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ADAPTRONICS AND ACOUSTICS

F R A U N H O F E R I N S T I T U T E F O R M A C H I N E T O O L S A N D F O R M I N G T E C H N O L O G Y I W U

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Adaptronics is a synonym for a technology of intelligent

structures with a large scale of integration. The first develop-

ments worthy of mention took place in the mid-80s in the

aerospace and military applications sectors in the USA and

Japan. By the beginning of the 1990’s this technology was

also beginning to emerge in Europe and in Germany, likewise

initially in the aerospace sector. Since the turn of the century

well-known research establishments such as the Fraunhofer-

Gesellschaft, the German Aerospace Center (DLR) and the

Leibniz-Gemeinschaft (Gottfried Wilhelm Leibniz Scientific

Community) have turned their attention to the application

potential of adaptronics for civil usage as well.

Sensing and acting functions are integrated into parts of

the supporting structure which is able to adapt to modified

conditions independently. Therefore active or „smart”

materials are used which are activated by electric, magnetic

or thermal fields. Active materials are especially piezoelectric

ceramics, magnetostrictive alloys, shape memory alloys and

electro- / magnetorheological fluids. They are characterized by

the transformation of a field unit into a mechanical effect and

the change of the material properties under field influence,

respectively. The essential ingredient of a complete adaptronic

system is, in addition to the sensor and actuator characteristic

of the material, open and closed loop control technology

which also demonstrates real time capability and energy

self-sufficiency.

Adaptronics is recognized as one of the central key technolo-

gies when it comes to innovative products in the mobility,

energy and health sectors of the market. Any sub-assemblies

or components where the aim is to influence vibration behav-

ior, sound radiation, the contour and geometry characteristics

or even the damage tolerance may be considered as potential

application scenarios. A particularly significant increase in

anticipated performance would appear to be evident within

the sectors of automotive manufacturing, energy technology,

mechanical engineering, rail vehicle manufacture, medical

technology and building and housing technology.

ADAPTRONICS – BREATHING LIFE INTO PASSIVE STRUCTURES

The manufacturing plant and production technology sector

demands systems which not only display a high level of

precision but are also simultaneously characterized by a high

degree of dynamism in relation to the process conditions as

well as considerable influence on the part of the environment.

Because adaptronic components adapt very well to changes in

external conditions and individual production tasks, machines

and machine components can be designed to be more ac-

curate, more robust and more flexible – a field of parameters

that otherwise frequently appear to be diametrically opposed

in classical design methodology.

At Fraunhofer IWU research in the field of adaptronics has

been actively conducted for many years. The Dresden branch

of the Institute, with a test area of 600 square meters, offers

optimum conditions for handling research projects starting

with the active material and culminating in trialling prototypal

sub-assemblies. Materials scientists, technical mechanics and

designers, control and automation engineers together with

measuring technicians and acoustics engineers handle the

full spectrum of complex projects related to adaptronics and

acoustics.

Macro-fiber composite actuators

applied on a drive shaft with 45°

alignment reduce troublesome

bending and torsional vibra-

tions.

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Thermal Shape Memory Alloys

A selected range of metal alloys, various plastics and

composite fiber materials, together with a few chemical

substances, are capable of „remembering“ defined geometric

shapes when a certain physical indicator magnitude acts on

them. This process is also described as „memory effect“. It

presupposes special material conditioning that is of critical

importance in memorizing shape. In the case of thermal shape

memory materials, temperature is the physically indicative

magnitude.

Thermal shape memory materials have been the subject of

materials research for some time. In the metal alloy sector

semi-finished products in the form of wires, rods, tubes and

sheets are available today. Thermal shape memory alloys have

the special characteristic of being able to „remember“ and

re-assume their original shape following permanent plastic

distortion below a specific critical temperature by means of

heating to above this temperature.

A reversible austenite-martensite phase transformation is a

pre-condition for the occurence of the shape memory effect.

In an ideal situation, the austenite phase is converted into the

martensite phase as a result of shear. Due to diffusion-free

rearrangement processes in relation to the atoms, this gener-

ates a change in the stacking sequence of the crystal lattice

levels and hence a change in the structure of the crystal lat-

tice. Thermal shape memory alloys demonstrate good sensor

characteristics due to the fact that the electrical resistance is

dependent on the strain of the material as well as very good

actuator characteristics because of the transformation of aus-

tenite into martensite at a particular transition temperature.

