Crack initiation at dislocation cell boundaries in the ductile fracture of metals

1977 ◽  
Vol 29 (2) ◽  
pp. 169-174 ◽  
Author(s):  
R.N. Gardner ◽  
T.C. Pollock ◽  
H.G.F. Wilsdorf
Keyword(s):  
Crack Initiation ◽  
Ductile Fracture ◽  
Dislocation Cell

The J-Integral for a Single-Edge Cracked Panel Subjected to Combined Remote Tension and Bending

2009 ◽  
Author(s):  
Masaaki Matsubara
Keyword(s):  
Crack Initiation ◽  
Ductile Fracture ◽  
Strain Hardening ◽  
Structural Integrity ◽  
Crack Size ◽  
Strain Hardening Exponent ◽  
J Integral ◽  
Single Edge ◽  
Energy Concept

On structural integrity evaluation, a single-edge cracked panel subjected to combined remote tension and bending is the typical one. The J-integral is a valid way for handling the ductile fracture problem immediately after stable crack initiation. The complimentary energy concept combined with fully plastic solutions to make it to estimate the J-integral of the panel. The proposed method is able to give us the J-integral as a function of the crack size/panel width and the strain hardening exponent.

Crack Propagation in Mixed-Mode Ductile Fracture with Continuum Damage Mechanics

1989 ◽  
Vol 203 (3) ◽  
pp. 189-199 ◽  
Author(s):  
C L Chow ◽  
J Wang
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Ductile Fracture ◽  
Crack Growth ◽  
Mixed Mode ◽  
Damage Mechanics ◽  
Continuum Damage Mechanics ◽  
Propagation Model ◽  
Element Formulation ◽  
Continuum Damage

This paper presents a crack propagation model based on an anisotropic theory of continuum damage mechanics proposed earlier by the authors capable of characterizing sub-critical crack growth in mixed-mode ductile fracture. The embedded β angles of mixed-mode specimens include 75, 60, 45 and 30 degrees. The crack growth criteria chosen are essentially those developed for crack initiation and are postulated as: 1. A crack propagates in the direction of maximum effective damage equivalent stress αd. 2. The threshold condition of crack initiation is satisfied when the overall damage w in an element ahead of the crack tip at the prospective crack growth direction reaches its critical value, wc. The crack growth behaviours of the mixed-mode specimens are analysed using a finite element formulation of the non-proportional loading based on the anisotropic model, and the predicted and measured results are found to be satisfactory. The proposed model is also adapted to predict the critical loads of unstable crack propagation and the results are compared favourably with those determined experimentally. Hence the application of the above two fracture criteria can be made to address the entire history of crack development from initiation to rapid growth.

scholarly journals Micromechanical modelling of ductile fracture – local approach

10.30544/459 ◽  
2020 ◽  
Vol 25 (04) ◽  
pp. 263-286
Author(s):  
Aleksandar S Sedmak ◽  
Marko Rakin ◽  
Bojan Medjo ◽  
Bashir Younise
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Crack Initiation ◽  
Ductile Fracture ◽  
Fracture Process ◽  
Three Dimensional ◽  
High Strength ◽  
Local Approach ◽  
Micromechanical Modelling ◽  
Ductile Fracture Process

Micromechanical modelling of ductile fracture by using the local approach has been presented as the review of previously obtained results for welded joints made of low alloyed high strength steel. Experimental work was performed on 3PB specimens and tensile panels, which were then modelled by finite element method, using two- and three-dimensional meshes, respectively. The local approach was used to simulate both for crack initiation and growth during ductile fracture process.

Crack Arrest Testing of High Strength Steels

2012 ◽  
Author(s):  
Andre Hasenhütl ◽  
Marion Erdelen-Peppler ◽  
Christoph Kalwa ◽  
Martin Pant ◽  
Andreas Liessem
Keyword(s):  
Crack Initiation ◽  
Ductile Fracture ◽  
Impact Energy ◽  
Fracture Propagation ◽  
Charpy Impact ◽  
Impact Testing ◽  
Charpy Impact Energy ◽  
Line Pipe ◽  
Test Standards ◽  
Charpy Impact Testing

