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The energy dissipation rate approach to tearing instability

Journal from JIPTUMM / 2003-12-22 09:55:48
By : J.D.G.Sumpter, Engineering
Created : 2003-12-22, with 1 files

Keyword : Ductile fracture;R curve tests;Stable crack growth;Unstable crack growth;
Url : http://


Abstract
Stable and unstable tearing in metals is currently analysed by J integral theory,or by the G R curve approach.This paper explains an alternative analysis route based on energy dissipation rate,D .It is shown that the implication of increasing toughness with crack growth in G R and J R curves is misleading.Even in small scale yielding (SSY),it is possible to have stable tearing under increasing G or J whilst at the same time D is constant (or even reducing)with crack growth.New terms:C for crack driving force,D for geometry normalised D ,D ssy for D in SSY,and crack stability index are explained.A D based fracture analysis diagram is introduced.Comparisons are made between energy dissipation rate,Jintegral,and G R curve instability prediction methods.It is shown that,in most instances,thes di fferent approaches are compatible;but that the use of J R curves derived in fully yielded test pieces to predict failure in SSY has the potential to lead to anunconservative instability prediction.The practical advantage of the energy dis-sipation rate approach is that it can be applied to all product thicknesses at any extent of crack growth.The major advantage compared to the G R approach is that toughness measurements can be made on much smaller specimens.

Description Alternative :


Abstract
Stable and unstable tearing in metals is currently analysed by J integral theory,or by the G R curve approach.This paper explains an alternative analysis route based on energy dissipation rate,D .It is shown that the implication of increasing toughness with crack growth in G R and J R curves is misleading.Even in small scale yielding (SSY),it is possible to have stable tearing under increasing G or J whilst at the same time D is constant (or even reducing)with crack growth.New terms:C for crack driving force,D for geometry normalised D ,D ssy for D in SSY,and crack stability index are explained.A D based fracture analysis diagram is introduced.Comparisons are made between energy dissipation rate,Jintegral,and G R curve instability prediction methods.It is shown that,in most instances,thes di fferent approaches are compatible;but that the use of J R curves derived in fully yielded test pieces to predict failure in SSY has the potential to lead to anunconservative instability prediction.The practical advantage of the energy dis-sipation rate approach is that it can be applied to all product thicknesses at any extent of crack growth.The major advantage compared to the G R approach is that toughness measurements can be made on much smaller specimens.

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