Rate Dependency During Relaxation of Superelastic Orthodontic NiTi Alloys After Hydrogen Charging

Letaief, Wissem Elkhal; Hassine, Tarek; Gamaoun, Fehmi

doi:10.1007/s40830-016-0051-6

Cited by 12 publications

(8 citation statements)

References 26 publications

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“…Table 2 presents all the values of material parameters needed to simulate the numerical response of the developed model. The parameters related to the hydrogen effects are calibrated from our previous experimental tests (Elkhal Letaief et al, 2016, 2017a, 2017b). The parameters f h and y h , which present the transformation delay and the dissipation induced by hydrogen, are obtained through one-cycle tensile tests after charging wire with hydrogen (Elkhal Letaief et al, 2016).…”

Section: Methodsmentioning

confidence: 99%

“…The parameters related to the hydrogen effects are calibrated from our previous experimental tests (Elkhal Letaief et al, 2016, 2017a, 2017b). The parameters f h and y h , which present the transformation delay and the dissipation induced by hydrogen, are obtained through one-cycle tensile tests after charging wire with hydrogen (Elkhal Letaief et al, 2016). The chemical expansion coefficient β and the constants related to hydrogen-induced residual martensite ( C A , C M ) are obtained through in situ tests that consist in charging wires with hydrogen during applying tensile load (Elkhal Letaief et al, 2017a, 2017b).…”

Section: Methodsmentioning

confidence: 99%

“…Concerning hydrogen, it has shown important impacts on the mechanical behavior of the NiTi alloys during tensile tests, such as embrittlement and sudden fracture (Gamaoun et al, 2011; Yokoyama et al, 2016). In addition, a heightening in the transformation stress and a decrease in its strain have been noticed since the hydrogen obstructs some austenitic NiTi lattices to transform to the martensite phase (Elkhal Letaief et al, 2016; Gamaoun and Hassine, 2014).…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Finite element analysis of hydrogen effects on superelastic NiTi shape memory alloys: Orthodontic application

Letaief

Fathallah

Hassine

et al. 2018

Journal of Intelligent Material Systems and Structures

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Thanks to its greater flexibility and biocompatibility with human tissue, superelastic NiTi alloys have taken an important part in the market of orthodontic wires. However, wire fractures and superelasticity losses are notified after a few months from being fixed in the teeth. This behavior is due to the hydrogen presence in the oral cavity, which brittles the NiTi arch wire. In this article, a diffusion-mechanical coupled model is presented while considering the hydrogen influences on the NiTi superelasticity. The model is integrated in ABAQUS finite element software via a UMAT subroutine. Additionally, a finite element model of a deflected orthodontic NiTi wire within three teeth brackets is simulated in the presence of hydrogen. The numerical results demonstrate that the force applied to the tooth drops with respect to the increase in the hydrogen amount. This behavior is attributed to the expansion of the NiTi structure after absorbing hydrogen. In addition, it is shown that hydrogen induces a loss of superelasticity. Hence, it attenuates the role of the orthodontic wire on the correction tooth malposition.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Finite element analysis of hydrogen effects on superelastic NiTi shape memory alloys: Orthodontic application

Letaief

Fathallah

Hassine

et al. 2018

Journal of Intelligent Material Systems and Structures

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“…To the best of our knowledge, these tests have been conventionally used for determination of equilibrium stress, yet none of them could precisely indicated equilibrium stress levels of the materials. 61–65…”

Section: Introductionmentioning

confidence: 99%

An observation of the evolution of equilibrium stress on poly(lactic acid) and poly(lactic acid)/hydroxyapatite nanocomposites

Düşünceli

2020

Proceedings of the Institution of Mechanical Engineers, Part C:

