Unit 2 Ch.6,7,8

Percent elongation

((Final length)-(original(gauge) length)/original (gauge) length

Shear modulus

(G) the slope of the linear region of the shear stress-strain curve

Yield point

(Yield strength) the value of stress of which there is significant/noticeable strain w/o any increase in stress

Modulus of elasticity

(Young's modulus) is a measure of the stiffness of a metal which is determined by the straight line portion of the stress vs strain curve/diagram

Design properties of metals

-strength -stiffness -ductility -toughness -hardness

6 types of stress

1) tension 2) compression 3) bearing 4) flexural/bending 5) shear 6) torsional

Grain size reduction, solid solution alloying, strain hardening

3 mechanisms to make metals harder by restricting dislocation motion

File

A ____________ is a good way to tell a metals hardness (HR_c 55-65)

Cold working

A form of strain hardening in which the temperature at which deformation takes place is "cold" relative to the absolute melting temperature of the metal.

Highly ductile

A high percent elongation indicates a _________________ metal

Toughness

A measure of the energy absorbed during the fracture of a material

Brittle

A metal thwart experiences very little to no plastic deformation upon fracture

Strain hardening

A phenomenon by which a ductile metal becomes harder and stronger as it is plastically deformed

Temperature

A significant variable to a metals toughness is ______________.

Torsion

A variation of shear stress on which a structural member is twisted

Strain hardening

AKA cold working(cold rolled) or work hardening

Grain growth

After recrystallization is complete, the strain-free grains will continue to grow if the metal specimen is left at the elevated temperature

Solid solution alloying

Alloying of metals with impurity atoms (substitutional or interstitial)

Modulus of elasticity

Also known as Young's modulus. Is is = stress/strain which is a version of hookes law

Safe stress

Also known as working stress is used instead of design stress and is based on the yield strength of the material and is defined as the yield strength divided by the factor of safety

Working stress

Another name for safe stress which is based on the yield strength of the material and is defined as the yield strength divided by a factor of safety

Fracture toughness

Another name for toughness which is indicative of a materials resistance to fracture when a crack is present

Plastic deformation

As materials are deformed past elastic deformation, the stress is no longer proportional to strain, and this permanent, nonrecoverable deformation occurs.

Decreases

As temperature ____________ so does the materials ability to be tough.

Modulus of resilience

Associated with resilience, it is the strain energy per unit volume required to stress a material from an unloaded state u to the point of yielding

Plastic deformation

Atomic slip --> dislocation sliding --> slip system

Grain size

Can be regulated/controlled(manageable) by the rate of solidification I) grain size reduction

Annealing process

Cold worked materials can be "altered" restored back to pre-cw conditions through the __________________.

True stress

Defined as the load F divided by the instantaneous cross sectional area Ai, over which deformation is occurring

Poisson's ratio

Defined as the ratio of lateral and axial strains; v=-Ex/Ez= -Ey/Ez. For virtually all structural materials, Ex and Ez will be opposite signs. Theoretically For isotopic materials this ratio will be 1/4, furthermore the maximum value is .5

Elastic deformation

Deformation in which stress and strain are proportional. A plot of stress (ordinate) and strain (abscissa) results in a linear relationship.

Resolved shear stress

Dependence on applied stress and orientation of stress direction relative to slip plane normal and slip direction

Ductility

Do NOT over cold work a material or you will lose all ______________.

Tougher

Ductile metals are normally __________than brittle ones

Percent elongation

Ductility is characterised by and can be quantitatively expressed as ______________.

Axial elongation

Ductility is defined by __________________ or known as percent elongation

Tensile

Ductility represents ____________stresses

Anelastic

Elastic deformation that is dependent on time

True strain

Equal to the natural logarithm of the ratio of instantaneous and original specimen lengths

Fatigue

Failure under applied cyclic stress

Slip

For crystalline solids, deformation is accomplished by this process which involves the motion of dislocations

Proportional limit

For metals that experience this gradual elastic-plastic transition, this point of yielding may be determined as the initial departure from linearity of the stress strain curve; this is sometimes called the ______________.

Engineering strain

Force/cross-sectional area; force is applied perpendicular to the specimen in newtons or pound force and the cross-sectional area is the area where the load is applied

Ductile

Hot rolled is much more ___________ than cold rolled

Soft, hard, hardest

In an example of the classification of hardness of a metal Ex. 35HR_c the c could be represented by a, b, or c in which the a = _________, the b = ___________, and the c = ____________.

