FLEXINOL®
DYNALLOY, Inc.
Makers of Dynamic Alloys
Technical Characteristics of
Actuator Wires
Flexinol® Actuator Wires are small diameter wires which contract like muscles when
electrically driven. Smaller than motors or solenoids, cheaper and generally easier to use,
these wires perform physical movement across an extremely wide variety of applications.
14762 Bentley Circle, Tustin, California 92780 USA 714-436-1206 714-436-0511 fax
http://www.dynalloy.com
Table of Contents
Physical Properties Summary
Introduction
Section 1. Movement
Section 2. Electrical Guidelines
Section 3. Cycle Time
Section 4. Miscellaneous
2
3
4
6
7
9
Section 5. Underlying Technology 11
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FLEXINOL®
DYNALLOY, Inc.
Makers of Dynamic Alloys
NICKEL - TITANIUM ALLOY PHYSICAL PROPERTIES
1. Density
2. Specific Heat
3. Melting Point
4. Latent Heat of Transformation
5. Thermal Conductivity
6. Thermal Expansion Coefficient
Martensite
Austenite
7. Electrical Resistivity (approx.)
Martensite:
Austenite:
0.235 lb/in (6.45 g/cm )
0.20 BTU/lb * °F (0.2 cal/g * °C))
2370 °F (1300 °C)
10.4 BTU/lb (5.78 cal/g)
10.4 BTU/hr * ft * °F (0.18 W/cm * °C)
3.67x10 /°F (6.6x10 /°C)
-6
-6
6.11x10 /°F (11.0x 10 /°C)
32 micro-ohms * in (80 micro-ohms * cm)
39 micro-ohms * in (100 micro-ohms * cm)
-6
-6
3
3
14762 Bentley Circle, Tustin, California 92780 USA 714-436-1206 714-436-0511 fax
http://www.dynalloy.com
Typical Temperature vs. Strain Characteristics for Dynalloy’s standard 158°F (70°C)
“LT” and 194°F (90°C) “HT” Austenite start temperature alloys, at 172 MPa
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FLEXINOL®
DYNALLOY, Inc.
Makers of Dynamic Alloys
Introduction
Flexinol® is a trade name for shape memory alloy actuator wires. Made of nickel-titanium these small
diameter wires contract like muscles when electrically driven. This ability to flex or shorten is
characteristic of certain alloys that dynamically change their internal structure at certain temperatures.
The idea of reaching higher temperatures electrically came with the light bulb, but instead of producing
light these alloys contract by several percent of their length when heated and can then be easily stretched
out again as they cool back to room temperature. Like a light bulb both heating and cooling can occur
quite quickly. The contraction of Flexinol® actuator wires when heated is opposite to ordinary thermal
expansion, is larger by a hundredfold, and exerts tremendous force for its small size. The underlying
technology that causes the effect is discussed in Section 5. The main point is that movement occurs
through an internal "solid state" restructuring in the material that is silent, smooth, and powerful.
This effect can be used in many ways. The list of viable applications is too long for any single listing. A
safe assumption is that any task requiring physical movement in a small space with low to moderate
cycling speeds is something that most likely will be better done with actuator wires. Many of the tasks
currently being done with small motors or solenoids can be done better and cheaper with Flexinol®
actuator wires. Since the actuator wires are much smaller for the work they do a number of new products
and improved designs on existing products are readily accomplished.
For new users of Flexinol® actuator wires Dynalloy, Inc. strongly recommends that an overview of what
can be done first be established. This can be done by obtaining one of the Dynalloy, Inc. kits, which are
made for such familiarization. Secondly, new users should consider obtaining from Dynalloy, Inc. or
other consultants a "Proof of Concept" working model. This is not only useful as an internal marketing
and sales tool, it also helps the new user to see how those with more experience approach the specific
task in hand. Knowing this provides immeasurable insight into how to proceed and helps reduce the
redundancy of reinventing existing techniques. One can always improve on existing methods and
sufficient legal and other safeguards can be readily employed to ensure protection of proprietary ideas.
14762 Bentley Circle, Tustin, California 92780 USA 714-436-1206 714-436-0511 fax
http://www.dynalloy.com
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FLEXINOL®
DYNALLOY, Inc.
Makers of Dynamic Alloys
Section 1. Movement
The movement or stroke of Flexinol® actuator wire is measured as a percentage of the length of the wire
being used and is determined, in part, by the level of stress one uses to reset the wire, or to stretch it in its
low temperature phase. This opposing force, used to stretch the wire, is called the bias force. In most
applications, the bias force is exerted on the wire constantly, and on each cycle as the wire cools, this
force elongates it. If no force is exerted as the wire cools, very little deformation or stretch occurs in the
cool, room temperature state and correspondingly very little contraction occurs upon heating. Up to a
point the higher the load the higher the stroke. The strength of the wire, its pulling force and the bias
force needed to stretch the wire back out are a function of the wire size or cross sectional area and can be
measured in pounds per square inch or “psi”. If a load of 5,000 psi (34.5 MPa) is maintained during
cooling, then about 3% memory strain will be obtained. At 10,000 psi ( 69 MPa), about 4% results, and
with 15,000 psi (103 MPa) and above, nearly 5% is obtained. However, there is a limit to how much
stress can be applied.
14762 Bentley Circle, Tustin, California 92780 USA 714-436-1206 714-436-0511 fax
http://www.dynalloy.com
Far more important to stroke is how the wire is physically attached and made to operate. Dynamics in
applied stress and leverage also vary how much the actuator wires move. While normal bias springs that
increase their force as the Flexinol® actuators contract have only 3-4% stroke, reverse bias forces which
decrease as the actuator wires contract can readily allow the wire to flex up to 7%. Mechanics of the
device in which it is used can convert this small stroke into movements over 100% of the wires' length
and at the same time provide a reverse bias force. The stress or force exerted by Flexinol® actuator
wires is sufficient to be leveraged into significant movement and still be quite strong. Some basic
structures, their percent of movement, and the approximate available force they offer in different wire
sizes are as follows:
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FLEXINOL®
DYNALLOY, Inc.
Makers of Dynamic Alloys
14762 Bentley Circle, Tustin, California 92780 USA 714-436-1206 714-436-0511 fax
http://www.dynalloy.com
Stroke and Available Force Table
Approx.
Stroke
Normal
Bias
Spring
3%
Dead
Weight
Bias
4%
Leaf
Spring
Bias
7%
Right
Angle
Pull
14%
Simple
Lever
(6:1
ex)
30%
Adjusting
Curvature
110%
Clam
Shell
100%
0.003”
Wire
(0.076
mm)
0.18
lb
(80
g)
0.18
lb
(80
g)
0.18
lb
(80
g)
0.04
lb
(20
g)
0.024lb
(11
g)
0.006
lb
(3
g)
0.007
lb
(3.2
g)
0.006”
Wire
(0.15
mm)
0.73
lb
(330
g)
0.73
lb
(330
g)
0.73
lb
(330
g)
0.18
lb
(83
g)
0.10
lb
(47
g)
0.026
lb
(12
g)
0.028
lb
(13
g)
0.010”
Wire
(0.25
mm)
2.05
lb
(930
g)
2.05
lb
(930
g)
2.05
lb
(930
g)
0.51
lb
(232
g)
0.29
lb
(133
g)
0.075
lb
(34
g)
0.082
lb
(37
g)
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