MEEN 361 Final Review
What is fatigue strength? What is the magic number of cycles?
Fatigue strength is the maximum stress for which fatigue will not occur within a particular number of cycles, such as 500,000,000. 5*10^8 cycles
Minimum distance between indentation sites?
At least 2.5 D. Lowers risk of tainting your new test site because of strain hardening effects in the neighborhood.
What should be the minimum distance between indentation sites for legitimate hardness measurement?
At least 2.5 D. Lowers risk of tainting your new test site because of strain hardening effects in the neighborhood.
At the back page Figure 1 for the TTT diagram, what line you need to follow for the heat treatment that will give you 50% Pearlite, 50% Martensite?
B
Brittle fracture is characterized by A. large permanent deformation prior to failure B. abrupt (catastrophic) failure with little or no warning. C. blunting of crack tips D. All of the above
B. abrupt (catastrophic) failure with little or no warning.
True or false: It is O.K. to keep at least two indent diameter spacing between the hardness readings.
False: three* indent diameter
What are the two methods by which polymerization occurs?
(1) addition or chain polymerization and (2) step polymerization, also known as condensation polymerization.
The arrangement of repeating units in a copolymer can vary. What are some of the possible arrangements?
(1) alternating, (2) random, (3) block, and (4) graft
What are the common forms of the reinforcing phase in composite materials?
(1) fibers, (2) particles and flakes, and (3) an infiltrated phase in skeletal structures.
What are the two forms of sandwich structure among laminar composite structures?
(1) foamed-core sandwich, in which the core is polymer foam between two solid skins; and (2) honeycomb, in which the core is a honeycomb structure sandwiched between two solid skins.
Identify some of the characteristic properties of composite materials.
(1) high strength-to- weight and stiffness-to-weight ratios; (2) good fatigue properties and toughness; (3) anisotropic properties in many cases; and (4) other properties and features that are difficult or impossible to obtain with metals, ceramics, or polymers alone.
What are some of the factors that influence a polymer's tendency to crystallize?
(1) only linear polymers can form crystals; (2) copolymers do not form crystals; (3) stereoregularity - isotactic polymers always form crystals, atactic polymers never form crystals, and syndiotactic polymers sometimes form crystals; (4) slow cooling from the molten states promotes crystal formation; (5) plasticizers inhibit crystal formation; and (6) stretching the polymer tends to promote crystallization.
Cross-linking (curing) of thermosetting plastics is accomplished by one of three ways. Name the three ways.
(1) temperature-activated systems, in which elevated temperatures accomplish curing; (2) catalyst-activated systems, in which small mounts of a catalyst cause cross-linking; and (3) mixing-activated systems, in which two reactive components are mixed and curing occurs by their chemical reaction.
What are the three general factors that determine the properties of a composite material?
(1) the component materials; (2) the geometric shapes of the constituents - the reinforcing phase in particular - and the resulting structure of the material; and (3) the interaction of the phases
What are the three basic categories of polymers?
(1) thermoplastics, (2) thermosetting polymers, and (3) elastomers.
How are thermoplastic elastomers different from conventional rubbers?
(1) they exhibit thermoplastic properties, and (2) their extensibility derives from physical connections between different phases in the polymer
Rank metal from lowest to highest hardness
(Annealed, Quenched, Tempered, As Received)
A branched molecular structure is stronger in the solid state and more viscous in the molten state than a linear structure for the same polymer: (a) true or (b) false.
(a)
Degree of polymerization is which one of the following? (a) average number of mers in the molecule chain; (b) proportion of the monomer that has been polymerized; (c) sum of the molecule weights of the mers in the molecule; or (d) none of the above.
(a)
If strain measurements were made during a tensile test, which of the following would have the higher value? (a) engineering stain, or (b) true strain.
(a)
Most hardness tests involve pressing a hard object into the surface of a test specimen and measuring the indentation (or its effect) that results: (a) true or (b) false.
(a)
Of the three polymer types, which one is the most important commercially? (a) thermoplastics, (b) thermosets, or (c) elastomers.
(a)
Polystyrene (without plasticizers) is amorphous, transparent, and brittle: (a) true or (b) false.
(a)
The basic difference between low density polyethylene and high density polyethylene is that the latter has a much higher degree of crystallinity: (a) true or (b) false.
(a)
The fiber rayon used in textiles is based on which of the following polymers: (a) cellulose, (b) nylon, (c) polyester, (d) polyethylene, or (e) polypropylene.
(a)
Which of the following types of stress strain relationship best describes the behavior of metals at temperatures above their respective recrystallization points: (a) elastic and perfectly plastic, (b) elastic and strain hardening, (c) perfectly elastic, or (d) none of the above.
(a)
Which one of the following materials has the highest hardness? (a) alumina ceramic, (b) gray cast iron, (c) hardened tool steel, (d) high carbon steel, or (e) polystyrene.
(a)
Which one of the following reinforcing geometries offers the greatest potential for strength and stiffness improvement in the resulting composite material? (a) fibers, (b) flakes, (c) particles, or (d) infiltrated phase.
(a)
Which one of the three polymer types does not involve cross- linking? (a) thermoplastics, (b) thermosets, or (c) elastomers.
