A new measurement technique for the estimation of core shear strain in closed sandwich structures

Sandwich structures have been widely used for many years in applications su ch as aircraft panels, marine-craft hulls, racing car bodies and spacecraft solar arrays. Most sandwich panel designs include a lightweight core such as paper honeycomb or closed cell foam encased between two face plates, and in the case of aircraft panels constructed from carbon fibre reinforced pl astics, the core is bevelled and edge pan plies are included to totally enc lose the core. This type of design restricts access to the core making it a lmost impossible for the engineer to measure the shear strain developed in the core during in-service static or dynamic loading. This paper introduces a new measurement technique whereby the shear strain in the core can be es timated from face plate measurements using a linear finite difference appro ximation. The estimation method is presented and supported by calculations on a statically loaded sandwich beam. Static and dynamic experiments were c onducted in order to validate the technique using a honeycomb sandwich beam instrumented with strain gauges on the core and face plates. The results s howed excellent agreement between measured and estimated core shear strain for sandwich configurations with thin face plates, such as those encountere d in aircraft and marine-craft constructions. (C) 2001 Elsevier Science Ltd . All rights reserved.