When observing the fracture surface, ripples that spread inward from the corners of the terminals were observed, so it is judged that some mechanical stress was applied to the relevant part.
When the observation of the broken cross-section was carried out, it is judged that some mechanical stress was added to the place because the ripple which spread from the terminal corner to the inside was seen.
When the observation of the fracture surface was carried out, the ripple was spread from the terminal angle toward the inside, and it is judged that some mechanical stress was applied to the place.