Fatigue Analysis of Ti-55 Alloy Material for Multifunctional Surgical Instruments in Medical Engineering

A new approach is proposed for fatigue prediction in medical engineering of multifunctional microforceps-scissors (MFS), transconjunctival sutureless vitroretinal metal surgical instrument that removes, grasp, chops tissues and inserts new in a cell. Cyclic loads can result in the fatigue failure of MFS at stress levels below the yielding stress of material. Hence, research of the material and mechanical behavior of a MFS structure under a cyclic load is required. The numerical modeling of a cyclic load fatigue test was performed for a biocompatible MFS, by using finite element analysis (FEA). To verify the data gathered from von Mises' yield condition, Haigh diagram was developed to predict fatigue life. Fatigue behavior of the MFS was analyzed in ANSYS LS-DYNA under operation load conditions in vitrectomy. This research analyzes the application of forces to the examined MFS, resulting in different movements, which cause fatigue during surgery. The numerical analysis consisted in solving the strains and stresses distribution in the operating part of the MFS, made of Ti-55 alloy (Ti-5Al-4Sn-2Zr-1Mo-0.25Si-1Nd) medical material. The maximum values of strain and stress were calculated for the Ti-55 alloy, using values of elasticity modulus of 119 GPa, and Poisson's ratio of 0.32. The outcomes of the fatigue analysis from this research will be beneficial for micro component manufacturers in medical engineering and for clinic surgeons.