Abstract
Fracture toughness (KIC) of high purity cold isostatically pressed alumina ceramic (CIP-Al2O3) was determined from the size of cracks induced by Vickers hardness testing at wide range of loads. The observed cracks appeared at following loads: 4.905 N, 9.81 N, 29.43 N and 49.05 N. The studied material exhibits half-penny crack system at lower load of 4.905 N, but it proceeds as the Palmqvist crack system at higher loads, which was determined computationally. For the fracture toughness calculation different models were compared. It was found that fracture toughness increases by rising applied load for all kind of models, which is explained by the indentation size effect. As the fracture toughness overestimation can lead to product malfunction, it is suggested to use the Niihara model, which gives the smallest fracture toughness values.
Kurzfassung
Die Bruchzähigkeit KIC von hochreiner isostatisch kaltgepresster Aluminiumoxidkeramik (CIP-Al2O3) wurde anhand der Rissgröße bestimmt, die durch Vickershärtemessungen bei einer großen Bandbreite von Lasten induziert wurde. Die Risse traten bei den folgenden Lasten auf: 4,905 N, 9,81 N, 29,43 N und 49,05 N. Die untersuchten Materialien weisen ein so genanntes Half-Penny-Risssystem bei niedrigeren Lasten von 4,905 N auf. Es schreitet jedoch im Palmquvist-Risssystem bei höheren Lasten fort, was rechnerisch ermittelt wurde. Für die Berechnung der Bruchzähigkeit wurden verschiedene Modelle verglichen. Es wurde herausgefunden, dass die Bruchzähigkeit mit zunehmender angelegter Last in allen angewandten Modellen steigt, was mit der Größe des Indenters erklärt wurde. Da eine Überschätzung der Bruchzähigkeit zu einem Funktionsausfall eines Produktes führen kann, wird vorgeschlagen das Niihara Modell zu verwenden, das die niedrigsten Bruchzähigkeitswerte liefert.
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