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Modelling of Fracture Processes During Fast Crack Growth

Ståhle, P. LU (2005) In Advances in Fracture Mechanics p.41-71
Abstract
The role of the fracture process region during fast fracture is discussed. Reviewed experiments on modern pressure vessel steels show that already at crack tip speeds of one or two hundred mls fracture processes are dominantly brittle. Modelling of the process region is discussed in the light of asymptotic elastic plastic fields and process region autonomy. It is suggested that a fraction of the crack surface (0.1 to 0.2) is created by ductile tearing of ligaments remaining after most of the crack surface has failed through cleavage. Ligament like test specimens of sub mm size are used to detennine the constants of an elastic viscoplastic model assumed for both the surrounding continuum and the crack bridging ligaments, The latter are... (More)
The role of the fracture process region during fast fracture is discussed. Reviewed experiments on modern pressure vessel steels show that already at crack tip speeds of one or two hundred mls fracture processes are dominantly brittle. Modelling of the process region is discussed in the light of asymptotic elastic plastic fields and process region autonomy. It is suggested that a fraction of the crack surface (0.1 to 0.2) is created by ductile tearing of ligaments remaining after most of the crack surface has failed through cleavage. Ligament like test specimens of sub mm size are used to detennine the constants of an elastic viscoplastic model assumed for both the surrounding continuum and the crack bridging ligaments, The latter are replaced with a cohesive zone model embedded by an elastic viscoplastic continuum. The process region model captures cleavage in a foremost patt with very high cohesive stresses and rupture of ligaments in a trailing part where stresses are assumed to be rate dependent. In the surrounding continua the plastic deformation work is calculated considering high strain rate effects. The energy release rate in the process region is estimated. A balance between elastic energy release rate, energy dissipated at plastic deformation work in the plastic zone and energy release rate in the process region is examined. The energy released in the process region is consumed a) at cleavage and b) during rupture of ligaments. A cohesive zone model is used for the process region. The conclusion is that the experimental results can be explained only if the ligaments are considered. Crack growth rates down to one to two hundred mls are predicted by the model. Energy balance is possible at lower speeds but the crack immediately switches to a higher speed or comes to instant arrest as has been observed in experiments. (Less)
Abstract (Swedish)
The role of the fracture process region during fast fracture is discussed. Reviewed experiments on modern pressure vessel steels show that already at crack tip speeds of one or two hundred mls fracture processes are dominantly brittle. Modelling of the process region is discussed in the light of asymptotic elastic plastic fields and process region autonomy. It is suggested that a fraction of the crack surface (0.1 to 0.2) is created by ductile tearing of ligaments remaining after most of the crack surface has failed through cleavage. Ligament like test specimens of sub mm size are used to detennine the constants of an elastic viscoplastic model assumed for both the surrounding continuum and the crack bridging ligaments, The latter are... (More)
The role of the fracture process region during fast fracture is discussed. Reviewed experiments on modern pressure vessel steels show that already at crack tip speeds of one or two hundred mls fracture processes are dominantly brittle. Modelling of the process region is discussed in the light of asymptotic elastic plastic fields and process region autonomy. It is suggested that a fraction of the crack surface (0.1 to 0.2) is created by ductile tearing of ligaments remaining after most of the crack surface has failed through cleavage. Ligament like test specimens of sub mm size are used to detennine the constants of an elastic viscoplastic model assumed for both the surrounding continuum and the crack bridging ligaments, The latter are replaced with a cohesive zone model embedded by an elastic viscoplastic continuum. The process region model captures cleavage in a foremost patt with very high cohesive stresses and rupture of ligaments in a trailing part where stresses are assumed to be rate dependent. In the surrounding continua the plastic deformation work is calculated considering high strain rate effects. The energy release rate in the process region is estimated. A balance between elastic energy release rate, energy dissipated at plastic deformation work in the plastic zone and energy release rate in the process region is examined. The energy released in the process region is consumed a) at cleavage and b) during rupture of ligaments. A cohesive zone model is used for the process region. The conclusion is that the experimental results can be explained only if the ligaments are considered. Crack growth rates down to one to two hundred mls are predicted by the model. Energy balance is possible at lower speeds but the crack immediately switches to a higher speed or comes to instant arrest as has been observed in experiments. (Less)
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author
publishing date
type
Chapter in Book/Report/Conference proceeding
publication status
published
subject
keywords
dynamic, fracture, fracture processes
host publication
Crack Dynamics : Computational Mechanics - Computational Mechanics
series title
Advances in Fracture Mechanics
editor
Aliabadi, A.Ivankovic and Aliabadi, M. H.
pages
31 pages
publisher
WIT Press
ISBN
1-85312-948-8
978-1853129483
language
English
LU publication?
no
id
f3c37f86-28d8-45e2-b2a5-ef1420395b08
date added to LUP
2019-06-25 14:30:31
date last changed
2020-03-26 10:11:30
@inbook{f3c37f86-28d8-45e2-b2a5-ef1420395b08,
  abstract     = {The role of the fracture process region during fast fracture is discussed. Reviewed experiments on modern pressure vessel steels show that already at crack tip speeds of one or two hundred mls fracture processes are dominantly brittle. Modelling of the process region is discussed in the light of asymptotic elastic plastic fields and process region autonomy. It is suggested that a fraction of the crack surface (0.1 to 0.2) is created by ductile tearing of ligaments remaining after most of the crack surface has failed through cleavage. Ligament like test specimens of sub mm size are used to detennine the constants of an elastic viscoplastic model assumed for both the surrounding continuum and the crack bridging ligaments, The latter are replaced with a cohesive zone model embedded by an elastic viscoplastic continuum. The process region model captures cleavage in a foremost patt with very high cohesive stresses and rupture of ligaments in a trailing part where stresses are assumed to be rate dependent. In the surrounding continua the plastic deformation work is calculated considering high strain rate effects. The energy release rate in the process region is estimated. A balance between elastic energy release rate, energy dissipated at plastic deformation work in the plastic zone and energy release rate in the process region is examined. The energy released in the process region is consumed a) at cleavage and b) during rupture of ligaments. A cohesive zone model is used for the process region. The conclusion is that the experimental results can be explained only if the ligaments are considered. Crack growth rates down to one to two hundred mls are predicted by the model. Energy balance is possible at lower speeds but the crack immediately switches to a higher speed or comes to instant arrest as has been observed in experiments.},
  author       = {Ståhle, P.},
  booktitle    = {Crack Dynamics : Computational Mechanics},
  editor       = {Aliabadi, A.Ivankovic and Aliabadi, M. H.},
  isbn         = {1-85312-948-8},
  language     = {eng},
  pages        = {41--71},
  publisher    = {WIT Press},
  series       = {Advances in Fracture Mechanics},
  title        = {Modelling of Fracture Processes During Fast Crack Growth},
  year         = {2005},
}