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This document summarizes a seminar presentation on shape memory alloys and their applications in civil engineering. It begins with an introduction to shape memory alloys, including their ability to return to a predetermined shape with temperature changes. It then reviews the history, properties, working principles, literature on the topic, types of shape memory alloys, and applications in civil engineering structures. These include use as reinforcement, prestressing, braces, damping elements, and for structural self-rehabilitation. The document concludes with case studies on retrofitting historic structures in Italy with shape memory alloys.
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- 1. Veermata Jijabai Technological Institute Mumbai Shape Memory Alloys and its Applications in Civil Engineering Seminar on Under The Guidance of Dr. Priyanka Jadhav By Pankaj Dhangare M. Tech I(Structural) Roll No-142040013
- 2. Content Introduction History Literature reviews Types of SMAs Properties Working principle Applications Case study Conclusion
- 3. Introduction SMAs are the Materials which have the ability to return to a predetermined shape when heated or cooled. When it is heated above its transformation temperature it undergoes a change in crystal structure which causes it to return to its original shape. The most common shape memory material is an alloy of nickel and titanium called Nitinol This particular alloy has very good electrical and mechanical properties, long fatigue life, and high corrosion resistance
- 4. History 1932: Chang and Read recorded the first observation of the shape memory transforation. 1938: Greninger and Mooradian observed the formation and disappearance of martensitic phase by varying the temperature of a Cu-Zn alloy. 1951: Shape memory effect was observed 1962-63: Ni-Ti alloys were first developed by the United States Naval Ordnance Laboratory. Mid-1990s Memory metals start to become widespread in medicine and soon move to
- 5. Literature reviews "Applications of Shape Memory Alloys in Civil Engineering Structures - Overview, Limits and New Ideas by JANKE, L., et al.(2005). "Materials and Structures 38(June 2005): 578-592. A basic description of SMA highly non-linear material behaviour in terms of shape memory effect and superelasticity. It is followed by a brief introduction to Ni-Ti and Fe-Mn-Si SMAs. Pre-existing and new applications in the fields of damping, active vibration control and prestressing or posttensioning of structures with fibres and tendons are being reviewed with regard to civil engineering. New ideas for using SMAs in civil engineering structures are proposed such as an improved concept for the active confinement of concrete members.
- 6. Literature reviews. Applications of Shape Memory Alloys in Civil Structures by Song, G., Ma, N., and Li, H.-N. (2006)., Engineering Structures, 28, 1266-1274. The shape memory effect (SME) and pseudoelasticity, two major properties of SMA associated with the thermal-induced or stress-induced reversible hysteretic phase transformation between austenite and martensite are reviewed. These unique properties enable SMA to be used as actuators, energy dissipaters and dampers for civil structure control. Various applications in civil structures.
- 7. Literature reviews. APPLICATION OF SMART MATERIALS IN CIVIL ENGINEERING STRUCTURES, by T.S. Thandavamoorthy(2013) , Research in Civil Engineering Structures-05 251-263. He described the characteristics of smart materials, the use of SMA in construction and research, and their beneficial aspects by reviewing the available information. He considered Shape Memory Alloy as SMART MATERIAL or INTELLIGENT MATERIAL.
- 8. Types of SMAs Alloy Composition Transformation temperature(K) Mf Ms As Af NiTi 50.5, 49.5 277.0 306.0 317.0 335.0 NiTi 50.8, 49.2 227.0 252.0 270.0 284.0 NiTi 50.9, 49.1 157.4 242.5 275.1 317.8 NiTi 50.0, 50.0 245.2 310.7 321.4 351.0 NiTiCu 40.0,50.0,10. 0 294.1 314.6 325.9 339.8 CuZnAl 25.6, 4.2, 70.2 288.5 292.3 293.2 298.3 CuAlNi 82.0, 14.0, 4.0 252.0 246.0 274.0 285.0 11.6, 0.6,
- 9. Properties Mechanical properties Tensile and compressive behavior
- 10. Properties. Unique properties of shape memory alloys 1. Shape Memory Effect 2. Pseudo-Elasticity Shape Memory Effect
- 11. Properties. Austenite and Martensite Two phases exhibited by SMAs in solid state. If deformed in martensite phase, the parent shape is regained upon heating. As and Af are the temperatures at which transformation from martensite to austenite starts and finishes. Transition dependant on temperature and stress. Repeated use of shape memory effect leads to functional fatigue.
- 12. Properties. Pseudo-Elasticity o Occurs without temperature change. o Based on stress induced mechanism o This property allows the SMAs to bear large amounts of stress without undergoing permanent deformation.
- 13. Working principle A molecular rearrangement in the SMAs austenite and martensite phase is responsible for its unique properties. Martensite is relatively soft and occurs at lower temperatures. Austenite occurs at higher temperatures.
- 14. Working principle.. The shape of austenite structure is cubic. No change in size or shape is visible in shape memory alloys until the Martensite is deformed. To fix the parent shape, the metal must be held in position and heated to about 500属C. The high temperature causes the atoms to arrange themselves into the most compact and regular pattern possible resulting in a rigid cubic arrangement (austenite phase).
