Larson-Miller Parameter

This parameter, denoted by m, is expressed as

                        m = T (ln t − C )                                    -------------(23)

or,                    ln t = ((m/T) + C )                                  ---------- (24)

and                   ln σ = k₁ m + c₁                                    ---------- (25)

In above equations, T is temperature in K, t is time for rupture or a specified deformation in hours, σ is stress in N/mm² or MPa. C, k1 and c1 are constants which are determined from experiment. The advantages of the parameter is that by performing quick rupture test or creep test at high temperature and high stress

Eq. (25) can be established. Then this equation can be extrapolated for any combination of σ, t; σ, T or T, t in which t can be large, σ can be small and T can be large or small. This parameter can determine T for a given combination of σ and t or σ for a given combination of T and t or t for a given combination of σ and T. This parametric method is a good design tool.