Optimized truss structures

Key words cellular metals, metallic foam, open- and closed-cell foam, hollow-sphere foam, optimized truss structures, honeycomb. 

Cellular solids are a class of materials with low densities and novel physical, mechanical, thermal, electrical, and acoustic properties. Low-density cellular metals can feature a wide variety of topologies to include open-cell foam, closed-cell foam, hollow-sphere foam, periodic/optimized truss structures, and honeycomb. Metallic foams consist of air dispersed in a solid matrix, similar to polymer foams such as polystyrene or food foams such as whipped cream. Closed-cell foams feature solid faces such that each cell is independently sealed from its neighboring cells, whereas open-cell foams (also known as porous metals, metal sponges and truss-type materials) do not contain cell walls they only have cell edges. Hollow-sphere foams consist of an assembly of individual hollow spheres. 

Optimized truss structures are produced in a similar fashion to open-cell foams. Virtually any castable alloy can be used to form a trass structure (Federal... 

The relative strength of hollow-sphere foams lies between the theoretical performance of open- and closed-cell foams. The performance of optimized truss structures is similar to that of closed-cell foams and, for the Kagome truss, approaches the behavior of a Hashin-Shtrikman porous material. Honeycombs are the most efficient structures when loaded purely out-of-plane. However, plastic buckling can decrease its performance at low relative densities. Further, since honeycomb is highly anisotropic, any inplane loading results in severely reduced performance. Although the theoretical performance of closed-cell foams far exceeds that of open-cell foams, processing defects result in commercially available material that behaves similar to an open-cell material at low relative densities. Commercially available samples of other types of low-density metallic structures behave nearly as predicted. [17]... 

Luh, G.C. Chuen, C.H. 2004. Multi-Objective optimal design of truss structure with immune algorithm . Computers and Structures, 82, pp. 829-844. 

Chen, G. S., Rruno, R. J., Salama, M. (1991). Optimal placement of active/passive members in truss structures using simulated annealing. AIAA Journal, 29(8), 1327-13 34. doi 10.2514/3.1073 9... 

Models were produced for two structure types a square truss and a sheet-stringer assembly. A variation of the sheet stringer, referred to as the stringer ring, was also modeled, but it did not show advantage over the others. Sensitivity studies were established to determine stability of the model and the basic parameter effects on the natural frequencies for each structure. The structures could then have the secondary structure, piping, and micrometeoroid protection incorporated so they could be optimized for strength and mass requirements. The optimizations would also include variations to the foot print of the structures- Once optimized, the structures could be compared. The thermal requirements would be incorporated based on results of the preliminary studies. 

Kowaliw et al.6 presented a new model of AE, Deval. Deval has been shown to be capable of evolving plane trusses, that is, evolving designs of structure that are stable, capable of effectively distributing external forces, and also optimizing other constraints imposed by a fitness function. 

Hajela, P. and Lee, E. (1995). Genetic algorithms in truss topological optimization. Journal of Solids and Structures, 32(22), 3341-3357. 

Kaveh, A., Talatahari, S. (2009). Particle swarm optimizer, ant colony strategy and harmony search scheme hybridized for optimization of truss stractures. Computers Structures, 87, 267-283. doi 10.1016/j. compstmc.2009.01.003... 

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