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Demonstration of Shape Memory and Super-elastic Effects of Nitinol Alloys

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2020 ASEE Virtual Annual Conference Content Access


Virtual On line

Publication Date

June 22, 2020

Start Date

June 22, 2020

End Date

June 26, 2021

Conference Session

Materials Division Technical Session 4

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Mohamed Samir Hefzy The University of Toledo

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Mohamed Samir Hefzy served as the Associate Dean of Graduate Studies and Research Administration of the College of Engineering (COE) at The University of Toledo (UT) for 14 years from 2004 until January 2018. He is a tenured Professor of Mechanical, Industrial and Manufacturing Engineering (MIME) and served as Graduate Program Director of the MIME department from August 2018 and from 2000 to 2007, and also was the first to hold that position during the 1994-95 academic year. Additionally, he serves as the Director of the COE Biomechanics and Assistive Technology Laboratory at UT. He has been on the faculty of The UT since 1987. He graduated from Cairo University, Egypt, with a B.E. (Honors) in Civil Engineering in 1972, and a B.Sc. in Mathematics from Ain-Shams University in 1974. He earned his M.S. in Aerospace Engineering in 1977 and his Ph.D. in Applied Mechanics in 1981, both from The University of Cincinnati. He then received training as a Postdoctoral Research Associate for two years in the Department of Orthopedic Surgery at The University of Cincinnati’s College of Medicine. In 1983, Dr. Hefzy joined the faculty of Grand Valley State University in Allendale, Michigan as their first engineering faculty. He then returned to the University of Cincinnati as a Research Assistant Professor in 1985.

In December 2003, Dr. Hefzy was elevated to the Grade of American Society of Mechanical Engineers
(ASME) Fellow in recognition of his outstanding contributions to research and development, to education and leadership in the Engineering Profession. Dr. Hefzy has published with his students more than 40 peer reviewed journal papers and 100 peer reviewed national and international conference papers, and coauthored more than 19 book chapters in his research areas: Orthopedic Biomechanics and Assistive
Technology. Dr. Hefzy has secured more than $5 million in funding as a PI, CO-PI, and CI to support his research program, with sponsors including the OBOR, the NSF and the NIH. He has supervised two postdoctoral fellows and has served as primary graduate advisor to more than 30 masters and doctoral students. In addition, he has supervised more than 130 undergraduate senior design projects at UT as part of his community engagement and service learning activities..

Dr. Hefzy is the recipient of many awards, including the 2011 Distinguished Service Award from the ASME, the Edith Rathbun Award for Excellence in Outreach and Engagement from The University of Toledo in 2006, the University of Toledo Outstanding Faculty Research Award in 2004 and the College of Engineering’s Outstanding Teacher Award and the Outstanding Undergraduate Research Mentoring Award in 1999 and 2001, respectively. His engineering experience and familiarity with recent educational practices led to his selection by the ASME as a Mechanical Engineering Evaluator for the Accreditation Board for Engineering and Technology (ABET). At the national level, Dr. Hefzy has served two consecutive three-year terms as the Treasurer and member the ASME’s Executive Committee of the Bioengineering Division (BED) (2010-2013 and 2007-2010). He has also served as a member at large on the ASME’s Executive Committee of the BED from 1999 to 2002 and as Chair of the BioSolids Technical Committee of the BED from 2004-2007. He has also served a two-year term on the basic Engineering Group Operating Board (BEGOB) as a representative to the Committee on Administration and Finance of the ASME (2011-2013) and a two-year term (2013-2015) on BEGOB as a rep. to the strategic planning committee. He has also served as a judge for the ASME Scholarship Program’s University applications from March from 2016 to 2018.

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Mohammad Elahinia The University of Toledo

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Dr. Elahinia is a University Distinguished Professor in Engineering and Chair in the Mechanical, Industrial, and Manufacturing Engineering (MIME) Department at The University of Toledo. He graduated with his doctorate in Mechanical Engineering from Virginia Polytechnic Institute and State University in August 2004. After graduation, he joined the faculty of the Mechanical, Industrial, and Manufacturing Engineering Department, where he is the director for the Dynamic and Smart Systems Laboratory. He was promoted to the rank Associate Professor with tenure in 2010 and Professor in 2015. Dr. Elahinia’s research interests are advance manufacturing, modeling, control, and design of smart materials with an emphasis on additive manufacturing of functional materials such as shape memory alloys for aerospace and biomedical application.

At UToledo he has served as an investigator on several funded projects with a total budget of more than $15 million. These projects are funded by NSF, EPA, US Army, US DOT, Ohio Department of Development, Ohio Board of Regents, and the UT. Dr. Elahinia is a Fellow of the American Society of Mechanical Engineers. He has received several awards, including the University of Toledo 2019 Outstanding Teacher Award, Outstanding University of Toledo 2017 Faculty Research Award, ASME 2010 Adaptive Structures and Material Systems Gary Anderson Early Achievement Award, University of Toledo 2010 College of Engineering Faculty Excellence Award, University of Toledo 2006 Outstanding Young Faculty Research Award and Virginia Tech 2004 Torgersen Graduate Research Excellence Award.

Dr. Elahinia has also been active in translating research out of his laboratory. Three startup companies have been formed to commercialize three medical devices and technologies in the area of smart materials. These companies have raised more than $2 million in external funding.

