scholarly journals A fracture criterion for ductile metals based on critical damage parameters

2020 ◽  
Author(s):  
Michael Brünig ◽  
Marco Schmidt ◽  
Steffen Gerke
Keyword(s):  
Stress State ◽  
Fracture Criterion ◽  
Evolution Equations ◽  
Damage Model ◽  
Strain Tensor ◽  
Ductile Metals ◽  
Fracture Modes ◽  
Damage And Fracture ◽  
Damage Condition ◽  
Critical Damage

Abstract The paper deals with the effect of different stress-state-dependent damage mechanisms on the onset of fracture in ductile metals. A continuum damage model is discussed using a strain tensor as an appropriate damage variable. It takes into account the influence of stress state on the damage condition and on the evolution equations of damage strains. A fracture condition based on critical damage parameters is developed analyzing results of a series of new experiments with different biaxially loaded specimens. After the tests, fracture modes are visualized by scanning electron microscopy. Numerical simulations of the biaxial experiments elucidate the stress states in critical regions of the specimens which are used to explain formation of different damage and fracture modes on the micro-level. Analysis of numerically predicted damage strains for different loading cases leads to a generalized fracture criterion.

Modeling of Stress-State-Dependent Damage and Failure of Ductile Metals

2015 ◽  
Vol 784 ◽  
pp. 35-42 ◽  
Author(s):  
Michael Brünig ◽  
Daniel Brenner ◽  
Steffen Gerke
Keyword(s):  
Stress State ◽  
Evolution Equations ◽  
Damage Model ◽  
Continuum Damage ◽  
Ductile Metals ◽  
Damage And Failure ◽  
State Dependent ◽  
Wide Range ◽  
Stress States ◽  
Failure Conditions

The paper discusses an anisotropic continuum damage model. It takes into account the effect of stress state on damage and failure conditions as well as on evolution equations of damage strains. To validate the proposed framework experiments with biaxially loaded specimens and corresponding numerical simulations are performed covering a wide range of stress states. In addition, scanning electron microscope images of the fracture surfaces show different fracture modes corresponding to stress states revealed by numerical analyses.

scholarly journals Numerical Analysis of Experiments on Damage and Fracture Behavior of Differently Preloaded Aluminum Alloy Specimens

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 381
Author(s):  
Michael Brünig ◽  
Moritz Zistl ◽  
Steffen Gerke
Keyword(s):  
Stress State ◽  
Numerical Analysis ◽  
Fracture Behavior ◽  
Image Correlation ◽  
Experimental Program ◽  
Failure Behavior ◽  
Strain Fields ◽  
Fracture Modes ◽  
Damage And Fracture ◽  
Damage Criteria

A large amount of experimental studies have shown significant dependence of strength of ductile metals on stress state and stress history. These effects have to be taken into account in constitutive models and corresponding numerical analysis to be able to predict safety and lifetime of engineering structures in a realistic manner. In this context, the present paper deals with numerical analysis of the influence of the load path on damage and fracture behavior of aluminum alloys. A continuum damage model is discussed taking into account the effect of stress state and loading history on damage criteria and on evolution equations of damage strains. Experiments with the biaxially loaded H-specimen have been performed and different preloading histories have been taken into account. Evolution of strain fields is monitored by digital image correlation, and fracture modes are visualized by scanning electron microscopy (SEM). In addition, numerically predicted stress states are used to explain occurrence of different stress-state- and preloading-path-dependent localization behavior in critical specimens areas, as well as damage and fracture modes, revealed by SEM. The experiments with newly developed biaxially loaded specimens and corresponding numerical simulations show that the preloading history remarkably affects the occurrence of width and orientation of localized strain fields, as well as evolution of damage mechanisms and fracture modes. Therefore, characterization of materials must be based on an enhanced experimental program including biaxial tests with different loading histories. The observed damage and failure behavior can be predicted by the proposed continuum model taking into account stress-state-dependent damage criteria and damage strains.

scholarly journals A Modified Phase-Field Damage Model for Metal Plasticity at Finite Strains: Numerical Development and Experimental Validation

Metals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 47
Author(s):  
Jelena Živković ◽  
Vladimir Dunić ◽  
Vladimir Milovanović ◽  
Ana Pavlović ◽  
Miroslav Živković
Keyword(s):  
Phase Field ◽  
Damage Evolution ◽  
Deformation Gradient ◽  
Damage Model ◽  
Steel Structures ◽  
Plasticity Model ◽  
Metal Plasticity ◽  
Damage And Fracture ◽  
Von Mises ◽  
Von Mises Plasticity

