Issue 30

A. Fernàndez-Canteli et alii, Frattura ed Integrità Strutturale, 30 (2014) 327-339; DOI: 10.3221/IGF-ESIS.30.40 327 Focussed on: Fracture and Structural Integrity related Issues A probabilistic interpretation of the Miner number for fatigue life prediction A. Fernández-Canteli, S. Blasón University of Oviedo afc@uniovi.es , sergioblasonglez@gmail.com J.A.F.O. Correia, A.M.P. de Jesus University of Trás-os-Montes e Alto Douro, Vila Real, Portugal UCVE-IDMEC-LAETA/School of Sciences and Technology jcorreia@utad.pt , ajesus@utad.pt A BSTRACT . The Miner number M, used as a tool for lifetime prediction of mechanical and structural components in most of the standards related to fatigue design, is generally accepted as representing a damage stage resulting from a linear progression of damage accumulation. Nonetheless, the fatigue and damage approach proposed by Castillo and Fernández-Canteli, permits us to reject this conventional cliché by relating M to the normalized variable V, which represents percentile curves in the S-N field unequivocally associated to probability of failure. This approach, allowing a probabilistic interpretation of the Miner rule, can be applied to fatigue design of mechanical and structural components subjected to variable amplitude loading. The results of an extensive test program on concrete specimens under compressive constant and load spectra, carried out elsewhere, are used. A parallel calculation of the normalized variable V and the Miner number M is performed throughout the damage progression due to loading allowing probabilities of failure to be assigned to any value of the current Miner number. It is found that significant probabilities of failure, say P=0.05, are attained for even low values of M, thus evidencing the necessity of a new definition of the safety coefficient of structural or machine components when the Miner rule is considered. The experimental and analytical probability distributions of the resulting Miner numbers are compared and discussed, the latter still providing a non- conservative prediction in spite of the enhancement. A possible correction is analyzed. K EYWORDS . Cumulative damage; Miner number; Statistical interpretation. I NTRODUCTION he cumulative concept proposed by Palmgren and Miner maintains that the damage level can be expressed in terms of the number of cycles applied at a given stress range divided by the number of cycles needed to produce failure for the same stress range. Failure occurs when the summation of these damage increments at several stress T