Constraint Effects in Fracture
Constraint Effects in Fracture

Author: E. M. Hackett

Publisher: ASTM International

Published: 1993

Total Pages: 514

ISBN-13: 0803114818

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Papers 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

CONSTRAINT EFFECT IN FRACTURE WHAT IS IT.
CONSTRAINT EFFECT IN FRACTURE WHAT IS IT.

Author:

Publisher:

Published: 2008

Total Pages:

ISBN-13:

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The 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.

Modeling the Constraint Effects on Fracture Toughness of Materials
Modeling the Constraint Effects on Fracture Toughness of Materials

Author: Sunil Kumar Prakash

Publisher:

Published: 2009

Total Pages: 87

ISBN-13:

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"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.

Constraint Effect in Brittle Fracture
Constraint Effect in Brittle Fracture

Author: Y-J Chao

Publisher:

Published: 1997

Total Pages: 20

ISBN-13:

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Variation of apparent fracture toughness under predominantly (elastic) brittle fracture is investigated. Williams' asymptotic series solutions, including higher order terms, are used to characterize the crack tip stress and strain fields for various specimen geometries. Using a fracturing stress or a strain as the material property, it is demonstrated that a fracture event can be quantified by two mechanics parameters, K and A3 for stress-controlled fracture or K and T for strain-controlled fracture. A set of test data that covers a wide range of T and A3 is used to demonstrate the proposed fracture assessment procedure. Constraint-related issues such as size, crack depth, and biaxial stress effect are investigated. The material's failure locus is discussed relative to the ASTM recommended specimen geometries. It is shown that the ASTM in-plane size requirements place a finite-size window on the complete material failure locus. Since real structures may possess constraint levels either higher or lower than the ASTM standard test specimens, structures may fracture at an applied K either higher or lower than KIC. It is demonstrated that KIC determined according to ASTM E 399 and based on a linear elastic solution is not conservative when used to predict the fracture of specimens with low-constraint geometries. This trend is opposite to the corresponding constraint effect in cleavage fracture when the crack tip deformation at fracture is characterized by large-scale yielding.

Constraint Effects on Fracture Toughness
Constraint Effects on Fracture Toughness

Author:

Publisher:

Published: 2001

Total Pages: 47

ISBN-13:

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The 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.