Smart Maetrials

7/29/2019 Smart Maetrials

1/10

www.co-nan.eu/pdf/fs2.pdf

strlab.iitd.ac.in/SSDL/smart.pdf

www.iitk.ac.in/directions/dirnet7/P~S-Kamle~F.pdf

dbtindia.nic.in/women/paper15.htm

STRUCTURAL APPLICATION OF SMART MATERIALSDr. K. Muthumani, Assistant Director & Dr. R. Sreekala, Scientist

Structural Engineering Research Centre,Chennai

Introduction

The development of durable and cost effective high performance constructionmaterials and systems is important for the economic well being of a country mainly

because the cost of civil infrastructure constitutes a major portion of the national

wealth. To address the problems of deteriorating civil infrastructure, research isvery essential on smart materials. This paper highlights the use of smart materials

for the optimal performance and safe design of buildings and other infrastructuresparticularly those under the threat of earthquake and other natural hazards. The

peculiar properties of the shape memory alloys for smart structures render apromising area of research in this field.

Materials and Application

Shape Memory Alloys(SMA)

The term shape memory refers to the ability of certain alloys (Ni Ti, Cu Al Zn

etc.) to undergo large strains, while recovering their initial configuration at the endof the deformation process spontaneously or by heating without any residualdeformation .The particular properties of SMAs are strictly associated to a solid-solid phase transformation which can be thermal or stress induced. Currently, SMAs

are mainly applied in medical sciences, electrical, aerospace and mechanicalengineering and also can open new applications in civil engineering specifically in

seismic protection of buildings.

Its properties which enable them for civil engineering application are

1. Repeated absorption of large amounts of strain energy under loading withoutpermanent deformation. Possibility to obtain a wide range of cyclic behaviour

from supplemental and fully recentering to highly dissipating-by simplyvarying the number and/or the characteristics of SMA components.

2. Usable strain range of 70%3. Extraordinary fatigue resistance under large strain cycles4. Their great durability and reliability in the long run.

Structural Uses
http://www.co-nan.eu/pdf/fs2.pdfhttp://www.co-nan.eu/pdf/fs2.pdfhttp://www.iitk.ac.in/directions/dirnet7/P~S-Kamle~F.pdfhttp://www.iitk.ac.in/directions/dirnet7/P~S-Kamle~F.pdfhttp://www.iitk.ac.in/directions/dirnet7/P~S-Kamle~F.pdfhttp://www.co-nan.eu/pdf/fs2.pdf


2/10

1. Active control of structures

The concept of adaptive behavior has been an underlying theme of active control ofstructures which are subjected to earthquake and other environmental type of

loads. The structure adapts its dynamic characteristics to meet the performanceobjectives at any instant. A futuristic smart bridge system (An artist rendition) is

shown below :Fig.1 (3)

(Courtesy: USA Today dt. 03.03.97). Sun and Sun (6) used a thermo mechanicalapproach to develop a constitutive relation for bending of a composite beam with

continuous SMA fibers embedded eccentric to neutral axis. The authors concludedthat SMAs can be successfully used for the active structural vibration control.

Thompson et al (3) also conducted an analytical investigation on the use of SMAwires to dampen the dynamic response of a cantilever beam constrained by SMAwires.

Fig.1

2) Passive control of structures

Two families of passive seismic control devices exploiting the peculiar properties of

SMA kernel components have been implemented and tested within the MANSIDE

project (Memory Alloys for New Seismic Isolation and Energy Dissipation Devices).

They are

Special braces for framed structures and isolation devices for buildings and

bridges. Fig.2.shows the arrangement of SMA brace in the scaled frame model and

the reduced scale isolation system.


3/10

Fig-2

3) Smart Material Tag

These smart material tag can be used in composite structures. These tags can be

monitored externally through out the life of the structure to relate the internal

material condition . Such measurements as stress, moisture, voids, cracks anddiscontinuities may be interpreted via a remote sensor(6)

4) Retrofitting


4/10

SMAs can used as self-stressing fibres and thus they can be applied for retrofitting.

Self-stressing fibres are the ones in which reinforcement is placed into the

composite in a non-stressed state. A prestressing force is introduced into the

system without the use of large mechanical actuators, by providing SMAs. These

materials do not need specialized electric equipments nor do they create safety

problems in the field. Treatment can be applied at any time after hardening of the

matrix instead of during its curing and hardening. Long or short term prestressing is

introduced by triggering the change in SMAs shape using temperature or electricity.

