scholarly journals Fatigue crack micromechanisms in a Cu-Zn-Al shape memory alloy with pseudo-elastic behavior

2015 ◽  
Author(s):  
Vittorio Di Cocco ◽  
Francesco Iacoviello ◽  
Stefano Natali ◽  
Andrea Brotzu
Keyword(s):  
Plastic Deformation ◽  
Fatigue Crack ◽  
High Temperature ◽  
Shape Memory ◽  
High Speed ◽  
Martensitic Phase ◽  
Elastic Behavior ◽  
Cooling Process ◽  
Austenitic Phase ◽  
Structure Transition

Shape memory property characterizes the behavior of many Ti based and Cu based alloys (SMAs). In Cu-Zn-Al SMAs, the original shape recovering is due to a bcc phase that is stable at high temperature. After an appropriate cooling process, this phase (?-phase or austenitic phase) transforms reversibly into a B2 structure (transition phase) and, after a further cooling process or a plastic deformation, it transforms into a DO3 phase (martensitic phase). In ?-Cu-Zn-Al SMAs, the martensitic transformation due to plastic deformation is not stable at room temperature: a high temperature “austenitization” process followed by a high speed cooling process allow to obtain a martensitic phase with a higher stability. In this work, a Cu-Zn-Al SMA in “as cast” conditions has been microstructurally and metallographically characterized by means of X-Ray diffraction and Light Optical Microscope (LOM) observations. Fatigue crack propagation resistance and damaging micromechanisms have been investigated corresponding to three different load ratios (R=0.10, 0.50 and 0.75).

Role of severe plastic deformation on the cyclic reversibility of a Ti50.3Ni33.7Pd16 high temperature shape memory alloy

2010 ◽  
Vol 58 (19) ◽  
pp. 6411-6420 ◽  
Author(s):  
B. Kockar ◽  
K.C. Atli ◽  
J. Ma ◽  
M. Haouaoui ◽  
I. Karaman ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
High Temperature ◽  
Shape Memory Alloy ◽  
Severe Plastic Deformation ◽  
Shape Memory

scholarly journals Structural Change in Ni-Fe-Ga Magnetic Shape Memory Alloys after Severe Plastic Deformation

Materials ◽  
2019 ◽  
Vol 12 (12) ◽  
pp. 1939 ◽  
Author(s):  
Gheorghe Gurau ◽  
Carmela Gurau ◽  
Felicia Tolea ◽  
Vedamanickam Sampath
Keyword(s):  
Electron Microscopy ◽  
Plastic Deformation ◽  
Severe Plastic Deformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
High Speed ◽  
High Pressure Torsion ◽  
Magnetic Shape Memory ◽  
Two Phase ◽  
Ultrafine Grained

Severe plastic deformation (SPD) is widely considered to be the most efficient process in obtaining ultrafine-grained bulk materials. The aim of this study is to examine the effects of the SPD process on Ni-Fe-Ga ferromagnetic shape memory alloys (FSMA). High-speed high-pressure torsion (HSHPT) was applied in the as-cast state. The exerted key parameters of deformation are described. Microstructural changes, including morphology that were the result of processing, were investigated by optical and scanning electron microscopy. Energy-dispersive X-ray spectroscopy was used to study the two-phase microstructure of the alloys. The influence of deformation on microstructural features, such as martensitic plates, intragranular γ phase precipitates, and grain boundaries’ dependence of the extent of deformation is disclosed by transmission electron microscopy. Moreover, the work brings to light the influence of deformation on the characteristics of martensitic transformation (MT). Vickers hardness measurements were carried out on disks obtained by SPD so as to correlate the hardness with the microstructure. The method represents a feasible alternative to obtain ultrafine-grained bulk Ni-Fe-Ga alloys.

Experimental Investigation and Numerical Simulation of the Mechanical and Thermal Behavior of a Superelastic Shape Memory Alloy Beam During Bending

2014 ◽  
Author(s):  
Johannes Ullrich ◽  
Marvin Schmidt ◽  
Andreas Schütze ◽  
André Wieczorek ◽  
Jan Frenzel ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Phase Transformation ◽  
Thermal Behavior ◽  
Shape Memory ◽  
High Speed ◽  
Nickel Titanium ◽  
Martensitic Phase ◽  
Martensitic Phase Transformation ◽  
Research Association ◽  
Restoring Force

Superelastic Shape Memory Alloys (SMA) are typically used in applications where the martensitic phase transformation is exploited for its reversible, large deformation such as medical applications (e.g. stents). In this work, we focus on the mechanical and thermal behavior of a Nickel-Titanium SMA strip in bending mode. One possible application of this mode is to provide a restoring force when used in joints of SMA wire actuator systems making the need for an antagonistic SMA actuator redundant. In these applications mentioned above, typically only the mechanical properties are of interest while the temperature is considered constant, even though the martensitic phase transformation in SMA is a thermo-mechanically coupled process. As a part of the DFG (German Research Association) Priority Programme SPP1599 “Ferroic Cooling” which aims at advancing the development of solid state cooling devices, we have an equally large interest for the thermal evolution of Nickel-Titanium SMA during deformation and its induced phase transformation. In this paper we investigate the thermal and the mechanical response of a SMA beam during bending experiments in which the deformation is induced by holding one end of a SMA strip fixed while the other end is subject to a prescribed deflection. Sensors and high speed thermal cameras are used to capture reaction forces, deformations and temperature changes. We compare these experimental results with numerical simulation results obtained from Finite Element simulations where a thermo-mechanically coupled SMA model is implemented into a finite deformation framework.

