Shape Memory Alloys - Lecture Slides | AE 598, Lab Reports of Aerospace Engineering

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Shape Memory Alloys

History of shape memory alloys

^

:^ Discovery of reversible martensite to austenite

phase transformation in Au-Cd alloying system byChang & Read

^

:^ Discovery of recovery of deformed shape in Cu

based alloys by Genevray

^

Discovery of shape memory Effect in Ni-Ti

alloying system

^

First Commercial Use of Nitinol

in

F14 Tomcat

^2

SMA

^

SMA: Shape Memory Alloy

^

Exhibit thermomechanical coupling

^ Heating and cooling produce large mechanicaldeformations

^ Thermomechanical strains are typically 5-10%

^

Exhibit a

shape memory effect

in which a certain shape

is recoverable upon thermomechanical transformation

Shape Memory Alloys

http://www-civ.eng.cam.ac.uk/dsl/sma/spring.gif

http://www.talkingelectronics.com.au/Projects/Nitinol/Nitinol-1.html

One way Shape memory effect

Two way Shape memory effect

Types of martensitic transformations

^

Thermoelastic martensite:

^ The austenite and martensite interface are mobile andcan move with variation of temperature

^

Nonthermoelastic martensite:

^ The austenite and martensite interface are sessile and donot move with variation of temperature

Thermoelastic vs. nonthermoelastic martensite

^

Nonthermoelastic martensite has wide hysteresis whereasthermoelastic martensite is characterized with narrowhysteresis

^ R.W. Cahn, Peter Hassen, Physical Metallurgy,

th^ Edition, 1996

8

Transformation paths of

Nonthermoelastic Martensite

Cooling: Martensite plates grow and lock

Heating: The Martensite & Austenite interface remained locked and austenitephase nucleates and grow inside of martensite phase

M. FAROOQUE, H. AYUB, A. UL HAQ, A. Q. KHAN, JOURNAL OF MATERIALS SCIENCE 33 (1998) 2927

-^^2930

18% Ni 350 grade maraging steel

10

Strain

fi

eld around the martensite phase

Thermoelastic Martensite

:^ Pure

Shear:

Non Thermoelastic Martensite

:^ Shear +

Volume Change

11

SMA Microstructure Austenite (high temperature phase)

Martensite (low temperature phase)

Shape Memory Effect austenite

detwinned martensite

twinned martensite

heating

cooling

deformation

Stress-induced martensite

twinned martensite

detwinned martensite twinboundary

Constitutive Response

Pseudoelastic behavior

PSEUDO-

ELASTIC

LOOP

Superelastic (Pseudoelastics) Behavior

20