Determine the parameter - Larson-Miller parameters:
Larson-Miller parameters for an alloy at tests levels 10 MPa and 30 MPa are determined respectively as 18 × 104 and 16 × 104. Determine the parameter for 20 MPa.
Solution
Write equation
ln σ= k1 m + c1
where, m is Larson-Miller parameters. Use given values
ln 10 = k1 × 18 × 104 + c1 = 2.3
By subtraction
ln 30 = k1 × 16 × 104 + c1 = 3.4
2 × k1 × 104 = - 1.1
∴ k1 =- 0.55 × 10- 4
∴ c1 = 2.3 + 18 × 0.55 = 12.21
∴ ln σ= - 0.55 × 10- 4 m + 12.21
For
σ = 20 MPa
m =- ln 20 - 12.21 × 104 /0.55
= 16.75 × 104