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Shape memory alloy

bigspaggio's picture

Post Doc or PhD position open in design of shape memory composite

A PhD position or a Post-Doc position, depending on the candidate skills are available in the Department of Sciences and Methods fo Engineering at the University of Modena and Reggio Emilia, Italy. The research project is in the smart composite materials design. The candidate will have to design and optimize a composite structure with embedded SMA for morphing application. Candidates should have possibly a strong background in mechanics, finite elements simulations and smart materials.

Frank Richter's picture

ABAQUS built-in SMA model

Dear Mechanicians,

time and again the question of SMA (shape memory alloy) modeling pops up.

In ABAQUS, you can achieve this only by (V)UMAT coding or by using the little-known built-in SMA model.

In the past I have frequently responded to queries on SMA modeling and could refer to a customer help site of SIMULIA. That site is down, regrettably.

I decided to post the files here to avoid responding with a longer explanation to every individual seeking assistance and uploading the files as E-mail attachment every time.

R.Mehrabi's picture

Experimental Study of NiTi Thin-Walled Tubes Under Uniaxial Tension, Torsion, Proportional and Non-Proportional Loadings

The superelastic response of NiTi shape memory alloys under various loading conditions is experimentally investigated using thin-walled tube specimens. The isotropic relation between the elastic and shear moduli of austenite and martensite as well as the von Mises stress and strain equivalency are also studied in uniaxial tension and pure torsion. In addition to proportional loading, several non-proportional loading experiments based on both force and displacement control modes are conducted.

R.Mehrabi's picture

Constitutive modeling of tension-torsion coupling and tension-compression asymmetry in NiTi shape memory alloys

A 3D constitutive model is proposed and verified with experimental data. Tension-torsion coupling effect and tension-compression asymmetry effect is investigate for tube shape memory alloy.

R.Mehrabi's picture

Microplane modeling of shape memory alloy tubes under tension, torsion, and proportional tension–torsion loading

In this paper, a phenomenological constitutive
model based on microplane model is used to simulate tension, torsion and proportional tension-torsion on NiTi thin-walled tube. Validation of the
microplane model against experimental results in different loading conditions demonstrates
the capability of this approach.
This publication will benefit the numerical and experimental study on SMAs.

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binoddhakal's picture

Shape Memory Alloys: Evolutionary response of NiTi and their application in actuation

 

1.

http://jim.sagepub.com/content/24/1/70.short

Saleeb, A. F., Dhakal, B., Padula, S. A., & Gaydosh, D. J. (2013).
Calibration of a three-dimensional multimechanism shape memory alloy
material model for the prediction of the cyclic “attraction” character
in binary NiTi alloys. Journal of Intelligent Material Systems and Structures, 24(1), 70-88.

 

 

2.

Iterations in VUMAT

Dear all,

I' m trying to make a model in VUMAT for shape memory alloy based on Lagoudas 's thermomechanical constitutive model. It seems that It's necessary an iteration to evaluate the thermoelastic prediction.

My questions are : is it possible to use an iterative loop in the VUMAT or it's better to avoid it??Could someone suggest me a different way so that I can avoid the iterative loop?

Many thanks,

Cece

 

On the crack growth resistance of shape memory alloys

With the increasing use of shape memory alloys in recent years, it is important to investigate the effect of cracks. Theoretically, the stress field near the crack tip is unbounded. Hence, a stress-induced transformation occurs, and the martensite phase is expected to appear in the neighborhood of the crack tip, from the very first loading step. In that case, the crack tip region is not governed by the far field stress, but rather by the crack tip stress field. This behavior implies transformation toughening or softening.

Xiao-Yan Gong's picture

Nitinol, stent fracture and related issues

Choose a channel featured in the header of iMechanica: 

Stent and Nitinol have revolutionized the medicine.  In past decades, guidewires, stents, filters and many minimumly invasive devices and implants are made of Nitinol and they proved to be very successful.

However, the fatigue behavior of Nitinol has not been well understood.  As a consequences, many stent fractures have been observed in-vivo.  Below is a list of misconcepts that may contribute to the widely observed in-vivo fractures on Nitinol stents:

On the thermomechanical coupling of shape memory alloys and shape memory alloys composites

Smart materials have received much attention in recent years, especially due to their various applications in smart structures, medical devices, actuators, space and aeronautics. Among these
materials, shape memory alloys exhibit extremely large, inelastic, recoverable strains (of the order of 10%), resulting from transformation between austenitic and martensitic phases. This
transformation may be induced by a change, either in the applied stress, the temperature, or both.

Xi Wang's picture

Laser Annealing of Amorphous NiTi Shape Memory Alloy Thin Films to Locally Induce Shape Memory Properties

Xi Wang, Yves Bellouard, Joost J. Vlassak

Published in Acta Materialia 53 (2005) p4955-4961.

Abstract — We present the results of a crystallization study on NiTi shape memory thin films in which amorphous films are annealed by a scanning laser. This technique has the advantage that shape memory properties can be spatially distributed as required by the application. A kinetics study shows that nucleation of the crystalline phase occurs homogenously in the films. Consequently, the laser annealing process produces polycrystalline films with a random crystallographic texture. The crystallized films have a uniform microstructure across the annealed areas. The material in the crystalline regions transforms reversibly to martensite on cooling from elevated temperature and stress measurements show that a significant recovery stress is achieved in the films upon transformation.

Xi Wang's picture

Cross-section TEM micrograph of a NiTi crystal in a partially crystallized film

This micrograph indicates the nulceation and growth mechanism in the crystallization of amorphous near-equiatomic NiTi films. The crystal nucleates homogenously inside the bulk of the film, and quickly consume most of the film thickness, and then grows laterally in a two-dimensional growth mode. Heterogeneous nucleation at an interface was not observed due to the composition shift at those locations caused by interfacial reaction.

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