FREE VIBRATION ANALYSIS AND DESIGN OPTIMIZATION OF SMA/GRAPHITE/EPOXY COMPOSITE SHELLS IN THERMAL ENVIRONMENTS

Abstract

COMPOSITE SHELLS, WHICH ARE BEING WIDELY USED IN ENGINEERING APPLICA-TIONS, ARE OFTEN UNDER THERMAL LOADS. THERMAL LOADS USUALLY BRING THER-MAL STRESSES IN THE STRUCTURE WHICH CAN SIGNIFICANTLY AFFECT ITS STATIC AND DYNAMIC BEHAVIOR. ONE OF THE POSSIBLE SOLUTIONS FOR THIS MATTER IS EM-BEDDING SMA WIRES INTO THE STRUCTURE. IN THE PRESENT STUDY, THERMAL BUCKLING AND FREE VIBRATION OF LAMINATED COMPOSITE CYLINDRICAL SHELLS REINFORCED BY SHAPE MEMORY ALLOY (SMA) WIRES ARE ANALYZED. BRINSON MODEL IS IMPLEMENTED TO PREDICT THE THERMO-MECHANICAL BEHAVIOR OF SMA WIRES. THE NATURAL FREQUENCIES AND BUCKLING TEMPERATURES OF THE STRUCTURE ARE OBTAINED BY EMPLOYING GENERALIZED DIFFERENTIAL QUADRA-TURE (GDQ) METHOD. GDQ IS A POWERFUL NUMERICAL APPROACH WHICH CAN SOLVE PARTIAL DIFFERENTIAL EQUATIONS. A COMPARATIVE STUDY IS CARRIED OUT TO SHOW THE ACCURACY AND EFFICIENCY OF THE APPLIED NUMERICAL METHOD FOR BOTH FREE VIBRATION AND BUCKLING ANALYSIS OF COMPOSITE SHELLS IN THERMAL ENVIRONMENT. A PARAMETRIC STUDY IS ALSO PROVIDED TO INDICATE THE EFFECTS OF LIKE SMA VOLUME FRACTION, DEPENDENCY OF MATERIAL PROP-ERTIES ON TEMPERATURE, LAY-UP ORIENTATION, AND PRE-STRAIN OF SMA WIRES ON THE NATURAL FREQUENCY AND BUCKLING OF SHAPE MEMORY ALLOY HYBRID COMPOSITE (SMAHC) CYLINDRICAL SHELLS. RESULTS REPRESENT THE FACT THAT SMAS CAN PLAY A SIGNIFICANT ROLE IN THERMAL VIBRATION OF COMPOSITE SHELLS. THE SECOND GOAL OF PRESENT WORK IS OPTIMIZATION OF SMAHC CY-LINDRICAL SHELLS IN ORDER TO MAXIMIZE THE FUNDAMENTAL FREQUENCY PA-RAMETER AT A CERTAIN TEMPERATURE. TO THIS END, AN EIGHT-LAYER COMPOSITE SHELL WITH FOUR SMA-REINFORCED LAYERS IS CONSIDERED FOR OPTIMIZATION. THE PRIMARY OPTIMIZATION VARIABLES ARE THE VALUES OF SMA ANGLES IN THE FOUR LAYERS. SINCE THE OPTIMIZATION PROCESS IS COMPLICATED AND TIME CONSUMING, GENETIC ALGORITHM (GA) IS PERFORMED TO OBTAIN THE ORIENTA-TIONS OF SMA LAYERS TO MAXIMIZE THE FIRST NATURAL FREQUENCY OF STRUC-TURE. GA IS AN EVOLUTIONARY COMPUTATION METHOD BASED ON DARWINIAN THEORIES THAT SOLVES OPTIMIZATION PROBLEMS WITHOUT USING GRADIENT-BASED INFORMATION ON THE OBJECTIVE FUNCTIONS. THE OPTIMIZATION RESULTS SHOW THAT USING AN OPTIMUM STACKING SEQUENCE FOR SMAHC SHELLS CAN INCREASE THE FUNDAMENTAL FREQUENCY OF THE STRUCTURE BY A CONSIDERABLE AMOUNT.