Basic properties (for example NiTi):

– low operating frequencies (0 Hz – 20 Hz)

– high strain (up to 8 percent)

– very high forces (up to 250 N/mm²)

Common to all active materials is the sensor and actuator

function inherent in a material. This qualifies the group of

materials not only for sensor tasks but also for actuator tasks

and makes a new level of integration possible as well as

extreme consolidation of functions. Traditional construction

materials such as steel, aluminum or fiber plastic composites

are rendered more intelligent by the application or integration

of active materials and can be presented as an overall range

of components that are lighter and thus incorporate savings in

terms of weight and resources.

Piezoceramics

The way piezoceramics work is based on the electro-mechan-

ical interaction between the electrical and mechanical state of

a particular class of crystals. These are capable of converting

electrical energy into mechanical energy and vice versa. Under

mechanical load, piezoceramics generate an electrical field

(sensor effect) or deform as the result of the application of an

electrical field (actuator effect). This active mechanism may

be ascribed to the unusual Perowskit grid structure. In order

to also make the piezo-electric effect macroscopically usable,

piezoceramics are polarized during the manufacturing process

by the application of an electrical field.

This polarization is the reason why different deformation ef-

fects form, depending on the direction of the applied electrical

field along with the direction of polarization. Indexing the

effects provides information on the direction of deformation

(Index 1) subject to the direction of the applied electrical field

(Index 2), for example d31. The structural shapes and action

mechanisms of piezo-electrical actuators may differ widely. The

most common are the stack type and the strip type.

Basic properties:

– very high operating frequencies (0.1 Hz up to MHz)

– low strain (up to 0.2 percent)

– high forces (up to 4 kN/cm²)

ACTIVE MATERIALS – A SELECTION

There are numerous act ive mater ia ls with a very wide range of act ive mechanisms. The Adaptronics

and Acoust ics Department at Fraunhofer IWU is pr imar i ly concerned with piezoceramics, magnet ic

and thermal shape memory a l loys as wel l as e lectro- and magnetorheological f lu ids.

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Electro- and Magnetorheological Fluids

Electro- and magnetorheological fluids are materials that react

to the presence of electrical and / or magnetic fields with an

increase in their viscosity. They consist of a basic fluid (for

example, silicone oil) and particles of solids embedded in it.

ER- and MR fluids are generally of very low viscosity and one

of their characteristics is their ability to undergo a reversible

change into a state similar to a solid state body under the

effect of a field.

ERF’s are made up of solid particles of high disruptive strength

which are distributed throughout a base oil. If an electrical

field is applied vertically to the direction of flow, the resistance

of the fluid to the flow is thereby increased. Cellulose, silicium

compounds or materials on a carbon base may be regarded as

solid particles. The base oil used is often a silicone oil.

MRF’s typically consist of soft iron particles, 20 to 40 percent

by volume, suspended in a base fluid. Water, silicone oils and

carbon-based oils are used as base fluids. The achievable

limit shear stress of an MRF is essentially dependent on the

saturization magnetization of the particles of solids used. Pure

iron particles as well as alloys of iron and cobalt are some of

the solids used.

Basic properties of ERF:

– maximum limit shear stress 2 – 5 kPa

– density 1 – 2 g/cm³

– excitation with 2,000 – 5,000 V at 1 – 10 mA

Basic properties of MRF:

– maximum limit shear stress 50 – 100 kPa

– density 3 – 4 g/cm³

– excitation with 2 – 50 V at 1 – 2 A

Magnetic Shape Memory Alloys

Magnetic shape memory alloys have been the subject of

discussion only since a few years. Analogous to conventional

shape memory alloys, magnetic shape memory alloys show the

characteristic martensite phase transformation, particularly the

shape memory effect. In contradiction to the shape memory

material, the shape memory effect is not related to a thermal

stimulus but to a stimulus induced by a magnetic field.

As a result, it is possible, by contrast to conventional shape

memory alloys, for a considerably higher repetition rate to

be achieved in the operational sequences. By varying the

magnetic field force it is possible to control the transformation

process.

