Fatigue thresholds of Ni-Ti alloy near the shape memory transition temperature

1999 ◽  
Vol 21 ◽  
pp. 137-145 ◽  
Author(s):  
R HOLTZ
Keyword(s):  
Transition Temperature ◽  
Shape Memory ◽  
Ti Alloy

scholarly journals Buckling and vibration analysis of shape memory laminated composite beams under axially heterogeneous in-plane loads in the glass transition temperature region

2021 ◽  
Vol 3 (4) ◽  
Author(s):  
Nilesh Tiwari ◽  
A. A. Shaikh
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Boundary Conditions ◽  
Shape Memory ◽  
Transition Region ◽  
Shape Memory Polymer ◽  
Shear Deformation Theory ◽  
Effect Of Temperature ◽  
Glass Transition Region

AbstractBuckling and vibration study of the shape memory polymer composites (SMPC) across the glass transition temperature under heterogeneous loading conditions are presented. Finite element analysis based on C° continuity equation through the higher order shear deformation theory (HSDT) is employed considering non linear Von Karman approach to estimate critical buckling and vibration for the temperature span from 273 to 373 K. Extensive numerical investigations are presented to understand the effect of temperature, boundary conditions, aspect ratio, fiber orientations, laminate stacking and modes of phenomenon on the buckling and vibration behavior of SMPC beam along with the validation and convergence study. Effect of thermal conditions, particularly in the glass transition region of the shape memory polymer, is considerable and presents cohesive relation between dynamic modulus properties with magnitude of critical buckling and vibration. Moreover, it has also been inferred that type of axial loading condition along with the corresponding boundary conditions significantly affect the buckling and vibration load across the glass transition region.

Diffuse Yield drop and Snap Action in a Ni-Ti Alloy

1991 ◽  
Vol 246 ◽  
Author(s):  
T.W. Duerig ◽  
K.N. Melton
Keyword(s):  
Shear Stress ◽  
Shape Memory ◽  
Strain Energy ◽  
Martensite Plate ◽  
Cell Boundary ◽  
Ti Alloy ◽  
Yield Drop

AbstractAn unusual yield phenomenon is observed in a heavily worked NiTiFe alloy, which leads to snap action shape memory and superelasticity. The snap action occurs at extremely high velocities and is accompanied by a loud cracking sound. The cause of the instability is attributed to penning, in which martensite growth is halted by having to undergo a reorientation at low angle cell boundaries, which then lowers the resolved shear stress on the martensite plate. Once free of the cell boundary, the plate grows and its strain energy is reduced so that it is able to penetrate subsequent boundaries more easily. This results in a diffuse yield drop, and the said snap action motion.

scholarly journals The Effect of POSS Type on the Shape Memory Properties of Epoxy-Based Nanocomposites

Molecules ◽  
2020 ◽  
Vol 25 (18) ◽  
pp. 4203
Author(s):  
Avraham I. Bram ◽  
Irina Gouzman ◽  
Asaf Bolker ◽  
Noam Eliaz ◽  
Ronen Verker
Keyword(s):  
Transition Temperature ◽  
Shape Memory ◽  
Crosslinking Density ◽  
Mechanical Analysis ◽  
Thermomechanical Properties ◽  
Space Environment ◽  
Scanning Calorimetry ◽  
Space Applications ◽  
Curing Conditions ◽  
Oligomeric Silsesquioxane

Thermally activated shape memory polymers (SMPs) can memorize a temporary shape at low temperature and return to their permanent shape at higher temperature. These materials can be used for light and compact space deployment mechanisms. The control of transition temperature and thermomechanical properties of epoxy-based SMPs can be done using functionalized polyhedral oligomeric silsesquioxane (POSS) additives, which are also known to improve the durability to atomic oxygen in the space environment. In this study, the influence of varying amounts of two types of POSS added to epoxy-based SMPs on the shape memory effect (SME) were studied. The first type contained amine groups, whereas the second type contained epoxide groups. The curing conditions were defined using differential scanning calorimetry and glass transition temperature (Tg) measurements. Thermomechanical and SME properties were characterized using dynamic mechanical analysis. It was found that SMPs containing amine-based POSS show higher Tg, better shape fixity and faster recovery speed, while SMPs containing epoxide-based POSS have higher crosslinking density and show superior thermomechanical properties above Tg. This work demonstrates how the Tg and SME of SMPs can be controlled by the type and amount of POSS in an epoxy-based SMP nanocomposite for future space applications.

scholarly journals Triple-Shape Memory Behavior of Modified Lactide/Glycolide Copolymers

Polymers ◽  
2020 ◽  
Vol 12 (12) ◽  
pp. 2984
Author(s):  
Anna Smola-Dmochowska ◽  
Natalia Śmigiel-Gac ◽  
Bożena Kaczmarczyk ◽  
Michał Sobota ◽  
Henryk Janeczek ◽  
...  
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Shape Memory ◽  
Hydroxyl Groups ◽  
Butylene Succinate ◽  
Shape Memory Behavior ◽  
Triple Shape Memory ◽  
High Flexibility ◽  
Bioresorbable Implants

The paper presents the formation and properties of biodegradable thermoplastic blends with triple-shape memory behavior, which were obtained by the blending and extrusion of poly(l-lactide-co-glycolide) and bioresorbable aliphatic oligoesters with side hydroxyl groups: oligo (butylene succinate-co-butylene citrate) and oligo(butylene citrate). Addition of the oligoesters to poly (l-lactide-co-glycolide) reduces the glass transition temperature (Tg) and also increases the flexibility and shape memory behavior of the final blends. Among the tested blends, materials containing less than 20 wt % of oligo (butylene succinate-co-butylene citrate) seem especially promising for biomedical applications as materials for manufacturing bioresorbable implants with high flexibility and relatively good mechanical properties. These blends show compatibility, exhibiting one glass transition temperature and macroscopically uniform physical properties.

Free, partial, and fully constrained recovery analysis of cold-programmed shape memory epoxy/carbon nanotube nanocomposites: Experiments and predictions

2018 ◽  
Vol 29 (10) ◽  
pp. 2164-2176 ◽  
Author(s):  
R Abishera ◽  
R Velmurugan ◽  
KV Nagendra Gopal
Keyword(s):  
Glass Transition ◽  
Carbon Nanotube ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Shape Memory ◽  
Thermally Activated ◽  
Large Structures ◽  
Multi Walled Carbon Nanotube ◽  
Optical Strain Measurement ◽  
Optical Strain

Thermally activated shape memory polymers are typically programmed by initially heating the material above the glass transition temperature ( Tg), deforming to the desired shape, cooling below Tg, and unloading to fix the temporary shape. This process of deforming at high temperatures becomes a time-, labor-, and energy-expensive process while applying to large structures. Alternatively, materials with reversible plasticity shape memory property can be programmed at temperatures well below the glass transition temperature which offers several advantages over conventional programming. Here, the free, partial, and fully constrained recovery analysis of cold-programmed multi-walled carbon nanotube–reinforced epoxy nanocomposites is presented. The free recovery analysis involves heating the temporary shape above Tg without any constraints (zero stress), and for fully constrained recovery analysis, the temporary shape is held constant while heating. The partially constrained recovery behavior is studied by applying a constant stress of 10%, 25%, and 50% of the maximum recovery stress obtained from the completely constrained recovery analysis. The samples are also characterized for their thermal, morphological, and mechanical properties. A non-contact optical strain measurement method is used to measure the strains during cold-programming and shape recovery. The different recovery behaviors are analyzed by using a thermo-viscoelastic–viscoplastic model, and the predictions are compared with the experimental results.

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