Module 2

• An important aspect of manufacturing is the selection of [raw] materials
• Understanding the properties and behavior of materials is essential in understanding manufacturing
• Types of material properties

  • Mechanical
  • Physical
  • Chemical
• Mechanical properties

  • Strength
  • Ductility
  • Hardness
  • Toughness
  • Elasticity
  • Fatigue
  • Creep resistance
• Physical properties

  • Density
  • Specific heat
  • Melting point
  • Thermal expansion and conductivity
  • Electrical and magnetic properties
• Chemical properties

  • Oxidation
  • Corrosion
  • Degradation
  • Toxicity
  • Flammability
• The response of a material to applied forces depends on the type and nature of the bond and the structural arrangement of atoms, molecules or ions
• Basic deformation types for load carrying materials

  • Elastic deformation
  • Plastic deformation
  • Viscous deformation
• Elastic deformation


  Deformations are instantaneously recoverable
• Plastic deformation


  Non-recoverable
• Viscous deformation

  Plastic deformations in noncrystalline solids and liquids; time dependent deformation
• Viscous fluids

  Water has low viscosity; honey has high viscosity
• Tension test

  1. Determines: (1) strength, (2) elastic modulus, (3) ductility, (4) toughness, (5) strain hardening

  2. Tension-testing machines are equipped with controls that can test at different rates of deformation and temperature
• Stress


  Ratio of applied load P to the cross-sectional area Ao of the specimen
• Strain


  lo is the original gage length; l is the instantaneous length of the specimen
• Linear elastic behavior- When load is first applied, the specimen elongates in proportion to the load. If the load is removed, the specimen returns to its original length and shape
• Yield Stress- As the load is increased, specimen begins, at some level of stress, to undergo permanent (plastic) deformation. Stress and strain are no longer proportional.
• Beyond Y, cross sectional area decreases permanently and uniformly throughout the gage length
• Ultimate Tensile Strength- As it is further increased, stress eventually reaches a maximum and then begins to decrease
• At necking, slope of graph = 0
• Modulus of Elasticity (E)


  Measure of the slope of the elastic portion of the curve or the STIFFNESS of material
• Tensile strength


  The ability to resist stretching (tensile) load without fracture
• Compressive strength


  The ability of a material to resist squeezing (compressive) load without fracture
• Shear strength


  The ability of a material to resist transverse loads tending to separate (or cut) the material
• Ductility


  The extent of plastic deformation that the material undergoes before fracture
• Elongation


  Based on the original gage length of the specimen; calculated as a percentage
• Reduction of Area

  Areas are the original and final (fracture) cross-sectional areas of the test specimen
• Toughness


  The amount of energy per unit volume that the material dissipates prior to fracture
• As temperature increases, ductility and toughness increase, while yield stress and modulus of elasticity decrease
• Compression test

  1. Material subjected to compressive forces

  2. Friction prevents the top and bottom surface from expanding freely, dissipating energy and resulting in higher compressive forces
• Ductile metals have similar compressive and tensile properties, while brittle metals do not
• Brittleness


  The property of sudden fracture without any visible permanent deformation
• Malleability


  The ability of a material to be deformed plastically without rupture under compressive load
• Disk test


  For brittle materials such as ceramics and glasses
• Torsion test


  Used to determine properties of materials in shear
• Bend/Flexure test


  For brittle materials, with longitudinal stresses in the specimen being tensile at lower surfaces and compressive at their upper surfaces
• The higher the shear stress that the material can withstand, the greater its modulus of rigidity
• Hardness


  Resistance to permanent indentation
• Brinell hardness test


  Indentation geometry and formulas
• Vickers hardness test


  Developed in 1922, gives essentially the same hardness number regardless of the load and is suitable for testing materials with wide range of hardness, including heat-treated steels