This picture shows the major surface features seen on almost every fatigue fracture surface. The origin (initiation site) is where the crack actually started. The crack then grew slowly across the fatigue zone. During this slow crack growth, there were variations in the load that resulted in corresponding variations in the crack growth rate that appear as beach marks. Eventually, the crack reached the point where the remaining material was over-stressed, and the overload zone (fast fracture) resulted.
Locating
the fracture
origin is
a primary goal of fractography and is vital to successful failure
analyses.
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