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Probabilistic modelling of cleavage fracture
KTH, Superseded Departments, Solid Mechanics.
2001 (English)Licentiate thesis, comprehensive summary (Other scientific)
Place, publisher, year, edition, pages
Stockholm: KTH , 2001. , 6 p.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-1362OAI: oai:DiVA.org:kth-1362DiVA: diva2:7204
Presentation
(English)
Note
QC 20100511Available from: 2002-01-11 Created: 2002-01-11 Last updated: 2010-05-11Bibliographically approved
List of papers
1. A probabilistic model for cleavage fracture with a length scale-influence of material parameters and constraint
Open this publication in new window or tab >>A probabilistic model for cleavage fracture with a length scale-influence of material parameters and constraint
2002 (English)In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 118, no 2, 99-118 p.Article in journal (Refereed) Published
Abstract [en]

A probabilistic model for the cumulative probability of failure by cleavage fracture with a material related length scale is developed in this study. The model aims at describing the random nature of fracture in ferritic steels in the brittle-to-ductile transition temperature region. The model derives from use of an exponential function to describe the distribution of microstructural entities eligible to take part in the fracture initiation process, where also a dependence on effective plastic strain is incorporated. A nonlocal stress measure, calculated as the average stress in a spherical volume, drives the contribution to failure probability of an infinitesimal material volume. The radius of the spherical volume enters as the material length in this model. This length has a significant influence on failure probability predictions in geometries exposed to strong stress gradients as found ahead of cracks. The material length is associated with a fracture toughness threshold value. In a fracture application three model parameters need to be estimated based on testing; a parameter directly related to the mean fracture toughness, a parameter that primarily is related to crack-tip constraint effects and the material length parameter. The model is explored in a parametric study showing model features in concord with typical features found in toughness distributions from fracture mechanics testing in the transition region.

Keyword
cleavage fracture, failure probability, material length, threshold toughness
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-12789 (URN)10.1023/A:1022864513654 (DOI)000182131900001 ()
Note
QC 20100511Available from: 2010-05-11 Created: 2010-05-11 Last updated: 2017-12-12Bibliographically approved
2. A probabilistic model for cleavage fracture with a length scale - parameter estimation and predictions of stationary crack experiments
Open this publication in new window or tab >>A probabilistic model for cleavage fracture with a length scale - parameter estimation and predictions of stationary crack experiments
2004 (English)In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 71, no 1, 57-79 p.Article in journal (Refereed) Published
Abstract [en]

This study presents a large experimental investigation in the transition temperature region on a modified A508 steel. Tests were carried out on single-edge-notch-bend specimens with three different crack depth over specimen width ratios to capture the strong constraint effect on fracture toughness. Three test temperatures were considered, covering a range of 85 degreesC. All specimens failed by cleavage fracture prior to ductile tearing. A recently proposed probabilistic model for the cumulative failure by cleavage was applied to the comprehensive sets of experimental data. This modified weakest link model incorporates a length scale, which together with a threshold stress reduce the scatter in predicted toughness distributions as well as introduces a fracture toughness threshold value. Model parameters were estimated by a robust procedure, which is crucial in applications of probabilistic models to real structures. The conformity between predicted and experimental toughness distributions, respectively, were notable at all the test temperatures.

Keyword
cleavage fracture, failure probability, length scale, threshold toughness, fracture experiments, Master curve
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-12788 (URN)10.1016/S0013-7944(03)00066-3 (DOI)000185968600004 ()2-s2.0-0141993233 (Scopus ID)
Note
QC 20100511 QC 20111031Available from: 2010-05-11 Created: 2010-05-11 Last updated: 2017-12-12Bibliographically approved
3. A probabilistic model for cleavage fracture with a length scale - Parameter estimation and predictions of growing crack experiments
Open this publication in new window or tab >>A probabilistic model for cleavage fracture with a length scale - Parameter estimation and predictions of growing crack experiments
2008 (English)In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 75, no 8, 2398-2417 p.Article in journal (Refereed) Published
Abstract [en]

A probabilistic model for the cumulative probability of failure by cleavage fracture was applied to experimental results where cleavage fracture was preceded by ductile crack growth. The model, introduced by Kroon and Faleskog [Kroon M, Faleskog J. A probabilistic model for cleavage fracture with a length scale - influence of material parameters and constraint. Int J Fract 2002; 118:99-118], includes a non-local stress with an associated material related length scale, and it also includes a strain measure to account for the number of nucleated cleavage initiation sites. The experiments were performed on single edge cracked bend test specimens with three different crack lengths at the temperature 85 degrees C, which is in the upper transition region for the steel in question. The ductile rupture process is modelled using tile cell model for nonlinear fracture mechanics. The original cleavage fracture model had to be modified in order to account for the substantial number of cleavage initiators being consumed by the ductile process. With this modification, the model was able to accurately capture the experimental failure probability distribution.

Keyword
cleavage fracture, ductile cell model, failure probability, length scale, threshold toughness, fracture experiments, weakest link
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-12787 (URN)10.1016/j.engfracmech.2007.08.009 (DOI)000254354000030 ()2-s2.0-39149089655 (Scopus ID)
Note
QC 20100511Available from: 2010-05-11 Created: 2010-05-11 Last updated: 2017-12-12Bibliographically approved

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