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ENGINEERING MATERIALS
1. Metals and their alloys
2. Ceramics
3. Polymers
4. Composites
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Metals and Their Alloys
A metal is a category of materials generally characterized by properties of ductility, malleability, luster, and high electrical and thermal conductivity Includes both metallic elements and their alloys
An alloy is a metal composed of two or more elements, at least one of which is metallic
Generally classified into two groups:
1. Ferrous – steels and cast irons
2. Nonferrous – aluminum, copper, etc.©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Iron-Carbon Phase Diagram
Binary phase diagram for iron‑carbon system, up to about 6% carbon
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Steels
Iron-carbon alloy containing from 0.02% to 2.11% carbon (most steels are 0.05% and 1.1% C)
Steels often contain other alloying ingredients, such as manganese, chromium, nickel, and molybdenum
Categories of steels include:
1. Plain carbon steels
2. Low alloy steels
3. Stainless steels
4. Tool steels
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Plain Carbon Steels
Carbon is the principal alloying element, with only small amounts of other elements (about 0.5% manganese is normal)
Strength of plain carbon steels increases with carbon content, but ductility is reduced
High carbon steels can be heat treated to form martensite, making the steel very hard and strong
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Tensile strength and hardness as a function of carbon content in plain carbon steel (hot rolled)
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Properties of Steel
AISI-SAE Designation Scheme
Specified by a 4‑digit number system: 10XX, where 10 indicates plain carbon steel, and XX indicates carbon % in hundredths of percentage points For example, 1020 steel contains 0.20% C Developed by American Iron and Steel Institute
(AISI) and Society of Automotive Engineers (SAE), so designation often expressed as AISI 1020 or SAE 1020
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Plain Carbon Steels
1. Low carbon steels - less than 0.20% C Applications: automobile sheetmetal parts, plate
steel for fabrication, railroad rails2. Medium carbon steels - between 0.20% and 0.50% C
Applications: machinery components and engine parts such as crankshafts and connecting rods
3. High carbon steels - greater than 0.50% C Applications: springs, cutting tools and blades,
wear-resistant parts
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Low Alloy Steels
Iron‑carbon alloys containing additional alloying elements in amounts totaling less than 5% by weight
Mechanical properties superior to plain carbon steels for given applications
Higher strength, hardness, hot hardness, wear resistance, and toughness Heat treatment is often required to achieve these
improved properties
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
High strength Steel applications in new Mercedes Benz structure
Around 72 percent of all the bodyshell panels for the Mercedes-Benz E-Class e.g. are made from ultra-high-strength steel – a new record in passenger-car development. Three to four times the tensile strength of conventional high-strength steel grades. They are used at points where the material can be exposed to exceptionally high stresses during an accident – as a material for the B-pillars and the side roof frames to provide side impact protection,
AISI-SAE Designation Scheme
AISI‑SAE designation uses a 4‑digit number system: YYXX, where YY indicates alloying elements, and XX indicates carbon % in hundredths of % points
Examples:13XX - Manganese steel
20XX - Nickel steel
31XX - Nickel‑chrome steel
40XX - Molybdenum steel
41XX - Chrome‑molybdenum steel
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Stainless Steel (SS)
Highly alloyed steels designed for corrosion resistance Principal alloying element is chromium, usually
greater than 15% Cr forms a thin impervious oxide film that
protects surface from corrosion Nickel (Ni) is another alloying ingredient in certain SS
to increase corrosion protection Carbon is used to strengthen and harden SS, but
high C content reduces corrosion protection since chromium carbide forms to reduce available free Cr
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Properties of Stainless Steels
In addition to corrosion resistance, stainless steels are noted for their combination of strength and ductility These properties generally make stainless steel
difficult to work in manufacturing• But not impossible! (Jim comment)
Significantly more expensive than plain C or low alloy steels
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Types of Stainless Steel
Classified according to the predominant phase present at ambient temperature:
1. Austenitic stainless ‑ typical composition 18% Cr and 8% Ni
2. Ferritic stainless ‑ about 15% to 20% Cr, low C, and no Ni
3. Martensitic stainless ‑ as much as 18% Cr but no Ni, higher C content than ferritic stainless
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Designation Scheme for Stainless Steels
We start over again (3 digits) !!
