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