Fracture toughness of single crystal alumina in air and a simulated body environment.
The critical intensity factor KIC 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's solution for 4 months (n = 6). KIC was 2.345 +/- 0.072 MPam1/2 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 KIC decreased for specimens stored in Ringer's solution (P < .01), but it did not differ significantly between 2 and 4 months. The decrease of KIC is the stress corrosion effect of Ringer's solution at the crack tip, and is not associated with an overall 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 x 500 mm Hg). The stress intensity factor calculated was far less than the KIC. The single crystal alumina disk can endure a static pressure of 500 mm Hg.
Mitamura
Y
Y
Department of Electronic and Information Engineering, School of Engineering, Hokkaido Tokai University, Sapporo, Japan.
Wang
Y
Y
D000388:Air; D000537:Aluminum Oxide; D006350:Heart Valve Prosthesis; D007552:Isotonic Solutions; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D000077331:Ringer's Solution; D013314:Stress, Mechanical
D007552:Isotonic Solutions; D000077331:Ringer's Solution; D000537:Aluminum Oxide