(a)
Which of the following is not a common ingredient in cemented carbide cutting tools (two correct answers): (a) Al2O3, (b) Co, (c) CrC, (d) TiC, and (e) WC?
(a) Al2O3
In general, which one of the following materials has the highest machinability: (a) aluminum, (b) cast iron, (c) copper, (d) low carbon steel, (e) stainless steel, (f) titanium alloys, or (g) unhardened tool steel?
(a) aluminum
Most sheet metalworking operations are performed as which one of the following: (a) cold working, (b) hot working, or (c) warm working? Hint: Quality is surface finish is usually important in sheet metalworking operations.
(a) cold working
As an alloying ingredient in high-speed steel, tungsten (i.e. W) serves which of the following functions (select two best answers): (a) forms hard carbides to resist abrasion, (b) improves strength and hardness, (c) increases corrosion resistance, (d) increases hot hardness, and (e) increases toughness?
(a) forms hard carbides to resist abrasion (d) increases hot hardness
Which of the following are advantages and characteristics of hot working relative to cold working (four correct answers): (a) fracture of workpart is less likely, (b) friction is reduced, (c) increased strength properties, (d) isotropic mechanical properties, (e) less overall energy is required, (f) lower deformation forces is required, (g) more significant shape changes are possible, and (h) strain-rate sensitivity is reduced?
(a) fracture of workpart is less likely, (b) friction is reduced, (c) increased strength properties, (d) isotropic mechanical properties, (e) less overall energy is required, (f) lower deformation forces is required, (g) more significant shape changes are possible, and (h) strain-rate sensitivity is reduced
Identify which of the following materials are composites (more than one)? (a) cemented carbide, (b) phenolic molding compound, (c) plywood, (d) Portland cement, (e) rubber in automobile tires, (f) wood, or (g) 1020 steel.
(a), (b), (c), (e), and (f).
Which of the following materials are used as fibers in fiber-reinforced plastics (more than one): (a) aluminum oxide, (b) boron, (c) carbon/graphite, (d) epoxy, (e) Kevlar 49, (f) S-glass, and (g) unsaturated polyester.
(a), (b), (c), (e), and (f).
Which of the following polymers are normally thermoplastic (more than one): (a) acrylics, (b) cellulose acetate, (c) nylon, (d) polychloroprene, (e) polyethylene, or (f) polyurethane.
(a), (b), (c), and (e).
Viscoelasticity has features of which of the following more traditional material properties (more than one)? (a) elasticity, (b) plasticity, (c) viscosity.
(a), (b), (c). This answer may require some justification. Viscoelasticity is usually considered to be a property that combines elasticity and viscosity. However, in deforming over time it involves plastic flow (plasticity). Strictly speaking, the shape return feature in viscoelastic behavior violates the definition of plastic flow; however, many materials considered to be viscoelastic do not completely return to their original shape.
Polyurethanes can be which of the following (more than one): (a) thermoplastic, (b) thermosetting, or (c) elastomeric.
(a), (b), and (c)
Which of the following metals are most commonly used as the matrix material in fiber-reinforced MMCs (name three)? (a) aluminum, (b) copper, (c) iron, (d) magnesium, (e) titanium, or (f) zinc.
(a), (d), and (e).
Which one of the following are the three basic types of static stresses to which a material can be subjected (three answers)? (a) compression, (b) hardness, (c) reduction in area, (d) shear, (e) tensile, (f) true stress, and (f) yield.
(a), (d), and (e).
A copolymer is a mixture consisting of macromolecules of two different homopolymers: (a) true or (b) false.
(b)
Among the thermosetting polymers, the most widely used commercially is which of the following: (a) epoxies, (b) phenolics, (c) silicones, or (d) urethanes.
(b)
As temperature of a polymer increases, its density (a) increases, (b) decreases, or (c) remains fairly constant
(b)
If stress values were measured during a tensile test, which of the following would have the higher value? (a) engineering stress, or (b) true stress.
(b)
The reinforcing phase is the matrix within which the secondary phase is imbedded: (a) true or (b) false.
(b)
The shear strength of a metal is usually (a) greater than, or (b) less than its tensile strength.
(b)
Which of the following is the chemical formula for the repeating unit in polyethylene? (a) CH2, (b) C2H4, (c) C3H6, (d) C5H8, or (e) C8H8.
(b)
Which of the following plastics has the highest market share? (a) phenolics, (b) polyethylene, (c) polypropylene, (d) polystyrene, or (e) polyvinylchloride.
(b)
Which one of the following materials has the highest modulus of elasticity? (a) aluminum, (b) diamond, (c) steel, (d) titanium, or (e) tungsten.
(b)
Which one of the following types of stress strain relationship best describes the behavior of most metals at room temperature: (a) elastic and perfectly plastic, (b) elastic and strain hardening, (c) perfectly elastic, or (d) none of the above.
(b)
The plastic region of the stress-strain curve for a metal is characterized by a proportional relationship between stress and strain: (a) true or (b) false.
(b) It is the elastic region that is characterized by a proportional relationship between stress and strain. The plastic region is characterized by a power function - the flow curve.
