

Cited by 176 publications

(190 citation statements)

References 14 publications

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“…For the higher initial void volume fraction of f 0 0.1, the R-curves exhibit a wider region of increasing toughness until the steady-state value J ss R is reached. This behavior coincides with the results of [11] who observed a transition from void by void crack growth to a multiple void mechanism for increasing initial void volume fraction. …”

Section: Resultssupporting

confidence: 91%

Simulation of Crack Propagation under Small‐Scale Yielding by means of a Non‐local GTN‐Model

Hütter

Linse

Mühlich

et al. 2011

Proc Appl Math and Mech

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Today, the local approach to fracture is widely applied to simulate the failure of specimens. For ductile damage processes the Gurson-Tvergaard-Needleman model is the quasi-standard. In the last time non-local extensions allowed a mesh-size independent simulation of crack growth. However, most publications dealing with this subject focus upon the convergence regarding global quantities such as the load-displacement relation. Minor attention is paid to the fields directly at the crack tip. Correspondingly, the interrelationship between the intrinsic length of the model and relevant microscopic damage processes at the crack tip is only partly established until now. In the present study the crack propagation is simulated for an implicitly gradient enriched GTN-model within a boundary layer in order to overcome influences of the specimen geometry. The different stages of damage evolution are resolved by a fine mesh. ModelIn order to describe the ductile crack initiation and propagation a non-local extension of the widely used GURSON [1] model with the modifications of TVERGAARD and NEEDLEMAN (GTN,[2,3]) is employed. For this purpose, the volumetric plastic strain rate ε vol in the evolution equation of the local model for the void volume fraction f is replaced by its non-local counterpart ε nl using an implicit gradient enrichment [4]:Thereby, an intrinsic length scale l nl is introduced via the prefactor of the LAPLACE-operator ∆Ô Õ. The formulation can be interpreted as a spatial average over the local volumetric plastic strain ε vol around the actual point. The crack propagation behavior of the model is investigated under small-scale yielding conditions by means of a boundary layer approach. This has the advantage that a possible influence of the specimen geometry can be excluded. The hardening is described by a power law (exponent N ). In the FE-model elements with quadratic shape functions for the displacements and linear ones for the non-local strains are used, for details see [4]. Dynamic simulations are performed with implicit time integration under quasi-static loading [5].In the initial loading stages the plastic deformations occur within a region much smaller than the intrinsic length scale l nl . Hence, at this stage no void growth but pure crack tip blunting is predicted by the model which is physically reasonable. In order to handle the strain singularity at the crack tip coinciding with blunting of an ideal sharp crack, an initial radius is used at the crack tip, see fig. 1. This procedure allows to use elements with edge lengths h lig considerably smaller than the value of h lig Ô0.5 . . . 2.5Õ l nl used in the literature [6,7] where numerical problems with distorted elements were reported for finer meshes [7]. For comparison, simulations without rounded crack tip were performed as well. Fig. 1 Details of the finite element mesh at the crack tip with initial radius l nl ResultsFirst, simulations with a common set of parameters (f 0 0.01, f c 0.15, f f 0.25, N 0.1, E 250 σ y , ν 0.3) and several spat...

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Section: Resultssupporting

confidence: 91%

Simulation of Crack Propagation under Small‐Scale Yielding by means of a Non‐local GTN‐Model

Hütter

Linse

Mühlich

et al. 2011

Proc Appl Math and Mech

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“…It is noted that the value of c c used in an earlier analysis of crack growth through a row of discrete voids (Tvergaard and Hutchinson, 2002) was larger, 0.6 , while a smaller value 0.15 was used in a subsequent crack growth study (Tvergaard, 2007 …”

Section: Problem Formulation and Numerical Proceduresmentioning

confidence: 99%

“…Am important aspect of the present analyses is that void coalescence inside the cluster is accounted for, so that the cluster of small voids finally develops into a single larger void. Void growth and coalescence is modelled in a way rather similar to that used in studies of ductile crack growth through discretely modelled voids (Tvergaard and Hutchinson, 2002;Tvergaard, 2007).…”

