me_350_-_lect_15_-_ch_9.20090319.49c1d1516ac040.30091931.ppt

7/30/2019 me_350_-_lect_15_-_ch_9.20090319.49c1d1516ac040.30091931.ppt

1/20

ME 350 Lecture 15 Chapter 9

COMPOSITE MATERIALS:

1. Technology and Classification of Composite

Materials

2. Metal Matrix Composites

3. Ceramic Matrix Composites

4. Polymer Matrix Composites

5. Guide to Processing Composite Materials


2/20

Why Composites are Important

Composites can be very and , yetvery in weight

Strength-to-weight ratio stiffness-to-weight ratios are

several times greater than for steel or aluminum

properties are generally better than for

common engineering metals

Toughness is often greater


3/20

Disadvantages and Limitations

1. Properties of many important composites are(properties differ depending on the

direction in which they are measured)

May be an advantage or a disadvantage2. Many of polymer-based composites are

by chemicals or solvents

Just as the polymers themselves are susceptible

3. Composite materials are generally

Manufacturing methods for shaping composite

materials are often slow and costly


4/20

Components in a Composite Material

Most composite materials consist of two phases:

1. phase - forms the matrixwithin which the

secondary phase is imbedded

2. phase - imbedded phase sometimes

referred to as a reinforcingagent, because it

usually strengthens the composite material

The reinforcing phase may be in the form offibers,

particles, flakes or various other geometries


5/20

Classification of Composite Materials

1.Metal Matrix Composites (MMCs) - mixtures ofceramics and metals, such as cemented

carbides and other cermets

2.Ceramic Matrix Composites (CMCs) - Al2O3and SiC imbedded with fibers to improve

properties

3.Polymer Matrix Composites (PMCs) - polymerresins imbedded with filler or reinforcing agent

Examples: epoxy and polyester with fiber

reinforcement, and phenolic with powders


6/20

Functions of the Matrix Material

phase provides the bulk form of thepart or product made of the composite material

Holds the imbedded phase in place, usually

enclosing and often concealing it

When a load is applied, the matrix shares the

load with the secondary phase, in some cases

deforming so that the stress is essentially born

by the


7/20

The Reinforcing or Secondary Phase

Provide part

Imbedded phase is most commonly one of the

following shapes:

Carbide with 85% WC and 15% Co


8/20

Fiber Orientation Three Cases

One-dimensional reinforcement maximum strength

and stiffness obtained in the direction of the fiber

Planar reinforcement, i.e. two-dimensional woven

fabric

Random or three-dimensional in which the compositematerial tends to possess


9/20

Materials for Fibers

Fiber materials in fiber-reinforced composites most widely used filament

high elastic modulus

Boron very high elastic modulus

Polymers - Kevlar

Ceramics SiC and Al2O3

Metals - steel


10/20

Particles and Flakes

A second common shape of imbedded phaseisparticulate, ranging in size from microscopic

to macroscopic

Flakes are basically two-dimensionalparticles - small flat platelets

Distribution of particles in the composite matrix

is random Strength and other properties of the composite

material are usually


11/20

The Interface

There is always an interface betweenconstituent phases in a composite material

For the composite to function, the phases must

bond where they join at the interface


12/20

Interphase

In some cases, a third ingredient must beadded to bond primary and secondary phases

Called an interphase, it is like an


13/20

Three Factors that Determine Properties

1. Materials used as component phases in the

composite

2. Geometric shapes of the constituents and

resulting structure of the composite system

3. How the phases interact with one another


14/20

Example: Fiber Reinforced Polymer

Elastic modulus can be estimated by the rule of mixtures

(equation 9.5 & 9.6). Fibers are typically stiff and brittle, while

the matrix (commonly a polymer) is soft but ductile.


15/20

Variations in Strength and Stiffness

Variation in elastic modulus and tensile strength as a function

of direction of measurement relative to longitudinal axis of

carbon fiber-reinforced epoxy composite.


16/20

Composite Calculations

Density of a composite (weighted average):

c= fmm + frr

Where are densities and fm and frare the

volume fractions of the matrix and reinforcingphases respectively

Modulus of elasticity:

In the direction of the fibers:

Ec= fmEm+ frEr

Perpendicular to the direction of the fibers:

Ec = EmEr /( fmEr+ frEm)


17/20

Other Composite Structures

Laminar composite structure conventional

Sandwich structure

Honeycomb sandwich structure


18/20

Two or more layers bonded together in anintegral piece

Example: plywood, in which layers are thesame wood, but grains are oriented

differently to increase overall strength

Laminar Composite Structure


19/20

Relatively thick core of low density foambonded on both faces to thin sheets of a

different material

Sandwich Structure: Foam Core


20/20

Alternative to foam core Foam or honeycomb achieve high ratios of

strength-to-weight and stiffness-to-weight

Sandwich Structure: Honeycomb Core

me_350_-_lect_15_-_ch_9.20090319.49c1d1516ac040.30091931.ppt

Documents

Transcript of me_350_-_lect_15_-_ch_9.20090319.49c1d1516ac040.30091931.ppt