As the degree of crystallinity in a given polymer increases, the polymer becomes denser and stiffer, and its melting temperature decreases: (a) true or (b) false.
(b) Melting temperature increases with higher degree of crystallinity
Viscosity can be defined as the ease with which a fluid flows: (a) true or (b) false
(b) Viscosity is the resistance to flow
Which one of the following plate metals produces the hardest surface on a metallic substrate: (a)cadmium, (b) chromium, (c) copper, (d) nickel, or (e) tin?
(b) chromium
52. Welding can only be performed on metals that have the same melting point; otherwise, the metal with the lower melting temperature always melts while the other metal remains solid: (a) true, (b) false?
(b) false
53. Weld failures always occur in the fusion zone of the weld joint, since this is the part of the joint that has been melted: (a) true, (b) false?
(b) false
How does addition of C affect DBTT in steels?
An increase in the carbon content of plain carbon steel generally
Thermal energy is normally associated with which of the following changes in an altered metalliclayer (three best answers): (a) cracks, (b) hardness variations, (c) heat affected zone, (d) plastic deformation, (e) recrystallization, or (f) voids?
(b) hardness variations, (c) heat affected zone (e) recrystallization
Plain carbon steels are designated in the AISI code system by which of the following: (a) 01XX, (b) 10XX, (c) 11XX, (d) 12XX, or (e) 30XX?
(b)10XX
Anisotropic means which one of the following: (a) composite materials with composition consisting of more than two materials, (b) properties are the same in every direction, (c) properties vary depending on the direction in which they are measured, or (d) strength and other properties as a function of curing temperature.
(c)
Which of the following is the correct definition of ultimate tensile strength, as derived from the results of a tensile test on a metal specimen? (a) the stress encountered when the stress-strain curve transforms from elastic to plastic behavior, (b) the maximum load divided by the final area of the specimen, (c) the maximum load divided by the original area of the specimen, or (d) the stress observed when the specimen finally fails.
(c)
Which of the following metals is used as the matrix metal in nearly all WC cemented carbides? (a) aluminum, (b) chromium, (c) cobalt, (d) lead, (e) nickel, (f) tungsten, or (g) tungsten carbide.
(c)
Which of the following polymer types are most commonly used in polymer matrix composites? (a) elastomers, (b) thermoplastics, or (c) thermosets.
(c)
Which one of the following types of stress strain relationship best describes the behavior of brittle materials such as ceramics and thermosetting plastics: (a) elastic and perfectly plastic, (b) elastic and strain hardening, (c) perfectly elastic, or (d) none of the above.
(c)
Which one of the three polymer types is not normally considered to be a plastic? (a) thermoplastics, (b) thermosets, or (c) elastomers.
(c)
Wood is which one of the following composite types? (a) CMC, (b) MMC, or (c) PMC.
(c)
Which answers complete the following sentence correctly (more than one): As the temperature of an amorphous thermoplastic polymer is gradually reduced, the glass transition temperature Tg is indicated when (a) the polymer transforms to a crystalline structure, (b) the coefficient of thermal expansion increases markedly, (c) the slope of specific volume versus temperature changes markedly, (d) the polymer becomes stiff, strong, and elastic, or (e) the polymer solidifies from the molten state
(c) and (d)
An outside micrometer would be appropriate for measuring which of the following (two correct answers): (a) hole depth, (b) hole diameter, (c) part length, (d) shaft diameter, and (e) surface roughness?
(c) part length, (d) shaft diameter
The chemical formula for polyisoprene in natural rubber is which of the following: (a) CH2, (b) C2H4, (c) C3H6, (d) C5H8, or (e) C8H8.
(d)
Which of the following are the two main functions of a cutting fluid in machining (two best answers): (a) improve surface finish on the workpiece, (b) reduce forces and power, (c) reduce friction at the tool-chip interface, (d) remove heat from the process, and (e) wash away chips?
(d) remove heat from the process
Which one of the following manufacturing processes will likely result in the best surface finish: (a) arc welding, (b) grinding, (c) machining, (d) sand casting, or (e) sawing?
(d) sand casting
The leading commercial synthetic rubber is which of the following: (a) butyl rubber, (b) isoprene rubber, (c) polybutadiene, (d) polyurethane, (e) styrene-butadiene rubber, or (f) thermoplastic elastomers.
(e)
Ceramic matrix composites are designed to overcome which of the following weaknesses of ceramics (more than one)? (a) compressive strength, (b) hardness, (c) hot hardness, (d) modulus of elasticity, (e) tensile strength, or (f) toughness
(e) and (f)
Which of the following manufacturing processes are classified as material removal processes (two correct answers): (a) casting, (b) drawing, (c) extrusion, (d) forging, (e) grinding, (f) machining, (g) molding, (h) pressworking, and (i) spinning
(e) grinding, (f) machining
Of all of the current material addition rapid prototyping technologies, which one is the most widely used with hobbyist-level 3D Printers utilizing PLA or ABS filament : (a) ballistic particle manufacturing, (b) fused deposition modeling, (c) selective laser intering, (d) solid ground curing, and (e) stereolithography?
