Fracture mechanics of green products

doi:10.1016/0955-2219(93)90053-T

Journal of the European Ceramic Society

Volume 11, Issue 1, 1993, Pages 9-16

https://doi.org/10.1016/0955-2219(93)90053-T Get rights and content

Abstract

The tensile strength of ceramic green samples (binderless zirconia powder) was investigated within the formalism of linear fracture mechanics. Dry pressed samples were found to obey fairly well the classical laws (Weibull's statistics, the relationship between stress intensity factor and fracture energy). The comparison between the mechanical properties of pressed and cast samples showed that the interparticle forces responsible for the cohesion depend strongly on the shape-forming process. The mechanical interlocking of particle asperities is of primary importance in the strength of pressed samples. Moreover, for a given density the critical defect size is larger in cast than in pressed samples, while the pore size distribution is sharper (which is usually considered as a proof of ‘better’ microstructure). This sheds light on the differences between cracks in granular materials and pore structure.

Zusammenfassung

Die Zugfestigkeit keramischer Grünkörper (Zirkoniumdioxidpulver ohne Binder) wurde im Rahmen der Formalismen der Bruchmechanik untersucht. Trocken gepreßte Proben genügen weitgehend den klassischen Gesetzmäßigkeiten (Weibullstatistik, Zusammenhang zwischen dem Spannungsintensitätsfaktor und der Bruchenergie). Ein Vergleich der mechanischen Eigenschaften gepreßter und durch Schlickerguß hergestellter Proben zeigt, daß die für die Zugfestigkeit verantwortlichen Kräfte zwischen den einzelnen Teilchen im Grünkörper stark vom Formgebungsprozeß abhängen. Bei gepreßten Proben ist das mechanische Verhaken der Teilchen von entscheidender Bedeutung. Des weiteren ist bei gegebener Dichte die kritische Defektgröße in schlickergegossenen Proben höher als in gepreßten Proben, wobei jedoch die Größenverteilung der Poren ausgeprägter ist, was üblicherweise ein Kriterium für ein günstigeres Gefüge darstellt. Dieses Ergebnis verdeutlicht den Unterschied zwischen der Porosität und den Defekten in einem porösen Material.

Résumé

La cohésion de pièces céramiques crues (poudre de zircone sans liant) a été étudiée dans le cadre du formalisme de la mécanique de la rupture. Les pièces obtenues par compaction obéissent bien aux lois classiques (statistique de Weibull, relation entre le facteur d'intensité de contrainte et l'énergie de rupture). La comparaison entre les propriétés mécaniques de pièces obtenues par coulage et pressage montre que les mécanismes microscopiques de cohésion sont différents dans les deux cas. Notamment, l'accrochage mécanique des particules intervient de façon déterminante dans la cohésion des pièces pressées. Par ailleurs, quoique la répartition de taille des pores, pour une densité donnée, soit plus étroite pour les pièces coulées que pour les pièces pressées (ce qui est généralement admis comme la preuve d'une ‘meilleure’ microstructure), la taille de défaut critique est plus grande. Ce résultat éclaire la différence entre la porosité et les défauts dans un matériau granulaire.

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Fracture mechanics of green products

Abstract

Zusammenfassung

Résumé

Powder Technol.

Powder Technol.

Colloids and Surfaces

J. Colloid Interf. Sci.

Powder Technol.

Int. J. Pharm.

Powder Technol.

Powder Technol.

Powder Technol.

Ultimate tensile strength of cohesive powders based on non-uniform packing model

J. Chem. Ing. Japan