It is necessary to select a ceramic material to be stressed using a three-point loading scheme (Figure). The specimen must have a circular cross section and a radius of 2.5 mm (0.10 in.), and must not experience fracture or a deflection of more than 6.2 ( 10-2 mm (2.4 ( 10-3 in.) at its center when a load of 275 N (62lbf) is applied. If the distance between support points is 45 mm (1.77 in.), which of the materials in Table 12.5 are candidates? The magnitude of the center point deflection may be computed using the equation supplied in Problem 12.42.

Possible cross sections d Rectangular Circular Support A Me o = stress = T Modulus of Elasticity 10 psi Flexural Streng th Material MPa ksi GPa Silicon nitride (Si;N4) Zirconia" (ZrO2) Silicon carbide (SiC) Aluminum oxide (Al203) Glass-ceramic (Pyroceram) Mullite (3A1203-2SIO2) Spinel (MgAl,01) Magnesium oxide (MgO) Fused silica (SiO2) Soda-lime glass 304 44 250-1000 35145 205 800-1500 115-215 30 100-820 15-120 345 50 275-700 40-100 393 57 247 36 120 17 145 260 185 27 21 110-245 16-35.5 38 1055 110 155 225 33 16 73 11 69 10 69 10