MAT E Quizzes EXAM 2
Recall that, under standard conditions, the metalloid element Polonium exhibits the simple cubic crystal structure and is known to be brittle If a single crystal of Po is loaded in tension along the [001] axis of the crystal, which of the following candidate slip systems features a resolved shear stress of zero?
(001)[100] (001[010] (010)[100] (010)[001] (100)[010] (100)[001]
If a BCC single crystal is loaded along the [001] axis, which of the following slip systems is the least likely to experience slip?
(110)[1_ 11]
For a 1031 steel that is cooled relatively slowly to room temp, what is the expected weight fraction of cementite in the as-cooled microstructure?
.04 ( lever rule)
IF the surface energy of a magnesium oxide-nickel oxide solid solution is 1.21 J/m^2 and its elastic modulus is 211GPa, what is the maximum length of an internal elliptical flaw, in mm, if the ceramic part must survive an applied tensile stress of 59 MPa normal to the flaw?
.09mm
If the plain-carbon steel featured in the following micrograph was analyzed and found to contain proeutectoid ferrite(as the microconstituent that appears predominantly white), what is/are possible over carbon contents for the steel (picture on quiz 19, question11)
.10 wt%C .25 wt% C .45 wt% C
A cylindrical specimen of a metal alloy is stressed elastically in tension. The original diameter was 8mm and a force of 15,700N produces a reduction in diameter of 5x10^-3mm. Compute poisson's ratio for this allow if its modulus of elasticity is 140 GPa.
.28
Consider a metal alloy that melts at 1080C. What is the homologous temperature of this alloy, if it is equilibrated at 567C?
.62
What is the carbon content of a 1070 steel, in wt% C?
.7
If a steel containing 1.31 wt%C is cooled relatively slowly to room temp, what is the expected weight fraction of pearlite in the as-cooled microstructure?
.91
What is the maximum solutbility of carbon that is offered by the austenite phase at 800C?
1
Rank the following microstructures of steel in terms of their relative hardness, assuming they each feature the same overall composition an, as applicable, the same fractions of the phases present 1= highest hardness 6= lowest hardness -fine pearlite -coarse pearlite -tempered martensite -martensite -spheroidite -bainite
1- martensite 2- tempered martensite 3- bainite 4- fine pearlite 5- coarse pearlite 6- spheroidite
Rank the following microstructures of steel in terms of their relative ductility, assuming they each feature the same overall composition an, as applicable, the same fractions of the phases present 1=highest ductility 6=lowest ductility -fine pearlite -coarse pearlite -tempered martensite -martensite -spheroidite -bainite
1- spheroidite 2- coarse pearlite 3- fine pearlite 4- bainite 5- tempered martensite 6-martensite
Match the following temperature designations to their definition: 1. A3 2. Acm 3. A1 a- The temp at which ferrite begins to precipitate when hypereutectoid austenite is cooled relatively slowly b- The temp at which cementite begins to precipitate when hypereutectoid austenite is cooled relatively slowly c-The temp at which pearlite begins to form when steel in the form of austenite is cooled relatively slowly
1-a 2-b 3-c
Match each property/quality listed below to the tensile stress-strain curve that best demonstrates the property/quality: Picture: curve A is the steepest/ on top, followed by B, C and D being the shallowest 1. Lowest Hardness: 2. Lowest toughness 3. Most ductile 4. Most brittle 5. Highest tensile strength
1. D 2. A 3. D 4. A 5. A
WHich overall composition of steel is plausible for the IT diagram presented above? (Quiz 22, question 6)
1.13 wt%C
A cylindrical rod of metal allow is stressed elastically in tension, the original diameter was 11mm and a force of 52kN was applied. COmpute the diameter upon loading in millimeters, if the alloy has a modulus of elasticity of 142 GPa and a Poissons ratio of .28
10.988 (use poison's ratio to determine delta L)
Which material cold-works the fastest upon initial plastic deformation? 1040 Steel Brass Copper
1040 Steel
Imagine rapidly cooling austenite to 500C and holding it at this temp, how long does it take before the decomposition of austenite is complete?
10sec
A critical component for a mechanical system will be subjected to a .01Hz cyclical stress during operation The stress will fluctuate between a tensile load of 150MPa and a compressive load of -250MPa. The design calls for a survival confidence limit of 10% Approximately how long, in days, can the component be used before it must be replaced during maintenance?
11,574 days
What is the maximum temperature for which austenite is stable?
