Abstract
Available measures of the fracture energyG F obtained with the procedure proposed by RILEM TC-50 provide values that appear to change with sample size, calling into question the possibility of consideringG F as a material parameter. In previous papers several sources of energy dissipation were analysed and it was concluded that, although important, they were not enough to account for the measured size effect. Here, the dissipated energy at the very end of the test is analysed. It is shown that this energy cannot be neglected for small specimens if the tests are interrupted at a reasonably low rotation. When this energy is taken into account, the final values ofG F appear to be almost size-independent. This result supportsG F as a material parameter and provides further confidence in the RILEM proposal. Moreover, it furnishes a physical explanation for the perturbed ligament model previously developed by the authors.
Resume
Les mesures de l'énergie de ruptureG F obtenues selon la méthode préconisée par la Commission Technique 50, dont on dispose, fournissent des valeurs qui se trouvent changer avec la taille de l'éprouvette, ce qui met en question la possibilité de considérer GF comme un paramètre du matériau. Dans les articles précédents, on a examiné plusieurs sources de dissipation de l'énergie, et on a conclu que, tout en ayant de l'importance, elles ne suffisent pas à explique l'effet d'échelle mesuré.
Une solution semble résider dans le fait que, en flexion, l'essai ne peut être contrôlé jusqu'á rupture complète de l'éprouvette. Il doit être stoppé quelque part avant ce point, et la quantité d'énergie qui correspond au segment non enregistré de la courbeP-δ n'est pas prise en compte dans les mesures. Quand cette énergie est prise en compte, dans les résultats expérimentaux des auteurs, les valeurs, finales deG F semblent presque indépendantes de l'échelle. Ce résultat permet de considérerG F comme un paramètre du matériau à des fins de calcul, et constitue un encouragement pour la modélisation du béton en tant que matériau cohérent.
L'énergie comprise dans le segmentP-δ justifie une explication physique du concept phénoménologique dit ‘Perturbed Ligament Model’ que les auteurs ont précédemment élaboré.
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Elices, M., Guinea, G.V. & Planas, J. Measurement of the fracture energy using three-point bend tests: Part 3—influence of cutting theP-δ tail. Materials and Structures 25, 327–334 (1992). https://doi.org/10.1007/BF02472591
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DOI: https://doi.org/10.1007/BF02472591