Try hitting on another spot or try hitting with the other side of the stringbed.
On a more serious note, if its breaking near the frame is because when you hit too close to the edge, the stress is too much for the string to handle and it snaps. That has happened to many people including me. That means you are not hitting the sweetspot, you are a bit higher.
Well thats my explanation, im sure some other more expert members will give you another good reason why its happening.
Meanwhile, go eat a taco, enjoy!