Adaptive control of stiffness by electroactive polyurethane

For applications concerning vehicle suspension or the membranes of acoustic loud speakers, a conventional stiffness control method is both useful and desired. However, without total replacement of the material itself or its structure, modification of the stiffness is not an easy matter. Besides, the technology of electro active polymers (EAPs) is a fast-moving topic. The high electro-induced strain level of these materials is an attractive advantage compared to many other mechanical/electrical converging sensor/actuator materials such as piezo devices. This paper presents an easy and innovative method to control the stiffness of EAPs. First, a polyurethane (PU) sample was pre-stretched in the 1-direction, and clamped at both ends. Then, an electrical field was induced in the 3-direction. The positive elongation in the 1-direction created a force opposite to that of the pre-stretching since the specimen was clamped. From the equation of force valence, a simple stiffness equation was obtained with the ratio between the pre-stretching force and the force created by the electrical stimuli. Concerning the electrical saturation in the EAP material, the variation in stiffness could be expressed by the equation of electrical field. With a simple experimental viewing, more than 30% of stiffness variation could be obtained with a moderate electrical induction, <32 V/μm.