DEVELOPMENT OF A DEVICE TO STUDY THE FUNTIONAL FATIGUE IN A TI-NI SHAPE MEMORY ALLOY
Carlos Augusto do Nascimento Oliveira1; Karla Carolina Alvez da Silva1; José Orlando Silveira Rocha2; Cezar Henrique Gonzalez1; Euclides Apolinário Cabral de Pina1; Oscar Olímpio de Araújo Filho1
1 UFPE; 2 IFPE
doi:10.20906/CPS/COB-2015-2527
Resumo
Studies on functional materials has enabled the rise of actuators / sensors with applications in several fields of knowledge, changing from simples applications such as flow control valves to more complex situations such as polymeric actuators used in the human muscles simulation. The development of smart actuator has applied the memory effect and superelasticity to obtain elements capable of producing work from external stimulus. Ti-Ni alloy are an important class that have been used in the production of actuators for mechanical engineering, robotics, aerospace and oil and gas applications. The operation of Ti-Ni actuators/sensors is based on shape memory effect and superelasticity that are properties from thermoelastic martensite transformation. The work cycles, the stabilization of the phase transformation, the emergence of stress fields and phase precipitates can contribute to the material shape memory degradation, this phenomenon is known by the term functional fatigue. This research study the behavior of functional fatigue in Ti-Ni actuators in coil springs shape. The response of the actuator to external stimulus such as electric current, tensions and temperature variations were evaluated by differential scanning calorimetry, mechanical testing and thermomechanical fatigue. The thermomechanical fatigue test is performed in a device developed specifically for this purpose. The device works within a specific range of temperatures, and the force application, over thousands of cycles, simulates the phase transformation. The results will be discussed according to the material behavior due to modification on the critical temperatures of transformation behavior, influence of stress fields and behavior of functional fatigue on the actuator phase transformation.
Palavras-chave: Ti-Ni Alloy; Shape Memory Effect; Martensitic Transformation; Funtional Fatigue