Re: Margin of Safety for Medical Device Fatigue Testing
There is no single guideline for margin of safety for any failure mode. It depends on what happens if failure occurs. If the failure by itself (single failure mode) could cause harm, a higher margin should apply.
There's good information on this in the IEC 60601-1:2005 Standard-sections associated with Table 21. Even if that Standard doesn't apply to your product scope-wise, the principles it applies could be used as a foundation for your approach-justification.