scholarly journals A free energy model for thin-film shape memory alloys

2003 ◽  
Author(s):  
Jordan E. Massad ◽  
Ralph C. Smith ◽  
Gregory P. Carman
Keyword(s):  
Thin Film ◽  
Free Energy ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Energy Model ◽  
Free Energy Model

A Free Energy Model for the Inner Loop Behavior of Pseudoelastic Shape Memory Alloys

2005 ◽  
Vol 881 ◽  
Author(s):  
Olaf Heintze ◽  
Stefan Seelecke
Keyword(s):  
Free Energy ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Energy Model ◽  
Polycrystalline Materials ◽  
Internal Stresses ◽  
Control Programs ◽  
Rate Dependent ◽  
Numerical Effort ◽  
Free Energy Model

AbstractThe paper presents a free energy model for the pseudoelastic behavior of shape memory alloys. It is based on a stochastic homogenization process, which uses distributions in energy barriers and internal stresses to represent effects typically encountered in polycrystalline materials. This concept leads to a realistic desription of the rate-dependent inner loop behavior, but is characterized by rather long computation times. This is prohibitive in regard to a potential implementation into other numerical codes, such as finite element or optimal control programs or a Matlab/Simulink environment. For this purpose a parameterization method is introduced, which is derived from the concept of a representative single crystal. The approach preserves the desirable properties of the original formulation, at the same time reducing the numerical effort significantly. Finally, we show that the method can reproduce the experimentally observed behavior accurately over a large range of strain rates including the minor loop behavior.

scholarly journals Thermodynamic Modelling of Ferromagnetic Shape Memory Actuators

2009 ◽  
Vol 635 ◽  
pp. 175-180 ◽  
Author(s):  
Berthold Krevet ◽  
Manfred Kohl
Keyword(s):  
Free Energy ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Energy Model ◽  
Anisotropy Energy ◽  
Crystallographic Axis ◽  
Model Calculations ◽  
Free Energy Model ◽  
Ferromagnetic Shape Memory

We present a thermodynamic Gibbs free energy model for the finite element simulation of the coupled thermo-magneto-mechanical behavior of ferromagnetic shape memory alloys (FSMAs). Starting from a free energy model for the conventional shape memory effect, additional terms are included to take into account the magnetic anisotropy and the geometry-dependent magnetostatic energy. Different functions are considered for the strain dependence of the anisotropy energy in order to describe the experimentally found strong dependence of the anisotropy energy on the ratio of short and long crystallographic axis c/a. The resulting energy landscape is used to calculate the transition probabilities between three martensite variants and the austenite state under applied stress and external magnetic field. The magnetic shape memory effect is simulated for different loading conditions and sample geometries. We demonstrate the influence of the c/a dependence of the anisotropy energy as well as the influence of twinning strain and elastic modulus on the transition between martensite variants. The model calculations are compared with experimental results on Ni-Mn-Ga single crystals.

Hydrogen Atom Transfer Reaction Free Energy as a Predictor of Abiotic Nitroaromatic Reduction Rate Constants: A Comprehensive Analysis

2019 ◽  
Author(s):  
Dominic Di Toro ◽  
Kevin P. Hickey ◽  
Herbert E. Allen ◽  
Richard F. Carbonaro ◽  
Pei C. Chiu
Keyword(s):  
Free Energy ◽  
Hydrogen Atom ◽  
Hydrogen Atom Transfer ◽  
Energy Model ◽  
Second Order ◽  
Transfer Model ◽  
Atom Transfer ◽  
Order Rate ◽  
Linear Free Energy ◽  
Free Energy Model

<div>A linear free energy model is presented that predicts the second order rate constant for the abiotic reduction of nitroaromatic compounds (NACs). For this situation previously presented models use the one electron reduction potential of the NAC reaction. If such value is not available, it has been has been proposed that it could be computed directly or estimated from the electron affinity (EA). The model proposed herein uses the Gibbs free energy of the hydrogen atom transfer (HAT) as the parameter in the linear free energy model. Both models employ quantum chemical computations for the required thermodynamic parameters. The available and proposed models are compared using second order rate constants obtained from five investigations reported in the literature in which a variety of NACs were exposed to a variety of reductants. A comprehensive analysis utilizing all the NACs and reductants demonstrate that the computed hydrogen atom transfer model and the experimental one electron reduction potential model have similar root mean square errors and residual error probability distributions. In contrast, the model using the computed electron affinity has a more variable residual error distribution with a significant number of outliers. The results suggest that a linear free energy model utilizing computed hydrogen transfer reaction free energy produces a more reliable prediction of the NAC abiotic reduction second order rate constant than previously available methods. The advantages of the proposed hydrogen atom transfer model and its mechanistic implications are discussed as well.</div>

scholarly journals Affinity and Specificity of Protein U1A-RNA Complex Formation Based on an Additive Component Free Energy Model

2007 ◽  
Vol 371 (5) ◽  
pp. 1405-1419 ◽  
Author(s):  
Bethany L. Kormos ◽  
Yulia Benitex ◽  
Anne M. Baranger ◽  
David L. Beveridge
Keyword(s):  
Free Energy ◽  
Complex Formation ◽  
Energy Model ◽  
Additive Component ◽  
Free Energy Model ◽  
Rna Complex

A new approach to characterization of the transition temperatures of thin film NiTi shape memory alloys

2004 ◽  
Vol 19 (6) ◽  
pp. 1762-1767
Author(s):  
Nicholas W. Botterill ◽  
David M. Grant ◽  
Jianxin Zhang ◽  
Clive J. Roberts
Keyword(s):  
Thin Film ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Transition Temperatures ◽  
New Approach ◽  
Novel Approach ◽  
Potential Applications ◽  
Niti Shape Memory Alloys

A novel approach in determining the transition temperatures of NiTi shape memory alloys was investigated and compared with conventional techniques. The technique is based on microthemal analysis using a scanning thermal microscope (SThM). In particular, this method has the potential to allow the transformation temperatures of thin films to be investigated in situ. Thin film shape memory alloys have potential applications, such as microactuators, where conventional analysis techniques are either not directly applicable to such samples or are difficult to perform.

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