(e) stereolithography
Which one of the following is the most common reinforcing material in FRPs? (a) Al2O3, (b) boron, (c) carbon, (d) cobalt, (e) graphite, (f) Kevlar 49, or (g) SiO2.
(g)
What are the strengthening mechanisms in metals?
- Grain size control (grain refinement) - Alloying (solid solution hardening) - Precipitation hardening (if solubility of the parent medium is low) - Work hardening
How is the shear modulus of elasticity G related to the tensile modulus of elasticity E, on average?
0.4 E, on average.
How is shear strength S related to tensile strength TS, on average?
0.7 TS, on average.
Rank the following in descending (i.e. highest to lowest order based on their tensile strength (hardness). I. Bainite II. Martensite III. Tempered Martensit IV. coarse Pearlite
1.) Course Pearlite 2.) Bainite 3.) Tempered Martensite 4.) Martensite
What is the defining characteristic of a Newtonian fluid?
A Newtonian fluid is one for which viscosity is a constant property at a given temperature. Most liquids (water, oils) are Newtonian fluids.
What is a copolymer?
A copolymer is a polymer made up of two different types of mers, such as ethylene and propylene.
True or false: You can have viscosity on thermosets if you increase the temperature.
False: plastic* if you increase
Tensile testing is not appropriate for hard brittle materials such as ceramics. What is the test commonly used to determine the strength properties of such materials?
A three-point bending test is used to test the strength of brittle materials. The test provides a measure called the transverse rupture strength for these materials.
Work hardening is the result of A. increase in dislocation density upon deformation B. absence of slip systems C. presence of carbon atoms at the edge dislocations D. increase in grain boundary density
A. increase in dislocation density upon deformation
Which are the most important criteria for the materials selection process of a beverage can? (Select only 2) A. loading conditions B. material availability C. price and scalability (mass production compatibility) D. number of manufacturing operations E. recyclability F. corrosion resistance & reactivity with the beverage
A. loading conditions F. corrosion resistance & reactivity with the beverage
What happens to an elastomer when it is below its glass transition temperature?
An elastomer is hard and brittle below its Tg.
The sample on the right failed from A. ductile fracture under biaxial tension B. ductile fracture under uniaxial tension C. brittle fracture under tension D. transgranular fracture E. none of the above
B. ductile fracture under uniaxial tension
What happens to BCC metals (iron) when temperature is lowered?
BCC metals (iron) experiences sharp drop in impact energy absorbed when temperature is lowered.
Is Bainite a microstructure or phase morphology?
Bainite is a morphology. However, you can have two samples with different microstructures.
What is difference between a microstructure or phase morphology? Is Bainite a microstructure or phase morphology.
Bainite is a morphology. However, you can have two samples with different microstructures.
What is the complicating factor that occurs in a compression test?
Barreling of the test specimen due to friction at the interfaces with the testing machine platens.
Why cannot a direct conversion be made between the ductility measures of elongation and reduction in area using the assumption of constant volume?
Because of necking that occurs in the test specimen.
What can you say about the mechanical properties of material A shown in the plot below?
Brittle
In a peritectic reaction, on cooling A. liquid reacts to form two solid phases B. a solid phase reacts to form two different solid phases C. a solid phase and a liquid react to form a solid D. a solid phase reacts to form a liquid and a different solid phase
C. a solid phase and a liquid react to form a solid
Solid solutions have higher yield strength than corresponding pure metals because A. they have larger grains B. they contain more dislocations C. dislocations are more difficult to move D. dislocations cause work hardening
C. dislocations are more difficult to move
The fracture surface morphology on the right represents A. ductile fracture B. intergranular fracture C. transgranular fracture D. none of the above
C. transgranular fracture
What is the chemical formula of ethylene, the monomer for polyethylene?
C2H4
Correlation between wear, fracture toughness and ductility?
Case hardening hardens the surface and prevents cracks from growing
Which factors affect hardenability?
Composition of steel and the process of manufacturing Quenching media and method of quenching Size of grains (fine-grained steels have lower hardenability) Size and shape of the piece Presence of non-metallic inclusions and undissolved carbide
What kind of bond is in the polymer backbone?
Covalent bond
________is a phenomenon that having small voids during the plastic deformation on polymers which is perpendicular to uniaxial tensile stress direction.
Crazing
Ductile fracture process does not involve the following A. cavity formation B. crack formation and propagation C. crack changes direction to 45° D. crack propagates through grains (transgranular fracture)
D. crack propagates through grains (transgranular fracture)
The fatigue strength can be increased by A. rougher specimen surface B. softer specimen surface C. under chemical corrosion D. reducing stress concentration in structure design
D. reducing stress concentration in structure design
How are a polymer's properties affected when it takes on a crystalline structure?
Density, stiffness, and melting temperature increase.
Why are different hardness tests and scales required?
Different hardness tests and scales are required because different materials possess widely differing hardnesses. A test whose measuring range is suited to very hard materials is not sensitive for testing very soft materials.
What is the most common fiber material in fiber-reinforced plastics?
E-glass
Elastomers and thermosetting polymers are both cross- linked. Why are their properties so different?
