Mechanical behaviour of tear opening in injection moulded plastic tops

Abstract: The tear opening study is conducted with an example from the Tetra Pak package industry, the Tetra Top package. The top of the package is constructed by a injection molded low density thermoplastic. The package is opened with a tear opening located on the top part. In order to make tear opening more versatile, studies how opening forces reacts upon material modifications and alternative geometry has been made. The vertical displacement of the ’drawstring’ (i.e. pull-bridge) concentrate the stress around the tear opening and the shallow pit (e.g. notch) located were the fracture is supposed to initiate. The fracture initiates and the package opens when sufficient force is applied to the pull-bridge. The object of this study is how new materials affects the opening force. An alternate tougher material will in all cases increase the opening force. Modified geometry is hence, necessary to decrease the opening force. Computational studies has shown that a alternate geometry can decrease the opening force with 56%.