Scaling Effects In The Static Large Deflection Response Of Graphite-Epoxy Composite Beams

Scaling effects in the large deflection response of graphite-epoxy composite beams was investigated. Eight different scale model beams ranging from I/6 to full scale were subjected to an eccentric axial compressive load to promote large bending deformations and failures. Beams having laminate stacking sequences including unidirectional, angle ply, cross ply, and quasi-isotropic were tested to examine a wide variety of composite response and failure modes. The model beams were loaded under scaled test conditions until catastrophic failure. Data acquired included load, end displacement, and strain measurements, and qualitative failure measurements. The experimental data is compared to a large rotation beam analysis and a finite element model analysis. Results from the tests indicate that the beam response scales in the small deflection region, but deviates as the response becomes nonlinear. Failure modes are consistent between scale models within a laminate family,however, a significant scale effect is observed in strength of the scaled beams. Small scale beams fail at higher normalized load and significantly higher normalized end displacement levels than their full scale prototypes. It is important that this phenomenon be understood before strength testing of scale model composite structures can be utilized.