Conditions for laminated plates to remain flat under inplane loading

There is considerable confusion in the existing literature as to whether an unsymmetrically laminated, composite plate will remain flat due to the application of inplane compressive or shear loads. If it does not remain flat, then bifurcation buckling would not normally take place, and transverse displacements would occur no matter how small the inplane loads. This paper investigates the conditions under which arbitrarily laminated and arbitrarily loaded plates remain flat, and therefore when buckling can occur. It is demonstrated that for uniform or linearly varying inplane loads no transverse pressure is necessary to keep a plate flat, although edge moments or transverse forces may be required at the boundaries.