Biaxial Strength and Stress Rupture of Hot-Pressed Silicon Nitride
Abstract
Static fatigue failure of structural ceramics can be caused by a variety of phenomena including stress corrosion, slow crack growth, surface pit formation, and creep fracture. Hot-pressed silicon nitride (HSPN) with magnesia sintering aid has been extensively studied due to its extremely consistent behavior. Slow crack growth from preexisting flaws, or creep fracture, can control static fatigue in HPSN. An extensive data base of flexural stress rupture experiments has culminated in a fracture mechanism map. The vast majority of static fatigue experiments for engineering ceramics have been in a uniaxial stress state, indeed, usually in four-point flexure. Two studies have compared uniaxial and biaxial slow crack growth for alumina, glass, and a glass ceramic, and a vitreous-bonded abrasive. Testing done was only at room temperature, and with short duration, dynamic fatigue experiments. These studies were encouraging, however, showing that the multiaxial stress state had no effect upon crack growth parameters determined by strength test methods. This study reports high temperature and long duration equibiaxial stress rupture experiments for HPSN. HPSN was chosen because of its high static fatigue reproducibility. It was also possible to examine more than one failure mechanism. Biaxial testing was performed in both the slow crack growth and creep fracture regimes.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 1989
- Accession Number
- ADA216950
Entities
People
- George D. Quinn
- Gunter Wirth