- 15. Applications General applications Eyeglass Frames Helicopter blades Dental wires Applications in civil engineering/ structure 1. Reinforcement SMAs are particularly beneficial for construction in seismic regions. If SMA is used as reinforcement, it will yield when subjected to high seismic loads but will not retain significant permanent deformations.
- 16. Applications. 2. Prestressing The benefits of employing SMAs in prestressing include: i. No involvement of jacking or strand-cutting ii. No elastic shortening, friction, and anchorage losses over time SMA strands are used in pre tensioning and post tensioning.
- 17. Applications. 3. Braces for frame structures The SMA wire braces are installed diagonally in the frame structures. As the frame structures deform under excitation, SMA braces dissipate energy through stress-induced Martensite transformation (in the superelastic SMA case) or Martensite reorientation (in the Martensite SMA case).
- 18. Applications. 4. Damping element for Bridges(restrainer) One of the main problems of bridges during earthquakes is their unseating because of excessive relative hinge opening and displacement These limitations can be overcome by introducing SMA restrainers as they have larger elastic strain range and can be brought back to its original position even after deformation.
- 19. Applications. 5. SMA for structural self-Rehabilitation The IRC(Intelligent Reinforced Concrete ) uses stranded Martensite SMA wires for post- tensioning . By monitoring the electric resistance change of the SMA wires, the strain distribution inside the concrete can be obtained. In the presence of cracks due to explosions or earthquakes, by electrically heating the SMA wires, the wire strands contracts and reduce the cracks. This self-rehabilitation can handle macro-sized cracks. The concrete structure is intelligent since it has the ability to sense and the ability to self-
- 20. Applications. A small concrete block with SMA post-tensioned Test Set up of beam reinforced with SMA wire. A model by G. Song et. al(2006)
- 21. Applications. Cracked block on loading Closure of crack on unloading
- 22. Applications. 6. SMA as FRP SMA-FRP reinforcing bars behave in a ductile manner and are capable of dissipating energy. It was found that SMA-FRP bars have more potential to improve the ductility and energy dissipation capability of concrete structures compared to conventional FRP bars. 7. SMA as fibers The most crucial limitation of concrete is its low tensile strength, compared to its compressive strength, which results from the propagation of micro-cracks. This may be prevented by using prestrained SMA wires that are embedded in the concrete matrix. Upon activation, these wires regain their original shape, and consequently, initial compressive stresses are transmitted to the concrete matrix.
- 23. Advantages Bio-compatibility Diverse Fields of Application Good Mechanical Properties (strong, corrosion resistant) Disadvantages These alloys are still relatively expensive to manufacture and machine compared to other materials such as steel and aluminum. Most SMA's have poor fatigue properties; this means that while under the same loading conditions (i.e. twisting, bending, compressing) a steel component may survive for more than one hundred times more cycles than an SMA element.
- 24. Case study 1. Retrofitting Of the Basilica of San Francesco at Assisi, Italy The Basilica of San Francesco was restored after being strongly damaged by an earthquake of 1997 Umbria-March earthquake (Castellano 2000). The gable was completely disconnected from the roof and was then linked to the roof again by means of Shape Memory Alloy Devices (SMADs). Each SMAD is designed to take both tension and compression forces, while consisting of SMA wires which are only subjected to tension. In order to reduce the seismic forces transferred to the tympanum, a connection between it and the roof was created using superelastic SMAs The SMA device demonstrates different structural properties for different horizontal forces. Under extremely intense horizontal loads, the SMA stiffness increases to prevent collapse.
- 25. SMA Devices in the Basilica of St Francesco of Assissi Below figure shows the SMDs used in the retrofit.
- 26. Case study 2. Retrofitting of the bell tower of the Church of San Giorgio at Trignano, Italy The S. Giorgio Church, located in Trignano, Italy, was struck by a 4.8 Richter magnitude earthquake on October 15, 1996, resulting in significant damage to the bell tower within the church. Following the earthquake, the tower was rehabilitated using SMAs. The upgrade was carried out linking top and bottom of the tower by means of hybrid tendons. Four vertical prestressing steel tie bars with SMA devices were placed in the internal corners of the bell tower to increase the flexural resistance of the structure.
- 27. Case study The retrofit was tested by a minor m=4.5 Richter magnitude earthquake on June 18, 2000, with the same epicenter as the event in 1996. After the main shock, the tower was investigated and no evidence of damage was present (DESROCHES and SMITH 2003). Bell tower with tendons and SMA devices
- 28. Conclusion SMAs have the potential to be used effectively in seismic regions. The high cost of SMAs is a major limiting factor for its wider use in the construction industry. Their capability to allow the development of smart structures with active control of strength and stiffness and ability of self- healing and self-repairing opens the door for exciting opportunities, making them the construction material of the future.
- 29. THANK YOU.