Natural frequency analysis of functionally graded fiber metal laminates under thermal environments: A computational study

This study examines the natural frequency analysis of newly proposed functionally graded fiber metal laminate (FGFML) panels in thermal environments using the finite element method (FEM). The FGFML panels feature four carbon fiber composite cores with distinct stacking sequences, sandwiched between two layers of ZrO ₂ /Al functionally graded material (FGM), which exhibit temperature-dependent material properties. Two FEMs were used, first-order shear deformation theory with equivalent single-layer (ESL) shell elements and three-dimensional graded brick elements with user-defined subroutines (USDFLD). Therefore, validation studies demonstrated that 15-layer ESL models closely matched experimental data. The ESL method outperformed solid element simulations when the slenderness ratio was higher. The errors were usually less than 8% compared to the experimental values. Systematic parametric analyses revealed that natural frequencies decreased monotonically as the power law gradient index increased (n = 0 to 5), with ceramic-rich compositions (n = 0) exhibiting frequencies up to 15% higher than those of metal-rich configurations (n = 5). Temperature changes caused the frequency to drop by 26 to 42 Hz for every 100 K rise, with higher modes being more sensitive. Studies on fiber orientation have shown that [0₄] laminates exhibit the highest stiffness, while [90₄] configurations have the lowest frequencies. These findings are particularly relevant for aerospace applications, where FGFML structures are required to maintain structural integrity under combined thermal and mechanical loading conditions.