Advanced Materials - 230328

Question 1

Skin pass rolling

Answer 1

1 or 2 percent thickness reduction.
GOAL: Avoid pronounced yield point. Uniform location of the dislocations in the surface area, dislocations not blocked in their movement by foreign atoms.
Final step of sheet metal manufacture. Cold rolled sheet (After annealing)

Question 2

Thermal treatment

Answer 2

Annealing process: temperature profile. Thermal treatment.

Question 3

Types of tests:

Answer 3

Uniaxial : tensile test (get UTS, elongation at fracture, Young’s Modulus)
Multiaxial: Shearing test.
Process specific:
- Bending test.
- Hole expansion test.
- Cutting.

Question 4

Bending test:

Answer 4

check the surface fractures in the component while hemming, 3 point bending test: bending force. The elongation at fracture while bending is bigger than when doing the tensile test. When bending: the grain boundaries open

Question 5

Whats the problem with cutting in terms of formability

Answer 5

Predeformation of 20% in shearing zone, may produce fracture when forming in comparison with milling or laser.

Question 6

Standard test for deep drawing:

Answer 6

• SWIFT cup: the blank is not fixed, deep drawing happens, no stretching.
• Erichsen test: deep draw without letting the blank move, stretch behavior.

Question 7

Which tests you must do in a car manufacturing facility?

Answer 7

All the tests must be performed, as the processes are all involved in the manufacturing.
The material supplier usually only supplies the Uniaxial tensile test.
The more tests you wanna have, the more expensive becomes the material, to fullfill the additional requirements.

Question 8

How do you define the strain?

Answer 8

difference in length, divided by original length. Also called Engineering Strain.

Question 9

What’s the true strain?

Answer 9

Sigma = ln (L0+deltaL)/(L0), also called logarithmic strain. Final_length divided by initial_length

Question 10

True strains:

Answer 10

Sum of the three TRUE strains in the three basic dimensions (X, Y and Z) are zero. Any increase or decrease in any of the directions affect the other ones.

Question 11

Difference between engineering and true strains in multistage processes:

Answer 11

CANNOT: Add engineering strains.
CAN: Add true strains.

Question 12

Difference between engineering and true stresses:

Answer 12

Engineering: Area is the original.
True: Area is the reduced or true area.

Question 13

Draw the differences between the 3 stress-strain diagrams:

Answer 13

Stress-strain diagram (engineering).
True-stress
Flow curve. Only when flow starts, and no consideration of necking. Extrapolation after necking. Why do we end in necking?