Corrugated and diamond lattice materials have been manufactured as the cores of sandwich panels by slotting together stainless steel sheets and then brazing together the assembly. The out-of-plane compressive, transverse shear and longitudinal shear responses of the corrugated cores have been measured at three relative densities 0:03 < q 6 0:10 and compared with analytical and finite element (FE) predictions. Finite element models are in good agreement with the experimental measurements while the analytical models over-predict the measured strength due to a neglect of manufacturing imperfections. The out-of-plane compressive and transverse shear responses of the diamond cores have also been measured at three relative densities 0:08 6 q 6 0:25. The compressive strengths are sensitive to the aspect ratio of the specimens for L/H < 4 and again are below the analytical predictions due to imperfections. The longitudinal shear strength and energy absorption compare favorably with competing core topologies but the prismatic corrugated and diamond cores are weaker than the pyramidal and square-honeycomb under compression and transverse shear.
Stainless steel square-honeycombs have been manufactured by slotting together steel sheets and then brazing the assembly. Their out-of-plane compressive response has been measured as a function of the relative density, the ratio of specimen height to cell size, and the degree of constraint associated with bonding of the honeycomb to face-sheets. It has been found that, for the practical range of relative densities (less than 20%), the peak strength is relatively insensitive to both the ratio of the specimen height to cell size and to the presence or absence of bonding to face-sheets. An analytical model, derived from existing models for the buckling of shells, for elastic and plastic buckling of the square-honeycombs is shown to be in good agreement with the experimental measurements.
An experimental and analytical investigation is carried out to examine the in-plane compressive response of pyramidal truss core sandwich columns. The identified failure mechanisms include Euler buckling, shear buckling and face wrinkling. The operative mechanism is dependent on the properties of the bulk material and geometry of the sandwich columns and analytical formulae are derived for each of these modes. Failure maps are constructed for sandwich columns made from an elastic ideally-plastic material and AISI 304 stainless steel which has a strongly strain hardening response. Pyramidal core sandwich columns made from 304 stainless steel have been designed using these mechanism maps and the measured responses are compared with the analytical predictions. Finally, optimal single layer and multi-layer pyramidal sandwich column designs that minimize the weight for a given load carrying capacity are calculated using the developed analytical models for the failure of the sandwich columns. The results demonstrate that pyramidal core sandwich columns outperform the currently used hat-stiffened column design.
Sandwich panels with aluminum alloy face sheets and a hierarchical composite square honeycomb core have been manufactured and tested in out-of-plane compression. The prismatic direction of the square honeycomb is aligned with the normal of the overall sandwich panel. The cell walls of the honeycomb comprise sandwich plates made from glass fiber/epoxy composite faces and a polymethacrylimide foam core. Analytical models are presented for the compressive strength based on three possible collapse mechanisms: elastic buckling of the sandwich walls of the honeycomb, elastic wrinkling, and plastic microbuckling of the faces of the honeycomb. Finite element calculations confirm the validity of the analytical expressions for the perfect structure, but in order for the finite element simulations to achieve close agreement with the measured strengths it is necessary to include geometric imperfections in the simulations. Comparison of the compressive strength of the hierarchical honeycombs with that of monolithic composite cores shows a substantial increase in performance by using the hierarchical topology.
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