This report describes engineering studies that were conducted to examine thedeformation behavior of flat, welded steelsandwich panels under two quasi-static loading conditions: (1) uniaxial compression;and (2) bending with an indenter.Testingand analysisare conducted to studythe force-displacement response of sandwich structures with different core geometries: (1) pipe or tubular cores with outer diameters equal to 2, 3, and 5 in;(2) a 2-inchsquare diamond core;and (3) adouble corrugated core called an X-corewith a 5-inchcore height.Deformation and local collapse modes of sandwich panels...