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Measurement of the fracture energy using three-point bend tests: Part 2—Influence of bulk energy dissipation

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Abstract

Avialable measures of the fracture energy GF obtained with the procedure proposed by RILEM TC-50 provide values that appear to change with sample size, calling into question whether GF can be considered as a material parameter. In a previous paper, possible sources of energy dissipation from the testing equipment and lateral supports were considered. In this paper new possible sources of energy dissipation in the sample, apart from the fracture crack itself, are considered. Such dissipation will take place inside the bulk of the most stressed regions of the specimen and, if it is not taken into account, higher values of GF will be recorded than that strictly due to surface fracture energy. When this constribution and the possible energy dissipation analysed in previous work are considered, they are not enough to account for the measured size effect. If GF is to be considered a material parameter, the evaluation of the results from the RILEM method should be analysed more carefully. In any case, the dissipated energy reported here represents a non-negligible amount of GF and should be taken into account when performing measurements.

Resume

Les mesures de l'énergie de rupture GF obtenues selon la méthode préconisée par la Commission Technique 50 de la RILEM, dont on dispose, changent avec la taille de l'éprouvette, ce qui met en question la possibilité de considérer GF comme un paramètre du matériau. On a considéré, dans un article précédent, les sources possibles de dissipation de l'énergie due à l'équipemet d'essai et aux supports latéraux.

On examine dans cet article-ci de nouvelles sources éventuelles de dissipation de l'énergie dans l'éprouvette, excepté celle de rupture proprement dite. Cette dissipation se produira dans la masse, dans les régions les plus contraintes de l'éprouvette et, si on n'en tient pas compte, on energeistrera des valeurs de GF plus élevées que celles strictement inhérentes à l'énergie de rupture superficielle. Si on considère cet apport et la dissipation d'énergie éventuelle analysée dans le travail précédent, ils ne suffisent pas à expliquer l'effet d'échelle mesuré. Si on doit considérer GF comme un paramètre du matériau, il conviendrait d'analyser avec plus de soin l'évaluation des résultats obtenus avec la méthode RILEM. De toute façon, l'énergie dissipée, dont on fait mention ici, représente une part non négligeable de GF et devrait être prise en compte dans les mesures.

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References

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Planas, J., Elices, M. & Guinea, G.V. Measurement of the fracture energy using three-point bend tests: Part 2—Influence of bulk energy dissipation. Materials and Structures 25, 305–312 (1992). https://doi.org/10.1007/BF02472671

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