Measuring geometric imperfections of variable-angle filament-wound cylinders with a simple digital image correlation setup

Abstract

Measuring the geometric imperfections in cylindrical shells is a critical step necessary to create accurate numerical models that can capture the imperfection-sensitive behavior of these structures. Modern composite structures, such as variable-–angle filament-wound (VAFW) cylinders, have a unique imperfection signature that is still unknown to the scientific community. This new class of variable–stiffness structures developed by our research group combine wide tailoring capabilities with the efficient manufacturability enabled by filament winding process. The present study proposes an imperfection measurement method that is simple and applicable to both small and large structures. The topographic data is measured with only a pair of cameras. Practical aspects of using digital image correlation (DIC) are described and discussed in detail, such as lighting, focus adjustment, and calibration. State–of–the–art best–fit routines, based on least–squares optimization, are used to transform raw data into a common coordinate system. Finally, the transformed data is stitched together to build a full 3D imperfection pattern that can be readily used in a nonlinear finite element analysis. The developed method is used to measure the imperfections of 12 VAFW cylinders. The mass of the cylinders is used to validate the geometric imperfections and evaluate the variability of the proposed methodology.