actuators in smart materials

ACTUATOR & ACTUATOR MATERIALS

BY,SHEBINA. AROLL NO: 15

ACTUATOR :

Materials that respond to a stimulus in the form of a mechanical property change such as a dimensional or a viscosity change.Eg: Simple amplifier ( converts low energy signal into high power signal) Transducer( energy of the amplified control signal is converted into work)

Actuator Material Classes

Actuator Materials

• Shape Memory Alloys• Magnetostrictive Materials• Piezoelectric & Electrostrictive Materials• Electrorheological & Magnetorheological

Fluids

Shape Memory Alloys

• Ability of material to regain its original shape when heated to a temp, after being

deformed at a lower temp.

• Shape memory effect occurs in a no: of alloys, which undergo a special type of transformation called the ‘thermoplastic marten site transformation’.

• SMAs are useful for actuators as they change

shape

stiffness

position

natural frequency and

other mechanical characteristics

in response to temp or electromagnetic fields. The diverse applications for these metals have made them increasingly important

Types:-• Copper - aluminium - nickel• Copper - zinc - aluminium• Iron - manganese - silicon• Nickel-titanium (nitinol) – most useful

• Ni-Ti has super elastic spring property that this alloy exhibits above transformation temperature

• Transformation strain

~ for a single cycle max 8%

~ for 10,000 cycles 4%• Hysterisis 30 to 50degree celsius• Electrical and magnetic properties

resistivity

~ austenite 100 micro ohms*cm

~ martensite 80 micro ohms*cmMagnetic permeability < 1.002Magnetic susceptibility 3.06

• Mechanical Properties (youngs Modulus)

~ austenite 83GPa

~ martensite 28 to 41 Gpa

Applications…• Automobile transmissions • Shock Absorbers• Small Pumps• Window Openers• Automotive• Aerospace- • Medical• consumer

Magnetostrictive Material

• Materials which change shape when placed in magnetic field. Result of re-orientation of the

magnetic domains, which produces internal strain in the material

• Utilised in switches and sensors

Classification ~ materials of fixed structuremetal, ceramic and polymeric compositesElastomers filled with ferromagnetic material

powders (carbonyl iron)Solid magnetocaloric materials

~ Materials of variable internal structureMR FluidsFerro FluidsPorous materials saturated with MR Fluids

Magnetostrictive Actuators

Electrical energy mechanical energy

• Giant Magnetostrictive Materials such as rare earth-iron feature magnetostrains two orders of magnitude larger than Ni

• Terfenol – D : commercially available

• Positive microstrains of 1000 to 2000ppm are reported to terfenol-D

• NiMnGa alloys offering a microstrain up 6%

• Young's modulus- 2.5-3.5x1010 N/m3

• Tensile strength- 28MPa• Compressive strength- 300MPa• Density- 9250kg/m3

• Strain- 0.6%

• Force : offer large force

• Voltage : Its is adjusted by no:of turns in the coil. With high current and large section wires, required magnetic field produced with low voltage

Applications• Active noise and vibration cancellation• Sonar• Fuel injection• Medical• Nozzle anti-clogging system (paper)• Screening applications• Metals casting industry

• Sonar transducers – very high power transducers, long range transmissions and communication applications

• Hydraulic valves – high speed valves

• Inchworm motors – in low frequency sound transducers

• Materials that exhibit an electrical polarization with an applied mechanical stress

• 2 types

~ piezoceramic relatively stiffLarge piezoelectric constant

~ piezopolymerRelatively flexibleLarge voltage capacity

Piezoelectric material

Property PZT (Lead Zirconate Titanate) PVDF (PolyVinylidene Floride)

Curie temp (degree Celsius) 212 100

Young's modulus (N/m2 ) 59.51 310Piezoelectric constant 21210 2310

Maximum electric field .41 4010

Electrostrictive material• A change in dimensions of material

due to the application of electric field• Non – linear response• No hysteresis• A quick response time• Higher displacements with good

reproducibility

~ APPLICATIONS

• Micro positioned• Adaptive optics

ER Actuators

• Rheology is the science of the flow and deformation of matter. i.e., response of the matter to a force or stress

• Viscous fluid can be altered by ER fluids by application of electric field. Response time is typically a millisecond

• Colloidal suspensions of dielectric solids in non-conducting liquids

• In absence of electric field, colloidal suspension –fine particle, uniformly distributed

• Electric field applied – dielectric particles causes the particles to align with the electric field, causes them to adhere to adjacent particles which join to form fibrils

• Fibrils modifies the viscosity of fluid• When electric field is removed, alignment

disappears

Applications

• Tunable shock absorbers used in sports equipment

FACTORS CONSIDERED FOR ACTUATOR MATERIALS

• Actuation voltage• Speed of actuation• Actuation force• Stored energy• Electrical resistivity• Mechanical quality factors• Resistance to fracture• Young’s modulus• Density• Stress• Resistivity