CMM-Based Imperfection Mode Analysis and Buckling Performance of Tow-Steered vs. Quasi-Isotropic Cylinders

Measured geometric imperfections can substantially reduce the buckling strength of thin-walled composite cylinders under axial compression. This paper analyzes a University of Bristol dataset of two carbon/epoxy cylinders, one quasi-isotropic (baseline) and one with a tow-steered, variable-stiffness layup, to investigate correlations between imperfection topology and axial buckling performance. Coordinate Measurement Machine (CMM) scans provided high-resolution imperfection maps (out-of-roundness and surface waviness) for each cylinder. The most representative test cases were selected based on the completeness of imperfection data and buckling results. Imperfection fields were characterized via Fourier mode decomposition and compared against classical and nonlinear buckling predictions. The tow-steered cylinder achieved approximately ten percent higher experimental buckling load than the baseline, despite exhibiting a different imperfection pattern. Imperfections in the form of certain circumferential mode shapes were found to be most detrimental, correlating with reductions in buckling strength. Finite element analyses including measured imperfections, closely matched test outcomes (within three to four percent), confirming that imperfection-sensitive buckling behavior can be predicted with high fidelity. The study provides data-driven insights into imperfection sensitivity of composite shells, identifying which imperfection amplitudes and modes most influence axial compression strength, and suggesting design approaches for improved buckling reliability.