This introduction gives you an overview about shape memory alloys used as thermal and electric actuators.

1. SHAPE MEMORY ALLOY BASED ACTUATORS
Smart materials for intelligent mechatronic systems

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Preface
This publication is brought to you by:
Dr.-Ing. Alexander Czechowicz,
CTO at Hoffmann Kunststofftechnik +
Mechatronik Company in Germany
Dr.-Ing. Sven Langbein,
Group Leader Shape Memory Alloy
Technology at Feindrahtwerk A. Edelhoff
Company in Germany
additional content and scientific review by:
Forschungsgemeinschaft Werkzeuge und
Werkstoffe e.V,
Scientific Institute in Germany
Additional information on Shape Memory Alloys:
In English in German
2nd edition Summer 2020
www.hoffmann-kunststoffe.de
www.edelhoff-wire.de
www.fgw.de

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Content
§ Shape Memory Alloys (SMA): intelligent materials - basics
§ Application of SMA as actuators – two examples
§ Potentials and limits of SMA actuators
§ Outlook: What else can be done with SMA ?

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Shape Memory Alloys (SMA): intelligent materials - basics
§ Shape memory alloys (SMA) belong to the group of smart materials and are high-tech materials that have several
functional properties. They show actuator functions combined with sensor effects in one metallic part.
§ After deformation, SMA return to their imprinted shape through a phase change triggerd by temperature or electric
current flow (leading to self-heating).
§ If the imprinted shape of SMA wire is set to a straight wire, a high-power output is possible. An SMA wire of 0.5 mm
(0.019”) diameter can generate pulling forces up to 78 N (17.2 lb) by straight contraction of up to 8% of its initial
length.
In this experiment a piece of SMA wire is thrown into hot water. The SMA wire‘s
imprinted shape was set before to a spring element.

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Shape Memory Alloys (SMA): intelligent materials - basics
§ Commonly used SMA materials are Nickel-Titanium alloys (good for high cycling lifetime-performance). There are
also copper based SMA alloys on the industrial market (higher working temperatures).
§ Electric SMA actuators (based on NiTi-Alloys) can normally be operated in a range of -50°C (-58°F) to +85°C (185°F).
There are special SMA alloys available granting higher operation temperatures.
§ The imprinted shape is done by a thermomechanical treatment normally at temperatures higher than 400°C (752°F).
§ SMA can be used as thermal actuators, electric actuators and superelastic systems1.
§ All SMA show an intrinsic sensor function. With the shape change, the el.
resistance changes also significantly. This can be used as stroke, thermal
and force sensor.
1 not discussed in this presentation

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Shape Memory Alloys (SMA): intelligent materials - basics
§ In mechatronic systems, SMA are mainly activated by electric current flow.
§ If the pre-loaded SMA wire is heated, it starts it’s material phase transformation to the
imprinted shape – the short wire geometry.
§ The transformation is nearly linear on the time-scale.
§ It is possible to set and hold every intermediate position.
§ If the current is turned of, the SMA-wire starts to cool down. If a load is still applied, the
mass of the load elongates the SMA-wire to initial position.
NOTE that….
§ In many industrial application cases the cooling time can not be influenced in running systems
§ The lifetime performance of SMA –wires mainly depends on applied load, strain, current level, thermomechanical
treatment of the SMA material and boundary conditions.
SMA-wire
load
stroke
A B
el.resistance
stroke
Time
A B A

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Application of SMA as Acatuators
SMA-wire polymer-structure flap el. Connector solid-state joint
Example 1: Easy-unlocking system with SMA
inactive active
System
Feature
SMA based unlocking
system
Solenoid unlocking
system
Installation space in
mm³ [inch³]
48 x 23 x 4
[1.88 x 0.90 x 0.15]
50 x 32 x 24
[1.96 x 1.25 x 0.94]
Displacement at 4 N
load in mm [inch]
2,9 [0.11] 3,1 [0.12]
Self-weight in g [oz] 3 [0.10] 106 [3.73]
Description:
The unlocking system called „swan-actuator“ works with NiTi SMA wire. If the wire is heated, it
deforms a solid-state joint. Thus the activation results into a movement of the „swan‘s“ head, which
was holding a prestressed flap down. When the head is moving, the connection to the flap is opened.

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Application of SMA as Acatuators Example 2: Standardized SMA actuators
stroke
active moving direction
• Flat construction (only 6 mm
[0.21“] thick)
• Noiseless operation
• Low electrical operating voltage
(2.5-12V)
• High-strength construction made
of PA6 GF30
• Integrated overload protection
• Integrated displacement switch
• Very low weight (9g)
• High corrosion resistance
• Temperature range for use: -15 ° C
to + 50 ° C
• Competitive serial prices to other
small drives
Key features
stroke
on
load
SMA-wire
off
Description:
SMA does not need to be used as straight wire. The standardized SMA actuators „ONE“ use a bow-like
structure, so the SMA wire is mounted both sides. In the mid-section the load is applied onto the wire.
The plug & play design allows the user to reach strokes up to 4.3 mm [0.17“] at loads up to 20 N.
Within the design a mechanical switch is integrated for protection of the actuator against overloads
and overheating. Due to its linear stroke characteristic, the actuator can be controlled for positions in
less than 1 µm steps (using laser-sensor). Using the ONE‘s intrinsic sensor, position controll can be
implemented in 100µm steps.

