Smart materials and smart structures

Question 1

What is the definition of “Smart Structure” ?

Answer 1

Smart structure is a structure that exhibits additional functional properties (for example shape control, vibrations suppresion, health monitoring, self healing) with respect to the general mechanical, physical and chemical properties. Generally, we can call smart structure every structure that adds functional properties to mechanical ones.

Question 2

How can a smart structure be realised?

Answer 2

A smart structure can be realised by introducing sensors and actuators inside the structures. The most suitable way to do this is to use composite materials, since a component made of composites is produced by overlapping different plies and the sensors and actuators can be embbeded.

Question 3

How are smart materials classified?

Answer 3

Smart materials are classified based on their working principle:
- Property change
- Energy transformation

Question 4

Name some exmaples of property change smart materials.

Answer 4

• Thermochromic (ΔT, Colour change)
• Mechanochromic (Deformation, Colour change)
• Chemochromic (Δ Chemical Concentration, Colour change)
• Photochromic (Radiation (light), colour change)
• Fiber Optics (deformation, change of properties of optical signal)

This type of smart materials works as sensors.

• Electro/Magneto rheological can work as actuators (input electric/magnetic field and output viscosity change)

Question 5

Name some examples of energy transformation smart materials.

Answer 5

• Thermo-luminescent (ΔΤ, light emission)
• Electro-luminescent (Δelectric field, light emission)
• Chemo-luminescent (Δchemical concentration, light emission)
• Photo-luminescent (Radiation (light), light emission)
• Photo-voltaic (Radiation (light), Δelectric potential
• Shape-memory alloys (Δtemperature or Δσ, Strain)

This type of smart materials works as actuators.

Question 6

Name materials that can be used both as sensors and as actuators:

Answer 6

• Piezoelectric(Strain and Δelectric potential)
• Pyroelectric (ΔT and Δelectric potential)
• Thermoelectric (ΔT and Δelectric potential)
• Magnetostrictive (Strain and Magnetic field)
• Electrostrictive (Strain and Δelectric potential)

Question 7

What are the advantages of embedding the sensors/actuators?

Answer 7

1) The sensors/actuators are protected inside the structures (eg from environmental effects).

2) Whole structure size/weight is minimized.

3) Space-saving

4) Monitoring and actuation from the manufacturing process till the end of life. For example, the residual thermal stresses in composite materials can be monitored.

5) Reduction of inspection time

Question 8

What are the critical issues of smart structures?

Answer 8

1) Invasivity on host material. The proerties (eg Stiffness) of the host material can be reduced.

2) Invasivity on manufacturing process

3) Accuracy of sensors

4) Performance of actuators

Question 9

What are the criteria of the choice of suitable sensors/actuators?

Answer 9

• Morphology
• Compatibility with host material
• Invasivity (passive and active)
• Performance