Propagation Behavior of Machining Cracks in Delayed Fracture

Published

March 1, 2004

Author(s)

Yasumitsu Matsuo, L K. Ives

Abstract

The propagation behavior (subcritical crack growth) of machining induced cracks in silicon nitride was investigated by conducting constant stress (CS) and constant stress rate (CSR) tests. A dye impregnation technique that forces a palladium nitrate solution into cracks was applied to examine the geometry of both the initial machining cracks and the subcritical crack growth (SCG) area of specimens which survived the 10⁶ s duration of the CS test. Comparing both geometries provides important insights into the crack propagation mechanism. The fracture origin before SCG ws comprised of a main part having an elongated semi elliptical shape enclosing a series of smaller semi-elliptical cracks and smaller satellite cracks at the ends of the main crack. SCG resulted in the initial coalescent of many of the crack elements in the main crack and continued growth of all cracks. The initially higher SCG rate indicated by the CSR test results and subsequently lower SCG rate suggested by the longer term CS results is consistent with rapid initial crack growth by coalescence and subsequent exhaustion of this process with time.

Citation

Journal of the American Ceramic Society

Volume

87

Issue

No. 3

Pub Type

Journals

Keywords

delayed fracture, dye penetrant, flexure strength, fracture, grinding damage, machining damage, silicon nitride, slow crack growth

Citation

Matsuo, Y. and Ives, L. (2004), Propagation Behavior of Machining Cracks in Delayed Fracture, Journal of the American Ceramic Society (Accessed September 10, 2024)