OLIVEIRA, H. M. R.; http://lattes.cnpq.br/0260667673359516; OLIVEIRA, Henrique Martinni Ramos de.
Resumen:
Shape Memory Alloys (SMA) owe their behavior unique to a reversible phase
transformation between two crystalline structures: martensite (low temperature and
stiffness) and austenite (high temperature and stiffness). This phase change can occur
as a result of two distinct stimuli: a change in temperature or an applied mechanical
stress, both over certain critical values, characteristic of this materials. From the latter
it results the phenomenon of the superelasticity, which is the ability to totally recover a
deformation after simply ceasing the load. During this deformation occurs a stressinduced
martensitic transformation from austenite to martensite, being it an exothermal
process and that tends to stabilize after a certain number of cycles. Investigation
concerning dynamic properties of SMA demonstrate that its superelastic behavior
depends on the strain rate, or in other words, on the excitation frequency. This behavior
results from the complex combination of mechanical stress, temperature and rate of
latent heat dissipation generated in the material. It was also observed that high
frequencies diminish the capacity of dissipation of latent heat, resulting in an increase
in the material temperature and, therefore, in higher values of phase transformation
stresses. This kind of consideration is fundamental in dynamic behavior modeling,
applicable for instance, in vibration absorption systems in civil building. In this context,
the objective of this work is experimentally study the influence of the frequency on
superelastic behavior of pre-stabilized Ni-Ti SMA superelastic wires, as well as the
effects of heat generation on the evaluated mechanical properties. Dynamical tests
were performed in a uniaxial tensile mode in Ni-Ti SMA superelastic wires varying the
frequency and simultaneously monitoring sample’s temperature, using a test machine
from MTS, model MTS 793 series.