Damage Progression in Compressively Loaded Laminates Containing a Circular Cutout

A series of experiments have been performed to determine the mechanisms of failure in compressively loaded laminated plates in the presence of stress gradients generated by a circular cutout. Real time holographic interferometry and in situ photomicrography of the hole surface along with strain gauge measurements are used to study the progression of failure. The test specimens are multilayered composite flat plates that are loaded in compression. The laminates are made up of two material systems, T300/BP907 and IM7/8551-7. Two different lay-ups of both systems are investigated. The experimental results reveal that the failure is initiated as a localized instability in the 0 deg plies at the hole surface approximately at right angle to the loading direction. Subsequent to the 0 deg ply failure, extensive delamination cracking is observed with increasing load. The delaminated portions spread to the undamaged areas of the laminate by a combination of delamination buckling and growth, the buckling further enhancing the growth. '