Understanding Compressive Stress in Steel

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.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s