Fracture propagation is a major concern for the safe operation of gas transmission pipelines. Ductile fracture resistance, which is required according to line pipe standards, is commonly assessed by Charpy impact testing. If fracture occurs during pipe operation, fracture propagation is required to appear in ductile manner. The prerequisite for this is the demonstration of sufficient shear fracture in the BDWT test and minimum required Charpy impact energy. A combination of both requirements ensures avoidance of brittle fracture as well as control of ductile fracture propagation. The experimental chain of evidence and the Battelle-Two-Curve (BTC) model which is the most widely applied model to predict resistance against fracture propagation have been developed on basis of welded pipes of grade ≤ X70. The model has been calibrated against test data obtained from pipes with Charpy impact energy values below 100 J. In recent years, new material concepts were developed to increase material strength and material toughness. On the one hand, increase in material toughness, which is evaluated by Charpy impact testing, is often achieved by an increase in crack initiation resistance. On the other hand, crack propagation resistance, which is determined by BDWT testing with an instrumented striker, can remain on the same level. Increased material toughness and crack initiation resistance can be manifested by incomplete fracture of Charpy impact specimens in the upper shelf (ductile fracture). Actual Charpy impact test standards for metallic materials do not coincide with each other regarding the validity of Charpy energy of unbroken specimens. Increased crack initiation resistance also affects fracture initiation mechanism in BDWT tests, leading to invalid test results according test standards. Invalidity can be expressed by inverse fracture appearance. To avoid inverse fracture, crack initiation energy can be reduced by changing notch type and therefore changing the constraint in the root of the notch. BDWT test standards also do not agree with each other concerning allowable notch types. While the pressed notch type is the preferred one for low toughness steels and the Chevron notch type for higher toughness steels according some test standards, other test standards allow only for a pressed notch type. Being semi-empirical by nature, the BTC concept strongly depends on the input parameters derived from different material tests. Changing test conditions can have a direct impact on the assessment results.

scholarly journals Ductile Fracture Criteria in Prediction of Chevron Cracks

2013 ◽  
Vol 716 ◽  
pp. 653-658 ◽  
Author(s):  
Jindřich Petruška ◽  
Petr Kubík ◽  
Jiří Hůlka ◽  
František Šebek
Keyword(s):  
Carbon Steel ◽  
Crack Initiation ◽  
Ductile Fracture ◽  
Fracture Criteria ◽  
Forward Extrusion ◽  
Ductile Fracture Criteria ◽  
Simulation Results ◽  
Industrial Company

Selected ductile fracture criteria are introduced and applied to prediction of chevron crack initiation and development during forward extrusion of long shafts. We present the calibration of selected criteria for carbon steel, simulate the process of forward extrusion and compare the simulation results with real experiments realized in a cooperating industrial company.

scholarly journals Bayesian inversion for unified ductile phase-field fracture

2021 ◽  
Vol 68 (4) ◽  
pp. 943-980 ◽  
Author(s):  
Nima Noii ◽  
Amirreza Khodadadian ◽  
Jacinto Ulloa ◽  
Fadi Aldakheel ◽  
Thomas Wick ◽  
...  
Keyword(s):  
Crack Initiation ◽  
Ductile Fracture ◽  
Phase Field ◽  
Ductile Failure ◽  
Bayesian Inversion ◽  
Crack Initiation And Propagation ◽  
Posterior Density ◽  
Ductile Phase ◽  
Material Parameters ◽  
Initiation And Propagation

AbstractThe prediction of crack initiation and propagation in ductile failure processes are challenging tasks for the design and fabrication of metallic materials and structures on a large scale. Numerical aspects of ductile failure dictate a sub-optimal calibration of plasticity- and fracture-related parameters for a large number of material properties. These parameters enter the system of partial differential equations as a forward model. Thus, an accurate estimation of the material parameters enables the precise determination of the material response in different stages, particularly for the post-yielding regime, where crack initiation and propagation take place. In this work, we develop a Bayesian inversion framework for ductile fracture to provide accurate knowledge regarding the effective mechanical parameters. To this end, synthetic and experimental observations are used to estimate the posterior density of the unknowns. To model the ductile failure behavior of solid materials, we rely on the phase-field approach to fracture, for which we present a unified formulation that allows recovering different models on a variational basis. In the variational framework, incremental minimization principles for a class of gradient-type dissipative materials are used to derive the governing equations. The overall formulation is revisited and extended to the case of anisotropic ductile fracture. Three different models are subsequently recovered by certain choices of parameters and constitutive functions, which are later assessed through Bayesian inversion techniques. A step-wise Bayesian inversion method is proposed to determine the posterior density of the material unknowns for a ductile phase-field fracture process. To estimate the posterior density function of ductile material parameters, three common Markov chain Monte Carlo (MCMC) techniques are employed: (i) the Metropolis–Hastings algorithm, (ii) delayed-rejection adaptive Metropolis, and (iii) ensemble Kalman filter combined with MCMC. To examine the computational efficiency of the MCMC methods, we employ the $$\hat{R}{-}convergence$$ R ^ - c o n v e r g e n c e tool. The resulting framework is algorithmically described in detail and substantiated with numerical examples.

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