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Teacher Summer Research Program
Texas A&M University
June, 2007
Libana Zamudio-Sirman, Del Rio High SchoolDr. D. Lagoudas and Dr. D. Davis, Faculty Advisors
P. Kumar, PhD. CandidateF. Phillips, REU student
Aerospace Engineering Shape Memory Alloys
Shape Memory Alloy Research Team (SMART)
Faculty, research staff and students
Interest in developing experimentally verifiable constitutive models for Shape Memory Alloys (SMAs)
Design capabilities of active or "smart" structures that utilize the shape memory effect for shape and actuation control applications
http://smart.tamu.edu
Facilities and Support
Use of state of the art thermomechanical facilities integrated with dynamics, control, flight simulation, and fluid mechanics lab facilities called an Intelligent Systems Laboratory (ILS) network
Initiated by TAMU in 1992Supported by Army Research Office, Office of
Naval Research, Air Force Office of Scientific Research and the State of Texas
http://smart.tamu.edu
What is an SMA? Unique class of
metal alloys that can recover apparent permanent strains when they are heated above a certain temperature
Two stable phases1. high-temperature
phase - austenite 2. low-temperature
phase - martensite
http://smart.tamu.edu
Shape Memory Effect: Stress Free Shape Recovery
TEMPERATURE
STRESS
Mf Ms As Af
TEMPERATURE
STRESS
Mf Ms As Af
Twinned Martensite (unstressed)
Detwinned Martensite (stressed - deformed)
Detwinned Martensite (stressed - deformed)
Detwinned Martensite (unstressed - deformed)
Austenite (undeformed)
http://smart.tamu.edu
Shape Memory Effect: Shape Recovery Under Stress
TEMPERATURE
STRESS
Mf Ms
Detwinned Martensite(stressed) Austenite
As Af
http://smart.tamu.edu
The Pseudoelastic Effect
STRESS
TEMPERATURE
Mf Ms As Aff s s f
Austenite
Detwinned Martensite(stressed)
Links
Flexible tail
Joints
Model withoutskin
Model withskin
Rigid nose
SMAs as Linear Actuators
http://smart.tamu.edu
Using SMA and SMA technology in the Physics Classroom
Students will be introduced to the properties of SMAs and their usesAfter having completed Hooke’s Law and the elastic potential energy, they will be introduced to the properties of nonlinear springs, varying force constants, etc.Students will use the SMA springs (made by the AP Physics class for their experiments) and gather various data to calculate the spring constants Students will use different masses, different data collection devices to determine the constants and analyze sources of error. Students will measure and use the following:
Using SMA and SMA technology in the Physics Classroom
Students making the SMA springs will need to be prepared to work with sharp objects.
They will need goggles and must wear close-toed shoes, long pants and no billowing sleeves
If you have the proper furnace, it is recommended that you, the teacher place and remove the springs using high-heat tongs and heat resistant gloves, and only allow the students to handle the spring-bolts after sufficient cooling.
Using SMA and SMA technology in the Physics Classroom Timeline
Background on SMAs- one 50-minute class period
Preparing, training springs, and pre-lab assignment-one class period (if you are sending them to off-site to be cooked, then the pre-lab can be completed in class)
Pre-lab consists of any sample calculations that you may want to review
Lab- one class period\
Post lab extension- teacher preference
Making the SMA SpringBegin with “pickled”, low temperature Nitinol, 0.025” diameter, round wireWind the wire into the grooves of a 3/8’ diameter bolt with a pitch of 16 turns/inch to a desired lengthThe bolt should have small hex-bolt fasteners at the ends of the desired length.To train the Nitinol into a spring, place it in a furnace that has been pre-heated to 500oC for five minutesYou may have to set the springs and have them trained somewhere else such as metal-working plant, knife maker, or by someone with an industrial kiln for annealing.After removing it from the furnace allow it to cool, then undo the ends and uncoil it from the boltThe wire will not look like a spring until it is heated up again via a low voltage or a lighter.If the spring has twists and/or kinks, simply undo them and heat that part slowly until it is uniformAlways use tongs and heat resistant gloves when handling the hot spring and fire.
From forced coiled SMA wire to permanent SMA Spring
Untrained coiled Nitinol
wire
Heating the coil in
the furnace
Cooled wire pulled off the bolt
To make the spring coil
run a current thru it or
simply heat it from one
end to other slowly
removing the kinks bit
by bit
Pictures by: Libana Zamudio-Sirman, TAMU Bright Building
SMA Spring LabMetric ruler to determine the length of the spring before it is loaded at room temperatureStudents will load the spring and measure it’s displacement Students will heat the spring via a battery and record the temperature at which the mass began rising at a smooth rate of accelerationStudents will continue to heat the spring and record the temperature at which it begins to decelerateStudents will repeat this process 5 times Students will use 5 different masses and repeat the stepsStudents will use the information to determine two spring constants, one for the Martensite phase and one for the Austenite phase.They will compare this constant to those calculated from Hookian Springs in the previous lab.Students will be using digital thermometers and thermocouples to record the temperatures
Set up
Pictures by: Libana Zamudio-Sirman, TAMU Bright Building
Pictures by: Libana Zamudio-Sirman, TAMU Bright Building
SMA Lab Calculations
All students will have already studied the law of conservation of mechanical energy, conservative and nonconservative forces and have determined sources of work lost to heat and deformation.The data calculated in the lab with the SMA spring will be used to determine the energy stored in this spring versus the energy stored in a normal spring of the same length, number of turns, and approximate mass density
Calculations (continued)Students will plot the force versus displacement graph using F=mg for the force on the spring and the stretch of the spring as displacementThe average slope of the graph will be the spring constant k, the springSince the value k changes the students do not have a smooth graph and will have to use the graphing calculator to find a curve of best fitAfter inputting the data collected from the lab, students will use the calculation functions and take the first derivative of the function to find the slope of the line tangent to the curve at a specific point, this will be the k valueThe k value will be used for various calculations in the rest of the lab.
Extras• Lab-handout• Purchasing information for Nitinol-handout• The apparatus can be made from many
materials, but it should be a frame that is at least 16” tall and 8” wide with a solid base that can fit a metric ruler and possibly the battery. You will need L-brackets to secure the frame and ruler to the base. Several screws and washers (see pictures)
Many Thanks to the following• TAMU E3-Dr. Butler-Purry and Julianna
Camacho
• Aerospace Engineering- Dr. Lagoudas and Dr. Davis and Gary Siedel
• TAMU Aerospace Materials Lab- Parikshith Kumar and Francis Phillips and the SMART Team