Evaluation of the effects of geometric imperfections and wall thickness variation on the buckling behaviour of HDPE domes

This study investigates the buckling behavior of high-density polyethylene (HDPE) pressure vessel domes—including torispherical, hemispherical, and ellipsoidal heads (aspect ratios k = 1.25, 1.5, 1.75, 2.0)—under internal pressure. Thin-walled shells are highly prone to buckling, and even small geometric imperfections can greatly reduce the critical buckling pressure (often by up to ~ 50%). Using nonlinear finite element analysis (static Riks method), we evaluate several imperfection types (eigenmode-affine shape deviations, circular cutouts, single-point load dents, and flat patches) across a range of imperfection amplitudes (e.g., dent depths from 0.01 to 10 mm). A comprehensive parametric study reveals that buckling is predominantly elastic (occurring prior to significant plastic yielding in HDPE) and that imperfection sensitivity varies strongly with dome geometry: more curved shapes (hemispherical) have higher initial buckling strength but suffer larger strength reductions due to imperfections, whereas flatter shapes are less imperfection-sensitive. Notably, adopting a variable wall thickness profile (thicker at the apex and thinner toward the equator, 11.6 mm to 8.4 mm) substantially enhances buckling resistance—by roughly 20%—in the optimal elliptical domes (k = 1.25 and 1.5) compared to constant-thickness shells. These findings underscore the importance of managing geometric imperfections and demonstrate the potential of optimized thickness designs to improve the structural stability and performance of HDPE pressure vessels