Exam 3 Flashcards
Alloys containing more than 50wt.% Fe
Ferrous Alloys
Alloys containing less than 50wt.% Fe
Nonferrous Alloys
Based on carbon content:
(< 0.008wt% C)
Pure iron
Based on carbon content:
0.008 ~ 2.14wt% C
Steels
In most steels the microstructure consists of both
a and Fe3C phases
Carbon concentrations in commercial steels rarely exceed
1.0 wt%
Based on carbon content:
2.14 ~ 6.70wt% C
Cast irons
Commercial cast irons normally contain less than
4.5wt% C
Less than 0.25 wt%C, containing only residual concentrations of impurities and a little manganese.
Plain carbon steels
About 90% of all steel made is
carbon steel
more alloying elements are intentionally added in specific concentrations
Alloy steels
What are the 3 Ferrous Alloys — Steels?
Plain carbon steels
Alloy steels
Stainless steels
The first two digits indicate the
alloy content
The last two digits indicate the
the carbon concentration
For plain carbon steels, the first two digits are
1 and 0
alloy steels are designated by
other initial two-digit combinations (e.g., 13, 41, 43)
The third and fourth digits represent
the weight percent carbon multiplied by 100
For example, a 1040 steel is
a plain carbon steel containing 0.40 wt% C
A four-digit number
the first two digits indicate the alloy content; the last two, the carbon concentration
AISI
American Iron and Steel Institute
SAE
Society of Automotive Engineers
UNS
Uniform Numbering System
Low-carbon steels
Less than 0.25 wt%C
Medium-carbon steels
0.25 ~ 0.60 wt%C
High-carbon steels
0.60 ~ 1.4 wt%C
Unresponsive to heat treatments intended to form martensite; strengthening is accomplished by cold work
Low-Carbon Steels
Microstructures of low-carbon steel
ferrite and pearlite
Relatively soft and weak, but having outstanding ductility and toughness
Low-Carbon Steels
Typically, sy = 275 MPa, sUT = 415~550 MPa, and ductility = 25%EL
Low-Carbon Steels
Machinable, weldable, and, of all steels, are the least expensive to produce
Low-Carbon Steels
Applications for low-carbon steels:
automobile body components, structural shapes, and sheets used in pipelines, buildings, bridges, etc.
0.25 ~ 0.60 wt% C
Medium-Carbon Steels
May be heat treated by austenitizing, quenching, and then tempering to improve their mechanical
Medium-Carbon Steels
Often utilized in the tempered condition
Medium-Carbon Steels
Microstructures of medium carbon steel:
tempered martensite
Stronger than low-carbon steels and weaker than high-carbon steels
Medium-Carbon Steels
Applications for medium-carbon steels:
railway wheels and tracks, gears, crankshafts, and other machine parts and high-strength structural components calling for a combination of high strength, wear resistance, and toughness
0.60 ~ 1.4 wt%C
High-Carbon Steels
Used in a hardened and tempered condition
High-Carbon Steels
Hardest, strongest, and yet least ductile; especially wear resistant and capable of holding a sharp cutting edge
High-Carbon Steels
Containing Cr, V, W, and Mo; these alloying elements form very hard and wear-resistant carbide compounds (e.g., Cr23C6, V4C3, and WC)
High-Carbon Steels
Applications for high carbon steel:
cutting tools and dies for forming and shaping materials, knives, razors, hacksaw blades, springs, and high-strength wire
Stainless steels are selected for their excellent
resistance to corrosion
Stainless steels are divided into three classes:
martensitic, ferritic, or austenitic
The predominant alloying element in stainless steel is
chromium; a concentration of at least 11 wt% Cr is required
The predominant alloying element __________
permits a thin, protective surface layer of chromium oxide to form when the steel is exposed to oxygen
Aluminum and aluminum alloys are the most widely used
nonferrous metals
strengthened by cold working and alloying
Aluminum alloys
Nonheat-treatable: single phase, solid solution strengthening
Aluminum alloys
Low density (2.7 g/cm3), as compared to 7.9 g/cm3 for steel
High electrical and thermal conductivity
Resistant to corrosion in some common environments
Easily formed and thin Al foil sheet may be rolled
Al has an FCC crystal structure; its ductility is retained even at very low temperatures
Limitation: low melting temperature (660°C)
Properties of aluminum alloys
Al alloys can provide a weight savings of up to ___ compared to an equivalent steel structure
55%
________ is used in the manufacture of aircraft and for fuel tanks in spacecraft
Aluminum plate
- So soft and ductile that it is difficult to machine
- Unlimited capacity to be cold worked
- Highly resistant to corrosion in diverse environments
Unalloyed copper
strengthened by cold working and/or solid-solution alloying
Copper alloys
________ and _______ are two common copper alloys
Bronze and brass
Applications for copper alloys:
costume jewelry, cartridge casings, automotive radiators, musical instruments, electronic packaging, and coins
Bronze is an alloy of _______ and _____.
