Comparison of Fracture Models to Quantify the Effects of Material Plasticity on the Ductile Fracture Propagation in Pipelines

2018 ◽  
Author(s):  
Aida Nonn ◽  
Marcelo Paredes ◽  
Vincent Keim ◽  
Tomasz Wierzbicki
Keyword(s):  
Ductile Fracture ◽  
Fracture Resistance ◽  
Pipeline Steel ◽  
Ductile Failure ◽  
Fracture Propagation ◽  
Plastic Behavior ◽  
Wide Range ◽  
X100 Pipeline Steel ◽  
Fracture Models ◽  
Stress States

Various numerical approaches have been developed in the last years aimed to simulate the ductile fracture propagation in pipelines transporting CO2 or natural gas. However, a reliable quantification of the influence of material plasticity on the fracture resistance is still missing. Therefore, more accurate description of the material plasticity on the ductile fracture propagation is required based on a suitable numerical methodology. In this study, different plasticity and fracture models are compared regarding the ductile fracture propagation in X100 pipeline steel with the objective to quantify the influence of plasticity parameters on the fracture resistance. The plastic behavior of the investigated material is considered by the quadratic yield surface in conjunction with a non-associated quadratic plastic flow potential. The strain hardening can be appropriately described by the mixed Swift-Voce law. The simulations of ductile fracture are conducted by an uncoupled, modified Mohr-Coulomb (MMC) and the micromechanically based Gurson-Tvergaard-Needleman (GTN) models. In contract to the original GTN model, the MMC model is capable of describing ductile failure over wide range of stress states. Thus, ductile fracture resistance can be estimated for various load and fracture scenarios. Both models are used for the simulation of fracture propagation in DWTT and 3D pressurized pipe sections. The results from the present work can serve as a basis for establishing the correlation between plasticity parameters and ductile fracture propagation.

Prediction and analysis of ductile fracture in sheet metal forming—Part I: A modified Ayada criterion

2014 ◽  
Vol 23 (8) ◽  
pp. 1189-1210 ◽  
Author(s):  
HS Liu ◽  
MW Fu
Keyword(s):  
Finite Element ◽  
Plastic Strain ◽  
Ductile Fracture ◽  
Sheet Metal ◽  
Sheet Metal Forming ◽  
Metal Forming ◽  
Fracture Criterion ◽  
Ductile Fracture Criterion ◽  
Wide Range ◽  
Stress States

A modified ductile fracture criterion is proposed based on the traditional Ayada criterion and coded into the finite element simulation platform of VUMAT/ABAQUS for prediction and analysis of ductile fracture in metal plastic strain processes. In this modified ductile fracture criterion, stress triaxiality is taken into account, and more importantly, the exponential effect of the equivalent plastic strain on the damage behavior, which is generally ignored in other ductile fracture criteria, is also considered. The material related constants in the modified ductile fracture criterion are determined by tensile tests together with finite element simulations. The applicability and reliability of the ductile fracture criterion in ductile fracture prediction in two types of classic stress states, viz. shear stress, tensile stress in sheet metal forming, are investigated based on the deformation behavior and fracture occurrence in two case studies with two typical types of materials, i.e. Al 6061 and T10A. The materials have a wide range of plasticity. The simulation and experimental results verify the applicability and reliability of the developed ductile fracture criterion in prediction of the ductile fracture with and without necking in different stress states of plastic strain.

scholarly journals Comparison of MMC and BW fracture models for constructing 3D ductile fracture envelope of AA6063 during cold forming

2020 ◽  
Author(s):  
Jianye Gao ◽  
Tao He ◽  
Yuanming Huo ◽  
Miao Song ◽  
Tingting Yao ◽  
...  
Keyword(s):  
Ductile Fracture ◽  
Damage Model ◽  
Stress Triaxiality ◽  
Compression Tests ◽  
Cold Forming ◽  
Tension Tests ◽  
Wide Range ◽  
Round Bar ◽  
Fracture Models ◽  
Fracture Envelope

Abstract The 3D ductile fracture envelopes of AA6063-T6 was developed to predict and prevent its fracture. Smooth round bar (SRB) tension tests were carried out to characterize the flow stress, and a series of experiments were conducted to characterize the ductile fracture firstly, such as notched round bar (NR) tension tests, compression tests and torsion tests. These tests cover a wide range of stress triaxiality (ST) and Lode parameter (LP) to calibrate the ductile fracture criterion. Plasticity modeling was performed, and the predicted results were compared with corresponding experimental data to verify the plasticity model after these experiments. Then the relationship between ductile fracture strain and ST with LP was constructed using the modified Mohr–Coulomb (MMC) model and Bai and Wierzbicki (BW) model to develop the 3D ductile fracture envelope. Finally, a new ductile damage model was proposed based on the 3D fracture envelope of AA6063. The final results show that the predicted results from the proposed ductile fracture model showed good agreement with experimental results.