1493C
What is the maximum elastic service temp that a tungsten rod may experience if it supports a fixed tensile stress of 10MPA? (graph)
1500C
For an alumina specimen, what is the minimum stress at which failure is expected to occur in MPa if it features an elliptical surface scratch whose length is 2.43mm and whose tip radius is 190nm?
17.7
Imagine rapidly cooling austenite to 575C and holding it at this temp, How long does it take, before the decomposition of austenite begins to occur?
1sec
A 300mm long steel bar with a square cross section (25mm per edge) is pulled in tension with a load of 83,637N and experiences an axial elongation of .18mm. Assuming that the deformation is entirely elastic, calculate the elastic modulus of this steel in GPa.
223 GPa
If a tensile stress of 550 MPa is applied along the [110] direction of a Po single crystal, what is the resolves shear stress for the (010)[100] slip system?
275
The stress strain curve for a brass allow is provided below. The inset is a magnified view of the elastic regime of this stress strain response. What is the approximate elastic modulus of this brass, in units of psi? In picture: line crosses through point: (.005 (strain), 10x10^3psi), (.010, 20x10^3psi), (.015, 30x10^3psi), then starts to curve
2x10^6psi
If a steel cylindrical specimen is stressed nominally to 70MPa, what stress level exists at the tip of an elliptical surface flaw whose length is 5.3 microns and radius of curvature is 1074 nanometers?
311
A copper alloy cylinder that is 1.1 feet long with a diameter of 36.37inch is subjected to a tensile stress of 988psi along its length. Assuming this applied stress is purely elastic, calculate the diameter, in inches, of the cylinder under this load. For this alloy, the elastic modulus is 1,023,759psi and poisson's ratio is .31
36.36
Which of the following is a reasonable value for the yield stress (yield point) of a typical structural metal? .04 MPa 4MPa 400MPa 4000 MPa 4GPa 40GPa 400GPa
400 MPa
For the material in the previos question that yields at 200MPa, what is the maximum mass, in kg, that a cylindrical bar with diameter of 5.2cm can support without yielding? Recall that a mass of 1kg has weight of 9.81N
43,297kg (don't forget to use area not just diameter)
What is the expected as-cooled microstructure of a eutectoid steel that experiences the following cooling path: 1. cooled instantly from 800 to 450C 2. held at 450C for 10 seconds 3. Quenched to room temp
50% Bainite, 50% martensite
What is the expected as-cooled microstructure of a euectoid steel that experiences the following cooling path: 1. cooled instantly from 800C to 630C 2. helf at 630C for 10s 3. cooled to 400C and held for 200 seconds 4. Quenched to room temp
50% pearlite, 50% bainite
If a 1040 steel is cooled relatively slowly from 1000C, some of the gamma begins to decompose around _____C as it transforms into the ___________ phase. THe final microstructure with feature proeutectoid __________ and _________ as microconstituents after cooling below the eutectoid temp.
800 ferrite ferrite pearlite
Nickel is FCC under STP conditions and remains FCC upon heating until it melts at 1455C. If a Hastelloy X superalloy (FCC solid solution single crystal) is loaded to 206 MPa along its major axis, what is the resolved shear stress along the [011] direction on the (111_) plane?
84MPa
A specimen of a 4340 steel alloy has a plane-strain fracture toughness of 45 MPasqrtm It is known that the largest surface crack in a plate of this specimen is .82mm long. What is the maximum stress tensile normal to this crack that the specimen can tolerate without fracturing? Assume that the geometric parameter Y has a value of 1
892
A cylindrical rod of 316 stainless teel is stressed elastically in tension. The original diameter was 10mm and a force of 15kN was applied. Compute the diameter of the rod upon loading in millimeters.
9.997mm
What is the expected slip system for the simple cubic cystal structure?
<100>{100}
The crystal structure of an iron-carbon solid solution at 1500C is _______
BCC
The crystal structure of an iron-carbon solid solution at 600C is ______
BCC
Recalling that most brass for structural use is a single-phase alloy of Cu and Zn, what is the primary reason why brass is stronger than copper when comparing any two pieces of these materials that feature the same level of prior cold-working>
Brass leverages solution hardening
For the flawed and brittle specimen depicted below, which flaw is the least likely to propagate under the indicated tensile loading scenario?
C : vertical oval that goes with the stress
An aluminum metal rod is heated to 300C and upon equilibration at this temp, it features a diameter of 25mm. If a tensile force of 1kN is applied axially to this heated rod, what is the expected mechanical response? (aluminum melts at 660C) (graph)
Creep
This is the lowest-melting alkali metal, and therfore the most susceptible to creep deformation at room temp
Cs
A measure of a material's ability to deform plastically prior to failure:
Ductility
A cylindrical bar of annealed Ti-6Al-4V is loaded with 50,000 kg in tension. The bar is 3 meters long and has diameter of 38.10 mm. Determine whether this is an elastic loading condition or a plastic loading condition. (what must be ture about the stress and strain that the bar endures elastic loading?) From picture: .2% offset tensile yield strength: 825 MPa Tensile strength: 895MPa Tensile modulus of elasticity: 110 GPa Elongation in 50mm: 10%
Elastic
A quantity that is correlated with the bond strength of a material:
Elastic Modulus
A measure of a material's ability to absorb mechanical energy in the form of stretched bonds:
Elasticity
The crystal structure of an iron-carbon solid sollution at 1000C is _______
FCC
T/F : Four crystal-crystal phase changes are expected if this system is heated from 0 to 600C (graph in quiz 20, question 2)
False
T/F: All phase transformations proceed via a nucleation and growth mechanism
False
T/F: An elastic modulus of 500 MPa is a reasonable value for a structural metal
False
T/F: Coarsening refers to the scenario where, upon heating and/or annealing for sufficient time, the scale of a microstructure tends to reduce
False
T/F: Fast cooling rates tends to promote transformations that result in relatively course structures
False
T/F: For a system below is melting point, a glass configuration is the most energetically stable state that is possible, since it offers the lowest GIbbs free energy for all possible solid configurations
False
T/F: For a transformation that involves nucleation and growth of the product phase, the nucleation of all evolving phase particles must occur before they are allow to grow to consume the remaining colume of the system
False
T/F: For most materials, the formation of a glass from a liquid typically requires extremely slow cooling rates, thereby taking on the order of years or even centuries to produce
False
T/F: Nucleation and growth transformations are an exclusive transformation that is unique to metals
False
T/F: Small and sharp features on a metal specimen generally experience stress levels that are much lower than the nominal/macroscopic stress that is applied to the bulk specimen.
False
T/F: The gamma phase features the highest stability in the range of 0-510 (graph in quiz 20, question 2)
False
T/F: The transformation fo austenite to martensite only proceeds when austenite is held at temp for a long time at temps below 225C
False
T/F: When measured experimentally, most materials tend to exhibit the same exact temp value for both melting and freezing
False
T/F:A 10XX series steel is generally referred to as a stainless steel
False
T/F:All other factors the same, it is generally more difficult to form a fully martensitic microstructure for a hypoeutectoid steel compared to a hypereutectoid steel
False
T/F:Specimen containing iron and 4.12 wt% carbon is considered a steel.
False
The Fe-Fe3C phase diagram still serves as a decent foundation for understanding the thermodynamics of such systems, but often the relevant phase fields and transformation temps are changed by the alloying additions. Elements that expand the austenite phase field are called austenite stabilizers. Based on the data provided below, it appears that chromium acts a an austenite stabilizer when added to steels. True of False
False
To be "truly ductile", according to most design engineers, a metal must offer at least 5% or greater tensile plastic elongation.
False
A measure of a material's ability to withstand local deformation or wear. This value is correlated with the yield point
Hardness
Which of the following processes will not tend to significantly strengthen a typical pure metal?
Hot-working the pure metal Annealing the pure metal Melting then casting the pure metal decreasing the grain density increasing the avg grain size
The _____________ of a system dictates the rate and mechanisms of phase transformations, thereby dictating the microstructure that a system adopts for a given transformation path. Furthermore, this also dictates the time over which these microstructures tend to exist.
Kinetics
What microconstituents are expected to appear in the as-cooled microstructure of a eutectoid steel that experiences the following cooling path: 1. Held at 800C for 100 seconds 2. Quenched to room temp
Martensite
What microconstituents are expected to appear in the as-cooled microstructure of a eutectoid steel that experiences the following cooling path: 1. held at 800C for 100 seconds 2. Quenched to room temp
Martensite, Proeutectoid cementite
What is the expected microstructure if austenite is preserved to 600C, held there for 1000 seconds, and then quenched to room temp?
Pearlite
What microconstituents are expected to appear in the as-cooled microstructure of a eutectoid steel that experiences the following cooling path: 1. Held at 800C for 100 seconds 2. Quenched to room temp 3. Heated to 700C and held for 500 hours 4. Quenched to room temp
Spheroidite
For the factors/conditions listed, select those that tend to alleviate creep deformation for a metal sample with a random polycrystalline microstructure.
Substitute the metal for one with a higher melting point Decrease the applied stress on the metal part Apply an insulative (non-structural) ceramic coating to the part Switch to a single crystal or textured polycrystalline microstructure
The exact temp at which a transformation proceeds, or the exact rate at which a specimen's temperature is changed can influence what aspects of a phase transformation?
The identity of the phase(s) that form THe rate of transformation The amount of time required for the transformation to actually commence The elasped time of the transformation itself The microstructures that form The properties of the material after transformation
Even though metal parts are often intended to endure only elastic (reversible strain, they should generally offer at least some ductility to account for local stresses in a specimen that may exceed the metal's yield stress
True
T/F: At 525C, the solid solution phase is a more stable configuration compared to the crystalline compound. (graph in quiz 20 question 3)
True
T/F: Nucleation and growth transformations are commonly referred to as diffusion-controlled transformations
True
T/F: The melting point of the system is approximately 575C (graph in quiz 20, question 3)
True
T/F: The shape, position, and identities of "microstructure fields" on the IT curves for a steel depends on the overall composition of the steel. In other words, the austenite decomposition kinetics and as-cooled microstructure possibilities for a steel depend on the overall composition of the steel
True
T/F: gray iron is a microstructure that tends to result when a cast iron of appropriate composition is cooled fairly quickly
True
T/F:Ductile specimens are less affected by poor quality surface finish, since the propagation of microscopic flaws as cracks is generally less likely compared to plastic deformation
True
The stress at which dislocation motion and/or twinning is assumed to become the dominant response upon loading a material:
Yield Point
Metals with FCC packing like aluminum are often more ductile than metals with HCP packing like magnesium because the FCC structure has:
a higher number of slip systems than HCP
Metals with HCP packing like magnesium are often less ductile than metals with FCC packing like aluminum because the HCP structure has:
a lower number of slip systems than FCC
A ___________ pearlite structure is produced when austenite is allowed to transform into pearlite at a temp that is relatively ________ to the eutectoid temp, and such a structure will be relatively soft and ductile when compared to other fully pearlitic structural possibilities
coarse, close to
The formation of pearlite, spheroidite, and bainite are examples of _______________ transformation, whereas the formation of martensite is referred to as a __________ transformation
diffusion controlled, diffusionless
COmpletely brittle failure occurs while loading is _______
elastic
______________ strain is defined as the instantaneous dimension change a material exhibits along an axis of interest, divided by the original dimension of the material along that axis.
engineering
_______________ stress is defined as the instantaneous force applied to a material divided by the original cross sectional area over which the stress acts.
engineering
_______ is a material property that pertains to local resistance to plastic deformation, such as scratching or denting. It is often measured by poking a material with a very hard tip (like diamond) and measuring the size and depth of the resulting crater that forms
hardness
Hooke's Law applies in the _________ regime of the stress-s strain curve for materials that exhibit a linear elastic response
initial
Is it possible to form a fully martensitic microstructure if a eutectoid steel is held at some constant temp between 350 and 650C for more than 1000 seconds?
no
For a temp near but below the equilibrium transformation temp, the system is ___________ motivated to change phase, relative to lower temps In other words, the GIbbs free energy change upon transformation at T is ______ compared to the transformation proceeding that lower temps Therefore, the nucleation rate of the evolving phase at T is _______ relative to lower temps
not highly, low, low
The Fe-Fe3C system features _____ eutectic point(s) and ______ eutectoid point(s)
one, one
For most materials, a tensile stress results in a __________ strain, whereas a compressive stress results in a _________ strain
positive, negative
For a temp near but below equilibrium transformation temp, existing instances of the evolving phase are _______ to increase in size. In other words, diffusion is ______ at T, relative to lower temps Therefore, the growth rate is ______ at T, relative to lower temps
quick, fast, high
Macroscopic stress applied to a real specimen is magnified at sharp features, especially at microscopic internal voids, as well as surface scratches
sharp
Which of the following materials offers a yield point of around 200 MPa? (from picture)
structural steel (mild steel)
At best, the ____________ of a system tells us the phase(s) that are stable as well as their composition(s) and fraction(s), for a given set of state variables such as temperature, pressure, and overall composition.
thermodynamics
