The deformation response of ultra-thin polymer films on steel sheet in a tensile straining test: the role of slip bands emerging at the polymer/metal interface

Forming of pre-coated sheet metal becomes of increasing importance in various fields of industrial application. In the recent years, ultra-thin plasma-polymer films have emerged as promising candidates as pre-treatments for steel sheet. Not much, however, is known about the forming behaviour of ultra-thin polymer coatings on ductile substrates, while an extensive literature exists for the reverse case, metal films on polymer, or brittle films on deformable substrates in general. For these cases, advanced models exist, mostly based on the so-called shear lag approximation. The heterogenous, highly localized strain and stress distribution, typical of ductile substrates, as well as out of plane displacements at the interface are disregarded, but cannot be neglected at the high strain levels of interest for elastic polymer films. This paper will focus on the role of slip bands on cracking of ultra-thin polymer films.