First digit indicates general type, and last two digits give specific grade within type Type 302 – Austenitic SS
18% Cr, 8% Ni, 2% Mn, 0.15% C Type 430 – Ferritic SS
17% Cr, 0% Ni, 1% Mn, 0.12% C Type 440 – Martensitic SS
17% Cr, 0% Ni, 1% Mn, 0.65% C
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Cast Irons
Iron alloys containing from 2.1% to about 4% carbon and from 1% to 3% silicon
Highly suitable as casting metals Tonnage of cast iron castings is several times that of
all other cast metal parts combined, (excluding cast ingots in steel-making that are subsequently rolled into bars, plates, and similar stock)
Overall tonnage of cast iron is second only to steel among metals
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Types of Cast Irons
Most important is gray cast iron Other types include ductile iron, white cast iron,
malleable iron, and various alloy cast irons Ductile and malleable irons possess chemistries
similar to the gray and white cast irons, respectively, but result from special processing treatments
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Types of Cast Irons
Most important is gray cast iron Other types include ductile iron, white cast iron,
malleable iron, and various alloy cast irons Ductile and malleable irons possess chemistries
similar to the gray and white cast irons, respectively, but result from special processing treatments
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Nonferrous Metals 'Not Iron' – how clever!
Metal elements and alloys not based on iron Most important - aluminum, copper, magnesium,
nickel, titanium, and zinc, and their alloys Although not as strong as steels, certain nonferrous
alloys have strength‑to‑weight ratios that make them competitive with steels in some applications
Many nonferrous metals have properties other than mechanical that make them ideal for applications in which steel would not be suitable
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Aluminum and Magnesium
Aluminum (Al) and magnesium (Mg) are light metals They are often specified in
engineering applications for this feature
Both elements are abundant on earth, aluminum on land and magnesium in the sea Neither is easily extracted
from their natural states©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Aluminum and Its Alloys
High electrical and thermal conductivity Excellent corrosion resistance due to formation of a
hard thin oxide surface film Very ductile metal, noted for its formability Pure aluminum is relatively low in strength, but it can
be alloyed and heat treated to compete with some steels, especially when weight is taken into consideration– Where do you see a lot of aluminum today? What
other products are using it? ©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Auto Industry Embracing Aluminum as lightweight replacement for steel
2015 Ford F150 Pickup truck – saves 750 lbs, likely 30MPG highway
Aluminum and Its Alloys
High electrical and thermal conductivity Excellent corrosion resistance due to formation of a
hard thin oxide surface film Very ductile metal, noted for its formability Pure aluminum is relatively low in strength, but it can
be alloyed and heat treated to compete with some steels, especially when weight is taken into consideration
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Magnesium and Its Alloys
Lightest of the structural metals Available in both wrought and cast forms Relatively easy to machine In all processing of magnesium, small particles of the
metal (such as small metal cutting chips) oxidize rapidly Care must be exercised to avoid fire hazards Stuff burns REALLY well
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Copper
One of the oldest metals known to mankind Low electrical resistivity ‑ commercially pure copper is
widely used as an electrical conductor Also an excellent thermal conductor One of the noble metals (gold and silver are also
noble metals), so it is corrosion resistant
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Nickel and Its Alloys
Similar to iron in some respects: Magnetic Modulus of elasticity E for iron and steel
Differences with iron: Much more corrosion resistant - widely used as
(1) an alloying element in steel, e.g., stainless steel, and (2) as a plating metal on metals such as plain carbon steel
High temperature properties of Ni alloys are superior
(American nickel is 25% nickel)©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Nickel Alloys
Alloys of nickel are commercially important and are noted for corrosion resistance and high temperature performance
In addition, a number of superalloys are based on nickel
Applications: stainless steel alloying ingredient, plating metal for steel, applications requiring high temperature and corrosion resistance
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Titanium and Its Alloys
Abundant in nature, constituting 1% of earth's crust (aluminum is 8%)
Density of Ti is between aluminum and iron Importance has grown in recent decades due to its
aerospace applications where its light weight and good strength‑to‑weight ratio are exploited– Boeing 787 – 15% titanium by weight (39,000
lb/ac for 787-8)
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Applications of Titanium
In the commercially pure state, Ti is used for corrosion resistant components, such as marine components and prosthetic implants
Titanium alloys are used as high strength components at temperatures ranging up to above 550C (1000F), especially where its excellent strength‑to‑weight ratio is exploited
Alloying elements used with titanium include aluminum, manganese, tin, and vanadium
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Zinc and Its Alloys
Low melting point makes it attractive as a casting metal, especially die casting
Also provides corrosion protection when coated onto steel or iron The term galvanized steel refers to steel coated
with zinc Widely used as alloy with copper (brass)
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
My first car - 1970 Camaro– 90,000 miles At 6 years old, rusted wheelwells, surface rust all over.
