Group #4 9/14/05

David Reis Jeremy 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.

Hardness tests

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

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 or external of a material. either internal 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 Temperature

Almost 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 DT301 Smart 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

Thermal Expansion of Materials

  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

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

Electrical properties

  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

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

Corrosion

   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

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