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

摘要

An experimental program was conducted to quantify the effects of porosity, ply drop offs and fastener holes on the compression response of AS1/3501-6 graphite/epoxy laminates. Static tests yielded ultimate compressive strains (e(cu)), and constant amplitude fatigue tests yielded threshold strain levels (e(th)) below which fatigue failures will not occur in the specimens for at least a million cycles at R=10 and omega=10 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 E(cu) values significantly. E(cu) 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 E(cu) reductions that were dependent on the laminate configuration. The largest reduction was realized in (O(nt)) specimens. In specimens with a (O(16)/+ or -45(5)/90(4))c to (O(14)/+ or -45(5)/90(4))c configuration change at midlength, achieved by dropping two O(0) plies there, porosity introduced a slight reduction in E(cu) over that caused by ply discontinuities. When a 3/16 in. diameter hole was drilled at the ply drop-off location, the effect of porosity on E(cu) 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 E(cu) significantly.