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Compressive Stress is important in the forging, stamping, coining, and cold heading industries. It is compression stress that is used to change the shape of the product. This is different than in our machining industry, where we create the shape of the part by subtracting material by some means of stock removal.

Compressive stress is caused by an applied load that is acting to reduce the length of the steel in the axis of the applied load. Because the forces acting on steel are in the same axis (collinear) with the longitudinal axis of the member, these forces cause the steel to either shorten or stretch.

Compressive stress causes different failure modes in brittle and ductile steels.

Compressive strength is the limit of compressive stress that the steel can withstand before failing in a ductile failure.

  • When steel’s compressive strength is exceeded, the steel will fail in a brittle fashion, and it will shear, usually at a 30 to 45 degree angle.
  • When I see cracks at angles in the range of 30 to 45 degrees from the direction of applied load in steel, formed by cold working deformation, I know that the failure is a brittle mode.
  • This does not mean that the steel itself was too brittle, it may mean that the angles and loading in the process tooling were incorrect, causing the compressive limit of the steel to be exceeded.

When I installed a cold heading wire drawing line  in my mill, my employees preferred to call our compression or upset test the “Squeeze Test.”

We upset test (compression test ) small samples of steel from each coil of wire to see the failure mode of the material after drawing, and to see if any seams opened up as the section thickness increased.

Image from my archival copy of a chart from Steelways 1955.

1 thought on “Understanding Compressive Stress in Steel

  1. I wonder why the axial cracking (parallel to compressive load) is considered as ductile behaviour. This axial splitting in uniaxial compression loading is well-known for brittle materials like concrete and rocks.
    Shearing failure at some angle is observed in compression tests of brittle material if large friction occurs between load platens an specimen. In this case, the stress field is inhomogeneous and not completely uniaxial. The shearing is cuased by the effect of friction and does not show a change in material behaviour.
    I have discussed the axial splitting in:
    M. Staat: An extension strain type Mohr-Coulomb criterion. Rock Mechanics and Rock Engineering 2021;54(12): 6207-6233.

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