Introduction

The development of durable and cost effective high performance construction

materials and systems is important for the economic well being of a country mainlybecause the cost of civil infrastructure constitutes a major portion of the national

wealth. To address the problems of deteriorating civil infrastructure, research is

very essential on smart materials. This paper highlights the use of smart materialsfor the optimal performance and safe design of buildings and other infrastructures

particularly those under the threat of earthquake and other natural hazards. The

peculiar properties of the shape memory alloys for smart structures render apromising area of research in this field.

Materials and Application

Shape Memory Alloys(SMA)

The term shape memory refers to the ability of certain alloys (Ni Ti, Cu Al Znetc.) to undergo large strains, while recovering their initial configuration at the end

of the deformation process spontaneously or by heating without any residualdeformation .The particular properties of SMAs are strictly associated to a solid-solid phase transformation which can be thermal or stress induced. Currently, SMAs

are mainly applied in medical sciences, electrical, aerospace and mechanicalengineering and also can open new applications in civil engineering specifically in

seismic protection of buildings.

Its properties which enable them for civil engineering application are

1. Repeated absorption of large amounts of strain energy under loading withoutpermanent deformation. Possibility to obtain a wide range of cyclic behaviourfrom supplemental and fully recentering to highly dissipating-by simply

varying the number and/or the characteristics of SMA components.

2. Usable strain range of 70%3. Extraordinary fatigue resistance under large strain cycles

4. Their great durability and reliability in the long run.

Structural Uses

1. Active control of structures

The concept of adaptive behavior has been an underlying theme of active control ofstructures which are subjected to earthquake and other environmental type of


5/10

loads. The structure adapts its dynamic characteristics to meet the performance

objectives at any instant. A futuristic smart bridge system (An artist rendition) isshown below :Fig.1 (3)

(Courtesy: USA Today dt. 03.03.97). Sun and Sun (6) used a thermo mechanical

approach to develop a constitutive relation for bending of a composite beam with

continuous SMA fibers embedded eccentric to neutral axis. The authors concludedthat SMAs can be successfully used for the active structural vibration control.

Thompson et al (3) also conducted an analytical investigation on the use of SMAwires to dampen the dynamic response of a cantilever beam constrained by SMAwires.

Fig.1

2) Passive control of structures

Two families of passive seismic control devices exploiting the peculiar properties of

SMA kernel components have been implemented and tested within the MANSIDEproject (Memory Alloys for New Seismic Isolation and Energy Dissipation Devices).

They are

Special braces for framed structures and isolation devices for buildings and

bridges. Fig.2.shows the arrangement of SMA brace in the scaled frame model and

the reduced scale isolation system.


6/10

Fig-2

3) Smart Material Tag

These smart material tag can be used in composite structures. These tags can be

monitored externally through out the life of the structure to relate the internal

material condition . Such measurements as stress, moisture, voids, cracks anddiscontinuities may be interpreted via a remote sensor(6)

4) Retrofitting


7/10

SMAs can used as self-stressing fibres and thus they can be applied for retrofitting.

Self-stressing fibres are the ones in which reinforcement is placed into the

composite in a

They make active lateral confinement of beams and columns a more practical

solution. Self stressing jackets can be manufactured for rehabilitation of existinginfrastructure or for new construction

5) Self-healing

Experimentally proved self-healing behavior (5) which can be applied at a material

micro level widens their spectrum of use. Here significant deformation beyond the

first crack can be fully recovered and cracks can be fully closed.

6) Self-stressing for Active Control

Can be used with cementitious fibercomposites with some prestess, which impart

self-stressing thus avoiding difficulties due to the provision of large actuators in

active control which require continuous maintenance of mechanical parts and rapid

movement which in turn created additional inertia forces.

In addition to SMAs some other materials such as polymers can also be temporarily

frozen in a prestrained state that have a potential to be used for manufacturing of

self-stressing cementitious composites (4).

7.Structural Health Monitoring

Use of piezo transducers, surface bonded to the structure or embedded in the walls

of the structure can be used for structural health monitoring and local damagedetection. Problems of vibration and UPV testing can be avoided here. Jones et. al.,(7) applied neural networks to find the magnitude and location of an impact on

isotropic plates and experimented using an array of piezo-transuders surfacebonded to the plate.


