Hi
Beachmark is a surface phenomenon of a fatigue fracture surface of solid metals or sold polymers.The beachmark normally appears as a fatigue crack propagation in ,i.e., a low load-high cycle fatigue mode at the fracture surface of the solid metals or solid polymers . So, when the cross section area of the solids is no longer can sustain the cyclic loading, the final fracture will occur. In other words, the beachmark is a characteristic of the crack propagation region of the fracture surface. Therefore, one would not expect to see those beachmarks on that region over which the rapid failure occurs. It is worth noting that the fracture surface of solids consists of three regions. The regions are ;a crack initiation site, a crack propagation region, and the final rapid failure region. The final rapid failure might be a ductile or a brittle failure region dependent on the type of the material of the solids.
Basically benchmarks are associated with fatigue crack growth. In particular they depend on arrests or significant variations of the load history. They should not be confused with the striations that sometimes are observed and that mark the cyclical progress of the crack.
Cycling loading creates the beachmarks and after a point material rupture as ductile or britle so, no cycling any more means no beachmarks.
Yes, Indeed, I agree with Mr.Enrico Manfredi. One should not be confused by the difference between beachmarks and striations. The beachmarks can be observed at a macroscopic scale at the fracture surface. In contrast, the striation, can only be observed at a microscopic scale with the aid of an optical microscopy or a scanning electron microscopy.
Khaled sir and suna madam all which you are explained me its just the definition and I know definition very well but I want to know about what happens microscopically (mechanism) what is the reason and how it happens?
Hi Bhagwan
As I mentioned before, when the cross section area of the solids is no longer can sustain the cyclic loading, during the crack propagation, the final fracture will occur.
In other words, the beachmarks will stop to appear on the fracture surface as soon as the final fracture occurs. So, the final rupture region will be free of beachmarks
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