Double-Linear Cumulative-Damage Reliability Method

Fatigue reliability calculations during iterations of the design process have been demonstrated as practical using new analytical and numerical methods based on analytical cumulative-damage reliability tools (α-functions). Effects of fatigue strength and usage distribution may be studied in the presence of load variation. However, to date, the development of the α-functions has been centered on use of the Palmgren-Miner cycle-ratio summation rule for cumulative damage, also known as the Linear Damage Rule (LDR). This paper extends the α-function toolbox for use in determining reliability based on the Manson-Halford Double Linear Damage Rule (DLDR). Examples demonstrate use of the method and charts are provided to illustrate the sensitivity of the cumulative-damage reliability problem to load and strength variations. For a given reliability, probabilistic DLDR methods demonstrate significant reductions in life when compared to LDR methods. The importance of understanding and applying the appropriate LDR, DLDR, or other material characterization is apparent.