Mechanical & Aerospace Engineering

Biography

Biography: Karam Y Maalawi

Abstract

Functionally Graded Materials (FGM) are the new generation of advanced composites that has gained interest in several engineering applications such as, spacecraft heat shields, high-performance structural elements and critical engine components. Th ey are formed of two or more constituent phases with a continuously variable composition producing properties that change spatially within a structure. FGM possess a number of advantages that make them attractive in improving structural performance, such as higher natural frequencies of composite beams and plates and broader stability boundaries of aircraft wings. Th is paper presents practical realistic models for improving performance and operational effi ciency of some types of composite aero-structural elements. Th e concept of material grading has been successfully applied by incorporating the distribution of the volume fractions of the composite material constituents in the mathematical model formulation. Various scenarios in modeling the spatial variation of the material properties of functionally graded structures are addressed. Case studies include optimization of thin-walled composite box sections, spinning beams against torsional buckling and whirling and aeroelastic optimization of trapezoidal wings against divergence. Design variables encompass the distribution of volume fraction, ply angle and wall thickness as well. Several design charts that are useful for direct determination of the optimal design variables are given. It is shown that by using material and thickness grading simultaneously, the aeroelastic stability
boundary can be broadened by more than 50% above that of a known baseline design having the same total structural mass. Th e wing panel length is proved to be the most signifi cant design variable in the whole optimization process. Th e attained optimal solutions using continuous grading depend entirely upon the prescribed power-law expression which represents an additional constraint on the optimization problem. Results show that material grading in the spanwise direction is much better than grading through the wall thickness of the cross section.