U-shaped notch
<img src="https://eng-calculations.com/SVG/Peterson(and39)s_Stress_Concentration_Factors/Notches_and_grooves/U-shaped notch.svg" alt="U-shaped_notch" title="U-shaped_notch">
https://eng-calculations.com/SVG/Peterson(and39)s_Stress_Concentration_Factors/Notches_and_grooves/U-shaped notch.svg