Dr. Elahinia has served as the major advisor for 45 graduate students (10 Ph.D. and 35 M.S.). Seven of his former students are assistant and associate professors at other universities. To disseminate his research findings, Dr. Elahinia and his students co-authored 3 books, 7 book chapters, and more than 100 journal papers. Dr. Elahinia has also been active and engaged in professional societies. In 2004 Dr. Elahinia was elected a member of the ASME/SPIE Adaptive Structures and Material Systems Branch under the Aerospace Division. He has since served in several other elected positions including the chair of the branch. This branch has more than 1500 members. Dr. Elahinia serves as an associate editor for four journals in his area of research: Smart Material Research, The Scientific World Journal, Journal of Intelligent Material Systems and Structures as well as the Journal of Shock and Vibration.

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Ahmadreza Jahadakbar The University of Toledo


Bethany Arn The University of Toledo

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Graduate Assistant - Mechanical, Industrial, and Manufacturing Engineering Department, The University of Toledo. Biomechanics and Assistive Technologies Lab.

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Mohammadreza Nematollahi University of Toledo

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Shape memory alloys (SMAs) are a unique class of materials with the ability to recover their shape. Nitinol (Nickel-titanium, NiTi) alloys are the most used SMAs. NiTi alloys are widely used in numerous medical applications such as stents, blood clot filters, arch wires for orthodontic applications, orthopedic implants, and the development of surgical instruments. They exhibit two different behaviors: shape memory and superelastic effects. The shape recovery ability of the NiTi is due to a phase transformation between the austenite and the martensitic phases in a reversible way due to temperature and/or load changes. NiTi alloys can be found in three phases: austenite phase (A), twinned martensite phase (Mt), and detwinned martensite phase (Mdt). The austenite phase is called parent phase, which means that the material is in a high-temperature environment with respect to the martensite phases. The twinned and detwinned martensite phases occur in a low-temperature environment or due to loading. Martensitic start temperature Ms, martensitic finish temperature Mf, austenitic start temperature As and austenitic finish temperature Af are four material characteristics of the NiTi alloys that define the conditions for phase transformations between martensite and austenite. Shape memory and superelastic effect of NiTi are also highly dependent to thermomechanical loading level and rate, and this dependency must be considered in the design of components.

One of the outcomes of the course entitled: “Experimental Methods in Orthopaedic Biomechanics” is for mechanical and bioengineering undergraduate and graduate students to learn the design and implementation of NiTi alloys. This is achieved by conducting two experiments to observe the shape memory and superelastic effects of NiTi alloys. NiTi wires were tested in both experiments.

The superelastic behavior is exhibited when the material is in the Austenite phase and the environment temperature is higher than Af. This superelastic effect exhibits itself when a large enough mechanical load is applied to the material. A 0.025’’ diameter wire manufactured by Fort Wayne Metals, Inc. (Fort Wayne, IN) was used to demonstrate the superelastic effects of the NiTi alloys. The wire was tested under a displacement control mode using a BOSE ElectroForce® 3300 machine by applying a tension force at two different strain rates: an isothermal loading at a rate of 0.005 mm/s and a dynamic loading at a rate of 0.5 mm/s. In the beginning, the material is in the austenite phase. The external load causes a stress-induced transformation from Austenite to detwinned Martensite. The recoverable induced strain is much higher (about 7%) than that of conventional materials. By unloading the material, it transforms back to Austenite and recovers its shape. An infrared camera was used to record the temperature changes of the wire during loading and unloading. The loading rate was set using the Wintest®7 software. The wire was trained at the high strain rate to stabilize the cyclic response. Load-displacement curves, stress-strain curves, and temperature changes in the wires were plotted and analyzed. Students were asked to identify one example of the application of superelastic wires and describe how it works and its advantages compared to traditional materials.

The shape memory effect is the material behavior in response to temperature changes. A Flexinol actuator wire with a 250 µm diameter, manufactured by DYNALLOY, Inc. (Irvine, CA) is used for this demonstration. In this experiment, the NiTi wire is initially in its twinned martensitic phase. It is then loaded and transformed into the detwinned martensite phase. The load is removed, and the material remains in its detwinned martensite phase. Large residual strains (about 8%) can also be observed after removing the load. The wire is then heated which causes the material to transform back to the austenite phase, recovering all of the strains. When the heat is removed, the material returns to its original twinned martensite phase without any change in length. The experiment was repeated for three different loading levels. An Arduino board was used to command the power supply switch to turn on and off depending on the temperature, and to record the the real time temperature and displacement of the NiTi wire. The Arduino board utilized the Parallax Data Acquisition Excel add-on for data acquisition. Stress-strain curves were plotted. Students were also asked to identify one example of the application of the shape memory alloy (SMA) where the design is based on using the shape memory effect of the wire and describe briefly how the SMA wire works.

Hefzy, M. S., & Elahinia, M., & Jahadakbar, A., & Arn, B., & Nematollahi, M. (2020, June), Demonstration of Shape Memory and Super-elastic Effects of Nitinol Alloys Paper presented at 2020 ASEE Virtual Annual Conference Content Access, Virtual On line . 10.18260/1-2--34379

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