Nonlinear vibration effects on the fatigue life of fluid-conveying pipes composed of axially functionally graded materials

Fatigue is inevitable in pipes conveying fluid due to unwanted vibration. Internal resonance occurs in such pipes due to pre-pressure. For the first time, the effects of vibration on the fatigue of fluid-conveying pipes are investigated in this paper. The influences of the internal resonance and the axially functionally graded materials on the fatigue of the pipes are analyzed, aiming at improving mechanical properties and increasing fatigue life. The Galerkin method and the direct multi-scale method are used to construct the solvability condition for the primary resonance and 1:3 internal resonance. Approximate analytical solutions are derived for presenting the nonlinear dynamics of the pipes. The tensile, bending, and resultant stress distribution of the axially functionally graded pipe in internal resonance is determined. The results of the fatigue analysis demonstrate that internal resonance can shorten the fatigue life of axially functionally graded pipes. Reducing the distribution coefficient of functionally graded pipe is beneficial for reducing the resonance response and maximum stress of the pipe conveying fluid. The numerical integration results support the analytical results.