Abstract
Cracked plates with bonded elastic circular inclusions inside a matrix were subjected to an impact tensile loading. The influence of the inclusion on the propagation of an initial edge-crack was discussed in this paper. Two types of specimens were tested, that is with hard or soft inclusions surrounded by soft or hard matrices respectively. It has been shown that bi-, or tri-furcations of the propagating crack have persistently occured at the region of mesophase between matrix and circular inclusions. The phenomenon of splitting of the initial crack was common in both types of specimens.
For the definition of the prevailing stress field, the dynamic stress intensity factors were evaluated at different positions of the crack, as well as the crack-velocities along the main crack or its branches during their propagation. It was observed that the crack initiation in soft plates with hard inclusions was followed by the emission of Rayleigh waves, which contributed to the mode of fracture of the composite. Isochromatic patterns were also used to simulate the stress-field of the propagating cracks against the inclusions at distinct time-instants where the propagating crack was frozen at this instant and static photoelastic analysis was applied. These approximations gave satisfactory results with the cracks advancing inside the composite plates.
Résumé
On a soumis à des tractions par impact des plaques fissurées comportant des inclusions élastiques circulaires ancrées dans une matrice. On discute ici de l'influence de l'inclusion sur la propagation d'une fissure de bord initiale. On a essayé deux types d'éprouvettes, comportant respectivement des inclusions dures ou tendres, noyées dans une matrice tendre ou dure. On montre que, systématiquement, la fissure en propagation fait état de bifurcations dans la zone de mésophase située entre la matrice et les inclusions circulaires. Dans les deux types d'éprouvettes, on a constaté qu'il était courant que la fissure initiale subisse un phénomène de séparation. Pour définir le champ de contraintes déterminant, on a évalué les facteurs dynamiques d'intensité des contraintes à différentes positions de la fissure, ainsi que les vitesses de la fissuration suivant la fissure principale suivant ses branches au cours de la propagation. On observe que l'amorçage de la fissure dans les plaques tendres comportant des inclusions dures est suivi d'une émission d'ondes de Rayleigh qui contribuent à déterminer le mode de rupture du composite. On a également utilisé des tracés isochromatiques pour simuler le champ de contrainte, en figeant la fissure en cours de propagation et en procédant à une analyse photo-élastique. Ces approximations ont conduit à des résultats satisfaisants dans le cas de fissures qui s'avancent dans des plaques composites.
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Theocaris, P.S., Demakos, C.B. Crack bifurcation modes in composite plates under impact. Int J Fract 32, 71–92 (1986). https://doi.org/10.1007/BF00019785
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DOI: https://doi.org/10.1007/BF00019785