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Pook L.P.,21 Woodside Road | Berto F.,University of Padua | Campagnolo A.,University of Padua
Frattura ed Integrita Strutturale | Year: 2016

The linear elastic analysis of homogeneous, isotropic cracked bodies is a Twentieth Century development. It was recognised that the crack tip stress field is a singularity, but it was not until the introduction of the essentially two dimensional stress intensity factor concept in 1957 that widespread application to practical engineering problems became possible. The existence of three dimensional corner point effects in the vicinity of a corner point where a crack front intersects a free surface was investigated in the late 1970s: it was found that modes II and III cannot exist in isolation. The existence of one of these modes always induces the other. An approximate solution for corner point singularities by Bažant and Estenssoro explained some features of corner point effects but there were various paradoxes and inconsistencies. In an attempt to explain these a study was carried out on the coupled in-plane fracture mode induced by a nominal anti-plane (mode III) loading applied to plates and discs weakened by a straight crack. The results derived from a large bulk of finite element models showed clearly that Bažant and Estenssoro’s analysis is incomplete. Some of the results of the study are summarised, together with some recent results for a disc under in-plane shear loading. On the basis of these results, and a mathematical argument, the results suggest that the stress field in the vicinity of a corner point is the sum of two singularities: one due to stress intensity factors and the other due to an as yet undetermined corner point singularity. © 2016, Gruppo Italiano Frattura. All rights reserved.


Pook L.P.,21 Woodside Road
International Journal of Fatigue | Year: 2011

Coiled springs (mainsprings) are coiled steel ribbons that have been used as a power source for centuries. A major disadvantage of mainsprings is that they do not deliver a uniform torque during unwinding. Theoretical analysis of mainsprings is notoriously difficult, and they are usually designed using well established rules of thumb. In service mainsprings are subjected to low cycle fatigue loading. They can fail either by breaking due to fatigue, or by shakedown into a shape where they no longer deliver adequate power. Some features of the behaviour of mainsprings used as power sources are described and illustrated by examples. In particular, the importance of correct lubrication is emphasised. The primary loading on a mainspring is a bending moment, but sequential biaxial loading can occur, as can biaxial stresses due to distortion at end fittings. A fracture mechanics approach to some aspects of mainspring behaviour is promising. © 2010 Elsevier Ltd. All rights reserved.


Pook L.P.,21 Woodside Road | Campagnolo A.,University of Padua | Berto F.,University of Padua | Lazzarin P.,University of Padua
Engineering Fracture Mechanics | Year: 2015

The existence of three-dimensional effects at cracks has been known for many years, but understanding has been limited, and for some situations still is. Despite increased understanding, three-dimensional effects are sometimes ignored in situations where they may be important. The purpose of the present investigation is to study a coupled fracture mode generated by a nominal anti-plane (Mode III) loading applied to linear elastic plates weakened by a straight through-the-thickness crack. With this aim accurate 3D finite element (FE) analyses have been performed. The results obtained from the highly accurate finite element models have improved understanding of the behaviour of through cracked plates under anti-plane loading. The influence of plate bending is increasingly important as plate thickness decreases. It appears that a new field parameter, probably a singularity, is needed to describe the stresses at the plate surfaces. Discussion on whether KIII tends to zero or infinity as a corner point is approached is futile because KIII is meaningless at a corner point. Calculation of the strain energy density (SED) in a control volume at the crack tip allows us to predict the most critical point through the plate thickness. © 2015 Elsevier Ltd.


Berto F.,University of Padua | Kotousov A.,University of Adelaide | Lazzarin P.,University of Padua | Pook L.P.,21 Woodside Road
International Journal of Fracture | Year: 2013

It is now well-known that in plate problems with through-the-thickness cracks in-plane shear and anti-plane loadings generate coupled three-dimensional fracture modes. The dominance domain and intensity of the singular states associated with these 3D fracture modes are functions of the intensity of the primary loading (KII and KIII) and Poisson's ratio. A similar situation takes place for V-shaped notches. However, for geometrically similar notch geometries subjected the same nominal stress the intensity of the coupled modes is also a function of the plate thickness. Despite this almost all 3D effects are currently ignored in industrial standards and fracture assessment codes. Recent theoretical and numerical studies have demonstrated that in many practical situations the intensities of the coupled fracture modes for cracks and sharp notches are not negligible and can influence fracture conditions. The current paper extends this conclusion to rounded notches. By using the finite element modelling it is demonstrated that the intensity of the stress states associated with the coupled fracture modes in a sufficiently thick plate weakened by a rounded notch can exceed the magnitude of stresses due to the primary loading. This means that the coupled modes can dominate the stress state in the vicinity of the notch root and be primary responsible for fracture initiation. © 2012 Springer Science+Business Media Dordrecht.


Pook L.P.,21 Woodside Road | Berto F.,University of Padua | Campagnolo A.,University of Padua | Lazzarin P.,University of Padua
MATEC Web of Conferences | Year: 2014

The existence of three-dimensional effects at cracks has been known for many years, but understanding has been limited, and for some situations still is. Understanding improved when the existence of corner point singularities and their implications became known. Despite increased understanding, three-dimensional effects are sometimes ignored in situations where they may be important. The purpose of the present investigation is to study by means of accurate 3D finite element (FE) models a coupled fracture mode generated by anti-plane loading of a straight through-the-thickness crack in linear elastic discs. The results obtained from the highly accurate finite element analyses have improved understanding of the behaviour of through cracked discs under anti-plane loading. The influence of plate bending is increasingly important as disc thickness decreases. It appears that a new field parameter, probably a singularity, is needed to describe the stresses at the disc surfaces. Calculation of the strain energy density (SED) in a control volume at the crack tip shows that the position of the maximum SED is a function of disc thickness. © Owned by the authors, published by EDP Sciences, 2014.

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