NITINOL-REINFORCED PLATES .1. THERMAL-CHARACTERISTICS

The static and dynamic characteristics of NITINOL-reinforced composite plates are influenced primarily by the temperature distribution inside the composite matrix. Such distribution arises from the electrical heating of NITINOL fibers embedded along the neutral plane of these composite plates. When temperatures are developed above the martensite transformation temperature of the NITINOL fiber, the elastic modulus of the fibers increases approximately fourfold and significant phase recovery forces are generated. Such thermal activation of the NITINOL fibers increases the elastic energy of the fibers and enchances the stiffness of the plates, provided that the phase recovery forces are high enough to compensate for the loss of the modulus of elasticity of the composite and counterbalance the generated thermal loads. Understanding the interaction between the thermal, static and dynamic characteristics of the NITINOL-reinforced plates is essential to tailoring the performance of these plates to match changes in the operating conditions. Such an interaction is influenced primarily by the temperature distribution inside the plates during the activation and de-activation of the NITINOL fibers. In this study, a thermal finite element model is developed to determine steady-state and transient temperature distributions inside NITINOL-reinforced composite plates resulting from different activation strategies of the NITINOL fibers. The theoretical predictions are compared with experimental measurements in order to validate the thermal finite element model. The resulting temperature distribution can be used to determine an average modulus of elasticity of the composite. The average temperature rise above ambient can also be used to compute the axial thermal loading on the composite plate. Such predictions are utilized in computing the static and dynamic characteristics of NITINOL-reinforced plates which are presented in Parts II and III of this paper, respectively.