Mechanical Behavior

Question 1

When is there no volume change in a material during tensile testing?

Answer 1

After elastic deformation there is no volume change (all true strains add to 0, this is on a podcast but I haven’t fully understood/accepted it yet) since the bonds aren’t stretching they’re sliding past each other

Question 2

Traction

Answer 2

The force on a surface divided by the area of the surface. Find the traction in a particular direction by multiplying the stress tensor by the unit vector of that direction

Question 3

How to get the magnitude of a force vector in a certain direction

Answer 3

Dot product that vector with the unit vector in the direction you want. If you want the magnitude in the [680] direction you need to multiply the force by [6/10 8/10 0]

Question 4

Tensor ranks

Answer 4

Rank 0, represented by N^0 = 1 number, is a scalar

Rank 1, represented by N^1 = 3 numbers in 3D, is a vector

Rank 2, represented by N^2 = 9 numbers in 3D, is a 3*3 tensor

N is the number of dimensions of the space you’re working in

Question 5

Flow stress

Answer 5

Flow stress is the stress required to keep deforming a metal plastically. It is a function of strain.

Question 6

Strength coefficient K

Answer 6

Used when determining flow stress. Crack propagation (in fatigue failure) is inversely proportional to the flow stress of a material.

Question 7

Turn a deformation matrix into a strain matrix

Answer 7

Make it symmetrical by averaging the off diagonal terms that should be equal (Exy and Eyx, Exz and Ezx, Eyz and Ezy)