Before Auto Industry started to use zinc plated steel
Superalloys
High‑performance alloys designed to meet demanding requirements for strength and resistance to surface degradation at high service temperatures
Many superalloys contain substantial amounts of three or more metals, rather than consisting of one base metal plus alloying elements
Commercially important because they are very expensive
Technologically important because of their unique properties
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Why Superalloys are Important
Room temperature strength properties are good but not outstanding
High temperature performance is excellent - tensile strength, hot hardness, creep resistance, and corrosion resistance at very elevated temperatures
Operating temperatures often ~ 1100C (2000F) Applications: gas turbines ‑ jet and rocket engines,
steam turbines, and nuclear power plants (systems that operate more efficiently at high temperatures)
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Three Groups of Superalloys
1. Iron‑based alloys ‑ in some cases iron is less than 50% of total composition Alloyed with Ni, Cr, Co
2. Nickel‑based alloys ‑ better high temperature strength than alloy steels Alloyed with Cr, Co, Fe, Mo, Ti
3. Cobalt‑based alloys ‑ 40% Co and 20% chromium Alloyed with Ni, Mo, and W
Virtually all superalloys strengthen by precipitation hardening (hold at high temp for longer periods of time to optimize grain structure)
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Ceramic Defined
An inorganic compound consisting of a metal (or semi‑metal) and one or more nonmetals
Important examples: Silica - silicon dioxide (SiO2), the main ingredient in
most glass products Alumina - aluminum oxide (Al2O3), used in various
applications from abrasives to artificial bones More complex compounds such as hydrous
aluminum silicate (Al2Si2O5(OH)4), the main ingredient in most clay products
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Properties of Ceramic Materials
High hardness, electrical and thermal insulating, chemical stability, and high melting temperatures
Brittle, virtually no ductility - can cause problems in both processing and performance of ceramic products
Some ceramics are translucent, window glass (based on silica) being the clearest example
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Three Basic Categories of Ceramics
1. Traditional ceramics ‑ clay products such as pottery, bricks, common abrasives, and cement
2. New ceramics ‑ more recently developed ceramics based on oxides, carbides, etc., with better mechanical or physical properties than traditional ceramics
3. Glasses ‑ based primarily on silica and distinguished by their noncrystalline structure
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Traditional Ceramics
Based on mineral silicates, silica, and mineral oxides found in nature
Primary products are fired clay (pottery, tableware, brick, and tile), cement, and natural abrasives such as alumina
Products and the processes to make them date back thousands of years
Glass is also a silicate ceramic material and is sometimes included among traditional ceramics
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Raw Materials for Traditional Ceramics
Mineral silicates, such as clays and silica, are among the most abundant substances in nature and are the principal raw materials for traditional ceramics
Another important raw material for traditional ceramics is alumina
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Traditional Ceramic Products
Pottery and Tableware – based on clay usually combined with other minerals such as silica and feldspar
Brick and tile – based on low-cost clays and silica Refractories – alumina often used as a refractory
ceramic Abrasives – most grinding wheels are based on
alumina or silicon carbide
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
New Ceramics
Ceramic materials developed synthetically over the last several decades
Also refers to improvements in processing techniques that provide greater control over structures and properties of ceramic materials
New ceramics are based on compounds other than variations of aluminum silicate
New ceramics are usually simpler chemically than traditional ceramics; for example, oxides, carbides, nitrides, and borides
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Oxide Ceramics
Most important oxide ceramic is alumina Al2O3 Alumina is also produced synthetically from bauxite Control of particle size and impurities, refinements in
processing methods, and blending with small amounts of other ceramic ingredients, strength and toughness of alumina are improved substantially compared to its natural counterpart
Alumina also has good hot hardness, low thermal conductivity, and good corrosion resistance
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Products of Oxide Ceramics
Abrasives (grinding wheel grit) Bioceramics (artificial bones and teeth) Electrical insulators and electronic components Refractory brick Cutting tool inserts – REALLY hard Spark plug barrels Engineering components
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Alumina ceramic components (photo courtesy of Insaco Inc.)
