Localized buckling in sandwich struts with pre-existing delaminations and geometrical imperfections

A recent model for the nonlinear structural response of compression sandwich struts is developed further to account for pre-existing face-core delaminations and initial imperfections in the strut geometry. Whilst the pre-existing delaminations only take effect after the critical bifurcation for overall (Euler) buckling, it is found that the secondary instability associated with localized buckling occurs earlier than for the initially perfectly bonded strut. More severe instabilities can also be promoted by superimposing geometric imperfections. In combination with delamination, the practical structural response can be highly unstable.