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Small values problem on Fatigue life cycles
I'm performing a fatigue life analysis of some standard specimens. The problem is I always get very small values (less than 1e-5) for the number of load cycles for each step of crack propagation! I used Paris and NASGRO formulas, but quite the same results. The SIF calculations are wroking correctly, since I'm using a commercial code to do that and I did double checked them to see if they are accurate enough. So, only Paris or NASGRO's parameters may bring some errors. But, I got them from the literature, for example: c = 1e-13 and m = 3.2 for Al 7075-T6. It's a simple caculation, don't know what exactly causes the problem!
Any advice would be greatly appreciated,