It may be an issue with your Paris law units. The value of C depends on the units used to calculate the stress intensity factor range and da/dN for the Paris law curve, a C value of e-11 suggests that MPa sqrt m and m/cycle may have been used. For reference units of (metre , N) the SIF range should be in Pa sqrt m. An approximate conversion can be made by dividing your C value by (1×10^6)^m, which for your units would give a C value of 1.4264e-27, the value for m will remain the same. However, its important to double check what units were used in the derivation of your Paris law constants, as they may have used another unit system.
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