Computation of worst geometric imperfection profiles of composite cylindrical shell panels by minimizing the non-linear buckling load

Abstract

• Semi-analytical method is used to compute limit point loads of imperfect cylindrical shell panel. • Global imperfection is represented by double Fourier series . • The unknown Fourier coefficients are determined using genetic algorithm which gives the lowest limit point load. • The “worst imperfection” profile is reported for various stacking sequences of laminated composite cylindrical panel. In this article the “most unfavorable” shape of initial geometric imperfection profile for laminated cylindrical shell panel is obtained analytically by minimizing the limit point load. The partial differential equations governing the shell stability problem are reduced to a set of non-linear algebraic equations using Galerkin's technique. The non-linear equilibrium path is traced by employing Newton–Raphson method in conjunction with the Riks approach. A double Fourier series is used to represent the initial geometric imperfection profile for the cylindrical shell panel. The optimum values of these Fourier coefficients are determined by minimizing the limit point load using genetic algorithm. The results are determined for simply supported composite cylindrical shell panel. Numerical results show that more number of terms is needed in Fourier series representation to obtain the “worst” geometric imperfection profile which gives lower limit load compared to single term representation of imperfection. We have incorporated constraints on the shape of imperfection to avoid unrealistic limit point loads (due to imperfection shape) as we have assumed that the imperfection is due to machining/manufactuting.