Anelasticity

In most engineering materials, there will exist a time-dependent elastic strain component--that is, elastic deformation will continue after the stress application, upon load release, some finite time is required for complete recovery. This time dependent elastic behaviour is known as this

Grain size

Influences mechanical properties I) grain size reduction

Strain

Involves physical measurable deformation, sometimes referred to as unit deformation, Only can happen under stress

Recrystallization

Is the formation of a new set of strain free and equiaxed grains that have low dislocation densities and are characteristic of the pre cold-worked condition

Elastically anisotropic

Many materials are ______________; that is, the elastic behaviour (I.e., the magnitude of E) varies with crystallographic direction

>5%

Metals are considered highly ductile when their percent elongation is ___________.

3 design lab test factors

Nature of the applied load (tension, compression, shear), load duration, and environmental conditions

Recrystallization

New grains start to grow and as a result their dislocation density decreases (strain free - equiaxed grains)

Tension

One of the most common strain-stress tests is performed in this way

Plastic deformation

Permanent deformation (requires ductility)

Recovery stage

Results is removal of residual/internal stresses and the formation of low energy dislocation configurations

Elastic deformation

Reversible deformation (hookes law)

Tensile strength

Taken as the stress level at the maximum point on the engineering stress-strain curve

Solid solution strengthening

Technique used to harden and strengthen metals is allowing with impurity atoms that go in to either substitutional or interstitial solid solutions.

Stiffness, strength, hardness, ductility, toughness

The 5 key mechanical design properties

Modulus of elasticity

The __________________ is a measure of the stiffness of a material and is a function of the slope of the straight line portion of the stress-strain curve , per hookes law

Notch toughness

The ability of a material to absorb energy and plastically deform before fracturing

Toughness

The ability of a metal to deform plastically and to absorb energy in the process before fracture

Resilience

The capacity of a material to absorb energy when it is deformed elastic ally and then, upon loading, to have the energy recovered.

Mechanical properties

The characteristics that distinguish and identify a material

Slip system

The combination of the slip plane and the slip direction.

Ductility

The degree to which a metal will plastically deform by the time of actual fracture. The ability of metals to be deformed by working processes and to retain strength and freedom from cracks when the shape is altered

Engineering stress

The difference in length of original and instantaneous divided by the original length. The change in length is sometimes referred to as deformation elongation.

Recovery stage, recrystallization

The first stage of the annealing process is the _____________ and the second stage is _________________.

Tensile strength

The highest value of stress on the curve

Strength and ductility

The key to toughness is a good combination of ___________ and ______________.

Hardness

The measure of a materials resilience to localise plastic deformation.

Ductility

The measure of the degree of plastic deformation that has been sustained at fracture.

Ductility

The measure of the degree to which a material plastically deforms by the time fracture occurs

Rockwell hardness test

The most common test for hardness

Percent elongation

The percentage of plastic strain at fracture

Yielding

The phenomenon of __________ occurs at the onset of plastic?permanent deformation

Stiffness

The property that enables a metal to withstand high stress without great strain; also known as the resistance to any sort of deformation

Hardness

The resistance of a metal to "localize plastic deformation" (from indentation, scratching, cutting). It shows metals resistance to "wear" and is a tensile strength indicator

Tensile strength

The stress at the maximum on the engineering stress-strain curve. This corresponds to the maximum stress that can be sustained by the structure in tension; if this stress is applied and maintained, fracture will result.

Yield strength

The stress corresponding to the intersection of the linear elastic section and the plastic deformation curve

Yielding

The stress level at which plastic deformation begins.

Recrystallization temperature

The temperature at which recrystallization just reaches completion in 1 hour.

Rockwell and Brinell tests

The two most common hardness testing techniques

Elastic limit

The value of stress at which the metal has deformed plastically

Proportional limit

The value of stress where the curve first deviates from a straight line

Recovery

There is some relief of internal strain energy by dislocation motion. Dislocation density decreases, and dislocations assume low-energy configurations. Some material properties revert back to their pre cold-worked values.

Hardness tests

These are performed because the are simple and inexpensive, nondestructive, and mechanical properties often may be estimated

Tension, compression, shear

Three principle way in which a load may be applied

Anelasticity

Time needed to complete strain recovery

Strain hardening

When a normally ductile metal becomes harder and stronger as a result of plastic deformation. -metals can be expressed in terms of their "% cold worked"

Increasing temperature

With ___________________, values of elastic modulus and tensile and yield strengths decrease, whereas the ductility increases

Grain boundaries

_____________ act as barriers/impediments to dislocation motion I) grain size reduction

Cold rolled

_____________ has a much better surface finish than hot rolled

Hardness tests

______________ are used more frequently than any other mechanical test

Restricting

_________________ dislocation motion renders a metal harder or stronger

Hardness and strength

___________________ are related to the level of plastic deformation to occur. Hard it is the harder it is to deform (dislocations to move past one another).

Grain size

____________in metals can be regulated by its rate of solidification.

Toughness

is indicative of a materials resistance to fracture when a crack is present.