Understanding indentation-induced two-way shape memory effect

2007 ◽  
Vol 22 (10) ◽  
pp. 2851-2855 ◽  
Author(s):  
Yijun Zhang ◽  
Yang-Tse Cheng ◽  
David S. Grummon
Keyword(s):  
Experimental Data ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Contact Radius ◽  
Element Analysis ◽  
Austenitic Phase ◽  
Heating And Cooling ◽  
Surface Protrusion ◽  
Niti Shape Memory Alloys

Spherical indents in NiTi shape memory alloys can have reversible depth change: deeper depth in the martensitic phase at low temperature and shallower depth in the austenitic phase at high temperature. This is the indentation-induced two-way shape memory effect. After polishing the indents, two-way reversible surface protrusions can occur on the shape memory alloy surfaces upon heating and cooling. The height of the surface protrusion is about the same as the depth of the reversible indent. Further polishing reduces the height of the surface protrusion, which disappears completely when the polished depth is about the length of the contact radius. By comparing finite element analysis and experimental data, we show that the depth at which a protrusion disappears is close to the 10% strain boundary. This suggests that slip-plasticity is responsible for the observed indentation-induced two-way shape memory effect.

Modeling of Martensite Accommodation Effect on Mechanical Behavior of Shape Memory Alloys

1999 ◽  
Vol 121 (1) ◽  
pp. 102-104 ◽  
Author(s):  
M. E. Evard ◽  
A. E. Volkov
Keyword(s):  
Experimental Data ◽  
Plastic Deformation ◽  
Shape Memory Alloys ◽  
Mechanical Behavior ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Qualitative Agreement ◽  
Strain Accumulation ◽  
Good Qualitative Agreement

An approach has been presented to account for micro-plastic deformation and stress produced by accommodation of martensite. This has made it possible to describe such phenomena as incomplete recovery of strain, strain accumulation at thermocycling, and repeated two-way shape memory effect. Results of modeling are in good qualitative agreement with experimental data.

Sintering and Morphology of Porous Structure in NiTi Shape Memory Alloys for Biomedical Applications

2012 ◽  
Vol 570 ◽  
pp. 87-95 ◽  
Author(s):  
Irfan Haider Abidi ◽  
Fazal Ahmad Khalid
Keyword(s):  
Elastic Modulus ◽  
Shape Memory Alloys ◽  
Porous Structure ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Biomedical Implants ◽  
Recoverable Strain ◽  
Porous Niti ◽  
Niti Shape Memory Alloys

The combination of attractive properties of porous NiTi shape memory alloys like high recoverable strain due to superelasticity and shape memory effect, good corrosion resistance, improved biocompatibilty, low density and stiffness along with its porous structure similar to that of bone make them best materials for biomedical implants. In current study porous NiTi SMAs have been fabricated successfully by space holder technique via pressureless sintering using NaCl powder as a spacer. Various volume fractions of NaCl powders have been involved to study their effect on the pore characteristics as well as on mechanical properties of foam. Porous NiTi with average porosity in the range of 44.3%-63.5% have been fabricated having average pore size 419µm which were very appropriate for various biomedical implants. Porous NiTi SMAs exhibited superelasticity at room temperature and shape memory effect was also determined. Maximum recoverable strain of 6.79% was demonstrated by the porous NiTi alloy with 44.3% porosity and it was diminishing with increasing porosity. Compression strength and elastic modulus have shown a decreasing trend with increasing porosity content. Elastic modulus of porous NiTi extends from 1.38 to 5.42GPa depending upon the pore volume which was very much comparable to that of various kinds of bones.

Solid State Transformations and Equilibrium Crystal Structures of an Au-Cu Alloy with Shape Memory Effect

2012 ◽  
Vol 730-732 ◽  
pp. 859-864 ◽  
Author(s):  
Georgina Miranda ◽  
F.S. Silva ◽  
Delfim Soares
Keyword(s):  
High Temperature ◽  
Solid State ◽  
Shape Memory ◽  
Phase Transformations ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Equilibrium Phase ◽  
Lattice Parameters ◽  
Solid State Transformation ◽  
Heating And Cooling

Au-50%Cu (at. %) alloy presents the shape memory effect (SME), which is dependent of the solid state transformation that happens during heating, after the introduction of an internal stress in the quenched state. The solid state phase transformation temperatures were determined by means of Differential Thermal Analysis (DTA), both in heating and cooling cycles. With the obtained DTA results, a sequence of high temperature X-ray diffraction (XRD) experiments were made, in order to confirm the presence of the solid state phase transformations and to determine their stable crystal structure and lattice parameters. These XRD results were compared with those obtained from the literature. The displacements of the lattice parameters were determined, for each equilibrium phase, for measurements at room temperature and at high temperature. The characteristics of the quenched samples were also studied in order to determine the phase transformations that are responsible for the shape memory effect in this alloy.

scholarly journals Fabrication and Two-Way Deformation of Shape Memory Composite with SMA and SMP

