A granular core for self-healing, variable modulus sandwich composites

Sandwich composites that exhibit complete mechanical and geometric healing when subjected to three-point bending are realized using a novel, pressure-triggered granular core. The sandwich composites are constructed with fiberglass-reinforced, epoxy face sheets and a granular core consisting of noncohesive, glass microballoons. By controlling the granular core hydrostatic compression in the range of 0ĝ€"0.083 MPa, the observed shear modulus of the core spanned nearly three orders of magnitude. Core compression is achieved by evacuating the interior of the sandwich structure and allowing the atmospheric pressure acting on the sandwich to compress the core. Although the compressed cores typically begin to yield near 1% shear strain, the degenerate nature of the core allows for complete recovery of the modulus even after a large strain. By exploiting the inherent stiffness of the sandwich skin and the tunable modulus of the granular core, these sandwich composites are able to undergo healing cycles and completely recover both their mechanical and geometric properties.