what are composites? - materials education...

What are Composites?

SECTION A DESCRIPTION OF COMPOSITES SECTION B MATERIALS CONFIGURATIONS AND TYPES SECTION C EXAMPLE: SANDWICH PANEL MATERIALS

Jean Frank , Author

SECTION A – Definition and description of composites and evolution; Advantages and Disadvantages

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What are Composites?

What are Composites?

• Composites are defined as two or more materials – reinforcement + matrix,

they are combined to form a structure that is stronger than the individual

materials.

• Examples:

• Your leg – flesh in your leg reinforced with bone

• Concrete – steel rebar and sand mix

• Plywood – layers of wood veneers glued together

• Fiberglass – plastic matrix reinforced by glass fibers

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Composites Are

Composites are artificially produced multiphase materials

Composites allows for designing materials with properties better than those of conventional materials:

• Metals

• Ceramics

• Polymers

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History of Composites

Many industries use composites, and industries continue to evolve and transform manufacturing applications.

• Aerospace industry – lighter, stronger, temperature & wear resistance, smart structures

• Examples: aircraft components, rockets & missiles, satellites …

• Sporting goods – lighter, stronger, toughness, better aesthetics

• Examples: tennis, golf, baseball, bicycles, boats, hockey …

• Automotive – lighter, stronger, toughness

• Construction – lighter, stronger, toughness

• Examples: bridges, buildings, dams, railway

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Timeline of Composites

• One of the earliest examples of composites is the brick – made from mud and straw.

• Mongol warriors in 12th century A.D. crafted archery bows from tendons from cattle and pine resin.

• 1800’s – man made resins were developed by a chemical process called polymerization.

• 1930’s – Owens Glass Company developed a process for drawing glass into thin strands and began weaving them into fabric.

• 1942 – a dinghy is made from fiberglass and polyester resin.

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Timeline of Composites

• One of the earliest examples of composites is the brick – made from mud and straw.

• Mongol warriors in 12th century A.D. crafted archery bows from tendons from cattle and pine resin.

• 1800’s – man made resins were developed by a chemical process called polymerization.

• 1930’s – Owens Glass Company developed a process for drawing glass into thin strands and began weaving them into fabric.

• 1942 – a dinghy is made from fiberglass and polyester resin.

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Timeline of Composites

• One of the earliest examples of composites is the brick – made from mud and straw.

• Mongol warriors in 12th century A.D. crafted archery bows from tendons from cattle and pine resin.

• 1800’s – man made resins were developed by a chemical process called polymerization.

• 1930’s – Owens Glass Company developed a process for drawing glass into thin strands and began weaving them into fabric.

• 1942 – a dinghy is made from fiberglass and polyester resin.

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Timeline of Composites

• One of the earliest examples of composites is the brick – made from mud and straw.

• Mongol warriors in 12th century A.D. crafted archery bows from tendons from cattle and pine resin.

• 1800’s – man made resins were developed by a chemical process called polymerization.

• 1930’s – Owens Glass Company developed a process for drawing glass into thin strands and began weaving them into fabric.

• 1942 – a dinghy is made from fiberglass and polyester resin.

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Timeline of Composites

• 1940’s – aviation industry searched for materials that were lighter, stronger, and resistant to weather and corrosion.

• 1950’s – Corvette automobile was developed with fiberglass panels

• 1950’s-1960’s – manufacturing methods were developed; pultrusion, vacuum bag molding, and filament winding. Filament winding became the basis for large scale rockets.

• 1960’s-1970’s-1980’s – automotive, marine, and infrastructures become composite markets.

• 1990’s and present – Nano technology and 3D printing

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Industries that use Composites

• Marine boat hulls

• The aerospace industry (structural components as well as engines and motors)

• Automotive parts (panels, frames, dashboards, body repairs)

• Sinks, bathtubs, hot tubs, swimming pools

• Cement buildings, bridges

• Surfboards, snowboards, skis

• Golf clubs, fishing poles, hockey sticks

• Trees are technically composite materials, plywood

• Electrical boxes, circuit boards, contacts

• Many medical uses, including dental 11

Composite Advantages and Disadvantages

Composite parts have both an advantage and disadvantage when compared to metal components.

