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A design concept for composite wind tunnel compressor blades at NASA Ames Research Center was based on a sandwich construction composed of carbon fiber-reinforced polymer (CFRP) skins bonded to a syntactic foam core. The detailed design and analysis of this blade required the input of the elastic and strength properties of the sandwich constituents. Available standards that apply to regular foams and honeycomb cores were found to be partly inadequate for this purpose. An improved testing procedure and its analysis that provided the basic elastic and strength properties are reported in this paper. Tensile, compressive, and shear properties of the foam and skin are identified using beam deflection and failure mode analysis.
Constituent properties derived from beam flexure tests culminate in a general strategy of comparing analytical parameters to results found experimentally. The beam failure modes are found to be either in compressive failure of the skin or in shear failure of the core. This matched the analytical predictions. The deflection of the beam in a three-point flexure test was also found to correlate well with the analytical model.
The study concludes that the correlation between experimental results and the analytical predictions will enable the designer to predict the mechanical behavior and strength of a sandwich beam design. Furthermore, it allows for the experimental analysis of a sandwich beam without having to separate its constituent materials.
composite sandwich beams, syntactic foam, failure modes, optimized testing methodology, elastic behavior, strength (materials), composite materials, testing, design
Principal facility mechanical engineer, Calspan Corporation at NASA Ames Research Center, Moffett Field, CA
Principal investigator, Composite Materials Research Program, NASA Ames Research Center, Moffett Field, CA
Professorvisiting scientist, Technion-Israel Institute of TechnologyNASA Ames Research Center, HaifaMoffett Field, CA