Elastomers are lightly cross-linked, whereas thermosets are highly cross-linked. Light cross-linking allows extensibility; a highly cross-linked structure makes the polymer rigid.
Is there a correlation between hardness and tensile strength for steel? How about wear, fracture toughness and ductility?
Empirical relationship. Tensile strength can have an empirical relationship to hardness of steel. Case hardening hardens the surface and prevents cracks from growing
Correlation between hardness & tensile strength?
Empirical relationship. Tensile strength can have an empirical relationship to hardness of steel. (Review Hardness Testing Handout)
What is the difference between engineering stress and true stress in a tensile test?
Engineering stress divides the load (force) on the test specimen by the original area; while true stress divides the load by the instantaneous area which decreases as the specimen stretches
Which crystal structure is most likely not to exhibit ductile to brittle behavior as the temperature is lowered?
FCC
What happens to FCC metals at low temperatures?
FCC metals (Cu,Ni) remain ductile at low temperatures
Name some of the important applications of FRPs.
FRPs are used in modern aircraft as skin parts, automobile body panels, printed circuit boards, tennis rackets, boat hulls, and a variety of other items.
True or false: Amorphous is a crystalline structure.
False
True or false: Material properties are dependent on elemental composition only and not microstructure.
False
Do all crystalline metals become brittle at low temperature?
False (not FCC)
True or false: All crystalline metals become brittle at very low temperature (~10°K).
False (not FCC)
True or false: A stage of a process that relief of some of the internal strain energy of a previously cold-worked metal is called recrystallization.
False: A stage of a process that relief of some of the internal strain energy of a previously cold-worked metal is called annealing and recovery.
True or false: Decreasing the grain diameter increases the DBTT.
False: Decreasing the grain diameter decreases the DBTT.
True or false: Eutectoid reaction is a reaction wherein, upon cooling, a liquid phase transforms isothermally and reversibly into two new solid phases that are intimately mixed.
False: Eutectoid reaction is a reaction wherein, upon cooling, a solid phase transforms isothermally and reversibly into two new solid phases that are intimately mixed.
True or false: Cementite is a Body-Centered Cubic iron.
False: Ferrit is a Body-Centered Cubic Iron
An alloy has a composition of 60%B. The microstructure after slow cooling from liquid to room temperature can be described by A). Fig. (a) B). Fig. (b) C). Fig. (c)
Fig. (a)
Why are fillers added to a polymer?
Fillers are added to increase strength or simply to reduce the cost of the polymer.
State Hooke's Law
Hooke's Law defines the stress-strain relationship for an elastic material: sigma = E*epsilon, where E = a constant of proportionality called the modulus of elasticity
How do we define hypo-/hypereutectoid compositions?
Hypoeutectoid steels contain less than 0.77% C, and hypereutectoid steels contain more than 0.77% C.
At below what statements are NOT true for Recrystallization? I. The smaller the deformation, the lower the recrystallization temperature. II. The higher the temperature, the less time required for recrystallization. III. The greater the degree of deformation, the smaller the recrystallized grains. IV. The larger the original grain size, the less amount of deformation that is required to produce equivalent temperature. V. Recrystallization temperature increases with impurity of metals.
I, II
Which statement/s is/are TRUE about weaknesses of optical microscopy techniques? I. Rarefaction of light through lenses can scatter light and reduce image quality. II. Sometimes the electron beam is not focused well by electromagnetic lenses. III. Magnification is limited to light intensity. IV. Only I and III. V. All the above.
I, II, III
At below, what statement/s is/are true for Endurance Limit or Fatigue Limit? I. Certain materials, primarily Body Centered Cubic steels can have Endurance Limit or Fatigue Limit II. Stainless Steel materials can have Endurance Limit or Fatigue Limit III. Austenite low carbon steels can have Endurance Limit or Fatigue Limit IV. FCC structure materials can have Endurance Limit or Fatigue Limit V. Infinite life for Endurance limit is usually defined at 5 x 108
I, II, III, and V
What statements are true about hardness numbers may correlate? I. Tensile Strength II. Wear Resistance III. Ductility IV. Young's Modulus
I, II, and III
Which metals have endurance limit vs. fatigue limit?
I. Certain materials, primarily Body Centered Cubic steels can have Endurance Limit or Fatigue Limit II. Stainless Steel materials can have Endurance Limit or Fatigue Limit III. Austenite low carbon steels can have Endurance Limit or Fatigue Limit
Which of the following process can increase the yield strength of steel? I. Tempering II. Hot working III. Adding alloying elements IV. Quenching
III and IV
Rank the following in ascending (lowest to highest) order of their hardness (and tensile strength). I. Bainite II. Martensite III. Tempered Martensite IV. Course Pearlite
IV, I, III, II
What is grain growth in annealing?
If annealing is allowed to continue once recrystallization has completed, then grain growth (the third stage) occurs. In grain growth, the micro structure starts to coarsen and may cause the metal to lose a substantial part of its original strength. This can however be regained with hardening.
How does the change in cross-sectional area of a test specimen in a compression test differ from its counterpart in a tensile test specimen?
