Abstract

The deformation on cylindrical surfaces of holes in tensile-loaded laminated composite specimens was measured using new moiré interferometry techniques. Two composite tensile specimens, fabricated from IM7/5250-4 pre-preg with ply layups of [0°4/90°4]3s and [+30°2/-30°2/90°4]3s, were examined using the newly developed moiré interferometry techniques. Circumferential and thickness direction displacement fringe patterns (each 3° wide) were assembled into 90°-wide mosaics around the hole periphery for both composite specimens. Distributions of strain were calculated with high confidence on a sub-ply basis at select angular locations. Measured strain behavior was complex and displayed ply-by-ply treands. Large ply-related variations in the circumferential strain were observed at certain angular locations around the periphery of the holes in both composites. Extremely large ply-by-ply variations of the shear strain were also documented in both composites. Peak values of shear strain approached 30 times the applied far-field axial strain. Post-loaded viscoelastic shearing strains were recorded that were associated with the regions of large load-induced shearing strains. Large ply-group related variations in the thickness direction strain were observed in the [+30°2/-30°2/90°4]3s specimen. An important large-scale trend was observed where the thickness direction strain tended to be more tensile near the outside faces of the laminate than near the mid-ply region. The measured strains were compared with the three-dimensional analysis technique known as Spline Variational Elastic Laminate Technology (SVELT), resulting in a very close match and corroborating the usefulness of SVELT.

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