Finite element simulations for characterization of the composite material behavior of aluminium-polymer-laminate foils used for stretch forming pharmaceutical packagingWednesday (28.09.2016) 10:15 - 10:30 Part of:
Many pharmaceutical companies prefer blister packaging to protect their products. Thereby, two different types of blister packages are used. Based on the manufacturing process they can be divided into thermoformed and cold-formed packages. The thermoformed blister packs are produced by thermoforming of thermoplastic polymer foils into cavity moulds. The cold-formed packages are manufactured by cold stretch forming of aluminium-polymer laminate foils. This composite foil is composed of the three individual material layers polyvinyl chloride (PVC), aluminium and oriented polyamide (oPA). The advantage in using this type of foil for pharmaceutical packaging lies in their high barrier against environmental influences. Therefore, the life cycle of the packed tablets is extended. The disadvantage is the lesser formability which leads to bigger cavities than needed for the product being packed. As a consequence, the dimensions of the whole tablet packages are larger and more material is wasted.
Since the deformation and failure behavior of aluminium-polymer laminate foils is not yet well understood, the design of the punches that form the cavities is one of the critical development stages for the developer of cold-formed blister packaging machines. To be able to optimize the punch geometry and save resources our research activities are focused on the material description and stretch forming behavior of the aluminium-polymer laminate foils. The aim of the present work is to determine a homogenized elastic-plastic description of the laminate by micromechanics. Therefore, a micromechanical model based on the representative volume element (RVE) technique was developed. It consists of a layered structure with periodic boundary conditions. The single layers of the composite foil are mapped and assigned with individual linear elastic, rate independent plastic material behaviors with isotropic hardening. By simulations of different load cases with this model nominal stress-strain curves and shear stress-shear strain curves are determined. These curves give an insight into the anisotropy which results only through the laminate structure of the foil. Furthermore, these results are used to derive two simple homogenized material models.
In addition a stretch forming model close to the real manufacture process of blister packages was designed. Thereby, three simulations of the forming process were done. In the first calculation the foil was mapped with the three material layers of the composite. Each of them was assigned with the individual material properties used in the simulations with the RVE. In the second and the third simulation the two homogenized material models were used. Hypothesis regarding reasons for failure during stretch forming are postulated. According to these the results of the simulations are evaluated.