Asymptotic analysis of laminated composites with countersunk open- and fastened-holes

A linear stress analysis reveals singular stress fields at lamina (ply) interfaces in open- and fastened-hole problems, analogous to free-edge stress fields. An asymptotic analysis was performed in the vicinity of orthotropic ply interfaces at open- and fastened-hole edges to assess the power of singularity at critical locations. Three locations were examined through the thickness of the hole; vertical section (shank), countersunk section and intersection of the shank and the countersunk edge. The power of singularity was calculated around the hole edge at three countersunk angles (0°, 30° and 50°) and at three ply interfaces ([45/−45], [0/45] and [45/0]). In the open-hole case, the power of singularity at the vertical edge was weaker than 0.1 in all interface configurations and locations, and that at the 75° countersunk edge reached a maximum of 0.2876 at the [45/−45] interface as the countersunk angle increased. No singular root was found at intersection of the shank and any angles of the countersunk edges. In the fastened-hole edge case, the observed trends were largely opposite to the open-hole case. In the shank of the hole, the power of singularity reached 0.3010 at the [45/−45] interface, which was the strongest singularity found for all countersunk angles explored. The intersection of the shank and 50° countersunk edges exhibited the highest degrees of singularity of 0.7591 at the [45/−45] interface.