Yielding (e.g. defined by the von Mises criterion)

We reach this state when the stress in the metal exceeds the yield stress. When the metal yields, it changes behaviour from elastic to plastic. We will here loose much of the capacity, and yielding should of course be avoided. Some yielding are of course unavoidable, such as in weldings.

Buckling

Buckling is a state that shells or trusses reach when pressure loaded upto a certain critical stress. The component then buckles out and loses much or all of its capacity. This again, can lead to a total collapse of the entire structure. Buckling is an important problem in ships and offshore structures.

Plate/Shell buckling

Fatigue

Fatigue is a dynamic problem. The problem can arise when we have alternating loads. After a certain amount of load cycles, cracking will occur, and we can have structural damage. The amount of cycles needed before cracking is dependent of the magnitude and frequency of the alternating load conditions.