Originally Posted by rafazx10
Usually materials become more brittle as you work them, not more flexible.
Must be something else though, its not breaking close to the grommet.
But thanks for the help.
I believe that with tennis racquets you gradually break the graphite/fiberglas fibers as it flexes repeatedly. The tiny fibers are what contribute to the stiffness. The epoxy matrix may break down too, not sure. If the string didn't break at the frame, it is from something else. Sometimes the ball can pick up debris & nick the string. A nick can be all that's needed to cause a break.