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Carbide Ceramics
Includes silicon carbide (SiC), tungsten carbide (WC), titanium carbide (TiC), tantalum carbide (TaC), and chromium carbide (Cr3C2)
Production of SiC dates from a century ago, and it is generally included among traditional ceramics
WC, TiC, and TaC are hard and wear resistant and are used in applications such as cutting tools
WC, TiC, and TaC must be combined with a metallic binder such as cobalt or nickel in order to fabricate a useful solid product
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Nitrides
Important nitride ceramics are silicon nitride (Si3N4), boron nitride (BN), and titanium nitride (TiN)
Properties: hard, brittle, high melting temperatures, usually electrically insulating, TiN being an exception
Applications: Silicon nitride: components for gas turbines, rocket
engines, and melting crucibles Boron nitride and titanium nitride: cutting tool
materials and coatings
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Polymer
A compound consisting of long‑chain molecules, each molecule made up of repeating units connected together
There may be thousands, even millions of units in a single polymer molecule
The word polymer is derived from the Greek words poly, meaning many, and meros (reduced to mer), meaning part
Most polymers are based on carbon and are therefore considered organic chemicals
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Types of Polymers
Polymers can be separated into plastics and rubbers As engineering materials, it is appropriate to divide
them into the following three categories:
1. Thermoplastic polymers2. Thermosetting polymers3. Elastomerswhere (1) and (2) are plastics and (3) is Rubber
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Thermoplastic Polymers - Thermoplastics
Solid materials at room temperature but viscous liquids when heated to temperatures of only a few hundred degrees
This characteristic allows them to be easily and economically shaped into products
They can be subjected to heating and cooling cycles repeatedly without significant degradation
Symbolized by TP
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Thermosetting Polymers - Thermosets
Cannot tolerate repeated heating cycles as thermoplastics can When initially heated, they soften and flow for
molding Elevated temperatures also produce a chemical
reaction that hardens the material into an infusible solid
If reheated, thermosets degrade and char rather than soften
Symbolized by TS
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Elastomers (Rubbers)
Polymers that exhibit extreme elastic extensibility when subjected to relatively low mechanical stress
Some elastomers can be stretched by a factor of 10 and yet completely recover to their original shape
Although their properties are quite different from thermosets, they share a similar molecular structure that is different from the thermoplastics
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Market Shares
Thermoplastics are commercially the most important of the three types About 70% of the tonnage of all synthetic
polymers produced Thermosets and elastomers share the remaining
30% about evenly, with a slight edge for the former
On a volumetric basis, current annual usage of polymers exceeds that of metals
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Examples of Polymers
Thermoplastics: Polyethylene, polyvinylchloride, polypropylene,
polystyrene, and nylon Thermosets:
Phenolics, epoxies, and certain polyesters Elastomers:
Natural rubber (vulcanized) Synthetic rubber, which exceed the tonnage of
natural rubber (think car tires)
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Polymer Applications
Reasons Why Polymers are Important
Plastics can be molded into intricate part shapes, usually with no further processing Very compatible with net shape processing
WHY IS THIS IMPORTANT? On a volumetric basis, polymers:
Are cost competitive with metals Generally require less energy to produce than
metals Certain plastics are transparent, which makes them
competitive with glass in some applications©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
General Properties of Polymers
Low density relative to metals and ceramics Good strength‑to‑weight ratios for certain (but not all)
polymers High corrosion resistance Low electrical and thermal conductivity
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Limitations of Polymers
Low strength relative to metals and ceramics Low modulus of elasticity (stiffness) Service temperatures are limited to only a few
hundred degrees Viscoelastic properties, which can be a distinct
limitation in load bearing applications Some polymers degrade when subjected to sunlight
and other forms of radiation
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Synthesis of Polymers
Nearly all polymers used in engineering are synthetic (what's that?)
