SCATTER OF FATIGUE LIFE AND FATIGUE STRENGTH IN AIRCRAFT STRUCTURAL MATERIALS AND PARTS

摘要

The fatigue properties of a specimen or of a structural part subjected to some well-defined type of loading may be described by one single S-N curve, preferably the median one, and the probable deviations from this curve.nThis scatter, be it defined by a single figure such as the standard deviation or by the complete statistical distribution function, may be taken either in the hor¬izontal or in the vertical direction, i.e. in the N- or in the S-direction.nThe first alternative has been almost exclusively used on account of the fact that the scatter of fatigue life is directly given by the observations, whereas the scatter of fatigue strength has to be calculated by means of some mathematical procedure based on knowledge of the median S-N curve and of the variation of the vertical scatter with the number of stress cycles N.nWith respect to fatigue design the scatter of strength offers advantages over the scatter of life which make its determination worthwhile.