A Continuum Damage and Failure Model Based on Stress-State-Dependent Criteria

2012 ◽  
Author(s):  
Michael Brünig ◽  
Steffen Gerke ◽  
Vanessa Hagenbrock
Keyword(s):  
Stress State ◽  
Continuum Model ◽  
Stress Triaxiality ◽  
Failure Criteria ◽  
Basic Material ◽  
Failure Behavior ◽  
Deformation And Failure ◽  
Damage And Failure ◽  
Wide Range ◽  
The Continuum

The paper deals with the effect of stress state on inelastic deformation and failure behavior of ductile solids. The continuum model takes into account stress-state-dependence of the damage and failure criteria with different branches corresponding to different micro-mechanical mechanisms depending on the stress triaxiality and the Lode parameter. Basic material parameters are identified using various tests with smooth and differently notched tension and shear specimens. To get more insight in the complex damage and failure mechanisms on the micro-scale additional series of three-dimensional micro-mechanical numerical analyses of void-containing unit cells have been performed. These calculations cover a wide range of stress triaxialities and Lode parameters in tension, shear and compression domains. The numerical results are used to discuss general trends, to develop equations for the damage and failure criteria, and to identify corresponding parameters of the continuum model.

Modeling of Ductile Damage and Fracture Behavior Based on Different Micromechanisms

2010 ◽  
Vol 20 (4) ◽  
pp. 558-577 ◽  
Author(s):  
Michael Brünig ◽  
Daniel Albrecht ◽  
Steffen Gerke
Keyword(s):  
Continuum Model ◽  
Failure Modes ◽  
Three Dimensional ◽  
Stress Triaxiality ◽  
Yield Condition ◽  
Lode Parameter ◽  
Material Parameters ◽  
Damage And Failure ◽  
Damage And Fracture ◽  
The Continuum

The article deals with the effect of stress triaxiality on the inelastic deformation behavior of aluminum alloys. The proposed continuum model takes into account stress triaxiality dependence of the yield condition as well as of the damage criterion and the fracture condition with different branches corresponding to various damage and failure modes depending on the stress triaxiality and the Lode parameter. Results of numerical cell simulations on the microscale are presented and corresponding identification of micromechanically motivated material parameters is discussed. Furthermore, numerical results of three-dimensional macromechanical finite element analyses are compared with experimental data obtained from smooth and pre-notched tension specimens. The analyses allow verification of the continuum model and identification of further material parameters.

Ring Specimen Geometry for Determining the Ductility of Tubulars

2016 ◽  
Author(s):  
M. A. Al Khaled ◽  
I. Barsoum
Keyword(s):  
Stress State ◽  
Plane Strain ◽  
Stress Triaxiality ◽  
Ductile Failure ◽  
Pressure Vessels ◽  
Ring Specimen ◽  
Lode Parameter ◽  
Wide Range ◽  
Failure Locus

Pressure vessels designed in accordance with the ASME BPVC code are protected against local ductile failure. Recent work has shown that local ductile failure highly depends on the stress state characterized by both stress triaxiality (T) and the Lode parameter (L). In this paper, the effect of stress state on the ductility of a tubular steel is studied. Two ring specimen configurations were optimized to allow the determination of the ductile failure locus of both tensile and plane strain loadings. The geometry of both ring specimen configurations was optimized to achieve a plane strain (L = 0) condition and a generalized tension (L = −1) condition. Notches with different radii were machined on both types to achieve a wide range of stress triaxiality. Specimens were manufactured from SA-106 carbon tubular steel and were tested to determine the ductile failure loci as a function of T and L. Failure locus of SA-106 steel was constructed based on the failure instants and was found to be independent of the variation in the Lode parameter. The ASME-BPVC local failure criterion showed close agreement with experimental results.

scholarly journals Numerical analysis of stress-state-dependent damage and failure behavior of ductile steel based on biaxial experiments

2020 ◽  
Author(s):  
Michael Brünig ◽  
Marco Schmidt ◽  
Steffen Gerke
Keyword(s):  
Stress State ◽  
Numerical Analysis ◽  
Numerical Model ◽  
Evolution Equations ◽  
Image Correlation ◽  
Failure Behavior ◽  
Damage And Failure ◽  
State Dependent ◽  
Ductile Steel ◽  
Biaxial Experiments

Abstract The paper deals with a numerical model to investigate the influence of stress state on damage and failure in the ductile steel X5CrNi18-10. The numerical analysis is based on an anisotropic continuum damage model taking into account yield and damage criteria as well as evolution equations for plastic and damage strain rate tensors. Results of numerical simulations of biaxial experiments with the X0- and the H-specimen presented. In the experiments, formation of strain fields are monitored by digital image correlation which can be compared with numerically predicted ones to validate the numerical model. Based on the numerical analysis the strain and stress quantities in selected parts of the specimens are predicted. Analysis of damage strain variables enables prediction of fracture lines observed in the tests. Stress measures are used to explain different stress-state-dependent damage and failure mechanisms on the micro-level visualized on fracture surfaces by scanning electron microscopy.

