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College of Engineering and Computer Science
Mechanical Engineering Department
Peter L. Bishay, PhD
Intro to smart materials and structures
By:
Peter L. Bishay, PhD
Assistant Professor, Mechanical Engineering
College of Engineering and Computer Science
California State University, Northridge, CA
College of Engineering and Computer Science
Mechanical Engineering Department
Peter L. Bishay, PhD
Domains and state variables
2
• A domain is any physical quantity that we can describe by a set of two state
variables.
College of Engineering and Computer Science
Mechanical Engineering Department
Peter L. Bishay, PhD
Definition of Smart Materials
3
• 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.
College of Engineering and Computer Science
Mechanical Engineering Department
Peter L. Bishay, PhD
Coupling
4
• 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.
College of Engineering and Computer Science
Mechanical Engineering Department
Peter L. Bishay, PhD
Coupling
5
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.
College of Engineering and Computer Science
Mechanical Engineering Department
Peter L. Bishay, PhD
3 Types of Smart materials
6
• 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.
College of Engineering and Computer Science
Mechanical Engineering Department
Peter L. Bishay, PhD
PE, SMA and MRF
7
College of Engineering and Computer Science
Mechanical Engineering Department
Peter L. Bishay, PhD
Applications
8
• 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
College of Engineering and Computer Science
Mechanical Engineering Department
Peter L. Bishay, PhD
Applications
9
• 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.
College of Engineering and Computer Science
Mechanical Engineering Department
Peter L. Bishay, PhD
Applications
10
• 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.
College of Engineering and Computer Science
Mechanical Engineering Department
Peter L. Bishay, PhD
Applications
11
• Magnetorheological fluids and elastomers:
– Prosthetic devices
– MR Dampers
– MR Brakes
– Etc.
College of Engineering and Computer Science
Mechanical Engineering Department
Peter L. Bishay, PhD
Applications
12
• 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.
College of Engineering and Computer Science
Mechanical Engineering Department
Peter L. Bishay, PhD
Applications
13
• Integration:
(2) Control of a rotary aircraft:
Actuation elements to twist the rotor blade to enable higher authority flight control
College of Engineering and Computer Science
Mechanical Engineering Department
Peter L. Bishay, PhD
Other types of Smart materials
14
• 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,
• …
College of Engineering and Computer Science
Mechanical Engineering Department
Peter L. Bishay, PhD
Smart materials properties
15
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).
College of Engineering and Computer Science
Mechanical Engineering Department
Peter L. Bishay, PhD
Smart materials properties
16
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.
College of Engineering and Computer Science
Mechanical Engineering Department
Peter L. Bishay, PhD