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