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Relaxation behavior provides specific information that indicates stress development with elapsed time for the determination of material characterization and constituting of material modeling. In addition, anomalous relaxation behavior of polymeric materials enables experimental analysis of some theoretical variables in constitutive equation. Equilibrium stress is one of the most prevailing variables in material modeling and it is generally considered as unmeasurable. In this study, evolution of equilibrium stress was examined with relaxation tests of two semi crystalline polymer materials, one of which was found to reach precise equilibrium stress levels. In accordance with this purpose, extensive relaxation tests were conducted on poly(lactic acid) and poly(lactic acid)/hydroxyapatite nanocomposites specimens at a wide range of temperatures from 23 ℃ and 55 ℃, and stress levels from 1 MPa to 50 MPa for poly(lactic acid) and 51 MPa for poly(lactic acid)/hydroxyapatite nanocomposites. All the specimens were subjected tensile loading–unloading and partial retraction process. The starting points of the relaxation test were chosen on unloading segment of stress–strain curves. Evolution of stress may decay, increase or decay then increase depending on the test point on unloading curves. Relaxation behavior of poly(lactic acid) and poly(lactic acid)/hydroxyapatite nanocomposites was simulated using viscoplasticity theory based on overstress for polymeric materials. Experimental results of poly(lactic acid) and poly(lactic acid)/hydroxyapatite nanocomposites were matched with numerical results of viscoplasticity theory based on overstress for polymeric materials, and viscoplasticity theory based on overstress for polymeric material model was found to have an aptitude for predicting anomalous relaxation behavior of poly(lactic acid) and poly(lactic acid)/hydroxyapatite nanocomposites. Additionally, the effect of temperature on relaxation time was investigated with using Kohlraush–Williams–Watts time-decay function. Modeling capability of Kohlrausch–Williams–Watts model was reasonable to predict short-term simple relaxation of poly(lactic acid) and poly(lactic acid)/hydroxyapatite nanocomposites. Responses of the model showed that interaction between relaxation time and environmental temperature was related to transition from glass state to rubbery state.

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“…In monotonic tensile tests, the embrittlement of the NiTi alloy strongly depends on the imposed strain rate [28][29][30]. In fact, after 8 h of hydrogen charging with a current density of 10 A/m 2 , an embrittlement occurred for strain rates higher than 10 −3 s −1 , whereas no embrittlement is detected lower than 10 −4 s −1 .…”

Section: Introductionmentioning

confidence: 99%

Hydrogen Effect on the Cyclic Behavior of a Superelastic NiTi Archwire

Sarraj

Kessentini

Hassine

et al. 2019

Metals

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In this work, we are interested in examining the strain rate effect on the mechanical behavior of Ni–Ti superelastic wires after hydrogen charging and ageing for 24 h. Specimens underwent 50 cycles of loading-unloading, reaching an imposed deformation of 7.6%. During loading, strain rates from 10−4 s−1 to 10−2 s−1 were achieved. With a strain rate of 10−2 s−1, the specimens were charged by hydrogen for 6 h and aged for one day showed a superelastic behavior marked by an increase in the residual deformation as a function of the number of cycles. In contrast, after a few number of cycles with a strain rate of 10−4 s−1, the Ni-Ti alloy archwire specimens fractured in a brittle manner during the martensite transformation stage. The thermal desorption analysis showed that, for immersed specimens, the desorption peak of hydrogen appeared at 320 °C. However, after annealing the charged specimens by hydrogen at 400 °C for 1 h, an embrittlement took place at the last cycles for the lower strain rates of 10−4 s−1. The present study suggests that the embrittlement can be due to the development of an internal stress in the subsurface of the parent phase during hydrogen charging and due to the creation of cracks and local zones of plasticity after desorption.

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Rate Dependency During Relaxation of Superelastic Orthodontic NiTi Alloys After Hydrogen Charging

Cited by 12 publications

References 26 publications

Finite element analysis of hydrogen effects on superelastic NiTi shape memory alloys: Orthodontic application

Finite element analysis of hydrogen effects on superelastic NiTi shape memory alloys: Orthodontic application

An observation of the evolution of equilibrium stress on poly(lactic acid) and poly(lactic acid)/hydroxyapatite nanocomposites

Hydrogen Effect on the Cyclic Behavior of a Superelastic NiTi Archwire

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