Confused ! or am I to understand that the 45 degree lip occurs inwardly from the surface and thus can act as a pointer along the direction of the breaking strain?
Wish I had known about this when I examined the Valiant prototype No2 main spar failure at Boscombe Down in the mid 50s. Fortunately the flight load at max AUW was redistributed and we managed to get back to base with the broken wing.
Anyone for some diagrams?