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Size-effect testing of cohesive fracture parameters and nonuniqueness of work-of-fracture method / Bažant, Zdeněk P. in Journal of engineering mechanics, Vol. 137 N° 8 (Août 2011) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 137 N° 8 (Août 2011) . - pp.580-588 Titre : Size-effect testing of cohesive fracture parameters and nonuniqueness of work-of-fracture method Type de document : texte imprimé Auteurs : Bažant, Zdeněk P., Auteur ; Qiang Yu, Auteur Année de publication : 2011 Article en page(s) : pp.580-588 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Quasibrittle  fracture  Cohesive  crack  model  Fracture  mechanics  Cracks  Quasibrittle  materials  Concrete  Scaling  Testing  Brittleness Résumé : The cohesive crack model has been widely accepted as the best compromise for the analysis of fracture of concrete and other quasibrittle materials. The softening stress-separation law of this model is now believed to be best described as a bilinear curve characterized by four parameters: the initial and total fracture energies Gf and GF, the tensile strength ft′, and the knee-point ordinate σ1. The classical work-of-fracture test of a notched beam of one size can deliver a clear result only for GF. Here it is shown computationally that the same complete load-deflection curve can be closely approximated with stress-separation curves in which the ft′ values differ by 77% and Gf values by 68%. It follows that the work-of-fracture test alone cannot provide an unambiguous basis for quasibrittle fracture analysis. It is found, however, that if this test is supplemented by size-effect testing, all four cohesive crack model parameters can be precisely identified and the fracture analysis of structures becomes unambiguous. It is shown computationally that size-effect tests do not suffice for determining GF and ft′, which indicates that they provide a sufficient basis for computing neither the postpeak softening of fracturing structures nor the peak loads of a very large structure. However, if the size-effect tests are supplemented by one complete softening load-deflection curve of a notched specimen, an unambiguous calculation of peak loads and postpeak response of structures becomes possible. To this end, the notched specimen tests must be conducted in a certain size range, whose optimum is here established by extending a previous analysis. Combination of the work-of-fracture and size-effect testing could be avoided only if the ratios GF/Gf and σ1/ft′ were known a priori, but unfortunately their estimates are far too uncertain. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i8/p580_s1?isAuthorized=no [article] Size-effect testing of cohesive fracture parameters and nonuniqueness of work-of-fracture method [texte imprimé] / Bažant, Zdeněk P., Auteur ; Qiang Yu, Auteur . - 2011 . - pp.580-588. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 137 N° 8 (Août 2011) . - pp.580-588 Mots-clés : Quasibrittle  fracture  Cohesive  crack  model  Fracture  mechanics  Cracks  Quasibrittle  materials  Concrete  Scaling  Testing  Brittleness Résumé : The cohesive crack model has been widely accepted as the best compromise for the analysis of fracture of concrete and other quasibrittle materials. The softening stress-separation law of this model is now believed to be best described as a bilinear curve characterized by four parameters: the initial and total fracture energies Gf and GF, the tensile strength ft′, and the knee-point ordinate σ1. The classical work-of-fracture test of a notched beam of one size can deliver a clear result only for GF. Here it is shown computationally that the same complete load-deflection curve can be closely approximated with stress-separation curves in which the ft′ values differ by 77% and Gf values by 68%. It follows that the work-of-fracture test alone cannot provide an unambiguous basis for quasibrittle fracture analysis. It is found, however, that if this test is supplemented by size-effect testing, all four cohesive crack model parameters can be precisely identified and the fracture analysis of structures becomes unambiguous. It is shown computationally that size-effect tests do not suffice for determining GF and ft′, which indicates that they provide a sufficient basis for computing neither the postpeak softening of fracturing structures nor the peak loads of a very large structure. However, if the size-effect tests are supplemented by one complete softening load-deflection curve of a notched specimen, an unambiguous calculation of peak loads and postpeak response of structures becomes possible. To this end, the notched specimen tests must be conducted in a certain size range, whose optimum is here established by extending a previous analysis. Combination of the work-of-fracture and size-effect testing could be avoided only if the ratios GF/Gf and σ1/ft′ were known a priori, but unfortunately their estimates are far too uncertain. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i8/p580_s1?isAuthorized=no