Buckling Mechanics Metrology for Brittle Polymeric Thin Films

Thin films are widely commercially used in Industry and require a thorough understanding of their mechanical properties for application. For these commercial films, rapid and facile mechanical characterization is essential. There is currently a lack of mechanical characterization techniques for films with thicknesses in the meso-scale (~5µm to ~100µm). Therefore, a rapid technique that quantifies the modulus of brittle, meso-scale films is desirable. Here, the buckling mechanics of a thin plate are utilized to relate the critical buckling load and the elastic modulus (P_cr ~ EI/a²) where P_cr is the critical buckling load, E is the elastic modulus, I is the moment of inertia, and a is the sample length. Film geometries are varied from, 6mm < width < 18mm and 15mm < length < 45mm, and the critical buckling load is measured for each film. A custom mechanical frame is used to apply a uniaxial compressive force to a 60μm thick cellulose acetate film until buckling occurs. The load to induce buckling changes with geometry, and a constant elastic modulus is observed for all films independent of film geometry. It is shown that this technique has the potential to rapidly characterize the elastic modulus of brittle micron thick films.