Smart sandwich structures with dynamically switchable in-plane thermal expansion coefficients from positive to negative

Capacity to autonomously respond to external stimuli with some switchable structural shapes/properties/functions is highly desirable in many occasions where either system service environments or functional requirements are dynamically changing over time. In this paper, we conceptually propose a new type of smart sandwich structure with the ability to dynamically switch in-plane coefficients of thermal expansion (CTEs) from initially positive to negative or even zero value through internal microstructural transformation triggered solely by a certain temperature stimulus. To this end, a thermally driven snap-through action is purposely added into the design of the microstructure of periodic face-sheets by introducing an active spherical shell component constituted by two materials with different positive CTEs. The lattice core is connected to the upper and lower face-sheets for preventing the overall transverse deformation of face-sheet during temperature variation. Numerical simulations are subsequently carried out to demonstrate the completely reversible snap-through behavior, and the designed function of dynamically switchable in-plane CTE is also validated. Numerical results also reveal that the increasing thickness ratio of high CTE layer to low ones causes a decreased tendency for effective in-plane CTE before snapping, but the influence on after-snapping CTE is negligible. Similarly, the larger shell span brings an obvious increase in effective after-snapping in-plane CTE but without influence on before-snapping CTE. These significant results are beneficial to be summarized as practical design skills for simultaneously designing customized snap-through temperature and effective before or after-snapping in-plane CTE, all of which enable the proposed smart sandwich structure to be flexible to satisfy various requirements in more potential applications.