Self-sealing composite sandwich structures

Composite sandwich structures are used extensively in aerospace applications that require high bending stiffness without a weight penalty. Commercial transports rely on sandwich structures for many of the aircraft control surfaces while rotorcraft (e.g., helicopters) make use of composite sandwich panels for primary airframe components and rotor systems. The extreme environmental, thermal, and mechanical loading conditions associated with these applications can lead to matrix cracking of the composite face sheets and subsequent moisture ingress and degradation of the skin-to-core bond. Self-sealing functionality provides a potential solution to these problems. In this work, we adopt a dual microcapsule healing chemistry comprised of silanol terminated poly(dimethyl siloxane) plus a crosslinking agent and a tin catalyst, which is stable to 150 °C. The microcapsules are first incorporated into a woven glass fiber/epoxy composite and cured at 121 °C to yield a final glass transition temperature of 138 °C. The composites are damaged by cyclically driving an indenter tip to a prescribed load into opposing surfaces of the sample. As a crack propagates through the polymer matrix, microcapsules rupture and release the polymer, crosslinker, and catalyst, which combine to react in the crack plane. This healing chemistry achieved 100% sealing of composite samples when 7.5 wt% of 35 μm capsules were dispersed in the matrix. In addition, long term environmental stability using accelerated aging was explored along with the effect of microcapsules on composite mechanical properties. This self-healing system has the potential to increase longevity of the skin-to-core bond and prevent structural degradation such as delaminations.