Yield Criteria

Question 1

What does a uniaxial tensile test measure?

Answer 1

Mechanical properties like stress and strain.

Question 2

What is the formula for engineering stress?

Answer 2

σ = P / A

Question 3

What is the formula for engineering strain?

Answer 3

ε = δL / L

Question 4

What does the gradient of the stress-strain curve in the elastic region represent?

Answer 4

Young’s modulus (E)

Question 5

What separates the elastic and plastic regions on a stress-strain curve?

Answer 5

The yield point (σy₀)

Question 6

What happens in the elastic region?

Answer 6

All deformation is recovered.

Question 7

What happens in the plastic region?

Answer 7

Not all deformation is recovered.

Question 8

What happens when material is loaded past the yield stress?

Answer 8

It undergoes permanent deformation.

Question 9

How does unloading occur after plastic deformation?

Answer 9

Along the same gradient as the elastic portion but leaves permanent strain.

Question 10

What kind of stress-strain curve does grey cast iron show?

Answer 10

A steep curve with little strain – brittle behavior.

Question 11

What kind of stress-strain curve does mild steel show?

Answer 11

A curved path after yielding – ductile behavior.

Question 12

What kind of stress-strain curve does aluminium alloy show?

Answer 12

Smooth transition from elastic to plastic – no clear yield point.

Question 13

What is a ductile material?

Answer 13

A material that undergoes large deformation before failure.

Question 14

What is a brittle material?

Answer 14

A material that fractures with little deformation.

Question 15

When does failure occur in ductile materials?

Answer 15

At the onset of plastic deformation.

Question 16

When does failure occur in brittle materials?

Answer 16

At fracture.

Question 17

What is the yield criteria used for?

Answer 17

Predicting the initiation of yielding in ductile materials.

Question 18

How is ductility expressed?

Answer 18

As percentage elongation or percentage reduction in area at failure.

Question 19

What is used when a clear yield point isn’t observed?

Answer 19

Proof stress (e.g., 0.2% offset method).

Question 20

How is the 0.2% proof stress determined?

Answer 20

Draw a line parallel to the elastic gradient starting from 0.2% strain.

Question 21

What type of failure occurs in ductile materials under tensile test?

Answer 21

Cup and cone failure.

Question 22

At what angle does ductile fracture typically occur?

Answer 22

45°

Question 23

On what plane does ductile fracture occur?

Answer 23

Plane of maximum shear stress.

Question 24

What does the torque-angle graph for ductile materials like mild steel show?

Answer 24

Linear elastic region followed by yielding.

Question 25

What is the formula for torque in the elastic region?

Answer 25

T/J = Gθ/L

Question 26

Where does failure occur if torque is increased until failure?

Answer 26

On the plane of maximum shear stress.

Question 27

What is the orientation of the fracture surface under torsional failure?

Answer 27

Transverse to the axis.

Question 28

What kind of fracture surface does a brittle material like cast iron show under tensile loading?

Answer 28

Flat and perpendicular to the loading direction.

Question 29

On what plane does brittle fracture occur?

Answer 29

Plane of maximum principal stress.

Question 30

What kind of failure is observed in torsion tests on brittle materials?

Answer 30

45° helical failure.

Question 31

What stress causes failure in brittle materials under torsion?

Answer 31

Maximum principal stress.

Question 32

What fracture surface is observed in mild steel?

Answer 32

Cup and cone (ductile).

Question 33

What fracture surface is observed in cast iron?

Answer 33

Flat, perpendicular or helical (brittle).