Materials and Structure

The photographs show two tubes that have buckled and plastically deformed, a plastic buckling situation.

The square section low alloy steel tube on the left has a low slenderness and the end of the tube has been "concertinered" by a buckling instability followed by plastic deformation. The deformation rate in this experiment was controlled, however, a similar end shape was produced when an identical tube was loaded until it buckled under constant load. The highest force is required to start the buckling and a lower force will then bend the plastic hinge until the material is folded and a new buckle starts.

The circular cross-section aluminum alloy tube on the right has developed a "dog-leg" shape during buckling. The slenderness of this tube was higher and it buckled approximately at its center. The deformation rate was kept constant and plastic deformation occurred at the tube center and also at the ends that were in contact with the loading grips. Once again, the load required to initiate buckling was larger than that required to continue the plastic deformation.