Buckling of Rectangular Composite Pipes under Torsion

Abstract

The numerical buckling load of rectangular composite pipes under torsional load was derived by using the energy method. The authors found no available simple design method or chart for the buckling loads of rectangular composite pipes, which are often used airplanes, spacecraft, and other lightweight structures, through their involvement in a Mars exploration airplane project. Thus, numerical results were obtained for length-to-width ratios (l/b) from 1 to 20, width-to-height ratios (h/b) from 1 to 6, and [0/90] layer ratios (r) from 0 to 1, which means [(0/90)r,(±45)1-r]s. The layups were assumed to be symmetric, and tension-bending, torsion-bending, and tension-shear coupling stiffnesses were ignored. To establish a simple design method, a closed-form polynomial equation for the buckling load factor was derived by minimizing the weighted residuals of the safe and non-safe side errors, which were obtained by comparing the derived numerical results with the polynomial equations. As a result, the errors of the polynomial equation for the buckling load factor were 4.95% for the non-safe side and 12.4% for the safe side. The errors are sufficiently good for preliminary design use and for parametric design studies and optimization.