Manufacturing Chapter 2 and 3

What are some common point defects in a crystal lattice structure?

(1) vacancy ‑ a missing atom in the lattice structure; (2) ion‑pair vacancy (Schottky defect) ‑ a missing pair of ions of opposite charge in a compound; (3) interstitialcy ‑ a distortion in the lattice caused by an extra atom present; and (4) Frenkel defect ‑ an ion is removed from a regular position in the lattice and inserted into an interstitial position not normally occupied by such an ion.

Transverse rupture strength

1.5FL/bt^2

static stresses

1.Tensile - stretching the material Compressive - squeezing the material Shear - causing adjacent portions of the material to slide against each other

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 commonly used to test the strength of brittle materials. The test provides a measure called the transverse rupture strength for these materials

crystal structures is the strongest at room temperature when general application in "real world"

BCC

compression

Barreling of a test specimen due to frictional forces is a phenomenon occurring during which test?

What is the complicating factor that occurs in a compression test that might be considered analogous to necking in a tensile 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.

BCC

Bond centered cubic 9

Define the difference between elastic and plastic deformation in terms of the effect on the crystal lattice structure.

Elastic deformation involves a temporary distortion of the lattice structure that is proportional to the applied stress. Plastic deformation involves a stress of sufficient magnitude to cause a permanent shift in the relative positions of adjacent atoms in the lattice. Plastic deformation generally involves the mechanism of slip ‑ relative movement of atoms on opposite sides of a plane in the lattice.

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; whereas true stress divides the load by the instantaneous area which decreases as the specimen stretches

How is the shear modulus of elasticity G related to the tensile modulus of elasticity E, on average?

G = 0.4 E, on average.

crystal structures is the strongest at room temperature when considering ONLY the number of slip directions

HCP

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 area increases as the test progresses; while in a tensile test, the cross‑sectional area decreases

What is the difference between primary and secondary bonding in the structure of materials?

Primary bonding is strong bonding between atoms in a material, for example to form a molecule; while secondary bonding is not as strong and is associated with attraction between molecules in the bulk material.

Knoop Hardness Test

Pyramid shaped diamond. HK=14.2(F/D^2)

Vickers Hardness Test

Pyramid shaped diamond. HV =1.854F/D^2

How is shear strength S related to tensile strength TS, on average?

S = 0.7 TS, on average

What is the difference between crystalline and noncrystalline structures in materials?

The atoms in a crystalline structure are located at regular and repeating lattice positions in three dimensions; thus, the crystal structure possesses a long‑range order which allows a high packing density. The atoms in a noncrystalline structure are randomly positioned in the material, not possessing any repeating, regular pattern.

Which elements are the noble metals?

The noble metals are copper, silver, and gold.

The elements listed in the Periodic Table can be divided into three categories. What are these categories and give an example of each?

The three categrories of elements are metals (e.g., aluminum), nonmetals (e.g., oxygen), and semimetals (e.g., silicon).

Why are different hardness tests and scales required?

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

Engineering stress

divides the load (force) on the test specimen by the original area

Hooke's law

defines the stress‑strain relationship for an elastic material: = E, where E = a constant of proportionality called the modulus of elasticity.

Under what circumstances does the strength coefficient have the same value as the yield strength?

When the material is perfectly plastic and does not strain harden

covalent bond

a bond formed when atoms share one or more pairs of electrons

Interstitialcy

a distortion in the lattice caused by an extra atom present.

vacancy

a missing atom in the lattice structure

ion‑pair vacancy (Schottky defect)

a missing pair of ions of opposite charge in a compound

true stress

divides the load by the instantaneous area which decreases as the specimen stretches

Frenkel defect

an ion is removed from a regular position in the lattice and inserted into an interstitial position not normally occupied by such an ion

Describe how ionic bonding works?

atoms of one element give up their outer electron(s) to the atoms of another element to form complete outer shells.

yield point

beginning of plastic zone

How do grain boundaries contribute to the strain hardening phenomenon in metals?

block the continued movement of dislocations in the metal during straining. As more dislocations become blocked, the metal becomes more difficult to deform; in effect it becomes stronger.

metallic bond

cloud sharing outer shell electrons by all atoms

Engineering Strain

e= L-Lo/Lo

fluidity

ease to flow

FCC

face centered cubic 14

Plastic deformation

generally involves the mechanism of slip ‑ relative movement of atoms on opposite sides of a plane in the lattice

Identify some materials that possess a noncrystalline structure.

glass (fused silica), rubber, and certain plastics (specifically, thermosetting plastics and some thermoplastics).

HCP

hexagonal close packed 17

Plastic deformation

involves a stress of sufficient magnitude to cause a permanent shift in the relative positions of adjacent atoms in the lattice

Elastic deformation

involves a temporary distortion of the lattice structure that is proportional to the applied stress

secondary bonding

is not as strong and is associated with attraction between molecules in the bulk material

What is the defining characteristic of a Newtonian fluid?

is one for which viscosity is a constant property at a given temperature. Most liquids (water, oils) are Newtonian fluids.

Primary bonding

is strong bonding between atoms in a material

What is work hardening (strain hardening)?

is the increase in strength that occurs in metals when they are strained

tensile strength of a material

is the maximum load experienced during the tensile test divided by the original area.

yield strength of a material

is the stress at which the material begins to plastically deform. It is usually measured as the 0.2% offset value, which is the point where the stress‑strain curve for the material intersects a line that is parallel to the straight-line portion of the curve but offset from it by 0.2%

In Hooke's Law, the formula utilizes a constant of proportionality - E, which is a measurement of which of the following:

material's inherent stiffness

Identify some materials that have a crystalline structure.

metals and ceramics other than glass. Some plastics have a partially

IONIC BOND

one or more electrons are transferred from one atom to another

how is hardness generally tested?

pressing a hard object (sphere, diamond point) into the test material and measuring the size (depth, area) of the indentation

noncrystalline structure

randomly positioned in the material, not possessing any repeating, regular pattern

What is viscoelasticity, as a material property?

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.

crystalline structure

regular and repeating lattice positions in three dimensions; thus, the crystal structure possesses a long‑range order which allows a high packing density

Hooke's Law

s=Ee

What are the three types of static stresses to which materials are subjected?

tensile, compressive, and shear.

In a tensile test

the cross‑sectional area decreases

Define viscosity of a fluid

the resistance to flow of a fluid material

What is hardness?

the resistance to indentation of a material.

In a compression test

the specimen cross‑sectional area increases as the test progresses

Define the recrystallization temperature for a metal

the temperature at which a metal recrystallizes (forms new grains) rather than work hardens when deformed