A Finite-Element Work-Hardening Plasticity Model of the Uniaxial Compression and Subsequent Failure of Porous Cylinders Including Effects of Void Nucleation and Growth—Part II: Localization and Fracture Criteria

1996 ◽  
Vol 118 (2) ◽  
pp. 169-178 ◽  
Author(s):  
J. H. Lee ◽  
Y. Zhang
Keyword(s):  
Finite Element ◽  
Uniaxial Compression ◽  
Void Nucleation ◽  
Maximum Shear Stress ◽  
Stress Triaxiality ◽  
Void Coalescence ◽  
Plasticity Model ◽  
Fracture Criteria ◽  
Mixed Hardening ◽  
Porous Cylinders

In Part I [1] of this paper, Gurson’s mixed hardening plasticity model with strain and stress-controlled nucleations, was used in a large deformation finite element program to study the plastic flow and damage in the uniaxial compression of cylinders under sticking friction. Due to low stress triaxiality at the bulge of the cylinders, it was found that localization may occur before void coalescence. In this paper, necessary conditions of localizations are analyzed for the axial compression of porous cylinders under sticking friction. Shear band type of localization with a normal mode of fracture has been predicted for the majority of the cases studied. Various existing localization conditions and fracture criteria are assessed using the results from the simulation. The maximum shear stress at failure is approximately constant and a constant critical damage can not be found.

A Finite-Element Work-Hardening Plasticity Model of the Uniaxial Compression and Subsequent Failure of Porous Cylinders Including Effects of Void Nucleation and Growth—Part I: Plastic Flow and Damage

1994 ◽  
Vol 116 (1) ◽  
pp. 69-79 ◽  
Author(s):  
J. H. Lee ◽  
Y. Zhang
Keyword(s):  
Finite Element ◽  
Uniaxial Compression ◽  
Plastic Flow ◽  
Void Fraction ◽  
Void Nucleation ◽  
Stress Triaxiality ◽  
Nucleation And Growth ◽  
Plasticity Model ◽  
Mixed Hardening ◽  
Void Nucleation And Growth

Gurson’s mixed hardening plasticity model (which takes into account the progressive damage due to void nucleation and growth of an initially dense material), with strain and stress-controlled nucleations, was used in a large deformation finite element program to study the plastic flow and damage in the uniaxial compression of cylinders under sticking friction. Effects of strain hardening, nucleation models, yield surface curvature, and geometry on the distributions and evolutions of stresses, strains, mean stress, void fractions, and coalescence are studied in detail. Using Gurson’s isotropic hardening model, positive mean and axial stresses developed at the bulge of the cylinder with growth of voids at latter stages of deformation. Due low stress triaxiality (Σm/σe<0.6) at the bulge, the process is nucleation rather than growth dominated for the majority of the cases studied. At failure, the maximum void fraction at the bulge among all cases studied is 0.085 and is far less than the critical void fraction (≈0.15) for coalescence.

Finite Element Modeling of Ductile Tearing of Pipeline-Steel in Cracked Plates

2004 ◽  
Author(s):  
Yu Chen ◽  
Steve Lambert
Keyword(s):  
Finite Element ◽  
Void Nucleation ◽  
Pipeline Steel ◽  
Damage Model ◽  
Tensile Load ◽  
Maximum Load ◽  
Void Coalescence ◽  
Ductile Tearing ◽  
Numerical Predictions ◽  
Measured Load

The purpose of this work was to develop a three-dimensional finite element model to simulate ductile tearing in pipeline-steels. The measured load versus displacement histories for single edge notch tension (SENT) and surfaced-cracked wide plate specimens, both made of X-70 pipeline-steel plates and subject to tensile load, were numerically predicted using the proposed damage model. In the numerical model, progressive damage was restricted to a predetermined ductile tearing zone. The material damage behaviour in this tearing zone was described in terms of a Gurson-Tvergaard (G-T) isotropic constitutive model, which accounts for micro-void nucleation and growth. The criterion for the onset of void coalescence was determined via the Thomason criterion. Experimentally measured load-displacement histories for all specimens were accurately reproduced by the proposed model, irrespective of different plate width, thickness and crack configurations. The numerical predictions were in good agreement with experimental test data in terms of both the maximum load and the corresponding displacement at maximum load. The proposed damage model was also used to numerically estimate the effect of crack growth on maximum load for these cracked specimens. The results in this paper demonstrate the potential of the proposed damage model as an engineering tool for analyzing ductile tearing in application to defect assessment of surface cracked pipes.