Steel structures are designed to operate in an elastic domain, but sometimes plastic strains induce damage and fracture. Besides experimental investigation, a phase-field damage model (PFDM) emerged as a cutting-edge simulation technique for predicting damage evolution. In this paper, a von Mises metal plasticity model is modified and a coupling with PFDM is improved to simulate ductile behavior of metallic materials with or without constant stress plateau after yielding occurs. The proposed improvements are: (1) new coupling variable activated after the critical equivalent plastic strain is reached; (2) two-stage yield function consisting of perfect plasticity and extended Simo-type hardening functions. The uniaxial tension tests are conducted for verification purposes and identifying the material parameters. The staggered iterative scheme, multiplicative decomposition of the deformation gradient, and logarithmic natural strain measure are employed for the implementation into finite element method (FEM) software. The coupling is verified by the ‘one element’ example. The excellent qualitative and quantitative overlapping of the force-displacement response of experimental and simulation results is recorded. The practical significances of the proposed PFDM are a better insight into the simulation of damage evolution in steel structures, and an easy extension of existing the von Mises plasticity model coupled to damage phase-field.

Comparison of Two Time-Integration Algorithms for an Anisotropic Damage Model Coupled with Plasticity

2015 ◽  
Vol 784 ◽  
pp. 292-299 ◽  
Author(s):  
Stephan Wulfinghoff ◽  
Marek Fassin ◽  
Stefanie Reese
Keyword(s):  
Evolution Equations ◽  
Damage Model ◽  
Time Integration ◽  
Three Dimensional ◽  
Anisotropic Damage ◽  
Euler Scheme ◽  
The Finite Element Method ◽  
Time Step ◽  
Implicit Euler Scheme ◽  
Integration Algorithms

In this work, two time integration algorithms for the anisotropic damage model proposed by Lemaitre et al. (2000) are compared. Specifically, the standard implicit Euler scheme is compared to an algorithm which implicitly solves the elasto-plastic evolution equations and explicitly computes the damage update. To this end, a three dimensional bending example is solved using the finite element method and the results of the two algorithms are compared for different time step sizes.

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.

scholarly journals Analysis of Damage Evolution of Sandstone under Uniaxial Loading and Unloading Conditions Based on Resistivity Characteristics

2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
Guoyin Wu ◽  
Kui Wang ◽  
Mingjie Zhao ◽  
Zhichao Nie ◽  
Zhen Huang
Keyword(s):  
Stress State ◽  
Damage Evolution ◽  
Damage Model ◽  
Damage Variable ◽  
Uniaxial Loading ◽  
Experimental Comparison ◽  
Variable Expression ◽  
Cyclic Loading And Unloading ◽  
Sandstone Rock ◽  
Loading And Unloading

In complex rock engineering, understanding the stress state and determining stability and damage evolution are necessary. To more accurately provide a theoretical basis for judging the stress state of bedrock in engineering, this study experimentally addressed the damage evolution of sandstone under loading and unloading conditions. A theoretical relationship between rock resistivity and porosity was obtained according to the Archie formula, which allowed the derivation of the sandstone damage variable expression. Then, sandstone rock samples were used for experimental evaluation, and the feasibility of the theoretically determined damage variable was verified. Finally, through theoretical and experimental comparison analysis, we developed a correlative damage model for sandstone under uniaxial loading and unloading. The results show that the damage variable varies linearly with strain. The proposed correlative equation describes this behavior accurately for loading and unloading conditions. Based on the results of this study, the correlative damage model of sandstone under cyclic loading and unloading conditions can be further improved to be a complete constitutive damage model.

Evaluation of Bevarage Can End Forming Process Using Kolmogorov’s Fracture Criterion

2017 ◽  
Vol 746 ◽  
pp. 3-9
Author(s):  
Vladimir G. Kolobov ◽  
Evgenii V. Aryshenskii ◽  
Yaroslav A. Erisov ◽  
Alexander Nam ◽  
Maksim S. Tepterev
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Aluminum Alloy ◽  
Stress State ◽  
Strain State ◽  
Fracture Criterion ◽  
Relative Elongation ◽  
Rolling Direction ◽  
Forming Process ◽  
Stress Strain

The present study investigates the process of beverage can end forming from 5182 aluminum alloy. Stress-strain state during forming is analyzed using finite element method in PAM-Stamp 2G, and fracturing probability is evaluated based on V.L. Kolmogorov’s fracture criterion. It is established, that stress state does not provide the sufficient plasticity margin during ends forming. Blank material plasticity resource is depleted during preliminary and reverse drawing stages, defects accumulation during countersink forming is negligible. Minimum relative elongation value, responsible for fracture-free end forming, is 6% in the rolling direction.

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