Experimental investigation of surface instabilities in cylindrical tensile metallic specimens

The orange peel phenomenon which is characteristic of deformed coarse-grained materials is examined in order to supplement continuum theories of surface instabilities with microstructure related parameters. Specifically, the relationship between microstructure and wavelength of the surface instabilities is investigated. The approach is experimental and consists of spectral analysis of surface undulations in tensile cylindrical specimens. The results indicate that the fundamental wavelength of the phenomenon equals a certain number of average grain diameters and is therefore related to the grain size, but also probably to material hardening characteristics. The results also show that the longitudinal mode of undulation is predominant and induces the circumferential mode, suggesting that despite a lack of axial symmetry, an analytical solution of the longitudinal modes can accurately describe the physical picture. However, it is felt that additional research work is needed on both the experimental and theoretical levels in order to provide a deeper understanding of the phenomenon.