tensile testing lecture
TRANSCRIPT
8/2/2019 Tensile Testing Lecture
http://slidepdf.com/reader/full/tensile-testing-lecture 1/21
Tensile testing of Metals
Experiment 4
8/2/2019 Tensile Testing Lecture
http://slidepdf.com/reader/full/tensile-testing-lecture 2/21
Tensile testing
• Why?
• Mechanical
properties
• Design
• Fabrication
• Fracture and failure
(Safety)
8/2/2019 Tensile Testing Lecture
http://slidepdf.com/reader/full/tensile-testing-lecture 3/21
Mechanical properties
• Which?
• Strength (tensile, compression, shear)
• Deformation
• Stiffness
• Impact properties
• Elastic Limit
• Fatigue properties
• Creep and stress relaxation properties
8/2/2019 Tensile Testing Lecture
http://slidepdf.com/reader/full/tensile-testing-lecture 4/21
• How?
• Tensile testing
• Compressive testing• Torsion testing
• Impact testing
• Cyclic loading
Mechanical Testing
8/2/2019 Tensile Testing Lecture
http://slidepdf.com/reader/full/tensile-testing-lecture 5/21
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
8/2/2019 Tensile Testing Lecture
http://slidepdf.com/reader/full/tensile-testing-lecture 6/21
Stress-Strain Curve
8/2/2019 Tensile Testing Lecture
http://slidepdf.com/reader/full/tensile-testing-lecture 7/21
Properties need to be calculated
• Tensile strength
• Yield strength
• Failure strain• Ductility : % elongation and area
reduction
• Elastic modulus• Toughness
• Modulus of resisilience
8/2/2019 Tensile Testing Lecture
http://slidepdf.com/reader/full/tensile-testing-lecture 8/21
Properties
• Engineering stress= σ = force/ initial area• Engineering strain=ε = change in length/
original length• Elastic Modulus:- Measure of resistance to
elastic deformation• * E = stress / strain -> Hook’s law• * Units = Pa or MPa• * Slope of stress strain curve in elastic
region• * Steels – around 200 GPa, Aluminum –
70 GPa
8/2/2019 Tensile Testing Lecture
http://slidepdf.com/reader/full/tensile-testing-lecture 9/21
Properties
• Yield strength: - Point of significant plastic
deformation.
• * Stress at 0.2% plastic deformation
• Untimate tensile strength :- Maximumstrength reached in engineering stress strain
curve
• * Necking starts beyond this point• * More ductility: More necking
• * porosity and defects reduce UTS
8/2/2019 Tensile Testing Lecture
http://slidepdf.com/reader/full/tensile-testing-lecture 10/21
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
8/2/2019 Tensile Testing Lecture
http://slidepdf.com/reader/full/tensile-testing-lecture 11/21
Properties
• Modulus of resilience : Measure of energy absorbedbefore yielding
• Ur = σ2y / 2E
• Toughness : Measure of energy absorbed before
fracture• Ut = (σy + σu) εf / 2
• True stress :- stress based on instantaneous area
• True stress= σi = F / Ai
• * True strain = Sum of all instantaneous engineeringstrains = sum of all (dl / l ) = ln (li / l0)
8/2/2019 Tensile Testing Lecture
http://slidepdf.com/reader/full/tensile-testing-lecture 12/21
The test
Servo-
HydraulicUnit Frame
Computer
Load Cell
Upper Gripper Jaws
Sample
Lower Gripper Jaws
Load DataTransmissionCable
Position DataCable
Servo
8/2/2019 Tensile Testing Lecture
http://slidepdf.com/reader/full/tensile-testing-lecture 13/21
Sample dataMaterial :- 1018 cold rolled
gauge length = 1 inch
before test:-
diameter of test section:- 0.251 inches
length between fillets = 1.512 inches
After test:-
Diameter at fracture = 0.165 inch
length between fillets = 1.703 inches
8/2/2019 Tensile Testing Lecture
http://slidepdf.com/reader/full/tensile-testing-lecture 14/21
Sample data
8/2/2019 Tensile Testing Lecture
http://slidepdf.com/reader/full/tensile-testing-lecture 15/21
Curve
0
100
200
300
400
500
600
700
-0.02 -1E-16 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18
strain
s t r e s s M P a
Series1
8/2/2019 Tensile Testing Lecture
http://slidepdf.com/reader/full/tensile-testing-lecture 16/21
Modulus of elasticity
y = 197452x + 26.955
R2
= 0.9686
100
150
200
250
300
350
400
450
500
550
0.0005 0.001 0.0015 0.002 0.0025 0.003
Strain
S t r e s s M P a
Series1
Linear (Series1)
8/2/2019 Tensile Testing Lecture
http://slidepdf.com/reader/full/tensile-testing-lecture 17/21
Curve
-100
0
100
200
300
400
500
600
700
800
-0.02 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18
Strain
S t r e s s M P a
Series1
8/2/2019 Tensile Testing Lecture
http://slidepdf.com/reader/full/tensile-testing-lecture 18/21
Engineering and true curve
-200
0
200
400
600
800
1000
1200
-1.00E-
01
0.00E+0
0
1.00E-01 2.00E-01 3.00E-01 4.00E-01 5.00E-01 6.00E-01 7.00E-01 8.00E-01 9.00E-01
Strain
S t r e s s M P a
True Stress-strain
Engineering stress strain
8/2/2019 Tensile Testing Lecture
http://slidepdf.com/reader/full/tensile-testing-lecture 19/21
As carbon content increases,
– ultimate tensile strength and yield strength
increases
– low percent elongation
– low percent reduction in area
– No effect on young’s modulus
– Toughness decreases (depends on grain
size) – But effect of microstructure overshadows
effect of composition in steels.
8/2/2019 Tensile Testing Lecture
http://slidepdf.com/reader/full/tensile-testing-lecture 20/21
Annealing
– High % elongation
– High % reduction in area
– decreases strength
– May increase toughness
– Conversely, cold rolling increasing
brittleness
8/2/2019 Tensile Testing Lecture
http://slidepdf.com/reader/full/tensile-testing-lecture 21/21
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 mechanicalproperties