Buckling Knockdown Factors for Composite Cylinders

The buckling performance of thin-walled cylindrical shells is well known to be sensitive to small geometric and loading
imperfections. During design, this sensitivity is typically accounted for by multiplying the predicted buckling load of a
geometrically perfect structure by an empirical design factor known as a buckling knockdown factor (KDF). The most
widely used source of KDFs for cylindrical launch-vehicle structures is NASA SP-8007. However, general composite
shells are outside the original scope of SP-8007, and a universal KDF of 0.65 for all composite shell designs has
been used in several recent NASA studies, though the technical justification is unclear. If the NASA SP-8007 is used
to calculate KDFs for composite cylinders, the original assumptions and limitations should be understood and care
must be taken. Additionally, the universal KDF of 0.65 is thought to be unconservative for certain designs and is therefore not recommended.