Tensile Testing Lecture

8/2/2019 Tensile Testing Lecture

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Tensile testing of Metals

Experiment 4



Tensile testing

• Why?

• Mechanical

properties

• Design

• Fabrication

• Fracture and failure

(Safety)



Mechanical properties

• Which?

• Strength (tensile, compression, shear)

• Deformation

• Stiffness

• Impact properties

• Elastic Limit

• Fatigue properties

• Creep and stress relaxation properties



• How?

• Tensile testing

• Compressive testing• Torsion testing

• Impact testing

• Cyclic loading

Mechanical Testing



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



Stress-Strain Curve



Properties need to be calculated

• Tensile strength

• Yield strength

• Failure strain• Ductility : % elongation and area

reduction

• Elastic modulus• Toughness

• Modulus of resisilience



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



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



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



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)



The test

Servo-

HydraulicUnit Frame

Computer

Load Cell

Upper Gripper Jaws

Sample

Lower Gripper Jaws

Load DataTransmissionCable

Position DataCable

Servo



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



Sample data

http://var/www/apps/conversion/current/tmp/scratch14874/tensile%20test%20data.xls

http://var/www/apps/conversion/current/tmp/scratch14874/tensile%20test%20data.xls



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



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)



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



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



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.



Annealing

– High % elongation

– High % reduction in area

– decreases strength

– May increase toughness

– Conversely, cold rolling increasing

brittleness



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

Documents

Tensile Testing Lecture