Effect of isotropic and anisotropic damage and plasticity on ductile crack initiation

2018 ◽  
Vol 28 (6) ◽  
pp. 918-942 ◽  
Author(s):  
Arash Keshavarz ◽  
Rahmatollah Ghajar
Keyword(s):  
Finite Element ◽  
Crack Initiation ◽  
Pipeline Steel ◽  
Plastic Anisotropy ◽  
Ductile Failure ◽  
Ductile Material ◽  
Anisotropic Damage ◽  
Plastic Behavior ◽  
Ductile Crack ◽  
Anisotropic Plasticity

In this article, the effects of plastic anisotropy and damage on ductile crack initiation (ductile failure) are studied in a thermodynamically consistent framework. First, isotropic and anisotropic continuum damage models of Lemaitre are modified to incorporate anisotropic plasticity. In the next stage, a subroutine is developed to add the damage formulation to Abaqus finite element package. A highly ductile material with anisotropic plastic behavior, API 5L X100 pipeline steel, is selected for this study. Finite element analyses are done to simulate isotropic/anisotropic plasticity coupled with isotropic/anisotropic damage. Finite element results are compared with the result of tests on smooth and notched specimens, and the effects of anisotropic plasticity, anisotropic damage, geometry changes, triaxiality in stress and their mutual effects and interactions on post yield behavior and crack initiation are studied.

Ductile Fracture Resistance Measurements in High Grade Steels

2006 ◽  
Author(s):  
L. N. Pussegoda ◽  
A. Fredj ◽  
A. Fonzo ◽  
G. Demofonti ◽  
G. Mannucci ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Steady State ◽  
Ductile Fracture ◽  
Fracture Resistance ◽  
Process Zone ◽  
Fracture Propagation ◽  
Crack Tip ◽  
Opening Angle ◽  
Displacement Curve ◽  
High Grade

Recent developments in ductile fracture resistance measures in high grade steels in the pipeline industry include the crack tip opening angle (CTOA) and “steady state” fracture propagation energy, using 3-point bend specimens. The CTOA has been found to be a function of specimen ligament size. With the availability of instrumented hammers, it became possible to resolve propagation energy using the load-displacement curve using a single specimen. This paper focuses on refining the steady state fracture propagation energy, using back-slotted Drop Weight Tear Test (DWTT) specimens. The study included numerical simulation of the dynamic response of back-slotted specimens. The significance of the back-slot in altering the stress/strain field ahead of the propagation crack is discussed. The numerical simulation was also used to determine the strain rate in the “process zone” of the crack tip during steady state fracture propagation.

scholarly journals Micromechanical modelling of ductile fracture in pipeline steel using a bifurcation-enriched porous plasticity model

2020 ◽  
Vol 227 (1) ◽  
pp. 57-78
Author(s):  
Sondre Bergo ◽  
David Morin ◽  
Tore Børvik ◽  
Odd Sture Hopperstad
Keyword(s):  
Ductile Fracture ◽  
Pipeline Steel ◽  
Simulation Models ◽  
Void Coalescence ◽  
Explicit Finite Element ◽  
Gtn Model ◽  
Porous Plasticity ◽  
Tension Tests ◽  
Wide Range

AbstractIn this paper, we investigate the possibility of predicting ductile fracture of pipeline steel by using the Gurson–Tvergaard–Needleman (GTN) model where the onset of void coalescence is determined based on in situ bifurcation analyses. To this end, three variants of the GTN model, one of which includes in situ bifurcation, are calibrated for a pipeline steel grade X65 using uniaxial and notch tension tests. Then plane-strain tension tests and Kahn tear tests of the same material are used for assessment of the credibility of the three models. Explicit finite element simulations are carried out for all tests using the three variants of the GTN model, and the results are compared to the experimental data. The capability of the simulation models to capture onset of fracture and crack propagation in the pipeline steel is evaluated. It is found that the use of in situ bifurcation as a criterion for onset of void coalescence in each element makes the GTN model easier to calibrate with less free parameters, all the while obtaining similar or even better predictions as other widely used formulations of the GTN model over a wide range of different stress states.

