Fracture toughness of single crystal alumina in air and a simulated body environment

Abstract

The critical intensity factor K_IC of a single crystal alumina (1100)‐plane in air and in a simulated body environment was measured. Based on these measurements, the estimated durability of a single crystal alumina disk in a ceramic heart valve was determined. Standard single‐edge notched beam specimens were prepared. The specimens were classified into three groups: (a) stored in air (n = 10), (b) immersed in Ringer's solution for 2 months (n = 11), and (c) immersed in Ringer' solution for 4 months (n = 6). K_IC was 2.345 ± 0.072 MPam^½ for specimens stored in air, 2.141 ± 0.147 in Ringer's solution for 2 months, and 2.005 ± 0.153 in Ringer's solution for 4 months. The K_IC decreased for specimens stored in Ringer's solution (P < .01), but it did not differ significantly between 2 and 4 months. The decrease of K_IC is the stress corrosion effect of Ringer's solution at the crack tip, and is not associated with an over all deterioration of strength. The stress intensity factor for possible cracks (length: 0.4 mm) in the single crystal alumina was calculated. Maximum stress was assumed 2.668 MPa ( = 40 × 500 mm Hg). The stress intensity factor calculated was far less than the K_IC. The single crystal alumina disk can endure a static pressure of 500 mm Hg. © 1994 John Wiley & Sons, Inc.