Basic properties:

– high operating frequencies (0 Hz up to kHz)

– high strain (up to 10 percent)

– low forces (up to 5 N/mm²)

Optical Shape Memory Materials

Optical shape memory materials are currently available in the

form of light-sensitive shape memory polymers. As in the case

of the thermal shape memory polymers, the material may also

be converted from an amorphous state (flexible and elastic)

into a crystalline state (stiffening). The effect of the light

influences the density of cross-linkage and, at the same time,

the elastic characteristics of the material. Once the targeted

increase in cross-linking points is achieved, the actual shape

of the material will be fixed. On subsequent dissolution of

this fixed state, the material will „remember“ its fundamental

geometric state.

Basic properties:

– high strain

– very low forces

– cheaper to manufacture

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Adaptronics in Automotive Engineering

Applications of active systems based on „smart materials“ in

automotive engineering cover systems for intelligent automo-

tive production and the adaptive adjustment of bodywork

structures aimed at optimizing aerodynamic drag coefficient

and hence reducing fuel consumption.

Using an active tool based on piezo-actuators, for example,

the possibility exists of optimizing sheet metal blank insertion

in the deep draw process or of monitoring and controlling

the sheet metal insertion with the help of intelligent sensor

technology. Applications based on shape memory alloys, on

the other hand, enable cost-effective and weight-optimized

positioning drives to be created by way of a substitute for

conventional electric drives. A further considerable advantage

of an adaptronic shape memory alloy drive is the complete ab-

sence of any noise. This is of particular interest when it comes

to applications in the vehicle cockpit. In addition, energy

self-sufficient thermal management is possible thanks to the

sensor- and actuator-related characteristics of shape memory

alloys. The use of active materials in automotive engineering

means not only resource savings production but also highlights

the potential for resource-friendly automobile operation with a

number of additional functionalities.

INTELLIGENT SOLUTIONS FOR MECHANICAL, AUTOMOTIVE AND MEDICAL ENGINEERING

Performance capabi l i ty , durabi l i ty , funct ional i ty – the demands on industr ia l products are c lear ly def ined.

Competit ion and the race to achieve success in the market place cal ls for innovat ive ideas and solut ions.

Here adaptronics represents a key technology.

Adaptronics in Mechanical Engineering

The manufacturers of machine tools are facing major technical

challenges. The products developed by them need not only

to become more productive and more precise, but initial

investment costs for the customer as well as the life cycle costs

need to come down so as to enable them to hold their own

worldwide in a competitive environment.

Here too adaptronics have solutions to offer based on the use

of high-integration intelligent systems. Particular focal points

in the development and use of adaptronic components are

production systems and production technologies that demand

a high level of precision but which are at the same time also

characterized by a high degree of dynamism in terms of

process conditions or variable environmental conditions.

One potential solution to the problem of how to reduce

non-productive time is by increasing drive dynamics. This is

achieved by consistent adaptronic lightweight construction

and intelligent additional components that expand the limits

that have up to now existed as far as dynamics are concerned.

One specific example are piezoceramic sensor actuator units

for torsion, bending and / or axial vibration compensation in

feed drives on machine tools. By using adaptronics, however,

existing machining technologies can also be expanded and / or

completely new areas of technology opened up.

One of the ways of expanding machine tool function is to use

an adaptive spindle holder. One example is the hexapod kine-

matics developed at Fraunhofer IWU as a holder for an HSC

motor spindle and based on piezo-stack actuators. The kinetic

momentums are derived from the strokes and setting angles

of the piezo actuators. The decentralized control sub-system

consisting of sensor technology, actuating elements and

controller structure can be integrated into existing machine

tool concepts.

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Reducing the weight of a moving mass is an effective way of

increasing energy efficiency in production processes. However,

this will of necessity lead to a reduction in the rigidity of the

drive axles. Hence, the vibrations resulting from the process

forces will increase and the accuracy of the machine is re-

duced. These vibrations are precision recorded by the subkine-

matics and effectively combated by means of decentralized

controller. At Fraunhofer IWU the application limits for the

adaptive system were analyzed in relation to the quasi-static

characteristics of a piezo-based sub-assembly and the margin

of active vibration reduction was determined for the system.

Active control is effective up to 250 Hz and achieves a distinct

reduction in resonance peaks.

