Within the steel and metal world, there are a variety of different types of what are known as metal failures. Generally due to some combination of mechanical and environmental factors, metal failure can take place in the form of cracking, erosion, embrittlement and several other specific failure types.

At Wasatch Steel, we’re happy to detail potential failure risks for any of our steel products, from bulk steel pipe to steel tube, bar and numerous other materials. One particular type of metal failure that’s particularly risky, but also relatively subtle in its signs, is known as fatigue failure. In this two-part blog, we’ll start by defining fatigue failure and its general stages, then go over how to prevent fatigue failure and some of the common metal applications where fatigue must be prevented.

Stage 1 (Initiation)

Metal fatigue generally occurs when repeated, significant stresses take place on the metal and weaken it. The first stage of this process, the initiation stage, is the most complex – and also the one researchers have done the most work to prevent, as it kicks off the entire thing.

During stage one, small cracks (also called micro-cracks) begin to form in the metal after enough load cycles have been run. These load cycles cause what are known as shear stresses, and this damage accumulates more and more with each cycle. The cracks will begin extremely small and focused only on a single area, often forming around geometric features like the edges of the piece.

Just as troublesome as the formation of these cracks is the relatively low strength required to cause them. The stress required to create micro-cracks is often actually less than the ultimate tensile and yield tensile strength of the metal.

Stage 2 (Propagation)

During stage two, also known as propagation, the micro-crack that has formed begins to change direction. It starts to grow in a perpendicular manner to the tensile stress, generally caused by continued stress due to cyclic loading. The cracks also grow in size as they go through this stage, which is the easiest to note from a visual perspective.

Stage 3 (Final Rupture)

Finally, stage three involves the crack propagation continuing, slowly limiting the cross-sectional area of the metal piece. At a certain point, the micro-cracks reach such a size that rapid propagation takes place, to a point where the final fracture occurs at a certain load application. The fracture in question will either be ductile (with a dimpled surface) or brittle (with a cleavage or intergranular surface), depending on several factors.

For more on metal fatigue failure and how it may impact your steel products, or to learn about any of our steel services or materials, speak to the staff at Wasatch Steel today.