Ductile Fracture Resistance Modeling Approach in Two High Grade Steels

2006 ◽  
Author(s):  
L. N. Pussegoda ◽  
A. Fredj ◽  
A. Dinovitzer ◽  
D. Horsley ◽  
D. Carlson
Keyword(s):  
Steady State ◽  
Crack Propagation ◽  
Ductile Fracture ◽  
Fracture Resistance ◽  
Fracture Propagation ◽  
Tension Test ◽  
Model Parameters ◽  
High Grade ◽  
Damage Mechanisms ◽  
Point Bend

Recent developments in ductile fracture resistance measures in high grade steels in the pipeline industry include the crack tip opening angle (CTOA) and “steady state” fracture propagation energy, using 3-point bend specimens. The CTOA has been found to be a function of specimen ligament size. Alternatives would be “steady state” fracture propagation energy, critical fracture strain and adoption of damage mechanisms. This paper focuses on modeling approaches for crack propagation using damage mechanisms. The tension test is used to “calibrate” the damage model parameters and applied to the crack propagation in a 3-point bend specimen in candidate high grade steels. The effects of using parameters developed from tension test and extending to a 3-point bend crack propagation scenario is discussed.

Application of Coupled Ductile Fracture Criterion to Plane Strain Plates

2018 ◽  
Vol 382 ◽  
pp. 186-190 ◽  
Author(s):  
František Šebek ◽  
Petr Kubík ◽  
Jindřich Petruška
Keyword(s):  
Aluminum Alloy ◽  
Ductile Fracture ◽  
Fracture Criterion ◽  
Material Model ◽  
Plastic Behavior ◽  
Ductile Fracture Criterion ◽  
User Subroutine ◽  
Aa 2024 ◽  
Stress States ◽  
Subsequent Propagation

The paper presents a complex material model which covers the elastic-plastic behavior, material deterioration and ductile fracture. The calibration of such model was conducted for Aluminum Alloy (AA) 2024-T351 using specimens with various geometries and loading which covers various stress states. The model was then applied to the simulations of tensile test of plates. The computations were carried out in Abaqus/Explicit using the user subroutine Vectorized User MATerial (VUMAT), where the crack initiation and subsequent propagation was realized using the element deletion technique. The results were compared to the experimental observation in the end.

Application of EWK and Modified X-W Fracture Models to Load-Bearing Lug Joints

2014 ◽  
Vol 670-671 ◽  
pp. 1068-1072
Author(s):  
Chao Liu ◽  
Qin Sun ◽  
Yan Jie Liu
Keyword(s):  
Ductile Fracture ◽  
Fracture Initiation ◽  
Complex Stress ◽  
Loading Conditions ◽  
Load Bearing ◽  
Ductile Materials ◽  
Fracture Models ◽  
User Material Subroutine ◽  
Stress States ◽  
Lug Joints

In the aeronautic field, ductile structure usually undergoes local fracture under complicated service loading conditions, which may triggers collapse of a structure. As a result, it is very essential to study the mechanism of fracture initiation and propagation of ductile materials especially under complex stress states. In this paper, a comparative study of fracture patterns of a load-bearing lug joints structure under several loading conditions with two ductile fracture models is performed by using the commercial finite element platform ABAQUS/ Explicit through a user material subroutine VUMAT. The numerical comparisons using two ductile fracture models in predicting failure of load-bearing lug joints structure shows that modified X-W fracture model agrees well with the experimental observation under complex stress states.

Ductile failure of X100 pipeline steel – Experiments and fractography

2013 ◽  
Vol 43 ◽  
pp. 513-525 ◽  
Author(s):  
Rahmatollah Ghajar ◽  
Giuseppe Mirone ◽  
Arash Keshavarz
Keyword(s):  
Pipeline Steel ◽  
Ductile Failure ◽  
X100 Pipeline Steel

Application of Uncoupled Damage Models to Predict Ductile Fracture in Sheet Metal Blanking

2016 ◽  
Vol 725 ◽  
pp. 483-488
Author(s):  
Cristian Canales ◽  
Romain Boman ◽  
Jean Philippe Ponthot
Keyword(s):  
Ductile Fracture ◽  
Stress Triaxiality ◽  
Mechanical Tests ◽  
Proportional Loading ◽  
Damage Models ◽  
New Family ◽  
Numerical Predictions ◽  
Wide Range ◽  
Overall Performance ◽  
Stress States

The use of uncoupled damage models has been widely used over the years for the prediction of ductile fracture in engineering applications. Nevertheless, its applicability in the prediction of failure has been shown to be limited in the wide range of loading conditions encountered in different manufacturing processes. In order to enhance the formulation of former damage models, the Lode angle has been recently used to characterize the stress states along with the stress triaxiality. This new family of damage models has been demonstrated to give excellent results when proportional loading paths are considered, but its efficiency in more complex applications still need further analysis. To this end, a comparative study of former and recently developed uncoupled damage models is performed in this work. The identification of material parameters is done considering simple mechanical tests under different conditions. Then, the models are used to predict the onset and propagation of cracks during blanking, where numerical predictions are compared with experimental results. Finally, the selected damage models presented a remarkable overall performance in the range of clearances under study.

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