Vibration-assisted fabrication of thin shells with spatially distributed imperfections.

Thin-shell structures, found in biological systems such as beetle carapaces and widely used in aerospace and civil engineering, achieve remarkable strength-to-mass ratios given their slenderness and curved geometries. However, their load-bearing capacity is highly sensitive to geometric imperfections, which are often unavoidable during fabrication and can trigger subcritical buckling. Silicone-based hemispherical domes have served as an experimental surrogate to study this phenomenon, yet prior work has largely focused on localized imperfections, failing to capture the spatially distributed nature of real-world imperfection patterns. Here, we introduce a vibration-assisted method for fabricating thin shells with spatially distributed, mode-shaped imperfections. Silicone is cast onto a thick elastic mold excited by a speaker, and vibration-induced flow during curing creates thickness variations. High-speed imaging and destructive measurements reveal material accumulation at the antinodes of the mold's vibrational modes. The engineered imperfections can be tuned by excitation frequency and mold shape, while their amplitude increases with speaker volume. Buckling experiments demonstrate significant reductions in critical pressure, offering a scalable platform to study and tune imperfection-sensitivity. Beyond shell mechanics, this method enables patterning of soft materials for applications ranging from morphable surfaces to bioinspired design.