Finite element modeling to analyze creep behavior of functionally graded rotating discs with exponential reinforcement and thickness profiles

The study uses FEM to analyze the creep behavior of a rotating FGM disc made of Al-SiC_p. The disc thickness and SiC_p reinforcement in the disc are assumed to vary according to the exponential functions of the disc radius. The yielding and creep behavior of the disc material are described by Tresca’s criterion and threshold stress-based law, respectively. The disc is assumed to rotate at constant angular velocity under free-free boundary conditions. The disc domain is discretized radially using 3-noded one-dimensional elements with quadratic shape functions. Galerkin’s approach has been used to derive the expressions for stresses and strain rates in the disc. For numerical computation of the creep results, a MATLAB code has been developed corresponding to the FE formulation. The creep results estimated using the FE approach are noticed to be in excellent agreement with those obtained using the analytical technique (continuum mechanics approach), experiment results, and commercial FE software. The study reveals that with the increase in SiC_p gradient in the disc, the elastic as well as creep components of the tangential stress (near the inner radius) and the radial stress increase significantly, though the tangential stress exhibits a sizable decrease toward the outer radius. The increase in SiC_p gradient results in a significant reduction in the steady-state radial and tangential strain rates in the disc, besides resulting in a relatively more uniform distribution of the strain rates, which is desirable for reducing distortion in the disc. The study indicates that the rupture time of the FGM disc could be enhanced significantly by employing a steeper SiC_p gradient in the rotating disc.