Actuators in smart materials

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Information about Actuators in smart materials

Published on March 14, 2014

Author: shebinaa



Actuators and actuator materials


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 ‘

• SMAs are useful for actuators as they change shape  tiffness  osition  atural frequency and  ther 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 (nitinol) – most useful • Ni-Ti has that this alloy exhibits above transformation temperature

~ for a single cycle max 8% ~ for 10,000 cycles 4% 30 to 50degree celsius ~ austenite 100 micro ohms*cm ~ martensite 80 micro ohms*cm < 1.002 3.06 (youngs Modulus) ~ austenite 83GPa ~ martensite 28 to 41 Gpa

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

• 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

~ materials of fixed structure  metal, ceramic and polymeric composites  Elastomers filled with ferromagnetic material powders (carbonyl iron)  Solid magnetocaloric materials ~ Materials of variable internal structure  MR Fluids  Ferro Fluids  Porous materials saturated with MR Fluids

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 stiff Large piezoelectric constant ~ piezopolymer Relatively flexible Large voltage capacity

Property PZT (Lead Zirconate Titanate) PVDF (PolyVinylidene Floride) Curie temp (degree Celsius) 212 100 Young's modulus (N/m2 ) 59.51 310 Piezoelectric constant 21210 2310 Maximum electric field .41 4010

• 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

• 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

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