2010 ◽  
Vol 638-642 ◽  
pp. 2189-2194 ◽  
Author(s):  
Hisaaki Tobushi ◽  
Shunichi Hayashi ◽  
Y. Sugimoto ◽  
K. Date
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Shape Memory Polymer ◽  
Bending Deformation ◽  
Heating And Cooling ◽  
Round Shape ◽  
Heat Treated ◽  
Shape Memory Composite

The shape memory composite (SMC) with shape memory alloy (SMA) and shape memory polymer (SMP) was fabricated, and the two-way bending deformation and recovery force were investigated. The results obtained can be summarized as follows. (1) Two kinds of SMA tapes which show the shape memory effect and superelasticity were heat-treated to memorize the round shape, respectively. The shape-memorized round SMA tapes were sandwiched between the SMP sheets, and the SMC belt was fabricated. (2) The two-way bending deformation with an angle of 56 degrees is observed during heating and cooling. (3) If the SMC belt is heated and cooled by keeping the form, recovery force increases during heating and decreases during cooling.

The Shape Memory Effect in Melt Spun Fe-15Mn-5Si-9Cr-5Ni Alloys

2013 ◽  
Vol 738-739 ◽  
pp. 247-251 ◽  
Author(s):  
Ana Druker ◽  
Paulo La Roca ◽  
Philippe Vermaut ◽  
Patrick Ochim ◽  
Jorge Malarría
Keyword(s):  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Melt Spinning ◽  
Room Temperature ◽  
Tensile Tests ◽  
Argon Atmosphere ◽  
Austenitic Phase ◽  
Melt Spun ◽  
Shape Memory Behaviour

At room temperature, Fe-15Mn-5Si-9Cr-5Ni alloys are usually austenitic and the application of a stress induces a reversible martensitic transformation leading to a shape memory effect (SME). However, when a ribbon of this material is obtained by melt-spinning, the rapid solidification stabilizes a high-temperature ferritic phase. The goals of this work were to find the appropriate heat treatment in order to recover the equilibrium austenitic phase, characterize the ribbon form of this material and evaluate its shape memory behaviour. We found that annealing at 1050°C for 60 min, under a protective argon atmosphere, followed by a water quenching stabilizes the austenite to room temperature. The yield stress, measured by tensile tests, is 250 MPa. Shape-memory tests show that a strain recovery of 55% can be obtained, which is enough for certain applications.

Thermomechanical training and structural tests for adaptive SMA bumps with two-way shape memory effect

2021 ◽  
pp. 1045389X2110482
Author(s):  
Chen Zhang ◽  
Hongli Ji ◽  
Xing Chen ◽  
Jinhao Qiu
Keyword(s):  
Boundary Condition ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Testing Machine ◽  
Stable States ◽  
Austenitic Phase ◽  
Displacement Boundary ◽  
Finish Temperature ◽  
Structural Tests

In this paper, shape memory alloy (SMA) bumps with two-way shape memory effect (TWSME) are trained by simple but effective training approaches, which provides a new idea for the actuations of the shock control bump (SCB) on airfoil. Two different configurations of bump structures (2D and 3D SMA bumps) are designed and fabricated. The bumps are required to exhibit TWSME so that it can change its shape by heating and cooling between two stable states at austenitic phase and martensitic phase, respectively. To obtain the TWSME, the material is trained in the range of martensitic finish temperature and austenitic finish temperature whilst a displacement boundary condition is imposed. A set of fixtures, which can be assembled to the universal testing machine (UTM), are designed to achieve the clamped boundary condition during thermal cycles of the training process. After training, SMA bumps with the TWSME, that bulge at low-temperature and become flat at high, are obtained. Structural tests and deformation control are then carried out afterwards to show the deformation performance of the trained SMA bumps.

Indentation-induced two-way shape memory surfaces

2009 ◽  
Vol 24 (3) ◽  
pp. 823-830 ◽  
Author(s):  
Xueling Fei ◽  
Yijun Zhang ◽  
David S. Grummon ◽  
Yang-Tse Cheng
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Deformation Zone ◽  
Plastic Strains ◽  
Spherical Case ◽  
Indent Depth ◽  
Niti Shape Memory Alloys ◽  
Made In

A method is described for the creation of surfaces with cyclically reversible topographical form. Using spherical and cylindrical indenters applied to NiTi shape-memory alloys, an indentation-planarization technique is shown to result in a two-way shape memory effect that can drive flat-to-wavy surface transitions on changing temperature. First, it is shown that deep spherical indents, made in martensitic NiTi, exhibit pronounced two-way cyclic depth changes. After planarization, these two-way cyclic depth changes are converted to reversible surface protrusions, or “exdents.” Both indent depth changes and cyclic exdent amplitudes can be related to the existence of a subsurface deformation zone in which indentation has resulted in plastic strains beyond that which can be accomplished by martensite detwinning reactions. Cylindrical indentation leads to two-way displacements that are about twice as large as that for the spherical case. This is shown to be due to the larger deformation zone under cylindrical indents, as measured by incremental grinding experiments.

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