While adjusting a clasp for a RPD patient, after repeated adjustments, the clasp fractured. Which property is responsible for its fracture?

When the metal had been stressed beyond its proportional limit, the hardness and strength of the metal increases at the site of deformation, but ductility decreases. Further attempt to bend or stress metal at the same point, can lead to its fracture. This is called as Cold working, Strain hardening or Work hardening.