Thermomechanical Behavior of Shape Memory Polymer Films and Interfacial Characteristics of Metal – Film Laminates

Abstract

Metal polymer laminates have had wide applicability in the automotive industry. In recent times, there has been an interest to introduce polymer films over metal parts prior to their forming process. This can not only result in cost cutting, but also fulfill the need for polymer films serving as paint replacement product. However, the applicability of such laminates has been limited due to the tendency of the polymer films to delaminate and wrinkle during processing and usage. In this work a Shape Memory Polymer (SMP) – Stainless Steel (SS) laminate system has been studied for its integrity and interfacial strength under a wide range of test conditions. FE analysis of SMP – SS laminate systems have been done to help understand the role of stresses and strains in the polymer film and adhesive layers in relation to delamination and wrinkling. Further, the effect of the geometry of the laminate systems on the tendency for wrinkle formation has been analyzed. In addition, the shape recovery phenomenon of the polyurethane films has been studied in detail at temperatures below and above the glass transition temperature Tg. The polymer is found to have 100% shape recovery, even from large deformations as 40% strains at room temperature when the material is highly crystalline. As the temperature is increased to 50°C, the material becomes viscous due to plastic dislocations and slips occurring in the polymer chains which result in decreased shape recovery as compared to room temperature. At lower temperatures such as 10°C the material becomes very stiff and also exhibits high shape fixity and low strain recovery. A specialized constitutive material model incorporating the shape memory behavior of polyurethane has been used in conjunction with themo–mechanical cycling process within the temperature range of 15°C–40°C.