Damage-Based Finite Element Modeling of Stretch Flange Forming of Aluminium-Magnesium Alloy

2006 ◽  
Vol 519-521 ◽  
pp. 815-820 ◽  
Author(s):  
Zeng Tao Chen ◽  
Michael J. Worswick ◽  
David J. Lloyd
Keyword(s):  
Finite Element ◽  
Void Nucleation ◽  
Material Model ◽  
Void Coalescence ◽  
Particle Fraction ◽  
Element Calculation ◽  
Critical Porosity ◽  
Explicit Finite Element ◽  
Metallurgical Analysis ◽  
Flange Forming

The numerical simulation of the stretch flange forming operation of Al-Mg sheet AA5182 was conducted with an explicit finite element code, LS-DYNA. A Gurson-Tvergaard- Needleman (GTN)-based material model was used in the finite element calculation. A strain controlled void nucleation rule was adopted with void nucleating particle fraction measured directly from the as-received Al-Mg sheet. Parametric study was performed to examine the effect of void nucleation strain on the predicted onset of ductile fracture. Critical porosity levels determined through quantitative metallurgical analysis were adopted to predict the commencement of void coalescence in the GTN model. The numerical results were compared to the experimental ones and an applicable void nucleation strain was suggested.

scholarly journals On localization and void coalescence as a precursor to ductile fracture

2015 ◽  
Vol 373 (2038) ◽  
pp. 20140121 ◽  
Author(s):  
C. Tekoğlu ◽  
J. W. Hutchinson ◽  
T. Pardoen
Keyword(s):  
Ductile Fracture ◽  
Void Nucleation ◽  
High Stress ◽  
Three Dimensional ◽  
Stress Triaxiality ◽  
Normal Band ◽  
Void Coalescence ◽  
Softening Effect ◽  
Damage And Failure ◽  
Doubly Periodic Array

Two modes of plastic flow localization commonly occur in the ductile fracture of structural metals undergoing damage and failure by the mechanism involving void nucleation, growth and coalescence. The first mode consists of a macroscopic localization, usually linked to the softening effect of void nucleation and growth, in either a normal band or a shear band where the thickness of the band is comparable to void spacing. The second mode is coalescence with plastic strain localizing to the ligaments between voids by an internal necking process. The ductility of a material is tied to the strain at macroscopic localization, as this marks the limit of uniform straining at the macroscopic scale. The question addressed is whether macroscopic localization occurs prior to void coalescence or whether the two occur simultaneously. The relation between these two modes of localization is studied quantitatively in this paper using a three-dimensional elastic–plastic computational model representing a doubly periodic array of voids within a band confined between two semi-infinite outer blocks of the same material but without voids. At sufficiently high stress triaxiality, a clear separation exists between the two modes of localization. At lower stress triaxialities, the model predicts that the onset of macroscopic localization and coalescence occur simultaneously.

Analysis of the Necking Behaviors with the Crystal Plasticity Model Using 3-Dimensional Shaped Grains

2013 ◽  
Vol 684 ◽  
pp. 357-361 ◽  
Author(s):  
Jong Bong Kim ◽  
Jeong Whan Yoon
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Crystal Plasticity ◽  
Void Nucleation ◽  
Damage Model ◽  
Initial Imperfection ◽  
Plasticity Model ◽  
Element Analysis ◽  
3 Dimensional ◽  
Crystal Plasticity Model

Without initial imperfection and damage evolution model, it is difficult to analyze the necking behavior by finite element analysis with continuum theory. Moreover, the results are greatly dependent on the size of the initial imperfection. In order to predict necking phenomenon without geometric imperfection, in this study, a crystal plasticity model was introduced in the 3-dimensional finite element analysis of tensile test. Grains were modeled by an octahedron and different orientations were allocated to each grain. Damage model was also used to predict the sudden drop of load carrying capacity after necking and to reflect the void nucleation and growth on the severely deformed region. Well-known Cockcroft-Latham damage model was used. Void nucleation, growth and coalescence behavior during necking were predicted reasonably.

scholarly journals Effect of Stress Triaxiality on Plastic Damage Evolution and Failure Mode for 316L Notched Specimen

Metals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 1067 ◽  
Author(s):  
Peng ◽  
Wang ◽  
Dai ◽  
Liu ◽  
Liu ◽  
...  
Keyword(s):  
Finite Element ◽  
Finite Element Simulation ◽  
Failure Mode ◽  
Damage Evolution ◽  
Stress Triaxiality ◽  
Image Correlation ◽  
Void Coalescence ◽  
Notched Specimen ◽  
Plastic Damage ◽  
Element Simulation

