Although laminated plates have gained acceptance for use in primary aircraft structural components, their behavior is still not completely understood. The need to include multiple holes for fasteners, weight reduction, and access greatly complicates design processes developed for unnotched plates. In this paper, experimentally measured strains and calculated stress concentration factors are reported for “three hole” combinations representative of geometries found in composite aerostructures. Reasonable correlation is observed between measured strains and strain determined from finite element analyses.
Three different stacking sequences are considered, each representative of a bound on equivalent elastic constants for in-plane loading found in common design practice. The stacking sequences include (0/ + 45/-45/0)2s, (0/ + 45/-45/90)2s and (90/ + 45/ - 45/90)2s. After fabrication, a central hole and two symmetric “influencing” holes were cut in the panels. Strain gages were then applied to the inside of the central hole and in a region away from the holes to provide free field strains. During tensile loading, strains at both locations were recorded and scaled using a modified secant method to obtain the strain concentration factors. Material orientation was then considered in the computation of stress concentration factors. The experimentally obtained results presented in this paper represent design criteria for several geometries. Additional results from extensive finite element analyses are being compiled for publication as a family of design curves.