Nonlinear damping measurements applied to fatigue life prediction of structures

B. J. Lazan showed in 1951 that nonlinear damping coefficients measured from hysteresis loops with maximum stresses above the fatigue endurance limit are a function of fatigue life. A new methods of Lazan Coefficients derivation from different forms of hysteresis loops are discussed in this paper. Experimental results of Lazan Coefficients from a free vibration decay apparatus with a bending fatigue specimen as the hinge element are presented. An unexpected bulge in the Lazan Damping Coefficients with respect to fatigue life is demonstrated in the experimental results. Intermediate level hysteresis loops with maximum stresses between 10 percent and 80 percent of the fatigue endurance limit are used for the coefficient derivation. A hypothesis is given for the material physics that would explain the bulge in the damping coefficient measurements. Simulation studies of the Lazan Damping Coefficient detection ability on a simple mechanical structure are discussed. Areas of additional hysteretic damping research for advances into machine design fatigue damage evaluation are recommended.