On the Optimal Damping of a Vibrating Shape Memory Alloy Rod

2002 ◽  
Vol 124 (2) ◽  
pp. 97-102 ◽  
Author(s):  
Eduard R. Oberaigner ◽  
Franz D. Fischer ◽  
Kikuaki Tanaka
Keyword(s):  
Phase Transformation ◽  
Shape Memory ◽  
Stress Wave ◽  
Constitutive Law ◽  
Major Area ◽  
Static Approximation ◽  
Smart Systems ◽  
Optimal Damping ◽  
Basic Equations ◽  
The One

Vibration damping through phase transformation is one major area of application of shape memory alloys in smart systems and structures. The authors of this study have shown in earlier publications, how damping of vibrating rods can be accomplished. This paper is an extension and generalization. On the one side it uses the proper description of the stress-wave phenomenon instead of a quasi-static approximation, on the other side it describes, how the damping could be optimized. The basic equations of the underlying mathematical model are the stress-wave equation, the heat conduction equation, a kinetic and a constitutive law as well as a condition to ensure maximal damping. The major results are the heating history, which governs the phase transformation, and the domain splitting along the rod into elastic and inelastic regions.

Study on Martensite Phase Transformation near Crack Tip of Mode II in Shape Memory Alloy

2011 ◽  
Vol 148-149 ◽  
pp. 875-878
Author(s):  
Bo Zhou ◽  
Jun Lv ◽  
Gang Ling Hou ◽  
Ya Ru Pan
Keyword(s):  
Phase Transformation ◽  
Shape Memory Alloy ◽  
Shape Memory ◽  
Crack Tip ◽  
Complex Stress ◽  
Martensite Phase ◽  
Complex Stress State ◽  
Transformation Model ◽  
Mode Ii ◽  
The One

In this paper, the phase transformation behaviors of shape memory alloy (SMA) in the complex stress state are formulated based the one-dimensional phase transformation model supposed by Zhou and Yoon. The stress field near the crack tip of mode II in SMA is described based on linear elastic fracture mechanics. The phase transformation behaviors of SMA near the crack tip of Mode II are numerically investigated.

Study on Shape Memory Alloy Plate with Circular Hole under Biaxial Uneven Tension

2012 ◽  
Vol 457-458 ◽  
pp. 994-997
Author(s):  
Bo Zhou ◽  
Xu Kun Li ◽  
Gang Ling Hou
Keyword(s):  
Phase Transformation ◽  
Shape Memory Alloy ◽  
Shape Memory ◽  
Circular Hole ◽  
Complex Stress ◽  
Complex Stress State ◽  
Transformation Model ◽  
Alloy Plate ◽  
Linear Elastic ◽  
The One

This paper focuses on the thermo-mechanical behaviors of a shape memory alloy (SMA) plate with a circular hole under biaxial uneven tension. The phase transformation behaviors of SMA under complex stress state are formulated based on the one-dimensional phase transformation model developed by Zhou and Yoon. The stress field equation of the SMA plate with a circular hole is derived according to linear elastic mechanics. The phase transformation behaviors near the region around the circular hole are numerically simulated under different conditions of applied stress.

scholarly journals Investigation of the Propagation of Stress Wave in Nickel-Titanium Shape Memory Alloys

Materials ◽  
2018 ◽  
Vol 11 (7) ◽  
pp. 1215
Author(s):  
Yehui Cui ◽  
Xiangguo Zeng ◽  
Huayan Chen ◽  
Jun Chen ◽  
Fang Wang
Keyword(s):  
Phase Transition ◽  
Wave Propagation ◽  
Phase Transformation ◽  
Elastic Wave ◽  
Shape Memory ◽  
Wave Velocity ◽  
Stress Wave ◽  
Nickel Titanium ◽  
Plastic Wave ◽  
Transition Wave

