Non-linear Behavior Assessment and Fatigue Analysis of Ankle Foot Orthosis by Finite Element Method

Abstract

Thanks to the rapid development of orthopedic technology, many types of orthopedics have been created to help patients with disabilities. Orthopedic ankle-foot surgery (AFO) is one of the most common prescriptions for orthopedic lower extremities. In the past, there have been some experimental studies but not fully addressed analytically. This study begins with the modeling and prediction of the non-linear behavior of AFOs non-joint plastic. Large strain effects and non-linear materials are included in the formulation and their influence on results assessed. AFO has two important factors: rotational stiffness and fatigue life, which have not been widely studied. In this study, the Newton-Raphson method is used to investigate the non-linear behavior of plastic ankle insoles (AFOs) through finite element modeling; the results are compared with the reference study to clarify. Since then, the finite element method will be applied to all models to determine the relationship between AFO trimline position and rotational stiffness for moderate and large rotation in plantar flexion and dorsiflexion. The results of stiffness rotation suggested that stiffness analysis of the orthotropic is effective as the help for the doctor in prescribing patients. In the fatigue analysis, the structure is assumed that used in the range of repetitive loads, the S-N curve of the Polypropylene material was used to the definition of material. The number of steps is investigated to define the life cycles of the orthotropic through the variation thickness to find the optimum thickness to meet the fatigue strength. Through careful consideration and specification of key modeling parameters, the finite element method is a reliable and efficient alternative for analyzing the non-linear behavior and fatigue life of AFO designs, as simulation and empirical results are nearly possible.