Influence of phase shift between sinusoidal loadings on the fatigue safety of beams

Abstract

The paper deals with the stress-based fatigue analysis of beams fabricated from constructional steels and subjected to combined bending, tension- compression, and twisting. A complex state of stress with sinusoidal components of equal frequency and arbitrary phase angles is considered. Two functionals of safety are defined the minimum values of which in the time domain determine the safety factor in the safe range of the basic variable space and the number of stress cycles to failure in the high-cycle fatigue range. As an example the influence of the phase shift between bending moment and axial force on the safety factor and the number of cycles to failure is analyzed. It is shown that the more pronounced is the effect, the closer to n/2 is the phase shift, the smaller is the difference in values of the partial safety factors and the higher are the exponents in equations of S-N curves.