Section: Introductionmentioning

confidence: 99%

Effect of void cluster on ductile failure evolution

Tvergaard

2016

Meccanica

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Document VersionABSTRACT -The behavior of a non-uniform void distribution in a ductile material is investigated by using a cell model analysis to study a material with a periodic pattern of void clusters. The special clusters considered consist of a number of uniformly spaced voids located along a plane perpendicular to the maximum principal tensile stress. A plane strain approximation is used, where the voids are parallel cylindrical holes. Clusters with different numbers of voids are compared with the growth of a single void, such that the total initial volume of the voids, and thus also the void volume fractions, are the same for the clusters and the single void. In the comparison it is essential that local void coalescence inside the clusters is accounted for, since this allows for considering the rate of growth of the single larger void that results from coalescence in the cluster. To obtain a parametric understanding, different transverse stresses on the unit cell are considered to see the influence of different levels of stress triaxiality. Also considered are different initial ratios of the void spacing to the void radius inside the clusters. And results are shown for different levels of strain hardening in the material.

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“…The nucleation, growth, and coalescence of voids under positive triaxial loads have been studied extensively by many researchers (Hammi and Horstemeyer 2007;Tvergaard and Hutchinson 2002;Horstemeyer and Gokhale 1999). McClintock (1968) performed the first theoretical analysis of void growth by studying the growth of cylindrical holes of elliptical cross section with axes parallel to the principal directions of the applied stress.…”

Section: Introductionmentioning

confidence: 99%

Micromechanisms of ductile fracturing of DH-36 steel plates under impulsive loads and influence of polyurea reinforcing

Amini

Nemat‐Nasser

2010

Int J Fract

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Micromechanisms of ductile fracturing of DH-36 steel plates subjected to blast-induced pressure loads are studied experimentally using specially designed dynamic testing facilities. The sample geometry is such that it undergoes controllable fracturing, generally initiated near its center and grows first circumferentially and then radially. Selected fractured samples are sectioned normal to the fracture surfaces, at various intervals along the length of the fracture which extends into the necked and finally to the uniformlydeformed material. The thickness profile of the sample at each cross section is analyzed using optical and scanning electron microscopy. In this manner, we have been able to examine the microstructural evolution that has taken place, from necking inception to fracture initiation and growth, leading to a better understanding of the underpinning mechanisms of the fracturing of this material. The observed ductile fracture involves void nucleation, and void growth and coalescence, creating dimpled fracture surfaces. The examination of the microstructure of the deformed steel samples also revealed that the microstructure does not change M. R. Amini Omnicell Inc., 1201 Charleston Road, Mountain View, CA 94093, USA e-mail: mr_amini_2000@yahoo.com S. Nemat-Nasser (B) Center of Excellence for Advanced Materials, Department of Mechanical and Aerospace Engineering, University of California, La Jolla, San Diego, CA 92093-0416, USA e-mail: sia@ucsd.edu significantly during the deformation and that there are no shearbands developing in and around the fracture zones. Based on the observed micro-scale deformation, a finite-element model was developed to further study the fracturing process, using a physics-based and experimentally-supported temperature-and rate-sensitive constitutive model for DH-36 steel. The finiteelement model was capable of predicting the fracture process of the steel plates rather well. Additional finiteelement simulations are performed to investigate the effect of the polyurea coating on the fracturing and fracture resistance of the plates. These also correlated well with the experimental results.

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Two mechanisms of ductile fracture: void by void growth versus multiple void interaction

Cited by 176 publications

References 14 publications

Simulation of Crack Propagation under Small‐Scale Yielding by means of a Non‐local GTN‐Model

Simulation of Crack Propagation under Small‐Scale Yielding by means of a Non‐local GTN‐Model

Effect of void cluster on ductile failure evolution

Micromechanisms of ductile fracturing of DH-36 steel plates under impulsive loads and influence of polyurea reinforcing

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