In a compression test, the specimen cross-sectional are increases as the test progresses; while in a tensile test, the cross-sectional area decreases.
What is eutectic/eutectoid reaction?
In this chapter, we will concentrate on a solidification transformation by which a liquid freezes to simultaneously form two solid phases. This will be called a eutectic reaction and is of particular importance in cast irons and many aluminum alloys. In the next chapter, we will discuss the eutectoid reaction, by which one solid phase reacts to simultaneously form two different solid phases; this reaction is key in the control of properties of steels.
Why would you want to temper?
Introduce ductility back into part Tempering is a heat treatment technique applied to ferrous alloys, such as steel or cast iron, to achieve greater toughness by decreasing the hardness of the alloy. The reduction in hardness is usually accompanied by an increase in ductility, thereby decreasing the brittleness of the metal. Tempering is usually performed after quenching, which is rapid cooling of the metal to put it in its hardest state. Tempering is accomplished by controlled heating of the quenched work-piece to a temperature below its "lower critical temperature".
What is the basic difference between low density and high density polyethylene?
LDPE has a branched structure and is amorphous. HDPE is linear and highly crystalline. These differences account for HDPE higher density, stiffness, and melting point
FATIGUE: Endurance limit, S-N curve, which materials do not exhibit an endurance limit?
Many non-ferrous metals and alloys, such as aluminum, magnesium, and copper alloys, do not exhibit well-defined endurance limits. These materials instead display a continuously decreasing S-N response
What is the result of "Rapid Quenched Steel" after Austenite?
Martensite
Which one of the following will have a highest hardness value? a) Annealed brass b) Medium carbon steel austenitized at 850 C and slow cooled c) Medium carbon steel quenched and tempered at 400 C d) Medium carbon steel austenitized and quenched in water e) Impossible to tell
Medium carbon steel austenitized and quenched in water
Name the three basic categories of composite materials
Metal matrix composites (MMCs), ceramic matrix composites (CMCs), and polymer matrix composites (PMCs).
Are mechanical properties independent from microstructure?
NO! Mechanical properties are directly related to the microstructure of the material. Example: Same steel but different amount of coldworking (Higher tensile strength for coldworked material.)
Are mechanical properties independent from microstructure?
NO! Mechanical properties are directly related to the microstructure of the material. Example: Same steel but different amount of coldworking (Higher tensile strength for coldworked material.)
Does any polymer ever become 100% crystalline?
No
Do thermosets exhibit viscous behavior?
No. Thermosets "set" after curing and form a solid (i.e carbon composite)
Do thermosets exhibit viscous behavior?
No. Thermosets "set" after curing and form a solid (i.e carbon composite) They will exhibit viscoelastic behavior (strain/load rate dependent behavior)
Which of the following do you believe would characterize a hot-worked steel part in comparison to a coldworked part? I. Bainite II. Martensite III. Tempered Martensite IV. Course Pearlite
None of the above
Is heat treating reversible?
Once you start forming Pearlite, Bainite or Martensite, you are committed to the process.
The nylons are members of which polymer group?
Polyamides
What is the primary polymer ingredient in natural rubber?
Polyisoprene
What is hardenability?
Property of the material to harden in a desired direction
What does coldworking accomplish?
Pros and Cons of Coldworking: Increased strength and toughness Decreased ductility BETTER SURFACE FINISH
How does grain size affect DBTT?
Smaller grain size decreases DBTT
Is there a direct correlation between the grain size and DBTT?
Smaller grain size decreases DBTT
What is work hardening?
Strain hardening is the increase in strength that occurs in metals when they are strained
What is tempering? Which microstructures are formed when tempering steel
Tempering produces an overall compressive stress on the surface of glass. Thus, even if the glass surface reacts with water vapor, the cracks do not grow since the overall stress at the surface is compressive. If we create a flaw that will penetrate the compressive stress region on the surface, tempered glass will shatter. Tempered (Bainite & Pearlite)
How does recover in annelaing work?
The first stage is recovery, and it results in softening of the metal through removal of primarily linear defects called dislocations and the internal stresses they cause. Recovery occurs at the lower temperature stage of all annealing processes and before the appearance of new strain free grains. The grain size and shape do not change.
Define the recrystallization temperature for a metal.
The recrystallization temperature is the temperature at which a metal recrystallizes (forms new grains) rather than work hardens when deformed.
What is recrystallization in annealing?
The second stage is recrystallization, where new strain-free grains nucleate and grow to replace those deformed by internal stresses.
Define tensile strength of a material
The tensile strength is the maximum load experienced during the tensile test divided by the original area.
What are the three stages of the annelaing process?
The three stages of the annealing process that proceed as the temperature of the material is increased are: recovery, recrystallization, and grain growth.
Describe the difference between endurance limit vs. fatigue limit?
The very basic difference between fatigue and endurance limit is that the endurance limit has cycle number mentioned with it. We can look at it from the literal meaning of those words. Fatigue limit is that load limit below which material gains infinite life. Endurance limit is that load at which the material sustained defined number of cycles (Usually 10e7 cycles)
Define yield strength of a material
The yield strength is the stress at which the material begins to plastically deform. It is usually measured as the .2% offset value - the point at which the stress-strain for the material intersects a line which is offset from the elastic region of the stress-strain curve by 0.2%.