8/10

Substitute for steel?

It is reported that (4) the fatigue behaviour of CuZnAl-SMAs is comparable withsteel.If larger diameter rods can be manufactured. It has a potential for use in civil

engineering applications. Use of fibre reinforced plastics with SMA reinforcementsrequire future experimental investigations.

CARBON FIBRE REINFORCED CONCRETE(CFRC)

Its ability to conduct electricity and most importantly, capacity to change itsconductivity with mechanical stress makes a promising material for smart

structures .It is evolved as a part of DRC technology(Densified Reinforced

Composites).The high density coupled with a choice of fibres ranging from stainless

steel to chopped carbon and kelvar, applied under high pressure gives the product

with outstanding qualities as per DRC technology. This technology makes it possible

to produce surfaces with strength and durability superior to metals and plastics.

SMART CONCRETE

A mere addition of 0.5%specially treated carbon fibres enables the increase of

electrical conductivity of concrete. Putting a load on this concrete reduces theeffectiveness of the contact between each fibre and the surrounding matrix and

thus slightly reduces its conductivity. On removing the load the concrete regains its

original conductivity. Because of this peculiar property the product is called Smart

Concrete. The concrete could serve both as a structural material as well as a

sensor.


9/10

The smart concrete could function as a traffic-sensing recorder when used as road

pavements. It has got higher potential and could be exploited to make concrete

reflective to radio waves and thus suitable for use in electromagnetic shielding. The

smart concrete can be used to lay smart highways to guide self steering cars which

at present follow tracks of buried magnets. The strain sensitive concrete might even

be used to detect earthquakes.

Active railway track support

Active control system for sleepers is adopted (3)

to achieve speed improvements on existing bridges and to maintain thetrack in a straight and non-deformed configuration as the train passes Withthe help of optimal control methodology the train will pass the bridge withreduced track deflections and vibrations and thus velocity could be safelyincreased. Fig(3) shows various positions of the train with and withoutactive railway track support. Fig-3

Active structural control against wind

Aerodynamic control devices to mitigate the bi-directional wind induced vibrations

in tall buildings are energy efficient, since the energy in the flow is used to produce

the desired control forces. Aerodynamic flap system(AFS) is an active systemdrivenby a feedback control algorithm based on information obtained from the vibration

sensors(3).The area of flaps and angular amplitude of rotation are the principal

design parameters. fig.(4) shows an active aerodynamic control device.

CONCLUSION


10/10

The technologies using smart materials are useful for both new and existing

constructions. Of the many emerging technologies available the few described here

need further research to evolve the design guidelines of systems. Codes, standards

and practices are of crucial importance for the further development.

ACKNOWLEDGEMENT

The author thanks the Director, SERC for the constant encouragement and support

rendered in preparing this paper and also for giving permission to publish the

paper. The kind support and guidance of all the team members of Structural

Dynamics Laboratory is gratefully acknowledged.

REFERENCES

1.DuerigT.W, Melton K.N, Stoeckel D., Wayman C.M., Engineering aspectsof shape memory alloys, Butterwort heinemann Ltd:London,1990.

2.MauroDolce,D.Cardone and R.Marnetto, Implementation and Testing ofPassive control Devices based on Shape Memory Alloys,Earthquake engg.

And structuraldynamics,2000;Vol-29, pp945-96

3.J.Holnicki-szulc and J.Rodellar(eds), Smart Structures.,3.HighTechnology-Vol.65

4.N. Krstulovic-Opara and A.E. Naaman, ACI Structural Journal, March-April2000, pp335-344

5.Hannant, D.J and Keer, J.G.,Autogeneous Healing of Ti BasedSheets, Cement and Concrete Research, V-13,1983

6.Sun, G. and Sun, C.T., Bending of Shape Memory Alloy ReinforcedComposite Beam, Journal of Materials Science, Vol-30, No.13, pp5750-5754.

7.Jones,R.T.,Sirkis.J.S.,andFriebele,E.J.(1997)Detectionof impact locationand Magnitude for Isotropic plates Using Neural Networks,Journal of

Intelligentmaterial systems and Structures,7,pp90-99.

Smart Maetrials

Documents

Transcript of Smart Maetrials