Effect of Size and Orientation on Fatigue Crack Growth Rate in 4340 Steel.
WATERVLIET ARSENAL N Y
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Fatigue crack growth rate in 4340 is evaluated from the viewpoint of the effect of orientation and specimen thickness. It is shown that orientation has little effect on the relation between crack growth rate and stress intensity factor. This differs markedly from data on mild steel which showed a marked effect of orientation. The difference is interpreted in terms of the relative cleanliness of the 4340 steel. Increasing the specimen thickness from 116 inches to 12 inches caused a significant increase in the value of m in the relation dadN alpha times delta K to the m power, viz. 2.6 to 5.1. This is believed to show an effect of stress state in that, in the thicker specimens, fracture is flat and the stress state tends more toward plane strain. The data show that applying crack growth data from thin specimens to larger structural members can be misleading. Author
- Properties of Metals and Alloys