How do the properties of thermosetting polymers differ from those of thermoplastics?
Thermosets are more rigid, brittle, capable of higher service temperatures, and cannot be remelted.
Do thermosets exhibit viscoelastic behavior?
They will exhibit viscoelastic behavior (strain/load rate dependent behavior)
How can you achieve different microstructures in the same morphology?
Time and temperature are the deciding factors (Rate of cooling). Fast quenching produces smaller grains.
What is the dilemma between design and manufacturing in terms of mechanical properties?
To achieve design function and quality, the material must be strong; for ease of manufacturing, the material should not be strong, in general.
Purpose of minor load in hardness testing?
To remove slack from the machine. A perfect hardness tester will have an infinite stiffness however this is not possible.
What is the purpose of minor load during hardness testing?
To remove slack from the machine. A perfect hardness tester will have an infinite stiffness however this is not possible.
True or false: During the hardness test, minor load established reference depth and removes slack from machine.
True
True or false: For an alloy system displaying a eutectoid, an alloy for which the concentration of solute is less than the eutectoid composition is called Hypoeutectoid alloy
True
True or false: There is a good correlation between Brinell hardness and tensile strength for steel.
True
The difference between the stress-strain behavior of a ductile metal and a thermoplastic polymer (T> Tg) is:
True stress always increases with true strain for metals but does not for polymer
What is viscoelasticity, as a material property?
Viscoelasticity refers to the property most commonly exhibited by polymers that defines the strain of the material as a function of stress and temperature over time. It is a combination of viscosity and elasticity.
Define viscosity of a fluid
Viscosity is the resistance to flow of a fluid material; the thicker the fluid, the greater the viscosity.
In what case does the strength coefficient have the same value as the yield strength?
When the material does not strain harden.
Cemented carbides are what class of composites?
Yes; although the cemented carbide industry does not generally think of cemented carbides as cermets, they fit within the definition.
What does the term advanced composites mean?
a PMC in which carbon, Kevlar, or boron fibers are used as the reinforcing material
What is a cermet?
a composite material consisting of a ceramic and a metal. In the text, it is defined as a composite consisting of ceramic grains imbedded in a metallic matrix.
What is a polymer?
a compound that consists of long-chain molecules. The molecules consist of repeating units, called mers, connected end to end.
What is a hybrid composite?
a fiber-reinforced PMC in which two or more fibers materials are combined in the FRP.
What is a composite material?
a materials system consisting of two or more distinct phases whose combination results in properties that differ from those of its constituents.
What is unique about the polymer cellulose?
a polymer that grows in nature. Wood fiber contains about 50% cellulose and cotton fiber is about 95% cellulose
What is a terpolymer?
a polymer with three different mer types. An example is ABS (acrylonitrile-butadiene-styrene) plastic.
The purpose of drilling a pilot hole is to ... a) Ease the drill bit entry into the work piece and prevent drill bit drift and slipping offcenter. b) Make holes faster than you could with a conventional drill bit. c) Provide a surface upon which to add threads. d) Mark the center of the part. e) a, b, and c
a) Ease the drill bit entry into the work piece and prevent drill bit drift and slipping offcenter.
What are the safety concerns in the 361 Lab?
all above the above
Which of the following will affect the hardenability of steel? I. Higher Yield Strength II. Better Surface Finish III. Greater Hardness IV. Less Ductility
all of the above
Which of the following will influence the actual hardness of an alloy steel? a) Fractional amount of proeutectic and eutectic phases b) Carbon level c) Pearlite colony size (width of finite Fe3C layers) d) level of temper
all of the above
What does amorphous mean? Is it a crystal structure?
amorphous is not a crystal structure
What is the rule of mixtures?
applies to certain properties of composite materials; it states that the property value is a weighted average of the property values of the components, the weighting being by proportions of the components in the composite.
Give some examples of commercial products which are laminar composite structures.
automotive tires, honeycomb sandwich structures, fiber reinforced polymer structures such as boat hulls, plywood, printed circuit boards, snow skis made from fiber reinforced polymers, and windshield glass.
41. What process cannot be done by a lathe? a) Reducing the diameter of the workpiece b) Adding threads to the outside of a workpiece c) Adding a chamfer to the end of a square cross section bar of a workpiece d) Boring out a hole in the workpiece e) All of the above can be done with a lathe
c) Adding a chamfer to the end of a square cross section bar of a workpiece
Lattice types for cementide, ferrite, austenite, martensite?
cementite: orthorhombic alpha-Iron (ferrite): Ferrite is a body-centered cubic (BCC, alpha iron) form of iron. y-Iron (austentite): Iron transforms from a face-centered cubic (FCC) structure -- called the gamma phase, or austenite martensite: Martensite is a body-centered tetragonal form of iron in which some carbon is dissolved. Martensite forms during quenching, when the face centered cubic lattice of austenite is distored into the body centered tetragonal structure without the loss of its contained carbon atoms into cementite and ferrite.
