Tensile testing of Metals

1
Tensile testing of Metals

• Experiment 4

2
Tensile testing

• Why?
• Mechanical properties
• Design
• Fabrication
• Fracture and failure (Safety)

3
Mechanical properties

• Which?
• Strength (tensile, compression, shear)
• Deformation
• Stiffness
• Impact properties
• Elastic Limit
• Fatigue properties
• Creep and stress relaxation properties

4
Mechanical Testing

• How?
• Tensile testing
• Compressive testing
• Torsion testing
• Impact testing
• Cyclic loading

5
Tensile testing

• Measure the geometry of the specimen
• Pull the specimen to failure
• Record load deformation data
• Draw stress strain curve based on recorded data
  and geometry.
• Calculate properties

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Stress-Strain Curve
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Properties need to be calculated

• Tensile strength
• Yield strength
• Failure strain
• Ductility elongation and area reduction
• Elastic modulus
• Toughness
• Modulus of resisilience

8
Properties

• Engineering stress s force/ initial area
• Engineering straine change in length/
  original length
• Elastic Modulus- Measure of resistance to
  elastic deformation
• E stress / strain -gt Hooks law
• Units Pa or MPa
• Slope of stress strain curve in elastic
  region
• Steels around 200 GPa, Aluminum 70
  GPa

9
Properties

• Yield strength - Point of significant plastic
  deformation.
• Stress at 0.2 plastic deformation
• Untimate tensile strength - Maximum strength
  reached in engineering stress strain curve
• Necking starts beyond this point
• More ductility More necking
• porosity and defects reduce UTS

10
Properties

• Percent elongation - Measure of ductility
• (final length initial length) x
  100
• initial length
• Percent reduction in area Also measure of
  ductility
• initial area- Final area
  x 100
• Initial
  area

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Properties

• Modulus of resilience Measure of energy
  absorbed before yielding
• Ur s2y / 2E
• Toughness Measure of energy absorbed before
  fracture
• Ut (sy su) ef / 2
• True stress - stress based on instantaneous area
• True stress si F /
  Ai
• True strain Sum of all instantaneous
  engineering strains sum of all (dl / l )
  ln (li / l0)

12
The test
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Sample data
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Sample data
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Curve
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Modulus of elasticity
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Curve
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Engineering and true curve
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As carbon content increases,

• ultimate tensile strength and yield strength
  increases
• low percent elongation
• low percent reduction in area
• No effect on youngs modulus
• Toughness decreases (depends on grain size)
• But effect of microstructure overshadows effect
  of composition in steels.

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Annealing

• High elongation
• High reduction in area
• decreases strength
• May increase toughness
• Conversely, cold rolling increasing brittleness

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This experiment

• Tensile test 4 samples
• Low carbon steel (1018-cr) cast iron
• - As rolled Aluminum (2024-T4) Annealed
  aluminum (2024-O)
• effects of carbon content on mechanical
  properties
• Effects of annealing on mechanical properties