Group #49/14/05

David ReisJeremy Huckins Alberto Barraza

Nick Mellady

Mechanical and Physical Properties of Materials

When a product is designed the designers must choose the materials the product is made of

A number of factors influence this selection

The different properties of materials is the biggest consideration

Tension

A force tending to stretch or elongate something

Stretching a rubber band creates tension

Engineering Stress vs. Load Stress = load/area Two different pieces of the same

material can take different amounts of load before they break

The amount of load a material can take doesn’t tell us anything

The amount of stress is the amount we want to know

Strain

The percent that the length of the material changes

Strain = (length – length original)/

length

Tension Test

Stress-Strain Curves

True Stress and Strain

Engineering stress is a number that we look at to determine how strong a material is if it is in its original state

True stress and strain are instantaneous measurements and apply to a material as its cross section is changing

Ductility

The extent of the permanent (plastic) deformation that the material undergoes before failing

The ductility of gum or a balloon is high

The ductility of chalk is basically zero because it does not stretch

Stress during Manufacturing

Temperature Effects Rate of deformation Effects Hydrostatic Pressure Effects

Compression

A force that applies squeeze pressure

For ductile materials the true stress-strain curves coincide

For brittle materials the disk test is used

Disk Test

Pressure is applied to both sides of a disk

Eventually a fracture will develop in the direction of one point of force to the other

Stress= 2(load) / (diameter * thickness *

)

Torsion

A twisting force Sheer stress Punching a hole in sheet metal

produces sheer strain Tested by twisting a thin tube of

material

Bending

This is actually a bending test to used on brittle materials such as carbides or ceramics

The stresses can be calculated by a simple beam equation in a mechanics text.

Hardness Hardness is

generally strength and resistance to wear and scratches

Diamonds are the hardest material known

They are used is several hardness tests

Hardness tests

Various tests have been developed to determine the hardness of materials such as:

Brinell test- This test uses a 10 mm ball and is

pressed into the material, the hardness is determined by the diameter of the indention.

Rockwell test- Very similar to rockwell test. Uses the depth of penetration to determine

hardness

Vickers test- Uses pyramid shape with diamond at the tip This test can determine the hardness of most

materials

Hardness tests

Knoop test- This test uses a elongated pyramid with a

diamond tip. This test is considered a micro test because

of the light tools applied This test can do thin or brittle materials Scleroscope- This uses a diamond tipped hammer in a

glass tube Hardness is determined by rebound of

hammer

Hardness tests

Mohs hardness- This uses no tools Hardness is determined by

scratching two materials together Hot Hardness- This is bacially any test at elevated

temperature

Hardness tests

Fatigue Fatigue is considered when making tools

like dies, cams, gears, shafts, and springs that are subjected to rapid fluctuating.

Fatigue failure is when a crack is formed and continues to grow with every stress that is applied to it.

This failure is responsible for the majority of failures in mechanical components.

Creep

The permanent elongation of a component under static load maintained for a long period of time in high temp.

Such as turbine blades in a jet engine and components in a rocket motor.

Generally a great resistance to creep is using a material with very high melting point

Impact or dynamic loading Test

This test is used usually for bolts or drop forged materials

The test consists of notching material on one side and using a pendulum

From the amount of the swing of the pendulum, the energy dissipated is the impact toughness

The high strength materials also have a high impact toughness

Failure and Fracture of Materials in Manufacturing and Service Types of Failure 1.- Fracture: process of breaking either

internal or external of a material. 2.-Buckling: some products are designed in

such as way that failure is essential for their function.

Ductile fracture: is characterized by plastic deformation. Ductile fracture generally takes place along planes on which the shear stress is a maximum.

Brittle Fracture: occurs with little or no gross plastic deformation.

Plastic Deformation

Examples of fracture of a Material

Residual Stresses

When workpieces are subjected to plastic deformation that is not uniform through out the part, they develop residual stresses.

Reduction and elimination of residual stresses: Residual stresses can be reduced or eliminated by deformation of the part, such as stretching it.

Work, Heat, and TemperatureAlmost all of the mechanical deformation is

converted into heat.Temperature rise:

△Τ=ˍuˍ ρc

T = Temperature U = specific energy (work of deformation per

unit volume ρ= density c = specific heat of the material.

Physical Properties of Materials. Density: The density of a

material is its mass per unit volume.

Density=Mass/Volume

DT301Smart Concentration/Density Transmitter

Melting Point Melting point: The temperature at which

a solid substance changes into a liquid state

Depending on the composition of an alloy the melting point has a wide range of temperatures

When designing a component it is important to consider the temperature range that it will be functioning when choosing materials

The melting point has indirect effects on manufacturing such as, with the process of annealing,heat treating, hotworking, and with making castings

Specific Heat

Definition: The energy needed to raise the temperature of a unit mass by one degree

Alloying elements have a relative minor effect on specific heat of materials

If the temperature rises excessively in a workpeice it can be disastrous

Thermal Conductivity Definition: the rate at which heat

flows within and through a material In a product, when heat is generated

it needs to be conducted away at a high enough rate to prevent a severe rise in temperature

Low thermal conductivity can result in deformation of products

Thermal Expansion of Materials

The relative expansion and contraction of deferent materials in an assembly

Parts that utilize thermal expansion and contraction are known as shrink fit assembly

Thermal expansion along with conductivity together produce stresses on components and tools which are undesirable

The undesirable effects that occur during a product service life is known as thermal shock

To reduce the problems caused by thermal expansion, metals were replaced with iron-nickel alloys

Thermal Expansion of Materials

Electrical, and magnetic properties of materials

Electrical conductivity: used to specify the electrical characteristics of a material.

This is measured in mho not to be confused with the reverse; ohm, which is to measure electrical resistance

Different things that are include with electrical properties

Conductors: materials with high electrical conductivity

Insulators: the materials that have high electrical resistivity

Superconductors: materials that have resistivity at very low temperatures, that plunge from a finite value to one that is virtually zero

Superconductivity: electrical phenomenon where electrical resistivity occurs in some metals and alloys at temperatures around absolute zero (0K)

Simi-conductors: devise that is used in extremely miniaturized electronic circuitry

                                          

Electrical properties

Magnetic properties

Ferromagnetism: phenomenon characterized by high permanent magnetization due to the alignment of iron, nickel, and cobalt atoms

Ferrimagnetism: permanent and large magnetization exhibited by ceramic materials

Corrosion resistance

All materials; metal, ceramics, and plastics are all subject to forms of corrosion

Corrosion leads to deterioration of components

Resistance depends on the composition of the materials and the environment their in

Nonferrous metals have very high corrosion resistance

Cold worked metals are more susceptible to corrosion than hot worked metals

Tool and die materials are susceptible to chemical erosion from lubes and coolants

Corrosion

Conclusion

Mechanical and Physical properties of materials must be considered when choosing a material for your design

Your design will be better with the right material

References

Lindbeck, John R. . Product Design and Manufacture. Prentice Hall. 1995.

Kalpakjin and Shmid. Manufacturing Engineering and Technology. Prentice hall, 5th edition.

Callister, William. Materials Science and Engineering. John Wiley & Sons. 4th edition. 1997

www.dictionary.com Pictures: Railroad picture:

www.physics.brocku.ca/courses/1p23/Heat/rail.html

Corroding plate: ht

tp://www.sculptures.freeserve.co.uk/images/crack%20corrosion%202.jpg Corroded bolts: www.yachtsurvey.com/ corrosion.htm

www.pesprings.com http://www.madisongroup.com/Services/Failure/failureanalysis.html