•Polymers are synthesized by joining many small molecules together into very large molecules, called macromolecules, that possess a chain‑like structure The small units, called monomers, are generally
simple unsaturated organic molecules such as ethylene C2H4
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Polyethylene
Synthesis of polyethylene from ethylene monomers: (1) n ethylene monomers, (2a) polyethylene of chain length n; (2b) concise notation for depicting polymer structure of chain length n
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Polymer Molecular Structures
Linear structure – chain-like structure Characteristic of thermoplastic polymers
Branched structure – chain-like but with side branches Also found in thermoplastic polymers
Cross-linked structure Loosely cross-linked, characteristic of
elastomers Tightly cross-linked, characteristic of thermosets
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Polymer Molecular Structures
LinearBranched
Loosely cross-linked Tightly cross-linked
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Effect of Branching on Properties
Thermoplastic polymers always possess linear or branched structures, or a mixture of the two
Branches increase entanglement among the molecules, which makes the polymer Stronger in the solid state More viscous at a given temperature in the
plastic or liquid state
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Effect of Cross-Linking on Properties
Thermosets possess a high degree of cross‑linking; elastomers possess a low degree of cross‑linking
Thermosets are hard and brittle, while elastomers are elastic and resilient
Cross‑linking causes the polymer to become chemically set The reaction cannot be reversed The polymer structure is permanently changed;
if heated, it degrades or burns rather than melt
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Thermoplastic Polymers (TP)
Thermoplastic polymers can be heated from solid state to viscous liquid and then cooled back down to solid Heating and cooling can be repeated many times
without degrading the polymer Reason: TP polymers consist of linear and/or
branched macromolecules that do not cross‑link upon heating
Thermosets and elastomers change chemically when heated, which cross‑links their molecules and permanently sets these polymers
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Mechanical Properties of Thermoplastics
Low modulus of elasticity (stiffness) E is much lower than metals and ceramics
Low tensile strength TS is about 10% of metal
Much lower hardness than metals or ceramics Greater ductility on average
Tremendous range of values, from 1% elongation for polystyrene to 500% or more for polypropylene
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Commercial Thermoplastic Products and Raw Materials
Thermoplastic products include Molded and extruded items Fibers and filaments Films and sheets Packaging materials Paints and varnishes
Starting plastic materials are normally supplied to the fabricator in the form of powders or pellets in bags, drums, or larger loads by truck or rail car
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Thermosetting Polymers (TS)
TS polymers are distinguished by their highly cross‑linked three‑dimensional, covalently‑bonded structure
Chemical reactions associated with cross‑linking are called curing or setting
In effect, formed part (e.g., pot handle, electrical switch cover, etc.) becomes a large macromolecule
Always amorphous and exhibits no glass transition temperature
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
General Properties of Thermosets
Rigid - modulus of elasticity is two to three times greater than thermoplastics
Brittle, virtually no ductility Less soluble in common solvents than thermoplastics Capable of higher service temperatures than
thermoplastics Cannot be remelted ‑ instead they degrade or burn
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Cross-Linking in Thermosetting Polymers
Three categories:
1. Temperature‑activated systems 2. Catalyst‑activated systems 3. Mixing‑activated systems
Curing is accomplished at the fabrication plants that make the parts rather than the chemical plants that supply the starting materials to the fabricator
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Elastomers
Polymers capable of large elastic deformation when subjected to relatively low stresses
Some can be extended 500% or more and still return to their original shape
Two categories:
1. Natural rubber - derived from biological plants
2. Synthetic polymers - produced by polymerization processes like those used for thermoplastic and thermosetting polymers
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Characteristics of Elastomers
Elastomers consist of long‑chain molecules that are cross‑linked (like thermosetting polymers)
They owe their impressive elastic properties to two features:
