7a and 7b show typical examples of these structures. Representative substructure in fine-grained copper tested under load control at 98 MPa. Representative substructure in fine-grained copper tested under load control at 98 MPa. It is the flat and shiny part. In many occasions it has characteristic features called beach marks , which should be obvious to the reader in the low magnification picture of a fatigue fracture surface shown below.
Typical fatigue fracture surface on copper polycrystal broken under load control.
A detailed inspection of the flat portion of the fracture surface using SEM should reveal the presence of a series of marks approximately parallel to the crack front. Those are called fatigue striations and are characteristic of the growth of a fatigue crack in a ductile material. 9 shows an example of this. High magnification of Fig. 8. H. Mughrabi, Private Communication , 1991.