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MATERIAL SCIENCE LECTURE SERIES
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Lecture 35: Designing of Hybrid
Materials
Jayant Jain Assistant Professor,
Department of Applied Mechanics, IIT Delhi, Hauz Khas, 110016
Function will help in deciding the configuration
Decompose the requirements Seek good solutions for each Combine them in a chosen configuration Assess its performance, and Choose the combination that offers the best
Key steps involved in hybrid design
Hybrids of type 1: Composites
Composites
What is the most critical aspect in making the sound composite??
Four common configurations of composites
Components of Composite design
Remember property bounds cover all the possible configuration. By using them we escape from the need to model individual
geometries.
Properties of Composites
Density
Modulus (Voigt and Reuss bound)
m density of matrix r density of reinforcement f volume fraction of reinforcement
Upper Bound
Lower Bound
Er Youngs modulus of reinforcement Em Youngs modulus of matrix f volume fraction of reinforcement
Example: W particles dispersed in Cu matrix
Bounds of Elasticity
Bounds width measure of anisotropy
W particles dispersed in Cu matrix
Strength
Upper Limit
Lower Limit
The yield strength of the matrix enhanced slightly by the plastic constraint imposed by the reinforcement
Upper bound in strength can be given as similar to that for modulus
Mechanical Properties of Composites
Materials Selection in Mechanical Design, 4th Edition 2010 Michael Ashby
Specific heat
Thermal expansion
The heat capacity of composite would be similar to like density
Thermal Properties of Composites
Thermal conductivity
Thermal diffusivity
Thermal Properties of Composites
Fibre reinforced composite: Which direction the conductivity is highest??
Factors that can affect the conductivity??
Bonding between matrix and fibre
Large difference in properties of constituent
components
Its upper and lower bound can be obtained substituting appropriate conductivity
Materials Selection in Mechanical Design, 4th Edition 2010 Michael Ashby
Composite Design for stiffness at minimum mass
We seek a composite offering high stiffness-to-weight in structures subjected to bending loads. At present Al alloy is in use
Be and Al2O3 are two choices: they both are stiffer than Al and infact Be is lighter than Al Can hybrids or composites of Al with either of these offer improved performance? The criterion of excellence will be used to judge the performance of composite What should be the criterion of excellence when we talk about stiffness at minimum weight for a beam
Composite Design for controlled thermal response
Another application is demanding a material that requires minimum thermal distortion. At present Al is in use
We will be accessing the performance of Al-BN and Al-SiC composite The criterion of excellence will be used to judge the performance of composite: minimising thermal distortion
Al-SiC composites are significantly better than Al and Al-BN
Design and Properties of Sandwich
Hybrids of type 2: Sandwiches
Sandwich Structures
A sandwich panel combines two materials in a specified geometry and scale, configured such
that one forms the faces and the other the core to give a structure of high bending stiffness
and strength at low weight
Materials Selection in Mechanical Design, 4th Edition 2010 Michael Ashby
Sandwich Structure
Materials Selection in Mechanical Design, 4th Edition 2010 Michael Ashby
Designing of Sandwich structures
A refrigerator. The panels of the container unit must insulate, protect against the external environment, and be stiff and strong in bending.
This can be achieved by seeking materials or hybrids that maximize Eflex, the second by minimizing
Refrigerator Walls
We begin with a hybrid of type: Sandwich
Refrigerator Walls: Sandwich panel selection
Mild steel face PVC foam core
The panel offers the combination of stiffness and insulation that can not be matched by monolithic material, composites and foams
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