Implant Device Design based on Failure not Survival: A Damage-Tolerant Analysis of a Cardiovascular Stent

To design for fatigue, most implant devices are assessed on the basis of survival. This is an unsatisfactory approach as the safety factors, which essentially tell you how close you are to failure, remain unknown. The approach shown here is quite unlike that used in most others fields of engineering, e.g., in automobile or aerospace applications, where the probability of fatigue failure is instead assessed on the basis of failure. In the present work, a damage-tolerant methodology is presented for designing and quantitatively predicting the fatigue life of a cardiovascular stent. The primary fatigue-life is assessed utilizing the traditional, yet conservative version, of an S-N analysis, and then supplemented with a fracture-mechanics analysis in order to quantitatively evaluate the role of preexisting flaws.