A. Pineau        

Anales de la Mecánica de la Fractura, nº 24 . 2007 . Pág. 9 -24
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Resumen: This review paper is devoted to the local approach to fracture (LAF) for the prediction of the fracture toughness of structural steels. The bases of this relatively newly developed methodology are first presented. The LAF has been considerably developed over the past two decades, not only to provide a better understanding of the fracture behaviour of materials, in particular the failure micromechanisms, but also to deal with loading conditions which cannot easily be handled with the conventional LEFM and EPFM global approaches. Both ductile rupture and brittle cleavage fracture micromechanisms are considered. The ductile-to-brittle transition observed in ferritic steels is also briefly addressed. Two types of LAF methods are presented : (i) those assuming that the material behaviour is not affected by damage (e.g. cleavage fracture), (ii) those using a coupling effect between damage and constitutive equations (e.g. ductile fracture). The micromechanisms of brittle and ductile fracture investigated in elementary volume elements are briefly presented. The emphasis is laid on cleavage fracture in ferritic steels. The role of second phase particles (carbides or inclusions) and grain boundaries are more thoroughly discussed. The distinction between nucleation and growth controlled fracture is made. Recent developments in the theory of cleavage fracture incorporating both the effect of stress state and that of plastic strain are presented. These theoretical results are applied to the crack tip situation to predict the fracture toughness. It is shown that the ductile-to-brittle transition curve can reasonably be well predicted using this approach. Additional applications of the LAF approach methods are also shown, including : (i) the effect of loading rate and prestressing, (ii) the influence of residual stresses in welds, (iii) the mismatch effects in welds, (iv) the warmprestressing effect. An attempt is also made to delineate research areas where large improvements should be made for a better understanding of the failure behaviour of structural materials.


Centre des Matériaux, Ecole des Mines de Paris, UMR CNRS 7633, BP 87, 91003 Evry Cedex, France