Based on irreversible thermodynamic theory, a new constitutive model incorporating two internal variables was proposed to investigate the phase transformation and plasticity behavior in nickel-titanium (NiTi) shape memory alloys (SMAs), by taking into account four deformation stages, namely austenite elastic phase, phase transition, martensitic elastic phase, and plastic phase. The model using the material point method (MPM) was implemented by the FORTRAN code to investigate the stress wave and its propagation in a NiTi rod. The results showed that its wave propagation exhibited martensitic and austenitic elastic wave, phase transition wave, and plastic wave. However, a double-wave structure including the martensitic and austenitic elastic wave and plastic wave occurred when the martensitic elastic wave reached the phase transformation wave. Thus, the reflection wave at a fixed boundary exhibited a different behavior compared with the elastic one, which was attributed to the phase transition during the process of reflection. It was found that the stress increment was proportional to the velocity of phase transition wave after the stress wave reflection. In addition, the influences of loading direction and strain rate on the wave propagation were examined as well. It was found that the phase transition wave velocity increased as the strain rate increased. The elastic wave velocity of martensite under compressive conditions was larger than that under tensile loading. In contrast, the plastic wave velocity under compression was less than that subjected to the tensile load.

scholarly journals Validation of a one-dimensional model of the systemic arterial tree

2009 ◽  
Vol 297 (1) ◽  
pp. H208-H222 ◽  
Author(s):  
Philippe Reymond ◽  
Fabrice Merenda ◽  
Fabienne Perren ◽  
Daniel Rüfenacht ◽  
Nikos Stergiopulos
Keyword(s):  
Constitutive Law ◽  
Distributed Model ◽  
Arterial Tree ◽  
One Dimensional ◽  
Continuity Equations ◽  
Nonlinear Viscoelastic ◽  
Model Predictions ◽  
The One ◽  
D Model ◽  
Systemic Arterial Tree

A distributed model of the human arterial tree including all main systemic arteries coupled to a heart model is developed. The one-dimensional (1-D) form of the momentum and continuity equations is solved numerically to obtain pressures and flows throughout the systemic arterial tree. Intimal shear is modeled using the Witzig-Womersley theory. A nonlinear viscoelastic constitutive law for the arterial wall is considered. The left ventricle is modeled using the varying elastance model. Distal vessels are terminated with three-element windkessels. Coronaries are modeled assuming a systolic flow impediment proportional to ventricular varying elastance. Arterial dimensions were taken from previous 1-D models and were extended to include a detailed description of cerebral vasculature. Elastic properties were taken from the literature. To validate model predictions, noninvasive measurements of pressure and flow were performed in young volunteers. Flow in large arteries was measured with MRI, cerebral flow with ultrasound Doppler, and pressure with tonometry. The resulting 1-D model is the most complete, because it encompasses all major segments of the arterial tree, accounts for ventricular-vascular interaction, and includes an improved description of shear stress and wall viscoelasticity. Model predictions at different arterial locations compared well with measured flow and pressure waves at the same anatomical points, reflecting the agreement in the general characteristics of the “generic 1-D model” and the “average subject” of our volunteer population. The study constitutes a first validation of the complete 1-D model using human pressure and flow data and supports the applicability of the 1-D model in the human circulation.

Modeling of Internal Damage Evolution During Actuation Fatigue in Shape Memory Alloys

2018 ◽  
Author(s):  
Francis R. Phillips ◽  
Daniel Martin ◽  
Dimitris C. Lagoudas ◽  
Robert W. Wheeler
Keyword(s):  
Phase Transformation ◽  
Constitutive Model ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Damage Evolution ◽  
Low Cycle Fatigue ◽  
Cycle Fatigue ◽  
Internal Damage ◽  
Functional Fatigue ◽  
Non Linear

Shape memory alloys (SMAs) are unique materials capable of undergoing a thermo-mechanically induced, reversible, crystallographic phase transformation. As SMAs are utilized across a variety of applications, it is necessary to understand the internal changes that occur throughout the lifetime of SMA components. One of the key limitations to the lifetime of a SMA component is the response of SMAs to fatigue. SMAs are subject to two kinds of fatigue, namely structural fatigue due to cyclic mechanical loading which is similar to high cycle fatigue, and functional fatigue due to cyclic phase transformation which typical is limited to the low cycle fatigue regime. In cases where functional fatigue is due to thermally induced phase transformation in contrast to being mechanically induced, this form of fatigue can be further defined as actuation fatigue. Utilizing X-ray computed microtomography, it is shown that during actuation fatigue, internal damage such as cracks or voids, evolves in a non-linear manner. A function is generated to capture this non-linear internal damage evolution and introduced into a SMA constitutive model. Finally, it is shown how the modified SMA constitutive model responds and the ability of the model to predict actuation fatigue lifetime is demonstrated.

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