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Advantages of Composites

• Light Weight - Composites are light in weight, compared to most metals.

• Strength Related to Weight - material’s strength in relation to how much it weighs. Composite materials can be designed to be both strong and light.

• Corrosion Resistance - Composites resist damage from the weather and from harsh chemicals that can eat away at other materials.

• Design Flexibility - Composites can be molded into complicated shapes more easily than most other materials.

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Advantages of Composites

• Part Consolidation - A single piece made of composite materials can replace an entire assembly of metal parts. Reducing the number of parts in a machine or a structure.

• Dimensional Stability - Composites retain their shape and size when they are hot or cool, wet or dry.

• Radar Transparent - Radar signals pass right through composites, a property that makes composites ideal materials for use anywhere radar equipment is operating.

• Durable - Structures made of composites have a long life and need little maintenance. We do not know how long composites last, because we have not come to the end of the life of many original composites. Many composites have been in service for half a century.

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Disadvantages of Composites

• Delamination - Since composites are often constructed of different ply layers into a laminate structure, they can "delaminate" between layers where they are weaker.

• High Cost - They are a relatively new material, and as such have a high cost.

• Complex Fabrication - The fabrication process is usually labor intensive and complex, which further increases cost.

• Damage inspection and repairs - Delamination and cracks in composites are mostly internal and hence require complicated inspection techniques for detection, and repairing criteria.

• Composite to metal joining - Metals expand and contract more on variations in temperature as compared to composites. This may cause an imbalance at joinery and may lead to failure.

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SECTION B – Material configuration and types, advantages and disadvantages

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What are Composites?

Roles of Matrix and Reinforcement

• Composites are divided into two groups: reinforcing materials and the matrix

• made from a polymer matrix (resin) that is reinforced with an engineered, man-made or a natural fiber (example: glass, carbon, or aramid), or other reinforcing material.

• The matrix protects the fiber from mechanical and environmental damage, and transfers the load between the fibers. The fibers –reinforcement - provides the strength and stiffness to reinforce the matrix - resin.

• The reinforcement fiber is embedded into the matrix resin.

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1. MATRIX 2. FIBER/PARTICLE 3. INTERPHASE

Matrix and Their Properties

Glass Fiber (fabric) is incredibly strong. However fabric alone is not strong enough to support loading requirements. The fabric must be impregnated with a resin matrices

• The primary function of resin is to transfer stress between the reinforcing fibers

• Acts as a glue to hold fibers together

• Protects fibers from mechanical and environmental damage

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Matrix Thermosets and Thermoplastics

Matrix - Resin for composites is be broken down into two major categories – thermosets and thermoplastics

• Thermosets – must be mixed with a catalyst – crosslinking the molecules, this chemical reaction forms a solid – once hardened, cannot be reused/melted. Include epoxy, polyester, phenolic, polyurethane and silicone.

• Thermoplastics – not crosslinked, meaning the resin can be repeatedly melted and reused, no chemical changes occur – more difficult to prototype

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Crosslinking

(Commons.Wikimedia.org)

Types of Matrix

THERMOSET

• Thermosets start off as a liquid and then, through the addition of a catalyst or hardener – they are crosslinked, solidify and become permanently rigid after curing.

THERMOPLASTIC

• Thermoplastic polymers soften when heated above melting temperature, and becomes hard after cooling.

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Matrices Types

Polymers

Thermosets (Epoxy, Polyester)

Thermoplastics (Nylons)

Metals

Alloys

(Steel, Aluminum)

Ceramics

Glass

Semiconductors

Cements

Carbons

Role of Reinforcement

• Reinforcement fiber is much stronger and stiffer than the matrix, and carries the load

• Reinforcing forms: •particulate, flakes, discontinuous fiber and

continuous fiber

• Reinforcing materials fiber: • fiberglass, Kevlar/aramid and

graphite/carbon

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Commons.Wikimedia.org)

Reinforcement Fibers

• The fibers provide the primary strength of the composite structure

• Reinforcements can be engineered and designed to provide certain properties in the direction of the load.

