On Buckling of Unidirectional Boron/Aluminum Stiffeners — A Caution to Designers

Abstract

Unidirection boron/aluminum stiffeners have been used to save weight in stiffened panels, where the cross-sections were of such shapes as hats, rs, Z's, channels, etc. The buckling analysis of these structures is usually found to be unconservative when tests are performed. Even so, a weight saving of approximately 50% can be achieved in the stiffeners themselves by replacing their metal counterparts. A no-edge-free crippling test was performed on a unidirectional boron/aluminum laminated plate, where collapse occurred at a compressive load considerably below the theoretical bifurcation buckling point. This premature failure is explained by a numerical analysis of the test by the use of a nonlinear computer code, which revealed the presence of high transverse bending stresses beyond the capacity of the composite.