Question

Equiaxed MAR-M 247 alloy is used to support a stress of 25 ksi (172 MPA). Determine the time to stress rupture at 900*C.

Answer 1

Given: Stress= 25 ksi= 172 MPa

Temperature, T=900 ⁰C= 1173.15 K

Obtain the Larsen Miller (L.M) Parameter for Equiaxed MAR M-247 alloy at a stress of 172 MPa from the Larsen Miller Stree-Rupture Strength Graph.

Larsen Miller Parameter, P= 27.7*10³ K hr

Stress rupture time is calculated using the expression

P = T(log t_r+C)

where P is the Larsen Miller Parameter

T is the Temperature

t_r is the Stress Rupture Time

C is a Constant, usually taken as 20

Substitute the values

27.7*10³ K h = 1173.15 K*(log t_r+20)

log t_r + 20= 23.611

log t_r = 23.611-20

log t_r = 3.611

t_r = 10^3.611

t_r = 4083.19 h

Thus at 900⁰C, the stress rupture time is 4083.19 hour.