Shape Memory through Contact : Introduction of MagnetoFriction - Shape Memory Polymers (MF-SMPs)

Materials that have a shape memory are capable to switch between different stable states when external stimuli are applied. This work introduces a new, multi-physical concept for shape memory in assembled composite structures. The concept is called magnetofriction and is based on magnetism, elasticity, contact and friction. In assemblies of permanently magnetized MagnetoActive Elastomers (MAE), the contact pressure is established by magnetic attraction forces. When the assembly is deformed, the contact surfaces slide over each other and the deformed shape is locked by the friction in the interface. A loosening of the contact causes the friction forces to vanish and each part of the assembly recovers its initial state due to the elastic forces in the materials. The contact is restored after the shape recovery. A test assembly, called MagnetoFriction - Shape Memory Polymer (MF-SMP), is used to validate the concept experimentally. It consists of two stacked, permanently magnetized MAE beams. The assembled structure is subjected to a three-point bending test and retains a permanent deformation after the tests. The force displacement response of the MF-SMP reveals that the deformed configuration is stabilized after a first loading cycle. A digital image correlation reveals sliding in the contact interface of the assembly during the first loading. The adhesion, observed in the subsequent loading cycles, is responsible for the shape lock. When the beams are separated manually or by compressed air, the stored deformation vanishes. Magnetofriction is compared to other mechanisms to classify the new concept in the field of shape memory materials.