One key technology with high potential when it comes

to opening up future markets is micro-technology. The

introduction of micro-pockets is leading to an improved

lubrication effect and hence to a reduction in friction loss.

Up to now additional stages in the process have been used

to create micro-structuring. The time and effort required

for this precludes any wide-ranging application. With the

adaptive spindle holder, highly dynamic movements within the

micrometer range can be superimposed on the actual milling

process. Micro-structured surfaces are thus generated during

the milling process; additional stages in the process are either

dropped or substituted.

However, in mechanical engineering, shape memory alloys also

have their own application entitlement. For example, thermal

distortions of machine components and the machine frame

can be compensated for by using actuators of this type.

1 Road simulation tests are car-

ried out on an electro-dynamic

multi-axial vibration test rig.

2 An adaptive spindle holder

based on piezo-actuators helps to

compensate for vibration in ma-

chine tools.

3 The model parameters for a

pelvic bone are determined with

the help of a 3D laser vibro-

meter; these parameters are

necessary for creating realistic

bone models.

Adaptronics in Medical Engineering

Active materials such as shape memory materials (metals and

plastics) or piezoceramics also offer a wealth of possibilities in

the medical devices technology sector and in prosthetics. Due

to their high specific energy capacity these materials enable

compact actuators and sensors to be developed. They may

therefore be integrated into existing solutions as alternative

drive elements, but also allow the development of completely

new complex systems with new functionalities.

The use of so-called „self-sensing actuators“ based on shape

memory alloys makes it possible, for example, to develop

compact grab systems. This technical solution involving

a sensor-free drive and control concept offers a range of

approaches for supplementing existing drive systems in the

sectors of exoprosthetics and orthetics. In addition, active

elements based on „smart materials“ may have an effect on

contact force at the bone implant interface and thus make

active implants possible.

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As far as manufacturers of motor vehicles, engines and

machines are concerned, the topic of sound generation and

sound radiation is gaining increasing importance throughout

the development process. This may be attributed not only

to the increased demands of occupational safety and

environmental protection, but also to the trend towards ever

lighter structures that demonstrate savings in materials and

which have a clear effect on the vibration behavior of a given

structure.

In automotive manufacture topics such as noise reduction,

elimination of background noise or design of a vehicle- and

customer-specific noise characteristic (sound design) have

become a significant part of volume production.

It is therefore necessary, at an early stage in production, to

obtain information about sound sources as well as their loca-

tion and how they contribute to the overall noise level in order

to be able to incorporate noise optimization measures in the

design process at as early a stage as possible.

Fraunhofer IWU has extensive experience in the technical

acoustics sector and makes use of a very wide range of

analytical methods as well as acoustic measuring technology

for solving highly diverse problems.

Using Array Procedures for Locating Sound Sources

Microphone arrays, a large number of systematically arranged

microphones, are deployed to visualize sound fields (sound

mapping). The visualization of sound incidence not only makes

it possible to identify and localize relevant sources of noise but

also to quantify the individual contribution on the overall noise

level. A noise source ranking (an ordered list of all relevant

sound sources) can be generated as a result.

By combining acoustic holography and beamforming, the

analyse of steady state and non-steady state sound events in

the frequency range of about 80 Hz up to 12,800 Hz will be

possible.

For different applications, Fraunhofer IWU has the following

array measuring technology available:

– beamforming arrays: 90-channel full circle array (d = 1.05

m) and 90-channel semi full circle array for large objects of

investigation (d = 3 m)

– acoustic holography (NS-STSF / SONAH): 96-channel array

with 5 cm and 15 cm lattice parameter

– 105-channel transportable measuring system Brüel&Kjær

PULSE

– semi-anechoic chamber (class 1)

ACOUSTICS AND VIBRATION ENGINEERING

In an anechoic measuring cham-

ber the acoustic signals from a

1000 MZ are recorded at a range

of speeds using 96 high sensitiv-

ity measuring microphones.

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Transfer Path Analysis (TPA)

Noises and vibrations in motor vehicles and machines are

normally made up of a range of different input factors ema-

nating from various sources and transmission paths. Transfer

Path Analysis (TPA) makes it possible to determine these input

factors by means of a detailed study and modeling of the test

object. Problem transmission paths can thus be identified and

appropriate countermeasures tested and verified at a very early

stage in the development process.