Effect of stress redistribution during thermal actuation of shape memory alloys in notched cylindrical bars

2018 ◽  
Vol 29 (10) ◽  
pp. 2149-2163 ◽  
Author(s):  
Francis R Phillips ◽  
Dimitris C Lagoudas
Keyword(s):  
Phase Transformation ◽  
Shape Memory Alloy ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Martensitic Phase ◽  
Reverse Transformation ◽  
Cylindrical Shape ◽  
Austenitic Phase ◽  
Thermal Actuation ◽  
Forward Transformation

Shape memory alloys present a unique ability to undergo a solid-to-solid, diffusionless, reversible phase transformation. The forward phase transformation is commonly associated with transforming from the austenitic phase to the martensitic phase, while the reverse transformation is defined by going from the martensitic phase to the austenitic phase. In thermal actuation loading paths, forward transformation is generally associated with cooling, while reverse transformation is commonly associated with heating. In this article, however, it is shown that reverse transformation may occur during cooling of notched cylindrical shape memory alloy bars. The reversal in phase transformation is associated with the redistribution of stress in the shape memory alloy due to the phase transformation.

An Experimental Investigation on Wear of Rail in Different Curve Radius

2013 ◽  
Vol 739 ◽  
pp. 458-461
Author(s):  
W. Zhong ◽  
P. Chen ◽  
Y. Wang
Keyword(s):  
Plastic Deformation ◽  
Fatigue Crack ◽  
High Speed ◽  
Fatigue Behavior ◽  
Wear Volume ◽  
Fatigue Wear ◽  
Propagation Angle ◽  
Wear Process ◽  
Railway Rail ◽  
Curve Radius

Among the rail defects, the transverse fatigue crack, which has been the most dangerous damage, is developed near the rail running face and grows perpendicular to the rail surface. Finally, the transverse fatigue crack would result in the failure of railway rail. In this paper, the rolling tests were performed using a JD-1 wheel/rail simulation facility without any lubricant. The tester is composed of a small wheel served as rail and a larger wheel served as wheel. The fatigue behavior of rail rollers with different materials and curve radius were investigated in detail by examining wear volume and wear scar using optical microscopy (OM) and scanning electronic microscopy (SEM). The results indicate that with curve radius decreasing, the wear volume of rail roller increases rapidly and the fatigue damage becomes severe. Furthermore, the cracking propagation angle increases obviously with curve radius decreasing and fatigue wear is dominating during the wear process. There appears distinct plastic deformation on the section of rail roller under small curve radius condition. For the same curve radius, the wear volume of PD3 rail is more than that of PG4 rail and the plastic deformation is more obvious. Moreover, the cracking propagation angle of PD3 rail material is smaller than that of PG4 rail. In conclusion, PG4 rail material is not suitable for the high-speed railway.

Enhancement of Reliability of Machines and Materials by Friction Plating

2008 ◽  
Vol 59 ◽  
pp. 46-50
Author(s):  
L. Belevskiy ◽  
Vladimir A. Popov ◽  
S.A. Tulupov ◽  
Oleg M. Smirnov
Keyword(s):  
Plastic Deformation ◽  
Wear Resistance ◽  
Corrosion Resistance ◽  
Surface Layer ◽  
High Temperature ◽  
High Speed ◽  
Protective Coatings ◽  
Coating Material ◽  
Strong Adhesion ◽  
Modification Of The Surface

A process of friction plating was developed for modification of the surface of metal items by strain hardening combined with application of protective coatings aimed to improve corrosion resistance, hardness, wear resistance and other functional properties. Friction plating is performed by means of a metal wire brush rotating at high speed. Coating material in the form of a rod or strip is pressed with a certain force to the rotary wire brush. In the contact zone, coating material is heated up to a high temperature. Particles of coating material are picked up by the ends of brush wires and transferred onto the treated surface. At the same time, the surface of the product is conditioned and heated. Investigations of friction plating have shown that plastic deformation of the surface layer combined with application of coating material particles ensures their strong adhesion to the substrate.

Shape memory characteristics of Ti49.5Ni25Pd25Sc0.5 high-temperature shape memory alloy after severe plastic deformation

2011 ◽  
Vol 59 (12) ◽  
pp. 4747-4760 ◽  
Author(s):  
K.C. Atli ◽  
I. Karaman ◽  
R.D. Noebe ◽  
A. Garg ◽  
Y.I. Chumlyakov ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
High Temperature ◽  
Shape Memory Alloy ◽  
Severe Plastic Deformation ◽  
Shape Memory ◽  
Memory Characteristics
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