To reveal the effect of stress triaxiality on plastic damage evolution and failure mode, 316L notched specimens with different notch sizes are systematically investigated by digital image correlation (DIC) observation, plastic damage analysis by finite element simulation, and void mesoscopic observation. It was found that the plastic damage evolution and failure mode are closely related with notch radius and stress triaxiality. The greater the stress triaxiality at the root is, the greater the damage value at the root is and the earlier the fracture occurs. Moreover, void distribution by mesoscopic observation agrees well with damage distribution observed by finite element simulation with the Gurson-Tvergaard-Needleman (GTN) damage model. It is worth noting that, with the increase in stress triaxiality, the failure mode of notched specimen changes from ductility fracture with void coalescence at the center position to crack initiation at the notch root, from both mesoscopic observation and damage simulation.

scholarly journals Crystal plasticity-based micromechanical finite element modelling of ductile void growth for an aluminium alloy under multiaxial loading conditions

2018 ◽  
Vol 233 (1) ◽  
pp. 52-62
Author(s):  
He-Jie Guo ◽  
Dong-Feng Li
Keyword(s):  
Finite Element ◽  
Single Crystal ◽  
Aluminium Alloy ◽  
Crystal Plasticity ◽  
Void Growth ◽  
Crystallographic Orientation ◽  
Stress Triaxiality ◽  
Void Coalescence ◽  
Stress Strain ◽  
Crystallographic Slip

This work proposes a crystal plasticity-based micromechanical finite element model to account for the inelastic crystallographic slip in an aluminium alloy and its effect on the development of micro-voids. Three-dimensional unit cell with periodic boundary conditions is used to represent the porous single crystal, which is subject to multiaxial external loads with constant stress triaxiality. The effects of stress triaxiality and crystallographic orientation on the ductile failure response for the porous single crystal are then quantified. Through the Taylor–Reuss mean field homogenisation, the stress–strain responses for porous polycrystal under multiaxial stress states are also investigated and compared with the conventional modelling results. The present work indicates that void coalescence strain at single crystal level strongly depends on the crystallographic orientation, particularly when stress triaxiality is low, and the overall stress–strain response of porous polycrystal can be affected by the crystallographic slip-based micro-void growth and polycrystallinity of the material.

Atomistic simulation of the uniaxial compression of black phosphorene nanotubes

2018 ◽  
Author(s):  
Van-Trang Nguyen ◽  
Minh-Quy Le
Keyword(s):  
Finite Element Method ◽  
Molecular Dynamics ◽  
Finite Element ◽  
Uniaxial Compression ◽  
Critical Stress ◽  
Atomistic Simulation ◽  
Critical Strain ◽  
Bond Breaking ◽  
Black Phosphorene ◽  
Weber Potential

We study through molecular dynamics finite element method with Stillinger-Weber potential the uniaxial compression of (0, 24) armchair and (31, 0) zigzag black phosphorene nanotubes with approximately equal diameters. Young's modulus, critical stress and critical strain are estimated with various tube lengths. It is found that under uniaxial compression the (0, 24) armchair black phosphorene nanotube buckles, whereas the failure of the (31, 0) zigzag one is caused by local bond breaking near the boundary.

An Eight-Node Hexahedral Finite Element with Rotational DOFs for Elastoplastic Applications

2019 ◽  
Vol 11 (1) ◽  
pp. 54-66
Author(s):  
Ayoub Ayadi ◽  
Kamel Meftah ◽  
Lakhdar Sedira ◽  
Hossam Djahara
Keyword(s):  
Mathematical Model ◽  
Finite Element ◽  
Plastic Zone ◽  
Displacement Vector ◽  
Small Strain ◽  
Benchmark Problems ◽  
Plasticity Model ◽  
Vector Approximation ◽  
Calculation Code

Abstract In this paper, the earlier formulation of the eight-node hexahedral SFR8 element is extended in order to analyze material nonlinearities. This element stems from the so-called Space Fiber Rotation (SFR) concept which considers virtual rotations of a nodal fiber within the element that enhances the displacement vector approximation. The resulting mathematical model of the proposed SFR8 element and the classical associative plasticity model are implemented into a Fortran calculation code to account for small strain elastoplastic problems. The performance of this element is assessed by means of a set of nonlinear benchmark problems in which the development of the plastic zone has been investigated. The accuracy of the obtained results is principally evaluated with some reference solutions.

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