copper and tin
May contain up to 25% tin
Bronze
Brass is an alloy of ______
and ____.
copper
zinc
Contain 5-30% zinc
Brass
The zinc ________ the strength of the copper
increases
_______ and _______ are also increased by the zinc.
Ductility
formability
Relatively new engineering material that possess an extraordinary combination of properties
Titanium
Low density (4.5 g/cm3)
Titanium
High melting temperature (1668°C), high elastic modulus (107 GPa)
Titanium
What are the limitations of titanium?
- Chemical reactivity with other materials and oxidation problems at elevated temperatures
- Cost
What are the applications of titanium?
High-strength prosthetic implants, petroleum & chemical-processing equipment, airframe structural components
Most polymers are
hydrocarbons
Each carbon singly bonded to four other atoms
Saturated hydrocarbons
Example of a Saturated hydrocarbons
Ethane, C2H6
Double & triple bonds somewhat unstable – can form new bonds
Unsaturated Hydrocarbons
_______ found in ethylene (ethene) - C2H4
Double bond
_________ found in acetylene (ethyne) - C2H2
Triple bond
two compounds with same chemical formula can have quite different structures
Isomerism
Example of Isomerism
C8H18:
normal-octane
2,4-dimethylhexane
_______ is a long-chain hydrocarbon
polyethylene
Molecular Shape is also known as
Conformation
chain bending and twisting are possible by rotation of carbon atoms around their chain bonds
Molecular Shape
not necessary to break chain bonds to ________
alter molecular shape
two or more monomers polymerized together
Copolymers
A and B randomly positioned along chain
random
A and B alternate in polymer chain
alternating
large blocks of A units alternate with large blocks of B units
block
chains of B units grafted onto A backbone
graft
Crystallinity in Polymers
- Ordered atomic arrangements involving molecular chains
- Crystal structures in terms of unit cells
Polymer Crystalline regions
- thin platelets with chain folds at faces
- Chain folded structure
Polymers _____ 100% crystalline
rarely
in Polymer Crystallinity, it is difficult for all regions of all chains to become ________
aligned
Degree of crystallinity is expressed as
% crystallinity
Some physical properties depend on
% crystallinity
Heat treating causes crystalline regions to _____ and % crystallinity to _______
grow
increase
Some semicrystalline polymers form
spherulite structures
Alternating chain-folded crystallites and amorphous regions
Semicrystalline Polymers
Spherulite structure for relatively _____ growth rates
rapid
Mass of a mole of chains
Molecular weight
Not all chains in a polymer are of the
same length
there can be a ________ of molecular weights
distribution
average number of repeat units per chain
Degree of Polymerization, DP
The fracture strengths of polymers is _____ of those for metals
10%
Deformation strains for polymers are
> 1000%
for most metals, deformation strains are
< 10%
Drawing
- stretches the polymer prior to use
- aligns chains in the stretching direction
What are the results of drawing?
