تحليل كمانش پوسته‌هاي استوانه‌يي هدف‌مند تحت بارگذاري محوري با روش بي‌شبكه‌ي محلي پتروف گلركين براساس نظريه‌ي پوسته ي فلوگه

AXIAL BUCKLING ANALYSIS OF FGM CYLINDRICAL FLUGGE SHELLS USING THE MLPG METHOD

در اين نوشتار روش بي شبكه محلي پتروف گلركين (MLPG) براي تحليل كمانش پوسته‌ها ي استوانه‌يي هدف‌مند تحت بارگذاري محوري بررسي شده است. در اين تحليل معادلات ميدان جابه‌جايي برمبناي نظريه‌ي فلوگه استخراج ‌شده و پوسته متشكل از تركيب پيوسته ي سراميك و فلز فرض شده است. بنابراين مشخصات مكانيكي ماده ي تشكيل‌دهنده‌ي پوسته ي استوانه‌يي، مطابق با توزيع كسر حجمي تواني در راستاي ضخامت تغيير مي كند. معادلات پايداري حاكم بر پوسته به‌صورت عددي با روش MLPG حل شده است. بدين‌منظور، فرم جديدي از تابع تغيير طبق يك روش شبه معكوس در نظر گرفته شده كه منجر به دست‌يابي ماتريس هاي سفتي ‌شده و در نهايت بارهاي بحراني در شرايط مرزي مختلف محاسبه شده‌اند. نتايج حاصل از مطالعه‌ي تغييرات كسرهاي حجمي، مشخصات هندسي پوسته، و شرايط تكيه گاهي مختلف به‌خوبي بيان‌گر همگرايي و دقت بالا در روش مورد استفاده است.

In this paper, the meshless local Petrov-Galerkin (MLPG) method is implemented to study the buckling of FGM (Functionally Graded Material) cylindrical shells under axial load. Displacement field equations, based on the Flugge shell theory, are taken into consideration. Material properties are assumed to be temperature-dependent and graded in the thickness direction according to different volume fraction functions. A FGM cylindrical shell made up of a mixture of ceramic and metal is considered. The FGMs are multifunctional composite materials, the mechanical properties of which vary smoothly and continuously from one side to the other. This is achieved by a continuous change in composition of the constituent materials. The set of governing equations of motion are numerically solved by the Meshless method, in which a new variational trial-functional is constructed to derive the stiffness matrices, so that the critical buckling loads are obtained under various boundary conditions, using a discretization procedure and solving the general eigenvalue problem. The MLPG method, based on a local formulation, can include all other meshless methods based on a global formulation, as special cases, if the trial and test functions and the integration methods are selected appropriately. In the MLPG, the nodal trial and test functions can be different. Herein, the moving least squares (MLS) interpolation is employed to construct both trial and test functions. The present method is a truly meshless method based on a number of randomly located nodes, upon which no global background integration mesh is needed and no element matrix assembly is required. In the present MLPG formulation, a local variational form is constructed over a local sub-domain instead of using the conventional weighted-residual procedure. The influences of some commonly used boundary conditions, variations of volume fractions and effects of shell geometrical parameters are studied. The results show the convergence characteristics and accuracy of the mentioned method.