Quality Exponent Method for Planning and Interpretation of Results of Full-Scale, Low-Cycle Fatigue Tests

A method is presented for safe-life calculations of aluminum structures subjected to low-cycle fatigue loading. The method is based upon the linear relation between log S and log N in the domain of low-cycle fatigue. Miner's Rule obtains the following new formulation:

with

The use of the formulas involves a single parameter, q₀, or an equivalent-quality exponent to be found by test. Other quantities in the formulas are the variables: n_j-number of cycles, S_maxj-maximum stress of the loading cycle, S_aj-alternating stress of the loading cycle, and a material constant, K_s, named virtual ultimate fatigue stress.

The selection of a safe-life quality exponent results in specifying safe-life coupled to a certain probability of survival at a certain confidence level.