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Compression Properties of Porous Laminates in the Presence of Ply Drop-Offs and Fastener Holes.

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Final rept. Jun 82-Jun 84,

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An experimental program was conducted to quantify the effects of porosity, ply drop offs and fastener holes on the compression response of AS13501-6 graphiteepoxy laminates. Static tests yielded ultimate compressive strains ecu, and constant amplitude fatigue tests yielded threshold strain levels eth below which fatigue failures will not occur in the specimens for at least a million cycles at R10 and omega10 Hertz. Results from earlier studies on the same material quantified the effects of compressive loading on plain specimens, specimens with ply discontinuities drop-offs, and specimens with a near uniform porosity distribution. In the reported study, the interaction among the various stress raisers -- ply drop-offs, porosity and fastener holes -- was studied. Test environment affected the Ecu values significantly. Ecu decreased as the environment changed from -65 degrees F wet to room temperature dry, room temperature wet, 218 degrees F dry and 218 degrees F wet conditions, in the specified order. Porosity, approximately 2.5 to 4.5 by volume, caused significant Ecu reductions that were dependent on the laminate configuration. The largest reduction was realized in Ont specimens. In specimens with a O16 or -455904c to O14 or -455904c configuration change at midlength, achieved by dropping two O0 plies there, porosity introduced a slight reduction in Ecu over that caused by ply discontinuities. When a 316 in. diameter hole was drilled at the ply drop-off location, the effect of porosity on Ecu was minimal. Also, the transfer of 10 of the total load as a fastener bearing load at the ply drop-off location did not affect Ecu significantly.

Subject Categories:

  • Laminates and Composite Materials
  • Mechanics

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