I was looking at some tensile testing data of some round bars with grooves machined into them, and based on the geometry of the groove I could not figure out how it was possible to withstand the high loads that it was seeing. I was stumped, but by some blind luck I saw a property listed on Matweb as "Notched Tensile Strength" which was much higher than the regular tensile strength (e.g. Titanium 6al-4v, 170 ksi vs. 225 ksi with Kt=6.7). That lead me to notch strengthening, something I've never seen or explored before. The whole idea of stress concentration rings a bell, but it has been quite a while since I have looked at it. I really only found one source that did a decent job of briefly explaining it (see section 7.5): http://www.omegaresearchinc.com/Publications/getpub.cfm?pub_id=18 But, other than that I haven't found much. I was hoping someone here could help drive home the concept. I guess the main thing I am hung up on is calculating the notch tensile strength. Can the notched tensile strength be calculated based on the stress concentration factor of the groove (http://analysischamp.com/StressBook/TABA2513.htm)? Or is it something that can only be determined experimentally? What does the "notched tensile strength" in the Matweb specs do for me if every notch has a different Kt? Any help is appreciated! Also, if you know of any sources that discuss this, that would be great!