- increases the elastic modulus (E) in the stretching direction
- increases the tensile strength (TS) in the stretching direction
- decreases ductility (%EL)
Annealing after drawing:
- decreases chain alignment
- reverses effects of drawing (reduces E and TS, enhances %EL)
Predeformation by Drawing
Contrast to effects of cold working in metals
Compare elastic behavior of elastomers with the:
- brittle behavior (of aligned, crosslinked & network polymers)
- plastic behavior (of semicrystalline polymers) (as shown on previous slides)
-little crosslinking
- ductile
- soften w/heating
- polyethylene
polypropylene
polycarbonate
polystyrene
Thermoplastics
- significant crosslinking (10 to 50% of repeat units)
- hard and brittle
- do NOT soften w/heating
- vulcanized rubber, epoxies, polyester resin, phenolic resin
Thermosets
Decreasing T
- increases E
- increases TS
- decreases %EL
Increasing strain rate
- increases E
- increases TS
- decreases %EL
Both Tm and Tg increase with
increasing chain stiffness
Chain stiffness increased by presence of
- Bulky sidegroups
- Polar groups or sidegroups
- Chain double bonds and aromatic chain groups
formation prior to cracking
Craze
What happens during crazing?
- plastic deformation of spherulites
- formation of microvoids and fibrillar bridges
There are two types of polymerization:
- Addition (or chain) polymerization
- Condensation (step) polymerization
Polymer Additives can
Improve mechanical properties, process-ability, durability, etc.
Added to improve tensile strength & abrasion resistance, toughness & decrease cost
Fillers
What are some examples of Polymer fillers?
carbon black, silica gel, wood flour, glass, limestone, talc, etc
- Added to reduce the glass transition temperature Tg below room temperature
- Presence of plasticizer transforms brittle polymer to a ductile one
- Commonly added to PVC - otherwise it is brittle
Plasticizers
- can be reversibly cooled & reheated
i. e. recycled heat until soft, shape as desired, then cool
Thermoplastic
- when heated forms a molecular network (chemical reaction)
- degrades (doesn’t melt) when heated
- a prepolymer molded into desired shape, then chemical reaction occurs
Thermoset
Polymer Fibers - length/diameter
> 100
Primary use is in textiles
Polymer Fibers
Fiber characteristics:
- high tensile strengths
- high degrees of crystallinity
- structures containing polar groups
Polymers fibers are formed by
spinning:
- extrude polymer through a spinneret (a die containing many small orifices)
- the spun fibers are drawn under tension
- leads to highly aligned chains - fibrillar structure
Coatings
thin polymer films applied to surfaces – i.e., paints, varnishes
- protects from corrosion/degradation
- decorative – improves appearance
- can provide electrical insulation
Coatings
bonds two solid materials
Adhesives (adherands)
bonding types:
Secondary – van der Waals forces
Mechanical – penetration into pores/crevices
produced by blown film extrusion
Films
gas bubbles incorporated into plastic
Foams
Limitations of polymers:
- E, σy, Kc, T application are generally small.
- Deformation is often time and temperature dependent
Thermoplastics (PE, PS, PP, PC):
- Smaller E, σy, T application
- Larger Kc
- Easier to form and recycle
Elastomers (rubber):
- Large reversible strains
Thermosets (epoxies, polyesters):
- Larger E, σy, T application
- Smaller Kc
Polymer Processing:
compression and injection molding, extrusion, blown film extrusion
Combination of two or more individual materials
Composite
What is the design goal of composites?
obtain a more desirable combination of properties (principle of combined action)
Multiphase material that is artificially made
Composite
Phase types:
- Matrix - is continuous
- Dispersed - is discontinuous and surrounded by matrix
Purposes of the matrix phase:
- transfer stress to dispersed phase
- protect dispersed phase from environment
Types matrix phase:
MMC, CMC, PMC (metal, ceramic, polymer)
Dispersed phase:
– Purpose:
MMC: increase σy, TS, creep resist.