What are the lattice types for cementite, α-Iron (ferrite), γ-Iron (austenite), martensite?
cementite: orthorhombic alpha-Iron (ferrite): Ferrite is a body-centered cubic (BCC, alpha iron) form of iron. y-Iron (austentite): Iron transforms from a face-centered cubic (FCC) structure -- called the gamma phase, or austenite martensite: Martensite is a body-centered tetragonal form of iron in which some carbon is dissolved. Martensite forms during quenching, when the face centered cubic lattice of austenite is distored into the body centered tetragonal structure without the loss of its contained carbon atoms into cementite and ferrite.
During the metal cutting process, there is a self-excited vibration occur, which is called________;
chatter
What is a plasticizer?
chemical added to the polymer to make it softer and more flexible. It is often added to improve the polymer's flow characteristics for shaping.
What kind of bonding do polymers have along the backbone and between the chains?
covalent bonding
40. What is the best way to measure specimen strain during a tensile test? a) An extensometer b) Determine it from cross head displacement and time measurements c) Determine it after specimen fracture providing fracture is within the gage strength. d) Either a or b e) From the load versus time data
d) Either a or b
All of the followings are true regarding to our machining lab, except which one? a) The oblique model machining is a three-force cutting process. b) Cutting fluid aids in the cooling of the tool c) Primary cutting force Fc is the largest force and accounts for 99%. d) Feed force is a thrust or radial force acting perpendicular to the machined surface. e) Cutting sped decreases as DOC or feed increases.
d) Feed force is a thrust or radial force acting perpendicular to the machined surface.
Which polymer exhibited crazing? Why is crazing a useful property?
polystyrene
What should not affect the actual hardness of an alloy steel? a) Fractional amount of proeutectic and eutectic phases b) Carbon level c) Pearlite colony size (width of finite Fe3C layers) d) Level of temper e) None of the above (all will influence hardness)
e) None of the above (all will influence hardness)
What can NOT be obtained from tensile test data?
fracture toughness
Identify some of the important properties of fiber- reinforced plastic composite materials
high strength-to-weight ratio, high modulus-to-weight ratio, low density, good fatigue strength, good corrosion resistance, and low thermal expansion for many FRPs.
An increase in the carbon content of plain carbon steel generally does what to the DBTT?
increases it
What are some of the weaknesses of ceramics that might be corrected in fiber-reinforced ceramic matrix composites?
low tensile strength, poor toughness, and susceptibility to thermal cracking.
How do the properties of polymers compare with those of metals?
lower strength, hardness, stiffness, density, and temperature resistance compared to metals. In addition, are low in electrical and thermal conductivity
In addition to fillers and plasticizers, what are some other additives used with polymers?
lubricants - to reduce friction and improve flow; flame retardents; colorants; cross-linking agents, antioxidants, and ultraviolet light absorbers.
What are the units of strain and strain rate?
m/m and m/m/s
The units for strain rate are:
m/m/s
What type of microstructure is formed when you quench steel rapidly?
martensite
What does amorphous mean? Is it a crystal structure?
non crystalline
What is fatigue life?
number of cycles to fail at a specified stress level
What happens to resistivity with an increase in temperature, deformation, and alloying
resistivity increases
Describe the difference in mechanical properties as a function of temperature between a highly crystalline thermoplastic and an amorphous thermoplastic.
retains rigidity during heating until just before its Tm is reached. An amorphous TP shows a significant drop in deformation resistance at its Tg as temperature is raised; it becomes increasingly like a liquid as temperature continues to increase.
During cold working, at certain value of thickness dimension reduction there was some degree of increase at the thickness after the rolling. That phenomenon is called ____________.
springback
What are the axis labels of a S-N curve?
stress vs cycles
What is fatigue strength?
stresss at which fracture occurs after a specified number of cycles
What are the three types of static stresses to which materials are subjected?
tensile, compressive, and shear
What does the degree of polymerization indicate?
the average number of mers or repeating units in the polymer molecule
What is meant by the term interface in the context of composite materials?
the boundary between the component phases in a composite material.
What is cross-linking in a polymer and what is its significance?
the formation of connections between the long-chain molecules in a polymer. It causes the polymer structure to be permanently altered. If the amount is low, the polymer is transformed into an elastomer; if it is significant, the polymer is transformed into a thermosetting polymer.
What does the term anisotropic mean?
the properties of a material vary depending on the direction in which they are measured.
What is hardness and how is it generally tested?
the resistance to indentation of a material. It is tested by pressing a hard object (sphere, diamond point) into the test material and measuring the size (depth, area) of the indentation.
Define the term tacticity as it applies to polymers.
the way the atoms or atom groups replacing H atoms in the molecule are arranged.
What is a whisker?
thin, hairlike crystal of very high strength.
When you heated/soaked the bolts for the heat treatment of the steel lab, what was the purpose of the austenitizing step?
to dissolve iron carbide (Fe3C)
Knurling is performed on a lathe, but it is not a metal cutting operation: (a) true or (b) false?
true
How are traditional composites distinguished from synthetic composites?
used for decades or centuries; some of them are obtained from sources in nature, such as wood. Synthetic composites are manufactured.
