A note on notch shape optimization to minimize stress concentration effects

Notches induce localized stress concentration effects that can affect many failure mechanisms, in particular the initiation and growth of short cracks under fatigue loads, significantly reducing the strength of structural components under service loads. To decrease such nocive effects, notches are usually designed with as large as possible circular arc tips, even though it has long been recognized this is not the best solution to minimize such problems. Indeed, notches with properly shaped variable tip radii can have a much smaller deleterious influence on fatigue strength, but such optimized notches still are not routinely used in structural design. In fact, not even standard fatigue specimens specify them. Nevertheless, such improved notches can be a very good design option to augment the strength of structural components, since they barely affect their global dimensions or weight. Moreover, nowadays they can be economically built due to the widespread availability of CNC machine tools. After comparing the improvements achievable by some classic variable radii receipts, two simple and robust numerical routines developed to optimize notch shapes for components that work under general multiaxial loading conditions are presented and evaluated.