1. Molecules are tightly kinked when unstretched2. Degree of cross‑linking is substantially less
than thermosets
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Vulcanization
Curing to cross‑link most elastomers Vulcanization = curing in the context of natural
rubber and some synthetic rubbers (just add sulphur) Typical cross‑linking in rubber is one to ten links per
hundred carbon atoms in the linear polymer chain, depending on degree of stiffness desired Considerable less than cross‑linking in
thermosets
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Natural Rubber (NR)
NR = polyisoprene, a high molecular‑weight polymer of isoprene (C5H8)
It is derived from latex, a milky substance produced by various plants, most important of which is the rubber tree that grows in tropical climates
Latex is a water emulsion of polyisoprene (about 1/3 by weight), plus various other ingredients
Rubber is extracted from latex by various methods that remove the water
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Stiffness of Rubber
Increase in stiffness as a function of strain for three grades of rubber: natural rubber, vulcanized rubber, and hard rubber
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Synthetic Rubbers
Development of synthetic rubbers was motivated largely by world wars when NR was difficult to obtain
Tonnage of synthetic rubbers is now more than three times that of NR
The most important synthetic rubber is styrene‑butadiene rubber (SBR), a copolymer of butadiene (C4H6) and styrene (C8H8)
As with most other polymers, the main raw material for synthetic rubbers is petroleum
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Thermoplastic Elastomers (TPE)
A thermoplastic that behaves like an elastomer Elastomeric properties not from chemical cross‑links,
but from physical connections between soft and hard phases in the material
Cannot match conventional elastomers in elevated temperature strength and creep resistance– With some modern exceptions!
Products: footwear; rubber bands; extruded tubing, wire coating; molded automotive parts, but no tires
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Composite Materials
A materials system composed of two or more distinct phases whose combination produces aggregate properties different from those of its constituents
Composites can be very strong and stiff, yet very light in weight
Fatigue properties are generally better than for common engineering metals
Toughness is often greater Possible to achieve combinations of properties not
attainable with metals, ceramics, or polymers alone
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Disadvantages and Limitations of Composite Materials - maybe
Properties of many important composites are anisotropic (what's that mean?) May be an advantage or a disadvantage
So Waterman thinks it is a great advantage, especially when you can orient the fibers in the exact direction that you want strength.
Many polymer‑based composites are subject to attack by chemicals or solvents (that's why we have coatings)
•Composite materials are generally expensive Manufacturing methods for shaping composite materials are
often slow and costly – another opportunity for you in the workplace!
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Components in a Composite Material
Most composite materials consist of two phases:
1. Primary phase - forms the matrix within which the secondary phase is imbedded
2. Secondary phase - imbedded phase sometimes referred to as a reinforcing agent, because it usually strengthens the composite material The reinforcing phase may be in the form of
fibers, particles, or various other geometries
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Classification of Composite Materials
1. Metal Matrix Composites (MMCs) ‑ mixtures of ceramics and metals, such as cemented carbides and other cermets
2. Ceramic Matrix Composites (CMCs) ‑ Al2O3 and SiC imbedded with fibers to improve properties
3. Polymer Matrix Composites (PMCs) ‑ polymer resins imbedded with filler or reinforcing agent Examples: epoxy and polyester with fiber
reinforcement, and phenolic with powders
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Functions of the Matrix Material
Primary phase provides the bulk form of the part 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 reinforcing agent
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Reinforcing Phase
Function is to reinforce the primary phase Reinforcing phase (imbedded in the matrix) is most
commonly one of the following shapes: Fibers Particles Flakes
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Fibers
Filaments of reinforcing material, usually circular in cross section
Diameters from ~ 0.0025 mm to about 0.13 mm Filaments provide greatest opportunity for strength
enhancement of composites Filament form of most materials is significantly
stronger than the bulk form As diameter is reduced, the material becomes
