Advanced Materials - 230404

Question 1

Define the vertical anisotropy:

Answer 1

r = φwidth / φthickness = ln (w1/w0) / ln (t1/t0)
r value as high as possible, greater resistance against thinning

Question 2

Phases of uniaxial tensile test:

Answer 2

Yield point, uniform plastic elongation, necking, fracture

Question 3

How do the vertical anisotropy depends on the rolling direction:

Answer 3

r0, r45, r90. There are some materials where r90 is maximum, r0 is maximum, r45 is maximum.
Or other where the three are the same, isotropic material.
Planar anisotropy: rmax – rmin

Question 4

Influence of planar anisotropy

Answer 4

The higher the planar anisotropy is, the more asymmetric the flow of the material will be.

Question 5

What’s the Yield locus?

Answer 5

Yield locus or yield curve
When does the material starts to flow? Kf (equivalent stress): oval (Von Mises), Hexagonal (Tresca)

Question 6

Equivalent stress models

Answer 6

• Isotropic models:
  
  • Elastic range: Von Mises works.
  • Plastic range: No consideration of r values.
• Vertical anisotropic & Planar isotropic:
  
  • Hill 48 (first developed on 1948) could be used and the FEM simulation is way better. It involves an average r value. r0=r45=r90
• Vertical anisotropic & Planar anisotropic:
  
  • Extended Yield Criterion to Hill 48. r0 ≠ r90. If you do both rs as to be the same, then you come to the same Hill 48 eq.
  • Barlat 91. Experimentally obtain parameters, compute some parameters, very good prediction of aluminum alloys.

Question 7

Biaxial testing

Answer 7

Apply tensile tests on two directions. Cross Tensile Test.
In sheet metal experiments, there is a tensile-tensile testing. For sure not in compression-compression test.
Tension-compresion: for example in deep drawing anisotropic materials. Compression stresses in tangential direction.

Question 8

Anisotropic materials

Answer 8

Most of the materials have no isotropic hardening behavior, but an anisotropic hardening behavior.
The behavior depends on the stress conditions.