Anisogrid stiffened panel under axial compression: Manufacturing, numerical analysis and experimental testing

Abstract

Within the collaborative FP7 project PoLaRBEAR a high-performance anisogrid prepreg structure concept has been developed considering high quality assurance demands and the need of a state of art manufacturing process (advanced fiber placement). This paper reports on the design, analysis, manufacturing and test of an anisogrid prepreg panel under uniaxial compression. The anisogrid structures consist of intersecting, integral manufactured stiffeners with different directions (helical, circumferential and/or axial) and a load bearing skin. The stiffeners are manufactured from prepreg layers with 60% fiber volume ratio. An alternating pattern of cut and uncut layers is used within the intersection knots to avoid thickening. In addition, there are special interface layers in the stiffener laminate in order to ensure a proper connection between the grid and the load bearing skin even within the postbuckling range. Optical measurements showed that the panel was burdened by manufacturing induced geometric imperfections (process inducted deformations or spring-in) which caused a slight curvature of the anisogrid panel. Geometrically non-linear analyzes were performed using ABAQUS and B2000þþ in order to analyze the pre- and postbuckling response of the panel under axial compression with and without imperfections. Numerical and experimental results are in good agreement if the process induced deformations are considered.