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The results of an experimental investigation of the compressive behavior of T300/5208 graphite/epoxy laminated plates measuring 127.0 by 254.0 mm and containing circular holes ranging to 38.1 mm are reported. Two thicknesses, 24-ply and 48-ply, were chosen to differentiate between stability failures resulting from buckling and strength failures caused by the hole. Both quasi-isotropic and orthotropic stacking arrangements were used. The critical buckling load of the 24-ply panels was independent of hole size. Bifurcation occurred in the two half-wave mode longitudinally and one half-wave mode laterally in the quasi-isotropic panels. For the orthotropic 24-ply panels, bifurcation began in the one half-wave mode shape in each direction but changed to the two half-wave mode before failure. Consistent post-buckling strength was exhibited by both laminate configurations. The 48-ply quasi-isotropic specimens displayed decreasing strength with increasing hole diameter to approximately 50% of the ultimate strength of the panel without holes for a diameter-to-width ratio of 0.30. The 48-ply orthotropic panels displayed a strength/stability threshold between hole diameters of 3.175 and 6.35 mm. Panels with hole diameters below 3.175 mm displayed buckling before failure; those with holes larger than 6.35 mm experienced material failure around the hole before panel collapse. The 48-ply quasi-isotropic panels showed no comparable behavior; failure was induced by the stress concentration in these panels for all hole sizes.
Member of ASTM, Virginia Polytechnic Institute and State University, Blacksburg, Va.
Northrop Corp., Hawthorne, Calif.
Stock #: CTR10725J