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Author: E. M. Hackett
Publisher: ASTM International
Published: 1993
Total Pages: 514
ISBN-13: 0803114818
DOWNLOAD EBOOKPapers presented at the symposium on [title] held in Indianapolis, Indiana, May 1991, provide a framework for quantifying constraint effects in terms of both continuum mechanics and micro-mechanical modeling approaches. Such a framework is useful in establishing accurate predictions of the fracture
Author: Mark Kirk
Publisher: ASTM International
Published: 1995
Total Pages: 546
ISBN-13: 0803120133
DOWNLOAD EBOOKAuthor: Sunil Kumar Prakash
Publisher:
Published: 2009
Total Pages: 87
ISBN-13:
DOWNLOAD EBOOK"Cleavage fracture has been a very important subject for engineers for a long time because of the catastrophic result it may cause. The experimental results of cleavage fracture exhibit a large amount of scatter and show significant constraint effect, which motivated the development of statistical and micromechanics based methods in order to deal with such problem. The Weibull stress model, which is based on the weakest link statistics, uses two parameters, m and [sigma]u?, to describe the inherent distribution of the micro-scale cracks once the plastic deformation has occurred and to define the relationship between the macro and micro-scale driving forces for cleavage fracture. In this paper we examine constraint effects on cleavage fracture toughness numerically using a constraint function g(M) derived from the Weibull stress model. The non-dimensional function g(M) describes the evolution of constraint loss effects on fracture toughness relative to reference plane-strain small scale yielding (SSY) condition (T-stress=0). We performed detailed finite element analyses of single-edge notched bending speciments and compute g(M) functions for them. The g-function varies with parameters of the Weibull stress model, material flow properties and speciment geometry but not with absolute specimen size. Knowing the g-function one can construct fracture driving force curves for each absolute size of interest."--Abstract.
Author:
Publisher:
Published: 2008
Total Pages:
ISBN-13:
DOWNLOAD EBOOKThe meaning of the phrase 'constraint effect in fracture' has changed in the past two decades from 'contained plasticity' to a broader description of 'dependence of fracture toughness value on geometry of test specimen or structure'. This paper will first elucidate the fundamental mechanics reasons for the apparent 'constraint effects in fracture', followed by outlining a straightforward approach to overcoming this problem in both brittle (elastic) and ductile (elastic-plastic) fracture. It is concluded by discussing the major difference in constraint effect on fracture event in elastic and elastic-plastic materials.
Author:
Publisher:
Published: 2001
Total Pages: 47
ISBN-13:
DOWNLOAD EBOOKThe crack growth resistance (toughness) of a structural material depends on the geometry of the crack and the type of loading. These produce differences in the crack tip stress state referred to as the constraint. The stress state controls the deformation required to initiate fracture, and the mechanisms of fracture in steels are profoundly affected by the local constraint. This report describes the crack tip behaviour of 350WT ship steel, based on tests that characterized the fracture toughness of a ship steel plate over a range of constraint conditions. The tests were performed at room temperature on three-point bend bars that were pre-cracked to different crack depths. The mode of fracture was ductile tearing and resistance curves were calculated. Results for initiation toughness and growth resistance are characterized in both the linear elastic and elastic plastic formats. In addition, finite element modelling was used to determine numerically the crack tip stress fields, with special attention to the crack tip blunting behaviour.
Author: Walter G. Reuter
Publisher: ASTM International
Published: 1995
Total Pages: 842
ISBN-13: 0803119968
DOWNLOAD EBOOKAuthor: RH. Dodds
Publisher:
Published: 1997
Total Pages: 19
ISBN-13:
DOWNLOAD EBOOKSince the late 1980s there has been renewed interest and progress in understanding the effects of constraint on transgranular cleavage in ferritic steels. Research efforts to characterize the complex interaction of crack tip separation processes with geometry, loading mode and material flow properties proceed along essentially two major lines of investigation: (1) multi-parameter descriptions of stationary crack-tip fields under large-scale yielding conditions, and (2) rational micromechanics models for the description of cleavage fracture which also reflect the observed scatter in the ductile-to-brittle transition (DBT) region. This article reviews the essential features of a specific example representing each approach: the J-Q extension to correlative fracture mechanics and a local approach based on the Weibull stress. Discussions focus on the growing body of 3-D numerical solutions for common fracture specimens which, in certain cases, prove significantly different from long-established plane-strain results.
Author: J. A. Smith
Publisher:
Published: 1997
Total Pages: 43
ISBN-13:
DOWNLOAD EBOOKAuthor: B. R. Bass
Publisher:
Published: 1992
Total Pages:
ISBN-13:
DOWNLOAD EBOOKAuthor:
Publisher:
Published: 1991
Total Pages: 55
ISBN-13:
DOWNLOAD EBOOKMany naturally occurring cracks are three dimensional and cannot be evaluated using numerical techniques derived using two dimensional simplifications. The high stress and strain levels experienced in modern high toughness alloys prior to fracture require means to accurately simulate the nonlinear response of ductile materials in this regime. An accurate constitutive representation must be combined with a fracture criterion which is valid for the high strain regime to achieve accurate computerized simulations of fracture and near fracture behavior. In the current work, nonlinear numerical simulations are performed to determine the global and local responses of two surface cracked plates of HY-100 steel with varying crack propagation and crack depths. Failure is defined by a local fracture criterion using strain energy density. Differences in constraint along the crack perimeter are taken into account by recognizing the stress-strain history dependence of the critical strain energy density. Crack growth patterns determined from the numerical simulations accurately reflect experimental observations.
