Crack propagation in concrete subjected to flexuralcyclic loading

Fatigue tests were carried out on notched microconcrete beams subjected to three-point bending tests in a saturated atmosphere.The feature of the crack growth was studied by means of the replica technique associated with scanning electron microscopy, in conjunction with the measurement of the crack mouth opening displacement (CMOD). Two domains must be distinguished in which the fatigue can be considered, depending on the upper boundary of the cyclic load. Beyond a given threshold for the upper boundary of the cyclic load, the first cycle induces an actual crack at the tip of the artificial notch. Observations of fatigue crack propagation are presented in that case and compared with previous investigations in static tests. The influence of the load level on the crack growth rate is discussed.RésuméDes essais de fatigue ont été réalisés sur des éprouvettes encochées de microbéton, en flexion trois points sous atmosphère saturée.La topographie de la croissance de fissure a été observée au microsope électronique à balayage par la technique de la réplique, couplée avec la mesure de l'ouverture de la fissure.Deux domaines de comportement à la fatigue, dépendant du niveau maximal de charge doivent être distingués dans de tels essais de fatigue. Au delà d'un seuil de charge, le premier cycle provoque déjà l'ouverture d'une fissure réelle à la pointe de l'encoche artificielle. Les observations de la propagation de fissure par fatigue sont menées dans ce cas. L'influence du niveau de charge sur la vitesse de propagation est aussi étudiée.

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