New Ring Specimen Geometries for Determining the Failure Locus of Tubulars

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
M. A. Al-Khaled ◽  
I. Barsoum
Keyword(s):  
Stress State ◽  
Plane Strain ◽  
Stress Triaxiality ◽  
Ductile Failure ◽  
Pressure Vessels ◽  
Ring Specimen ◽  
Lode Parameter ◽  
Wide Range ◽  
Failure Locus

Pressure vessels designed in accordance with the ASME BPVC code are protected against local ductile failure. Recent work has shown that local ductile failure highly depends on the stress state characterized by both stress triaxiality (T) and the Lode parameter (L). In this paper, the effect of stress state on the ductility of a tubular steel is studied. Two ring specimen configurations were optimized to allow the determination of the ductile failure locus at both tensile and plane strain loadings. The geometry of both ring specimen configurations was optimized to achieve a plane strain (L=0) condition and a generalized tension (L=-1) condition. Notches with different radii were machined on both types to achieve a wide range of stress triaxiality. Specimens were manufactured from SA-106 carbon tubular steel and were tested to determine the ductile failure loci as a function of T and L. Failure locus of SA-106 steel was constructed based on the failure instants and was found to be independent of the Lode parameter. The ASME-BPVC local failure criterion showed close agreement with experimental results (EXP).

Numerical Damage Modelling of Aluminium Alloys for Wide Range of Stress Triaxiality

2014 ◽  
Vol 794-796 ◽  
pp. 646-651 ◽  
Author(s):  
Amir M. Horr ◽  
Richard Kertz ◽  
Michael Just
Keyword(s):  
Aluminium Alloys ◽  
Damage Accumulation ◽  
Pure Shear ◽  
Stress Triaxiality ◽  
Metal Alloys ◽  
Experimental Simulation ◽  
Pressure Casting ◽  
Damage Initiation ◽  
Damage And Failure ◽  
Wide Range

There have been many efforts to investigate and develop a mechanical plasticity, damage and failure models for metal alloys in the last couple of decades. These models (single and multi-damage parameters) are generally based on energy and constitutive equations to simulate the fracture and failure processes in metal alloys. The conventional fracture mechanics theory and its applications have been successfully employed to study fracture and failure processes. However, these methods have serious short comes in predicting the damage and failure in metal alloys where the fracture is dominated by the presence of defects like micro-voids (and their growth, nucleation and coalescence), oxides and inclusions. In the present study, following the in-depth study of damage initiation and progression in aluminium alloys, a frame work has been setup to develop a numerical model for damage accumulation. Based on the existing phenomenological damage theory, a mathematical basis for damage initiation and also damage accumulation under wide range of stress triaxiality (including near pure shear) has been developed. The damage model has been checked and verified using a result of experimental-simulation comparative study. The experiments have been carried out using samples made from squeezed and high pressure casting step plates. One of the main contributions of this paper is to show the advantages of using plasticity-based modified damage models to investigate the damage accumulation in cast aluminium alloys.

Crystallographic Analysis of Specimens Used for Calibrate a Failure Model for an Al 6061 – T6 Alloy

2011 ◽  
Vol 488-489 ◽  
pp. 89-92 ◽  
Author(s):  
Marco Giglio ◽  
Andrea Manes ◽  
Carlo Mapelli ◽  
Davide Mombelli ◽  
Claudio Baldizzone ◽  
...  
Keyword(s):  
Failure Criterion ◽  
Structural Integrity ◽  
Constitutive Relations ◽  
Stress Triaxiality ◽  
Failure Criteria ◽  
Crystallographic Analysis ◽  
Failure Behavior ◽  
Al 6061 ◽  
Extreme Loads ◽  
Full Scale Tests

Calibration and exploitation of failure criterion is at present a challenging field in the structural integrity scenario. Calibrated failure criteria allow the simulation/reproduction of damages using virtual approach and eventually further assessment of the residual integrity of the components. Therefore the increase of awareness in failure issues makes the numerical simulation an actual, useful and reliable tool for the analysis of complex structures under extreme loads, especially in aerospace field where full scale tests are often very expensive and difficult to carry out. With this aim, the constitutive relations of an Aluminium Al 6061-T6 alloy have been calibrated with dedicated focus on failure criterion. The results obtained have been discussed considering the crystallographic measurements that permit to point out the dissipative behavior on the basis of texture formation as a function of the load type. The final aim is to confirm and explain the different failure behavior depending on the different stress triaxiality.

