Abstract
The essential work of fracture concept has been extended to cover ductile tearing of polymeric materials that neck before fracture. It is shown that the plane stress specific essential fracture work (w e) can be obtained from deeply edge-notched tension specimens, containing either single or double notches, by extrapolating the straight line relationship between the total specific fracture work (w f) and ligament length (l) to zero ligament. In this way, specific essential fracture works have been obtained for nylon 66 and two polyethylenes. It seems that w eis a material property for a given sheet thickness being independent of specimen geometry. The straight line relationship between w fand l breaks down when the ligament length to sheet thickness ratio is less than about three, since the fracture data fall in the plane stress-plane strain transition region. However, a plane strain specific essential fracture work can still be obtained by extrapolating the least squares curve of the data to zero ligament provided the thickness satisfies plane strain condition. If this condition is not satisfied a near plane strain value is obtained which is dependent upon thickness. This method is also appropriate for ductile polymers like the rubber modified polystyrenes that craze rather than neck.
J Rcurves have also been obtained for nylon 66 and the polyethylenes. Under strictly J-controlled crack growth conditions, it is shown that the intercept and slope of the J Rcurve, i.e. J cand dJ/da, are related to the intercept and slope of the w fversus l plot. The limited amounts of J-controlled data available have precluded a more definite and general conclusion to be made. But based on what little is available, the comparisons of these two quantities in the J R-Δa and w f-l plots are not unreasonable.
Résumé
On a étudié le concept de travail essentiel de rupture pour couvrir l'arrachement ductile des matériaux polymères qui sont sujets à striction avant la rupture. On montre que le travail essentiel de ruptures (We) spécifique à l'état plan de tension peut être obtenu dans le cas d'éprouvettes de traction à entaille latérale profonde comportant une ou deux entailles, en extrapolant la relation linéaire qui lie le travail total de rupture (Wf) et la longueur de ligament (l) jusqu'à un ligament nul. De la sorte, on a obtenu le travail essentiel de rupture pour du nylon 66 et pour deux poly-éthylènes. I1 semble que We est une propriété du matériau pour une épaisseur de plaque donnée, qui est indépendante de la géométrie de l'éprouvette. La relation linéaire entre Wf et l par par un point de rebroussement lorsque le rapport de la longueur du ligament à l'épaisseur de la tôle devient inférieur à environ trois, ce qui correspond au passage des données de rupture dans la transition contrainte plane-déformation plane. Néanmoins, on peut encore obtenir un travail essentiel de rupture spécifique à l'état plan de déformation en extrapolant par les moindres carrés les données jusqu'à un ligament nul, pour autant que l'épaisseur satisfasse un état plan de déformation. Si cette condition n'est pas satisfaite, on obtient une valeur pour un état voisin de l'état plan de déformation, qui dépend de l'épaisseur. Cette méthode est également utilisable dans le cas des polymères ductiles qui, tels les polistyrènes de la famille des caoutchoucs, sont sujets à effritement.
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Mai, YW., Cotterell, B. On the essential work of ductile fracture in polymers. Int J Fract 32, 105–125 (1986). https://doi.org/10.1007/BF00019787
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DOI: https://doi.org/10.1007/BF00019787