Crack deflection processes—I. Theory
Abstract
A fracture mechanics approach has been used to predict fracture toughness increases due to crack deflection around second phase particles. The analysis is based on a determination of the initial tilt and the maximum twist of the crack front between particles, which provides the basis for evaluating the deflection-induced reduction in crack driving force. Features found to be important in determining the toughness increase include the volume fraction of second phase, the particle morphology and aspect ratio, and the distribution of interparticle spacing. Predictions are compared with expected surface area increases.
Résumé
Nous utilisons une approche de mécanique de la rupture pour prévoir l'augmentation de la résistance à la rupture due à la déviation des fissures autour de particules d'une seconde phase. Cette analyse repose sur une détermination de la flexion initiale et de la torsion maximale du front de la fissure entre les particules; on peut alors évaluer la réduction de force motrice pour les fissures, induite par la déviation. Les caracteres importants pour l'augmentation de la résistance comprennent la fraction volumique de la seconde phase, la morphologie et le rapport d'aspect des particules et la répartition des espacements entre particules. Nous comparons les prévisions avec l'augmentation de surface attendue.
Zusammenfassung
Mit einer Näherung der Bruchmechanik wird der Anstieg in der Bruchzähigkeit durch Riβumlenkung um ein Teilchen einer zweiten Phase beschrieben. Die Analyse baut auf der Bestimmung der anfänglichen Verkippung und der maximalen Verdrillung der Riβfront zwischen den Teilchen auf. Daraus läβt sich die durch die Abweichung induzierte Verringerung der treibenden Kraft für die Riβbildung ableiten. Als wichtig Tür die Zähigkeitserhöhung stellen sich u.a. heraus der Volumanteil der zweiten Phase, die Teilchenmorphologie und der Formfaktor, und die Verteilung der Abstände zwischen den Teilchen. Die Voraussagen werden mit den erwarteten. Oberflächenzunahmen verglichen.
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Present address: Department of Ceramic Engineering, The Ohio State University, Columbus, OH 43210, U.S.A.