• Many materials with a variety of strength properties, can be used to reinforce matrices, ex: wood. Glass fibers are the most common for many industries, because they are relatively inexpensive to produce and have excellent strength to weight ratios.

• The most common fibers are: glass, carbon, and aramid fibers.

• Regardless of the material, reinforcements are available in many forms: continuous (long or short), particle, or flake.

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Types of Fiber Reinforcements

• Fiber materials in fiber-reinforced composites:

• Glass – most widely used filament, stronger than steel, weighs more than other type fibers, naturally white in color

• Carbon – low weight, high strength and stiffness, high elastic modulus – stiffness, withstands hi temperatures, and naturally black in color

• Aramid – “Kevlar”, lightweight, hi toughness and damage/impact resistance, strong, abrasion and heat resistant, non-conductive, naturally yellow in color

• Boron – very high elastic modulus

• Hybrid weaves are created by interlacing two different reinforcement types

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Reinforcement Classification Types

• In industry, several names are given to composites to help differentiate them from the materials used. Some general composite types:

• FRP – (Fiber reinforced Plastic)

• GFRP – (Glass Fiber Reinforced Plastic) – this is the most common and inexpensive, and is typically called fiberglass.

• CFRP – (Carbon Fiber Reinforced Plastic) – this is widely used in aerospace and automotive because of its excellent stiffness and strength.

• AFRP – (Aramid Fiber Reinforced Plastic) – this as some of the highest relative strength because of the fibers ability to stretch rather than break. Most common example used in bullet proof vests.

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Forms of Fiber Reinforcements General Fiber characteristics/forms:

• Properties are determined by three factors: • The geometric shapes and structure of the composite system

• The manner in which the phases interact with one another

• The reinforcement may be in the form of fibers, particles, and flakes.

• (a) Fibers – Continuous long or short, aligned in one direction providing highest mechanical properties – continuous path for load to be carried

• (b) Flakes – (whiskers) flat platelet form and limited ability to share load

• (c) Particle - Chopped from continuous fiber, randomly oriented and spread out within matrix.

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(Commons.Wikimedia.org)

Reinforcements

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Reinforcement

Fibers

Short

Long

Plies

Whiskers Laminar Flakes Particles

Commons.Wikimedia.org (Commons.Wikimedia.org)

What are Composites?

SECTION C– Example: Sandwich Panel Materials

Sandwich Materials

• Sandwich panels are extremely strong and are very lightweight. The common sandwich panel is made with two outer face skins and an interior core material.

• The outer skin can be many materials, like aluminum, wood, or composite fiber. The core material maybe wood, foam, or honeycomb. The core gives structure to the panel and the skin protects the core.

Sandwich design

• Fabricated by attaching two thin but stiff skins to a lightweight but thick core.

• The core material is normally low strength material, but its higher thickness provides the sandwich composite with high bending stiffness with overall low density.

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(Image 2 – Commons.Wikimedia.org)

(Image 1 – Commons.Wikimedia.org)

A – entire assembly B – face sheet C – honeycomb core D – back sheet

Sandwich Panels

• By adding a core to a material, designers found that the strength and stiffness could be increased without adding a lot of additional weight.

• Bonding the sandwich structures has been a basic component for composites since the 60’s.

• The sandwich face and back sheet laminates are bonded to thicker core materials.

• The component is stronger, stiffer and extremely light. Many industries take advantage of core materials: autos, building panels, aviation and turbine blades, to name a few.

Sandwich Panel

Core can also be a foam material Face sheets can be composite, metal, etc.

(Commons.Wikimedia.org)

Types of Core Materials

• Balsa

• Foam

• Honeycomb – lightweight cellular structure made from metallic or non-metallic materials, formed into hexagonal cells – similar to a beehive.

Thank you!

This work is part of a larger project funded by the Advanced Technological Education Program of the National Science

Foundation DUE #1400619

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