The following procedures and equipment are used at Fraun-

hofer IWU for solving a wide variety of measuring problems:

Determination of structure borne sound sources

– direct force measurement with tri-axial load cells

– indirect force determination using the complex stiffness

method

– indirect force determination using the inertance matrix

method (matrix inversion)

Determination of airborne sound sources

– Source Substitution Method (matrix inversion)

Determination of the vibroacoustic transfer behavior

– direct measurement with shaker or impact hammer stimula-

tion

– inverse measurement with stimulation using volume noise

source

Technical equipment

– modular measuring system Brüel&Kjær PULSE (up to 150

channels)

– accelerometer and microphones (diverse models)

– impact hammers and electro-dynamic vibration exciters of

various magnitudes

– volume sound source (5 Hz – 5,000 Hz)

– electrodynamic vibration test stand

– TPA software by Brüel&Kjær for modeling and analyses

Modal Analysis

Noise problems frequently occur in a vibratory structure in

association with resonance phenomena predominantly where

excitation of the natural vibrations of a system as a result of

operational forces is involved.

In order to optimize sound radiation, but also in the interests

of optimizing vibration or the layout of a suspension system,

knowledge of the dynamic behavior of a vibratory system is

required. For this statements derived from the modal analysis

are used.

At Fraunhofer IWU a range of different procedures is used,

depending on the requirement:

– experimental modal analysis (EMA)

– operational modal analysis (OMA)

– numerical modal analysis

The aim with all the procedures is to determine the natural

vibrations specific to the component. It will then be possible

to derive measures for optimizing vibration and / or reducing

noise.

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Vibration Measuring Technology

In addition to the modal analysis tool, Fraunhofer IWU has

measuring technology at its disposal for investigating dynamic

behavior in relation to vibratory systems.

A multi-axial vibration test bench, consisting of four electro-

dynamic vibration exciters with random positioning facility,

each with a nominal force of 8,000 N, enables investigations

into comfort, reliability and strength to be carried out on the

vehicle as a whole or on individual sub-assemblies.

For localization and animation of periodically excited vibrations

– for example, on machine, housing and cladding components –

a 3D laser scanning vibrometer is used. By means of contact-

less measuring it is also possible to achieve reaction-free

identification of modal parameters based on the vibrations

measured and hence a validation of finite element models.

Analysis of rotary vibrations can be carried out using a

rotation vibrometer. The number of revolutions per minute

and the angular velocity can also be recorded contact-free on

rotating objects such as axles, crankshafts, gear components

and drive pulley, even at points that are hard to access. For

high-accuracy measurements of rotational vibrations and

angular movements / tilting there is also a 3-beam plane mirror

interferometer available.

Further Offers

– measurement and valuation the sound power of vehicles,

machines and systems

– dimensioning of active systems for vibration damping

– calculation of sound fields by boundary element method

(BEM)-sysnoise

– multi-body simulation with Ansys & SimulationX

– calculation of static and dynamic stiffness and flexibility

4 Sound field mapping for a

gearbox cover with the help of

beamforming

5 Modal analysis system (LAN-XI,

up to 16 tri-axial acceleration

sensors)

6 Laser heads on the 3D scan-

ning vibrometer

7 Studies into vibration and

comfort in relation to the vehicle

as a whole are carried out on a

4-stamp vibration test bench.

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Editorial Address

Fraunhofer Institute for

Machine Tools and Forming Technology IWU

Reichenhainer Straße 88

09126 Chemnitz, Germany

Phone +49 371 5397-0

Fax +49 371 5397-1404

info@iwu.fraunhofer.de

www.iwu.fraunhofer.de

Director

Scientific Field Mechatronics and Lightweight Structures

Prof. Dr.-Ing. Welf-Guntram Drossel

Phone +49 371 5397-1400

welf-guntram.drossel@iwu.fraunhofer.de

Department Adaptronics and Acoustics

Dipl.-Ing. André Bucht

Phone +49 351 4772-2344

Fax +49 351 4772-6-2344

andre.bucht@iwu.fraunhofer.de

© Fraunhofer IWU 2015

Photo Acknowledgments

p. 8: MOMENTPHOTO

All other photos: © Fraunhofer IWU

Reproduction of any material is subject to

editorial authorization.