Compressive Buckling Behavior of Graphite/Epoxy Isogrid Wide Columns with Progressive Damage

The damage tolerance of graphite/epoxy isogrid wide columns in compressive buckling is studied. The observed failure mode in bending was simulated on the panels by cutting grid ribs at nodal sites. The panels were tested nondestructively as clamped wide columns with buckling loads determined by a stiffness plotting technique. Degradation of buckling resistance was determined by progressively damaging lengthwise ribs and retesting the panels. Strains at selected rib sites were measured at each damage level to ascertain the redistribution of stresses. Also, flexual vibration tests were conducted at each damage level to assess the frequency reduction. A finite element analysis provided satisfactory correlation with test data. The results demonstrate that this type of structure is very tolerant to damage.