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Role of Plasticity in Nitinol Fatigue
Shayanfard, Pejman ; Seiner,, Hanuš (oponent) ; Dlouhý, Antonín (oponent) ; Šandera, Pavel (vedoucí práce)
This doctoral thesis deals with the analysis of the role of stress risers in NiTi elements on the local cyclic evolutions of martensitic transformation, plastic deformations, and mechanical gradients at the stress risers, under both iso-thermal cyclic loading in the superelastic regime and thermal cycling under external load in actuator regime. The methodology of investigation includes both experimental measurements and finite element simulations of notched thin NiTi superelastic/shape-memory ribbons. In the experimental part of the work, the DIC method is used to capture the spatial evolutions of strain gradients around the notch, and the X-ray microdiffraction is used to analyze the local strain fields around the notch and the plasticity induced remnant martensite at the notch-tip. Besides, the finite element results help assess the corresponding evolutions of stresses and strains, martensitic transformation, and the partitioning of total strains into elastic, plastic and residual strains around the notch. In addition, the thesis includes numerical analysis investigating the effect of the design of self-expanding NiTi stents on local cyclic evolution of martensitic transformation and its relation to fatigue performance.
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Role of Plasticity in Nitinol Fatigue
Shayanfard, Pejman ; Seiner,, Hanuš (oponent) ; Dlouhý, Antonín (oponent) ; Šandera, Pavel (vedoucí práce)
This doctoral thesis deals with the analysis of the role of stress risers in NiTi elements on the local cyclic evolutions of martensitic transformation, plastic deformations, and mechanical gradients at the stress risers, under both iso-thermal cyclic loading in the superelastic regime and thermal cycling under external load in actuator regime. The methodology of investigation includes both experimental measurements and finite element simulations of notched thin NiTi superelastic/shape-memory ribbons. In the experimental part of the work, the DIC method is used to capture the spatial evolutions of strain gradients around the notch, and the X-ray microdiffraction is used to analyze the local strain fields around the notch and the plasticity induced remnant martensite at the notch-tip. Besides, the finite element results help assess the corresponding evolutions of stresses and strains, martensitic transformation, and the partitioning of total strains into elastic, plastic and residual strains around the notch. In addition, the thesis includes numerical analysis investigating the effect of the design of self-expanding NiTi stents on local cyclic evolution of martensitic transformation and its relation to fatigue performance.
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