Extended finite element method (XFEM) was developed by the late, great Dr. Ted Belytschko et al. at the end of the 90’s (see Wikipedia for more details). Since he worked closely with the developers of LS-DYNA on many other topics, it is natural to see his work implemented within ‘DYNA. I first met him in the early 90’s when I took his and Prof. Hughes week-long Nonlinear FEA Methods in Palo Alto, CA. As for myself, I sat in the back with a post-doctoral student from Budiansky’s group out of Harvard so he could explain to me what was going on since I was pretty much dazed and confused during the whole week. A little side note, all three, Belytschko, Hughes and Budiansky were Timoshenko Medal recipients. We now fast forward to 2020 and the XFEM is still something of academic interest but finding traction in the world of engineering. It is a lot like eye-candy to see a crack growing magically thru your structure, but the mechanics are real. Predictive Engineering recently completed an engineering services contract with a large US Navy shipbuilder where we used XFEM to make structural integrity predictions. The challenge was to quantitatively calculate the energy required to propagate a crack from a hull engine vent up through the panel and across a stiffener. The goal was to demonstrate that the crack could be arrested prior to reaching the main deck. The work was backed up via fracture mechanics calculations and static work calculating the localized mode I stress intensity factor (KI). Using XFEM we were able to optimize the crack arrestor bulb from somewhat massive dimensions to something that could be reasonably manufactured and thereby shaving a few tons of weight off the FFG(X)’s design.