A phase transformational cellular material, including a plurality of bistable cells, each respective bistable cell operationally connected to at least one other respective bistable cell. Each bistable cell enjoys a first stable phase and a second stable phase. The first stable phase is a first geometric configuration and the second stable phase is a second geometric configuration different from the first geometric configuration. An energy transaction is required to shift each respective cell between stable phases. A mechanical energy transaction is required to shift from the first to the second phase, while a thermal energy transaction is required to shift from the second to the first phase.

An energy absorbing structure includes a base, a loading platform, a pair of side supports, a center support, and a pair of flexible segments. The loading platform is spaced apart from the base. The side supports project from the base toward the loading platform. The center support projects from the loading platform toward the base. The flexible segments extend from the side supports to the center support and connect the side supports to the center support. The flexible segments have straight edges and curved surfaces disposed between the straight edges. The straight edges extend from the side supports to the center support and are oriented at an oblique angle relative to the base. Each of the curved surfaces faces one of the base and the loading platform.

An energy absorbing structure includes a base, a loading platform, a pair of side supports, a center support, and a pair of flexible segments. The loading platform is spaced apart from the base. The side supports project from the base toward the loading platform. The center support projects from the loading platform toward the base. The flexible segments extend from the side supports to the center support and connect the side supports to the center support. The flexible segments have straight edges and curved surfaces disposed between the straight edges. The straight edges extend from the side supports to the center support and are oriented at an oblique angle relative to the base. Each of the curved surfaces faces one of the base and the loading platform.

An apparatus including polymer configured to have a first state or a second state, wherein the volume of the polymer in the first state is different to a volume of the polymer in the second state; an actuator configured to be controlled by an input signal to cause the polymer to change between the first state and the second state; and a constraint configured to constrain the polymer in at least a first direction when the polymer changes between the first state and the second state.

A phase transformational cellular material, including a plurality of bistable cells, each respective bistable cell operationally connected to at least one other respective bistable cell. Each bistable cell enjoys a first stable phase and a second stable phase. The first stable phase is a first geometric configuration and the second stable phase is a second geometric configuration different from the first geometric configuration. An energy transaction is required to shift each respective cell between stable phases. A mechanical energy transaction is required to shift from the first to the second phase, while a thermal energy transaction is required to shift from the second to the first phase.