here are some
pics (not sure if it's a good example, I've only done it once some time ago). It looks like you didn't get any flow, you probably are melting the rod but not the base. What tip size are you using?
Regarding the destructive testing. One thing to try is to place the cheater bar 3-4 inches from the joint. If you butt it against the bottom of joint it's guaranteed it will fail eventually. You want to test if the tubes bend before failure, although in your case it looks like the horizontal tube deformed a lot before you pulled the joint apart.