R (cross section ratio)

The Larson-Miller parameter is a means of predicting the lifetime of material vs. time and temperature using a correlative approach based on the Arrhenius rate equation. The value of the parameter is usually expressed as LMP=T(C + log t) where C is a material specific constant often approximated as 20, t is the time in hours and T is the temperature in Kelvin.

Creep-stress rupture data for high-temperature creep-resistant alloys are often plotted as log stress to rupture versus a combination of log time to rupture and temperature. One of the most common time–temperature parameters used to present this kind of data is the Larson-Miller (L.M.) parameter, which in generalized form is

$P(L.M.)=T[\log t_r+C]$

T = temperature, K or °R
$t_r$ = stress-rupture time, h
C = constant usually of order 20

According to the L.M. parameter, at a given stress level the log time to stress rupture plus a constant of the order of 20 multiplied by the temperature in kelvins or degrees Rankine remains constant for a given material.

References

• F.R. Larson & J. Miller, Transactions ASME, Vol. 74, p 765-771, 1952.
• G. E. Fuchs, High Temperature Alloys, Kirk-Othmer Encyclopedia of Chemical Technology
• Smith & Hashemi, Foundations of Material Science and Engineering
• G.E. Dieter, Mechanical Metallurgy, Third Edition, McGraw-Hill Inc., 1986, p 461-465, ISBN 0-07-016893-8.

See also

• Larson-Miller relation
• Creep (deformation)