CMC: increase Kic ( fracture toughness)
PMC: increase E, σy, TS, creep resist
Types of dispersed phase:
particle, fiber, structural
Estimate fiber-reinforced composite modulus of elasticity for continuous fibers
Continuous fibers
- Continuous fibers pulled through resin tank to impregnate fibers with thermosetting resin
- Impregnated fibers pass through steel die that preforms to the desired shape
- Preformed stock passes through a curing die that is
- -precision machined to impart final shape
- -heated to initiate curing of the resin matrix
Pultrusion
- Continuous reinforcing fibers are accurately positioned in a predetermined pattern to form a hollow (usually cylindrical) shape
- Fibers are fed through a resin bath to impregnate with thermosetting resin
- Impregnated fibers are continuously wound (typically automatically) onto a mandrel
- After appropriate number of layers added, curing is carried out either in an oven or at room temperature
- The mandrel is removed to give the final product
Filament Winding
- stacked and bonded fiber-reinforced sheets
- stacking sequence: e.g., 0º/90º
- benefit: balanced in-plane stiffness
Laminates
honeycomb core between two facing sheets
- benefits: low density, large bending stiffness
Sandwich panels
Costs are not effected by the level of production
Fixed costs
Includes both variable and semi-variable costs
Overhead costs
costs that are directly affected by the level of production
Variable costs
Variable costs
= UC = Total Unit Cost
Variable costs that have a minimum fixed value and then a variable component that fluctuates with the production level
Semi-variable costs
total income received from sales
Revenue
Selling Price times number of units sold
Revenue
the money you have after subtracting fixed and variable cost from the revenue
Profit BT
the money you have after subtracting fixed and variable cost and Taxes from the revenue
Profit AT
purchased material and lower level manufactured parts that include direct labor and overhead
Material
Pay to employees who add value to product
Often paid hourly, or per item, but can be salaried
Direct Labor
General term for all other variable costs that are NOT included in material and direct labor
Overhead (OH)
labor paid for non value added work such as: moving & stocking material, quality inspection, unloading trucks, receiving material (both purchased and manufactured). Includes fringe benefits
Indirect labor
for manufacturing and warehouse areas
Utilities
paint, jigs & fixtures, cutting oils, maintenance supplies, shipping supplies not on BOM, bolts, nails, glue not on BOM, etc
Production Supplies
shop/warehouse
Janitorial & maintenance Services
A decision-making aid for determining whether a particular production or sales volume will result in losses or profits
Break-Even Analysis
What is the break-even analysis used for?
Used to see if your income is more than your expense
Determine minimum price a product can be sold for
Determine the minimum quantity of sales
How do you set a selling price?
Need to know the Unit Cost = M, L, OH
Determine the margin profit
Based on competitive strategy
margin profit
Based on who you are selling to
margin profit
- Technique for evaluating process and equipment alternatives
- Objective is to find the point in dollars and units at which certain costs equals revenue
- Requires estimation of fixed costs, variable costs, and revenue
Break-Even Analysis
Revenue function begins at the _____ and proceeds ____ to the _____, increasing by the selling price of each unit
origin
upward
right
Where the revenue function crosses the total cost line is the
break-even point
What are the assumptions of a break-even analysis?
- Costs and revenue are linear functions
- -Generally not the case in the real world
- We actually know these costs
- -Although sometimes difficult to verify
- Time value of money is often ignored
Two basic approaches to Break-Even
- Fixed time period with variable production rate
- Fixed production rate with variable time period
The _________ is traditionally used
Fixed Time Period
Four different Break-Even Points:
- Shutdown Point
- Break-Even at cost
- Break-Even at required return
- Break-Even at required return after taxes
When the total revenue is equal to sum of variable and semivariable costs
Shutdown Point
When the total revenue is equal to total costs (variable, semi-variable, and fixed)
Break-Even at cost
When the total revenue is equal to the total costs plus the required return
Break-Even at required return
When the total revenue is equal to the total costs plus the required return plus the taxes on the required return
Break-Even at required return after taxes
Revenue (shutdown point) =
Variable costs + Semi-variable costs
Revenue (Break-Even Analysis: At Cost) =
Total costs =Fixed costs + Variable costs +Semi-variable costs
Revenue (At Required Return) =
Total cost + Required return
Revenue (At Required Return) =
Fixed costs + Variable costs + Semi-variable costs + Required return
Revenue (At Required Return After Tax) =
Total cost + Required return + Taxes on the required return