scholarly journals Analysis of Damage and Failure in Anisotropic Ductile Metals Based on Biaxial Experiments with the H-Specimen

2021 ◽  
Author(s):  
M. Brünig ◽  
S. Koirala ◽  
S. Gerke
Keyword(s):  
Stress State ◽  
Image Correlation ◽  
Experimental Program ◽  
Failure Behavior ◽  
Strain Fields ◽  
Ductile Metals ◽  
Damage And Failure ◽  
Loading Direction ◽  
Principal Axes ◽  
Biaxial Experiments

Abstract Background Dependence of strength and failure behavior of anisotropic ductile metals on loading direction and on stress state has been indicated by many experiments. To realistically predict safety and lifetime of structures these effects must be taken into account in material models and numerical analysis. Objective The influence of stress state and loading direction on damage and failure behavior of the anisotropic aluminum alloy EN AW-2017A is investigated. Methods New biaxial experiments and numerical simulations have been performed with the H-specimen under different load ratios. Digital image correlation shows evolution of strain fields and scanning electron microscopy is used to visualize failure modes on fracture surfaces. Corresponding numerical studies predict stress states to explain damage and fracture processes on the micro-scale. Results The stress state, the load ratio and the loading direction with respect to the principal axes of anisotropy affect the width and orientation of localized strain fields and the formation of damage mechanisms and fracture modes at the micro-level. Conclusions The enhanced experimental program with biaxial tests considering different loading directions and load ratios is suggested for characterization of anisotropic metals.

scholarly journals Biaxial Experiments and Numerical Analysis on Stress-State-Dependent Damage and Failure Behavior of the Anisotropic Aluminum Alloy EN AW-2017A

Metals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1214
Author(s):  
Michael Brünig ◽  
Steffen Gerke ◽  
Sanjeev Koirala
Keyword(s):  
Aluminum Alloy ◽  
Stress State ◽  
Numerical Analysis ◽  
Image Correlation ◽  
Experimental Program ◽  
Failure Behavior ◽  
Strain Fields ◽  
Damage And Failure ◽  
Damage And Fracture ◽  
Loading Direction

Many experiments indicated the remarkable dependence of the strength and failure behavior of anisotropic ductile metals on the loading direction and on the stress state. These influences have to be taken into account in accurate material models and in the numerical simulation of complex loading processes predicting the safety and lifetime of aerospace structures. Therefore, the present paper discusses the effect of loading direction and stress state on the damage and failure behavior of the anisotropic aluminum alloy EN AW-2017A. Experiments and corresponding numerical analysis with the newly developed, biaxially loaded X0 specimen have been performed and the influence of different load ratios is examined. The formation of strain fields in critical parts of the X0 specimen is monitored by digital image correlation. Different failure modes are visualized by scanning electron microscopy of fracture surfaces. Stress states are predicted by finite element calculations and they are used to explain damage and fracture processes at the micro-level. The experimental–numerical analysis shows that the loading direction and the stress state remarkably affect the evolution of the width and orientation of localized strain fields as well as the formation of damage processes and fracture modes. As a consequence, characterization of anisotropic metals is highly recommended to be based on an enhanced experimental program with biaxial tests including different load ratios and loading directions.

Notch Effects in Tensile Behavior of AM60 Magnesium Alloys

2006 ◽  
Vol 312 ◽  
pp. 59-64 ◽  
Author(s):  
Cheng Yan ◽  
W. Ma ◽  
V. Burg ◽  
Yiu Wing Mai ◽  
M.G.D. Geers
Keyword(s):  
Magnesium Alloy ◽  
Failure Mechanisms ◽  
Stress Triaxiality ◽  
Tensile Behavior ◽  
Failure Behavior ◽  
Finite Element Analyses ◽  
Deformation And Failure ◽  
Ductile Tearing ◽  
Notched Specimens ◽  
Failure Point

The deformation and failure behavior of an AM60 magnesium alloy was investigated using tensile test on circumferentially notched specimens with different notch radii. The strain and stress triaxiality corresponding to the failure point were evaluated using both analytical and finite element analyses. Combining with systematical observations of the fracture surfaces, it is concluded that deformation and failure of AM60 magnesium alloy are notch (constraint) sensitive. The failure mechanisms change from ductile tearing to quasi cleavage with the increase of constraint.

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