Intro to smart materials and structures - California …pbishay/PDFs/Intro to Smart Materials...

College of Engineering and Computer Science

Mechanical Engineering Department

Peter L. Bishay, PhD

Intro to smart materials and structures

By:


Assistant Professor, Mechanical Engineering


California State University, Northridge, CA




Domains and state variables

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• A domain is any physical quantity that we can describe by a set of two state

variables.




Definition of Smart Materials

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• Also called: intelligent, adaptive, and even structronic materials.

• Materials that exhibit coupling between multiple physical domains (convert

energy between multiple physical domains)

• Examples: (1) materials that can convert electrical signals into mechanical

deformation and can convert mechanical deformation into an electrical output.

(2) materials that convert thermal energy to mechanical strain.




Coupling

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• The bridge within the rectangle is the physical property that relates to the state

variables. Examples: (1) the elastic properties of a material relate the states of

stress and strain in the material, and (2) the dielectric properties relate the

electrical state variables.

• Coupling occurs when a change in the

state variable in one physical domain

causes a change in the state variable of a

separate physical domain.

• Coupling is generally denoted by a

term that is a combination of the names

associated with the two physical

domains.

Example: thermomechanical coupling:

changing the temperature of a material,

which is a state variable in the thermal

domain, can cause a change in the state of

strain, which is a mechanical state variable.




Coupling

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Coupling between the physical domains is represented by the arrows that connect

the rectangles.

Examples: (1) pyroelectric effect is the electrical output produced by a thermal

stimulus, (2) thermal expansion is the variation in mechanical stress and strain

due to a thermal stimulus.




3 Types of Smart materials

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• In this course: materials with electromechanical, magnetomechanical or

thermomechanical coupling

• Two-way coupling and one-way coupling

• Piezoelectric materials: convert energy between the mechanical and electric

domains.

• Shape memory alloys: are thermomechanical materials that deform when heated

and cooled.

Magnetorheological fluids and

elastomers: exhibit magnetomechanical

coupling.




PE, SMA and MRF

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Applications

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• Piezoelectric (Quartz, Barium Titanate, PZT):

– Transducers (Sensors) {Motion sensors, Force sensors, dynamic pressure

sensors, magnetic field probes, accelerometers, and infrared detectors},

– Oscillators, Actuators & activators, and load cells

– Microelectromechanical systems (MEMS): Miniature pumps

– MEMS cantilevers for atomic force microscopes (AFMs)

– Piezoelectric motor: inchworm motor

– Noise and vibration damping/suppression




Applications

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• Piezoelectric (Quartz, Barium Titanate, PZT):

– Memory elements and devices

– Imaging: Cracks detection, and ultrasound waves in medical devices

– Adaptive structures and intelligent systems

– Capacitors, watches, gas lighters, etc.

– Energy harvesting

• Ultra-flexible PZT element glued on body parts, like the heart and lungs, (without

constraining them) convert the movement into energy captured by a battery that could

be used to power implantable devices like pacemakers.




Applications

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• Shape memory alloys [Nitinol (Nickel–titanium–

Naval Ordnance Lab)]

{produce large strains and large amount of

deformation without undergoing plastic deformations,

silent operation, but large response time}

• active–passive vibration suppression systems

• positioning devices for systems such as robotic

applications and biomimetic hydrofoils

• Stents, which consist of cylindrical memory alloy

mesh that expands when placed in an artery or vein,

open the blood vessel and restore blood flow.




Applications

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• Magnetorheological fluids and elastomers:

– Prosthetic devices

– MR Dampers

– MR Brakes

– Etc.




Applications

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• Integration:

(1) Actuation elements for a deformable aircraft control surface:

SMA actuators for large-deflection, low frequency shape control,

Ultrasonic piezoelectric motors to control flexible surfaces on the trailing edge of

the wing.




Applications

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• Integration:

(2) Control of a rotary aircraft:

Actuation elements to twist the rotor blade to enable higher authority flight control




Other types of Smart materials

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• Electroactive polymers: exhibit electromechanical coupling that is functionally

similar to piezoelectric materials but exhibit much different electromechanical

response characteristics (Commercial uses have been limited by the lack of

suppliers for most of these materials)

• Magnetostrictive materials: couple a magnetic field to mechanical motion.

• Electrochromic materials: optical coupling properties,

• …




Smart materials properties

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Wave speed: square root of the modulus normalized to the density.

(The fundamental vibration modes of a structure are proportional to the material

wave speed).




Smart materials properties

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Extrinsic properties: properties that are functions of the geometry of the material

or device {Force; displacement}

Intrinsic properties: properties that do not depend on geometry {stress; strain}

Volumetric energy density: the capacity to do work per unit volume.

Intro to smart materials and structures - California …pbishay/PDFs/Intro to Smart Materials...

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