SEDL / STP / STP787-EB / STP28498S

Study of Compression Properties of Graphite/Epoxy Composites with Discontinuities

Grimes, GC
Engineering Specialist and Engineer, Northrop Corporation, Hawthorne, Calif.

Dusablon, EG
Engineering Specialist and Engineer, Northrop Corporation, Hawthorne, Calif.

Pages: 26    Published: Jan 1982

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Abstract

This study assesses the static compression and R=10 compression-compression fatigue properties of graphite/epoxy composites with ply drop-off discontinuities under severe operating environments, including room-temperature dry and wet, −65°F wet, and 218°F dry and wet. In 30-ply [(±45)⁵/0¹⁶/90⁴]^C laminates two 0-deg plies or four 45-deg plies are dropped off, symmetrically, in the middle one third of the specimen thickness. Static strength and moduli of elasticity are unaffected by these discontinuities; however, some proportional limit values and Poisson's ratio values are significantly changed. At 1.25 × 10⁶ cycles of constant frequency and amplitude fatigue, the algebraic minimum endurance limit stress level is degraded 15 to 30 percent by the two 0-deg ply drop-offs, but only 0 to 13 percent by the four 45-deg ply drop-offs, or is even increased somewhat. The endurance limits of the surviving specimens are lower than their residual strengths, which vary directly with maximum applied cyclic compressive stress up to a threshold level. Detailed data tables and plots are included.