An aircraft engine has turbine blades made of alloy A-286 (see properties below). One critical row of blades has the operating stress of o = 170 MPa (bending plus axial) and temperature T = 650 C. These values correspond to the most severe operating conditions the aircraft will normally encounter. (a) Determine the number of flight hours after which the blades should be replaced as a part of the maintenance schedule with the safety factor of SF, = 4. (b) Using the service life found in (a), evaluate the temperature margin Tmax - T (C). Constants for the Larson-Miller Parameter Polynomial Fit (units of hours, K, and MPa) Range of L-M Fit Material log (hours) b b bz O, MPa T, K A-286 (Fe-Ni-Cr alloy) 20 116,400 -120,500 53,460 -8,188 69-758 811-1089