Phenomena in the bifurcation of unsymmetric composite plates

The phenomena observed in the large scale bifurcation of unsymmetric composite plates are characterized. Such plates can exhibit more than one stable geometry and can be ‘snapped’ from one geometry to another. It is convenient to think of this process as providing sufficient strain energy to overcome an energy maximum and is analogous to an activation energy. To describe the snap-through process, 2-ply, [0, 90] unsymmetric plates were forced from one state to the other in rigid test rigs such that great control could be achieved over the process and loads and deformations were monitored throughout the bifurcation. A hitherto unrecognised phenomenon was noted in that the snap-through process was seen to take place not as a single bifurcation but as two closely coupled bifurcations, as first one side snaps through and then the other. The experimental approach taken here, coupled with the simple energy analysis, should be of value in understanding practical structures of multiple stable states, such as might be used in morphing or adaptive aircraft.