General expression to determine material cost:
C(u) = C(w) x W
C(u)
total unit cost, $
C(w)
cost per unit weight, $/weight ($/kg, $/lb)
W
weight (k,lb)
Weight can be expressed by:
W = d x V
d
density, weight/unit volume (kg/m^3, lb/in^3)
V
volume (m^3, in^3) `
Thus expression transforms to:
C(u) = C(w) x d x V
Volume can be expressed by:
V = L x A
L
design length (m, in)
A
design cross-sectional area (m^2, in^2)
Thus expression transforms to again:
C(u) = C(w) x d x L x A
Cross-sectional area frequently involved in
basic design relationships
Cross sectional area
usually determined by design requirements
Two of the most common design requirements are:
1) The product must support a design load (strength requirement)
2) The product is to be restricted in the amount of deflection (stiffness requirement)
Design relationships for cross-sectional area (A)
must be developed
Design relationship for simple tension in a solid bar:
S = P/A or A = P/S
S
material strength (MPa, kpsi)
P
load (kN, lb)
A
cross sectional area (m^2, in^2)
Sometimes a design calls for materials when
COST is not critical for a solid rod, bar or cylinder
Examples would be:
- Airplane / aerospace industry
- Hospital equipment (implants use Titanium…)
- Sports Equipment (bikes, carabiners…)
For more complex loadings than simple tension the expression in return is
more complex
In cases with multiple constraints (e.g., load AND elongation),
critical cross-sectional areas must be calculated
Cost performance is only comparable for
same criteria (that is, loading)
In cases where load is critical for one material and elongation for another ->
ratio should not be used
What type(s) of bonds is (are) found between atoms within hydrocarbon molecules?
Covalent bonds
How do the densities compare for crystalline and amorphous polymers of the same material that have identical molecular weights?
Density of crystalline polymer > density of amorphous polymer
Significant tensile deformation of a semicrystalline polymer results in a highly-oriented structure (T or F)
True. Significant tensile deformation of a semicrystalline polymer results in a highly-oriented structure
How does annealing an undeformed semicrystalline polymer affect its yield strength?
Annealing an undeformed semicrystalline polymer produces an increase in its tensile strength
Which of the following factor(s) favor(s) brittle fracture in polymers?
- Increasing in temperature.
- Increasing in strain rate.
- The presence of a sharp notch.
- Decreasing specimen thickness.
- Increasing strain rate
- the presence of a sharp notch
- decreasing temperature
The bonding forces between adhesive and adherend surfaces are thought to be
- Electrostatic
- Covalent
- Chemical
electrostatic
Deformation of a semicrystalline polymer by drawing produces what?
- an increase in strength in the direction of drawing
- a decrease in strength perpendicular to the direction of drawing
How does deformation by drawing of a semicrystalline polymer affect its tensile strength?
increases the tensile strength
How does increasing the degree of crystallinity of a semicrystalline polymer affect its tensile strength?
leads to an increase in its tensile strength. This is due to enhanced interchain bonding and forces in crystalline regions; in response to applied stresses, interchain motions become more restrained as degree of crystallinity increases
How does increasing the molecular weight of a semicrystalline polymer affect its tensile strength?
The tensile strength of a semicrystalline polymer increases with increasing molecular weight. This effect is explained by the increased chain entanglements at higher molecular weights
In order for a polymer to behave as an elastomer, what is necessary?
In order for a polymer to behave as an elastomer
- It must not crystallize easily
- Chain bond rotations must be relatively free
- The polymer must be above its glass transition temperature
A random and lightly crosslinked copolymer that has a glass-transition temperature of –40°C is an _______ since it is a random copolymer (i.e., is highly noncrystalline), is lightly crosslinked, and is above its glass transition temperature.
elastomer
A branched and isotactic polypropylene that has a glass-transition temperature of –10°C is a __________ since it has a branched structure.
thermoplastic
The polyethylene that has a glass-transition temperature of 0°C is a _________ since it is heavily crosslinked.
thermoset (nonelastomer)
Linear polyvinyl chloride that has a glass-transition temperature of 100°C is a __________ since it has a linear structure.
thermoplastic
What is the definition of glass transition temperature?
The glass transition temperature is the temperature at there is a slight decrease in slope of the temperature versus specific volume curve.
There is a definite temperature at which a liquid transforms to a glassy (or noncrystalline) solid. (T or F)
False. Unlike crystalline materials, a glassy or noncrystalline material does not transform into a solid at a definite temperature. Rather, upon cooling from the liquid, a glass becomes more viscous as the temperature decreases.
