ARAUJO, M. S. O.; http://lattes.cnpq.br/2589703016230329; ARAÚJO, Magna Silmara de Oliveira.
Résumé:
Shape Memory Alloys (SMA) belong to a class of metallic alloys that have unique
functional characteristics: Shape Memory Effect (SME) and Superelasticity (SE). The
Ni-Ti SMA system are the most widespread in the market and can be found in
diverse applications covering mainly medical and odontology. However, many of
these applications takes place under cyclic or variables loads, which makes it
necessary to study the fatigue life of these materials. Therefore, the present study
aims to analyze the fatigue behavior of Ni-Ti SMA superelastic wires with circular and
rectangular, cross sections subjected to dynamic tests in simple bending mode
(Single Cantilever) using a Dynamic Mechanical Analysis (DMA) equipment. The
fatigue life of the Ni-Ti wires was evaluated by the number of cycles until break as a
function of applied strain amplitudes during the mechanical cycling process. In
addition, functional fatigue was assessed by monitoring the evolution of the applied
force on the number of cycles for different deformation amplitudes (0.7, 1.0, 1.3 and
1.6%) and different levels of frequency loading (0.5 and 1.0Hz). The simultaneous
influence of strain amplitude and frequency on fatigue life of the wires was assessed
through a factorial design. It was observed generally that the strength under goes a
slight increase of approximately 5% during the first cycles, tending to stabilize and
remained virtually constant until starting a cyclic decay due to rupture process. It was
also observed by means of Wöhler curves, that circular section wires has a higher
fatigue life to that of the rectangular wires. The factorial design used allowed to
obtain significant statistical models, predictive and well adjusted. Furthermore, the
number of cycles to failure of the Ni-Ti wires depends directly of the cyclic strain
amplitude and frequency of testing, to stand in the range 103 -105 cycles, characterizing a low cycle fatigue.