oriented in the fiber axis direction and probability of defects in the structure decreases significantly
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Continuous Fibers vs. Discontinuous Fibers
Continuous fibers - very long; in theory, they offer a continuous path by which a load can be carried by the composite part
Discontinuous fibers (chopped sections of continuous fibers) - short lengths (L/D = roughly 100) Whiskers = discontinuous fibers of hair-like
single crystals with diameters down to about 0.001 mm (0.00004 in) and very high strength
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Materials for Fibers
Fiber materials in fiber‑reinforced composites Glass – most widely used filament Carbon – high elastic modulus Boron – very high elastic modulus Kevlar (a polymer) Al2O3 SiC
Most important commercial use of fibers is in polymer composites
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Particles and Flakes
A second common shape of imbedded phase is particulate, ranging in size from microscopic to macroscopic Flakes are basically two‑dimensional particles ‑
small flat platelets Distribution of particles in the matrix is random
Strength and other properties of the composite material are usually isotropic
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Metal Matrix Composites (MMCs)
Metal matrix reinforced by a second phase Reinforcing phases:
1. Particles of ceramic These MMCs are commonly called cermets
2. Fibers of various materials Other metals, ceramics, carbon, and boron
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Cermets
MMC with ceramic contained in a metallic matrix The ceramic often dominates the mixture, sometimes
up to 96% by volume Bonding can be enhanced by slight solubility between
phases at elevated temperatures used in processing Cermets can be subdivided into
1. Cemented carbides – most common2. Oxide‑based cermets – less common
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Cemented Carbides
One or more carbide compounds bonded in a metallic matrix
Common cemented carbides are based on tungsten carbide (WC), titanium carbide (TiC), and chromium carbide (Cr3C2) Tantalum carbide (TaC) and others are less
common Metallic binders: usually cobalt (Co) or nickel (Ni)
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Ceramic Matrix Composites (CMCs)
Ceramic primary phase imbedded with a secondary phase, usually consisting of fibers
Attractive properties of ceramics: high stiffness, hardness, hot hardness, and compressive strength; and relatively low density
Weaknesses of ceramics: low toughness and bulk tensile strength, susceptibility to thermal cracking
CMCs represent an attempt to retain the desirable properties of ceramics while compensating for their weaknesses
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Polymer Matrix Composites (PMCs)
Polymer primary phase in which a secondary phase is imbedded as fibers, particles, or flakes
Commercially, PMCs are more important than MMCs or CMCs Examples: most plastic molding compounds,
rubber reinforced with carbon black, and fiber‑reinforced polymers (FRPs)
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Fiber‑Reinforced Polymers (FRPs)
PMC consisting of a polymer matrix imbedded with high‑strength fibers
Polymer matrix materials: Usually a thermosetting plastic such as
unsaturated polyester or epoxy Can also be thermoplastic, such as nylons
(polyamides), polycarbonate, polystyrene, and polyvinylchloride
Fiber reinforcement is widely used in rubber products such as tires and conveyor belts
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Fibers in PMCs
Various forms: discontinuous (chopped), continuous, or woven as a fabric
Principal fiber materials in FRPs are glass, carbon, and Kevlar 49 Less common fibers include boron, SiC, and
Al2O3, and steel Glass (in particular E‑glass) is the most common fiber
material in today's FRPs Its use to reinforce plastics dates from around
1920
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
Common FRP Structures
Most widely used form of FRP is a laminar structure Made by stacking and bonding thin layers of fiber
and polymer until desired thickness is obtained By varying fiber orientation among layers, a
specified level of anisotropy in properties can be achieved in the laminate
Applications: boat hulls, aircraft wing and fuselage sections, automobile and truck body panels
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes
FRP Applications
Aerospace – much of the structural weight of today’s airplanes and helicopters consist of advanced FRPs Example: Boeing 787
Automotive – some body panels for cars and truck cabs Low-carbon sheet steel still widely used due to its
low cost and ease of processing Sports and recreation
FRPs used for boat hulls since 1940s Fishing rods, tennis rackets, golf club shafts,
helmets, skis, bows and arrows
©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes