Intro to material science- Chapter 6

During a tensile test, a dogbone shaped specimen is used because 

the dogbone shape helps confine deformation locations in a specimen, making the resulting tensile test data more reproducible

engineering stress

(sigma) it is force (instantaneous load applied perpendicular to the specimen cross section over the original cross-sectional area

engineering strain 

(epsilon) is the change in length from the original length l0 all over the original length. think back to sh3

shear (stress)

a force applied so as to cause or tend to cause two adjacent parts of the same body to slide relative to each other in a direction parallel to their plane of contact.

for shear stress how is the force imposed in relation to the faces

the force is imposed parallel to the upper and lower faces. Definition is this force over the initial area

torsion

is a varitation of pure shear where a structural member is twisted; torsional forces produce a rotational motion about the longitudinal axis of one end of the member realtive to the other end.

elastic deformation

deformation that is non-permanent- that is, totally recovered upon release of an applied stress

modulus of elasticity (E)

the ratio of stress to strain when deformation is totally elastic; also a measure of the stiffness of a material

the greater the modulus of elasticity then the stiffer or more flexible the material?

the stiffer

rank from smallest to greatest modulus of elasticity: titanium, carbon steel and aluminum

aluminum, titanium, carbon steel

the modulus of elasticity is a constant value when the engineering stress-strain relationship is what

linear

the magnitude of the modulus of elasticity is a measure of the resistance to what

to separation of adjacent atoms- interatomic bonding forces.

the stronger the atomic bones the less than or greater the modulus of elasticity

greater

for metals and metal alloys as temperature increases what happens to the modulus of elasticity

it decreases

anelastic deformation

time-dependent elastic (nonpermanent) deformation

for metals the anelastic component is normally small or large?

is normally small and is often neglected

anelasticity is a result of

atomic interactions

poisson’s ratio

for elastic deformation, the negative ratio of lateral and axial strains that result from an applied axial stress

plastic deformation

deformation that is permanent of nonrecoverable after releases of the applied load. It is accompanied by permanent atomic displacements.

yielding

the start of plastic deformation

proportional limit 

the point on a stress-strain curve at which the straight-line proportionality between stress and strain ceases.

yield strength (sigma y)

the stress required to produce a very slight yet specified amount of plastic strain; a strain offset of 0.002 is commonly used

tensile strength (TS)

the maximum engineering stress, in tension, that may be sustained without fracture. Often termed ultimate (tensile) strength.

ductility 

a measure of a materials ability to undergo appreciable plastic deformation before fracture; it may be expressed as percent elongation or percent reduction in area from a tensile test

resilience

the capacity of a material to absorb energy when it is elastically deformed

toughness

a mechanical characteristic that may be expressed in three contexts: (1) the measure of a materials resistance to fracture when a crack is present (2) the ability of a material to absorb energy and plastically deform before fracturing and (3) the total area under the materials tensile engineering stress-strain curve taken to fracture

the proportional limit is where blank elasticity ends, and the blank is where small plastic deformation occurs

linear elasticity and small plastic deformation occurs

metals exhibiting the yield point phenomenon have the yield strength reported as

the lower yield point value

viscoelastic deformation

deformation partially or completely recovers over time

fracture toughness

a materials resistance to fracture with a crack present

notch toughness

a materials ability to absorb energy and plastically deform at a high strain rate with stress raiser present

static toughness

the area under an engineering stress-strain curve up to fracture at a low strain rate

true stress

the instantaneous applied load divided by the instantaneous cross-sectional area of a specimen

true strain

the natural logarithm of the ratio of instantons gauge length to original gauge length of a specimen being deformed by a uniaxial force.

without load and cross-sectional dimensions calculated at each point engineering stress can be converted to true stress blank

only before necking begins, additionally, no volume change can occur for valid calculation conversion

during a stress-strain test, after the load is released, a portion of the specimen’s blank is recovered

elastic strain

while some bonds may break or change during plastic deformation the materials initial modulus of elasticity will or will not? be altered significantly without changes to the temperature or chemical structure

will not be

because the unloading point is typically higher than the initial yield strength, plastic deformation can cause the specimen to become relatively stronger through blank

strain hardening

metals may experience plastic deformation under the influence of applied compressive, shear and what loads?

torsional

compressive stress causes an increase in what?. what does this mean for force and stress

increase in cross-sectional area. Thus a larger applied force is needed to continue deformation as cross-sectional area increases. the larger the force will mean a larger stress for compression

does compressive stress cause necking?

no it does not, the applied force can continue to increase with strain until fracture

hardness

the measure of a materials resistance to deformation by surface indentation or by abrasion

the softer the materialthe larger and deeper the indentation and lower the hardness index number. 

Rockwell tests:

indenters include spherical and hardened steel balls having diameters of 1/16, 1/8, ¼ and ½ in. a hardness number is determined by the difference in depth of penetration resulting from the application of an initial minor load followed by a large major load

Brinell tests

a hard spherical indenter is forced into the surface of the metal to be tested. load is maintained constant for a specified time

for the brinell hardness test, specimen thickness should be at least blank times the indentation depth

ten

In an isomorphous alloy, adding small amounts of a second component will blank the tensile strength

increase

copper has a low melting point than nickel. Adding a small amount of copper to nickel will what the tensile strength for the alloy

increase tensile strength

in an isomorphous alloy, adding large amounts of a second component will what?

increase the decrease the tensile strength; The tensile strength for either pure component is less than the tensile strength for combining the components. When adding a second component, the alloy's tensile strength starts at the first component's tensile strength, increases to a maximum for the two-component system, then decreases to the other component's tensile strength.

for an alloy, such as a copper-nickel system if the tensile strength is at a maximum that means the ductility is at a what

minimum; Tensile strength and ductility tend to move in opposite directions as composition changes. So, a maximum in one property is a minimum in the other property.

solvus line

the locus of points on a phase diagram representing the limit of solid solubility as a function of temperature; separates a single solid phase region from a solid1+solid2 phase region, the solvus line determines one solids solubility in another

solidus line

on a phase diagram, the locus of points at which solidification is complete upon equilibrium colling, or at which melting begins upon equilibrium heating.; separates a single solid phase region from a liquid+sold phase region, during cooling, the last remaining liquid turns into solid.

liquidus line

on a binary phase diagram, the line or boundary separating liquid and liquid + solid phase regions. For an alloy, the liquidus temperature is the temperature at which a solid phase first forms under conditions of equilibrium cooling.; separates a liquid phase region from a liquid+solid phase region; during cooling, the first solid forms when crossing the liquidus line

eutectic reaction

a reaction in which, upon cooling, a liquid phase transforms isothermally and reversibly into two intimately mixed solid phases

any liquid is converted to two solids when crossing what line?

the eutetic isotherm

eutetic structure

a two-phase microstructure resulting from the solidification of a liquid having the eutectic composition; the phases exist as lamellae that alternate with one another

eutectic phase

one of the two phases found in the eutectic structure

primary phase

a phase that exists in addition to the eutectic structure

microconstituent

an element of the microstructure that has an identifiable and characteristic structure. it may consist of more than one phase, such as with pearlite.

blank forms when the composition is cooled below the liquidus line. what are the two phases in the region 

solid alpha. the two phases in the region are solid alpha and liquid

when crossing the solidus line what solidifies into what? what is the only phase present

the remaining liquid solidifies into alpha. the only phase present is solid alpha

with continued cooling, the what will continue to grow larger and having a changing composition because?

beta. and its because the composition is getting further away from the alpha phase boundary

when crossing eutectic line, liquid transforms into a microstructure that is

layered; eutectic microstructure is made of two sold phases in alternating layers

can the primary alpha have a composition change after a eutectic reaction

no, because the newly formed alpha is only involved in the eutectic structure

just after a eutectic reaction, the eutectic phase fraction is equal to the what fraction just before the reaction

liquid phase; in an eutectic reaction, all of the liquid phase converts to the eutectic microstructure so We=WL

After the eutectic reaction, the total Beta phase fraction is equal to the what phase fraction

eutectic beta

terminal solid solution

a solid solution that exists over a composition range extending to either composition extreme of a binary phase diagram

intermediate solid solution

a solid solution or phase having a composition range that does not extend to either of the pure components of the system

intermetallic compound

a compound of two metals that has a distinct chemical formula. On a phase diagram it appears as an intermediate phase that exists over a very narrow range of compositions.

a single intermetallic compound phase exists over

a single composition value; the number of atoms making up the compound cannot be altered without changing the compound or adding an additional phase