ISSN: 0884-6804
CODEN: JCTRER
Page Count: 12

The Compressive Failure of Graphite/Epoxy Plates with Circular Holes
Henneke, EG
Member of ASTM, Virginia Polytechnic Institute and State University, Va.

Knauss, JF
Northrop Corp., Calif.

Abstract

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.

Keywords:
composite materials, laminates, graphite composites, compressive properties, stress concentration, holes, buckling, stability, bifurcation, postbuckling

Paper ID: CTR10725J
DOI: 10.1520/CTR10725J
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