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Potentials and Limits of SMA Actuators
1 weight reduction 2 compact / flexible design
POTENTIALS
SMA based actuators are definitely powerful regarding their self-weight. With less
than 0.04 lb (200g) it is possible to generate forces up to 1000 kN.
0.0002 0.002 0.02 0.2 2 20
[g]
[lb]
SMA actuators, espescially SMA-wires, allow to
develop compact actuators – which have
commonly a small diameter but a specific
lenght.
In some cases a compact design is still due to
the needed lenght possilbe. For example in
order to implement the SMA wire acuator
directly into a polymer housing or mobile device.
As shown on the right, a thin SMA actuator
(ONE) can be implemented as an unlocking
device into a flap of an electronics control panel.
Another possibility to handle the dimensions can
be achieved by flexible actuator design.
A thin wire can move a mass, but it has
sometimes to be a long wire to generate a
usable stroke. It is recommended to use shape
memory alloys for drives with a stroke of up to
25 mm [~ 1”]. However, at 4% usable strain (for
moderate lifetime performance) an SMA wire
would be over 600 mm [24”] long. It is not easy
to implement such a drive. But SMA can be
designed as flexible drives, like the FG-FLEX
actuator which is built like a bowden-cable.
stroke

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Potentials and Limits of SMA Actuators
3 noisless actuation 6 Intrinsic sensor functions
4 no electromagnetic field emission
5 fast activation movement
POTENTIALS
SMA do not generate any noises during actuation.
SMA do not respond to magnetic field an do not generate electromagnetic signals.
Magnetic or pneumatic drives have a moving mass. This resembles an interia
which works against the moving direction, slowing down a fast moving actuator.
Since SMA have nearly no mass in comparision to the generated forces, you just
have to put enough energy in fast time in, so you can activate SMA wires even in
less than a milisecond.
stroke[mm]
el. Resistance(Ohm)
4
3
2
1
0
1,80 1,85 1,90 1,95 2,0
stroke(mm)
The electrical resistance of SMA
corresponds to mainly to the phase
transformation state. So it is possible
to use this resistance change as
sensor signal. With electronics
hardware defined positions can be
controlled without external sensor
hardware. The pictures show the
characteristics of the intrinsic sensor
function of the ONE actuator.

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Potentials and Limits of SMA Actuators
1 Development effort 2 Low cyclic dynamics
LIMITS
„Oh it is just a piece of wire, so put it into an actuator housing and we‘re finished“ is often
a misleading idea concerning the product development with SMA. The actuator‘s
parameter are connected to each other. If a product developer increases the wire cross
section (due to needs of a higher force) during the development, he has to consider that
chances of the mechanical mounting, the electrical energy and the actuator‘s dynamic
response will change. If then the electrical energy need will be adjusted to the new cross-
section, the control board, the electric connector to the SMA and even the control-
strategy have to be adapted too.
The picture shows a simplified connection between parameters which have to change.
Although SMA wires can be activated fast, their deactivation is a thermal cooling process.
This process can hardly be influenced in running systems. Additionally the cooling time is
bound to the ambient temperatures. The higher the ambient temperature is, the longer
takes it time for the SMA wire to cool down to it‘s cold state.
Hence calculating the application, it is necessary to to define working temperatures and
the needed cyclic dynamics. In many cases a continious cylcic ( „on-off-on-off….“)
application is not the best application category for SMA actuator devices considering
standard NiTi SMA alloys.
stroke
Time
activation
Cooling-time
@-10°C
[14°F]
@+20°C
[68°F]
@+55°C
[131°F]

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Potentials and Limits of SMA Actuators
3 restriction to ambient temperatures 4 too many too good ideas
LIMITS
stroke
temperature
As
Af
Ms
Mf
The transformation of an SMA wire is defined by four critic temperatures:
Austentie start (As) & austenite finish (Af) temperature during the heating as well as
martensite start (Ms) and martensite finish (Mf) during cooling down.
If the ambient temperature is higher than Ms, the material will not be activated by itself
(As still not reached), but after activation (up to Af) it will not cool down under ambient
temperature where Ms lies.
Example: If your NiTi SMA has As = 80°C, Af = 90°C, Ms = 70°C and Mf = 60°C it will not
active itself at room temperature of 75°C. But if you activate it by current pulse, it will not
start with the cooling down, because Ms < room temperature.
ambient temperature
Such a technology brings up many ideas: smallest drives in wearables, integrated
actuators in handhelds, smallest valve systems or even futuristic toys…
But the best idea is the most realistic idea. So keep focused on it.
Hence a strategic and guided product development method should be used for SMA
product development.
The German engineers association, VDI, has developed and published a guideline for
mechatronic product development for SMA actuators. It is the VDI2248 guideline and it
consist of 5 part:
VDI2248-1 Basics and application examples
VDI2248-2 Material selection and nomenclature
VDI2248-3 Test- and measurement - methods
VDI2248-4 Simulation and model development
VDI2248-5 Development methods
The guidelines are available in german and english language.

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Outlook B: What else can be done with SMA ?
SMA
actuator
sensor
connector
springsolid joint
plagiarism
protection
damper
If you like to see another presentation to
one of those topics, just comment this
publication with your request. We will
prepare other topics considering SMA.
Thank you for yoru attention.

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Questions? You can contact us at Linkedin, Xing or just email:
This publication is brought to you by:
Dr.-Ing. Alexander Czechowicz,
CTO at Hoffmann Kunststofftechnik +
Mechatronik Company in Germany
Dr.-Ing. Sven Langbein,
Group Leader Shape Memory Alloy
Technology at Feindrahtwerk A. Edelhoff
Company in Germany
additional content and scientific review
by:
Forschungsgemeinschaft Werkzeuge und
Werkstoffe e.V,
Scientific Institute in Germany
www.hoffmann-kunststoffe.de
www.edelhoff-wire.de
www.fgw.de
entwicklung@hoffmann-kunststoffe.de
langbein@edelhoff-wire.de
forschung@fgw.de