What is the most common failure mechanism associated with sharp fillets, notches, undercuts, and seams?

The most common failure mechanism associated with sharp fillets, notches, undercuts, and seams is fatigue cracking. This phenomenon occurs due to the presence of stress concentrators, which are typically found in sharp geometric features like fillets or notches. When a material is subjected to cyclic loading, these stress concentrators create localized areas of high stress that can lead to the initiation and propagation of cracks over time, eventually resulting in failure.

Fatigue cracking is particularly relevant in materials that are used in dynamic applications, where repetitive loading and unloading cycles are common. The sharp edges and discontinuities in the material's surface exacerbate the effects of these stresses, leading to quicker crack initiation compared to a smooth or well-rounded surface.

In contrast, other mechanisms like crystallization, shrinkage, and decarburization do not primarily relate to the geometric features of a component, but rather to material properties and state changes. These processes might contribute to material degradation or failure under specific conditions, but they are not directly correlated with the specific failure risks posed by design features like sharp fillets and notches, making fatigue cracking the most pertinent failure mechanism in this context.