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This report evaluates the sandwich beam in four-point bending as a compression test method for advanced composites. To accomplish this evaluation the test method was used to obtain preliminary compressive design data for the temperature range 117 to 589 K (−250 to 600°F) and was analyzed to determine any influence from the honeycomb core on composite mechanical properties. The , , [(±45)2]s, and [0/±45/90]s laminate orientations were investigated utilizing HTS1/PMR-15 graphite/polyimide composite material.
The experimental and analytical results indicated that the test method can be used to obtain compressive elastic constants for graphite/polyimide composites. Elastic data were obtained for a wide temperature range, although many failures were initiated by either load concentrations or top cover debonds. The analysis indicated that the honeycomb core had negligible effects on composite mechanical properties. The top cover carried essentially all the compressive load in the beam test section, and the stress state in the test section of the top cover was essentially uniform and uniaxial.
composites, test methods, compression, mechanical properties, graphite/polyimide, finite-element analysis
Aerospace technologist, Materials Division, NASA Langley Research Center, Hampton, Va.