Critical Frequency of Self-Heating in a Superelastic Ni-Ti Belleville Spring: Experimental Characterization and Numerical Simulation.

The mechanical loading frequency affects the functional properties of shape memory alloys (SMA). Thus, it is crucial to study its effect for the successful use of these materials in dynamic applications. Based on the superelastic cyclic behavior, this work presents an experimental methodology for the determination of the critical frequency of the self-heating of a NiTi Belleville conical spring. For this, cyclic compressive tests were carried out using a universal testing machine with loading frequencies ranging from 0.5 Hz to 10 Hz. The temperature variation during the cyclic tests was monitored using a micro thermocouple glued to the NiTi Belleville spring. Numerical simulations of the spring under quasi-static loadings were performed to assist the analysis. From the experimental methodology applied to the Belleville spring, a self-heating frequency of 1.7 Hz was identified. The self-heating is caused by the latent heat accumulation generated by successive cycles of stress-induced phase transformation in the material. At 2.0 Hz, an increase of 1.2 °C in the average temperature of the SMA device was verified between 1st and 128th superelastic cycles. At 10 Hz, the average temperature increase reached 7.9 °C and caused a 10% increase in the stiffness and 25% decrease in the viscous damping factor. Finally, predicted results of the force as a function of the loading frequency were obtained.

Avaliação da bioatividade de ligas de NiTi tratadas a laser para aplicação odontológica / Bioactivity evaluation of laser treated NiTi alloys for dental application

As ligas de NiTi são amplamente utilizadas em disposi-tivos da área odontológica, como na Implantodontia, devido as suas propriedades de biocompatibilidade, memória de forma e superelasticidade. Objetivo: Ava-liar a bioatividade e as características morfológicas de liga de NiTi (45,3% de Ni e 54,7% de Ti), tratadas a laser com e sem recobrimento de apatita. Materiais e método: As ligas de NiTi foram obtidas pela técnica Plasma Skull Push Pull, tratadas superficialmente. As amostras foram tratadas a laser (Yb:YAG) e pelo método biomimético em SBF-0 e SBF-6 (Simulated Body Fluid), ambas a 1,5M. A análise de bioatividade foi realizada por meio da pesagem, espectroscopia por energia dis-persiva de raios X (EDS) e microscopia eletrônica de varredura (MEV). Resultados: As espectroscopias reve-laram aumento na concentração de oxigênio e carbono após a ablação, favorecendo a difusão de átomos de oxigênio e formação de óxidos de titânio. Após a de-posição da apatita pelo método biomimético em SBF-0 e 6, o recobrimento apresentou uma razão molar de Ca/P de aproximadamente 1,0, caracterizando a forma-ção de apatitas de baixa cristalinidade. Conclusão: A associação da irradiação a laser e deposição química de apatitas pelo método biomimético em SBF-6, embo-ra tenha demonstrado um melhor desempenho quanto à bioatividade e topografia das ligas, o ganho de massa não foi estatisticamente significativo ao nível de 5%. Tais propriedades podem contribuir para maior inte-ração do biomaterial com o meio biológico e possível redução no tempo de osseointegração.

Artificial biometric finger driven by shape-memory alloy wires.

This paper presents the design and testing of an artificial finger based partly on biomechanics. The prototype was manufactured in acrylonitrile butadiene styrene plastic using a rapid prototyping three-dimensional printer. The flexing of the finger was realized by Ni-Ti shape-memory alloy (SMA) wires with diameters of 0.3 mm, activated by resistive heating. The results obtained show the new prototype to be superior in performance, mainly in terms of angles of rotation of the phalanges, compared with some SMA fingers discussed in the literature.

Effects of neuromuscular electrostimulation in patients with heart failure admitted to ward.

BACKGROUND: Neuromuscular electrostimulation has become a promising issue in cardiovascular rehabilitation. However there are few articles published in the literature regarding neuromuscular electrostimulation in patients with heart failure during hospital stay. METHODS: This is a randomized controlled pilot trial that aimed to investigate the effect of neuromuscular electrostimulation in the walked distance by the six-minute walking test in 30 patients admitted to ward for heart failure treatment in a tertiary cardiology hospital. Patients in the intervention group performed a conventional rehabilitation and neuromuscular electrostimulation. Patients underwent 60 minutes of electrostimulation (wave frequency was 20 Hz, pulse duration of 20 us) two times a day for consecutive days until hospital discharge. RESULTS: The walked distance in the six-minute walking test improved 75% in the electrostimulation group (from 379.7 ± 43.5 to 372.9 ± 46.9 meters to controls and from 372.9 ± 62.4 to 500 ± 68 meters to electrostimulation, p<0.001). On the other hand, the walked distance in the control group did not change. CONCLUSION: The neuromuscular electrostimulation group showed greater improvement in the walked distance in the six-minute walking test in patients admitted to ward for compensation of heart failure.