CONTACT MECHANICS IN LOW PLASTICITY BURNISHING OF BIOMEDICAL MAGNESIUM-CALCIUM ALLOY

摘要

Magnesium-Calcium (Mg-Ca) alloys are promising biomedical materials in manufacturing biodegradable orthopedic fixation implants. Low plastic burnishing (LPB) has emerged as an enabling manufacturing technique to produce superior surface integrity of orthopedic implants to increase corrosion resistance of Mg-Ca implants. The basic understanding on contact mechanics between burnishing ball and the workpiece is essential to understand process mechanics. The contact mechanics is further complicated by normal force reduction due to hydraulic pressure loss, the penetration depth, and elastic recovery. In this study, the measured rolling force shows maximum 23% reduction compared with the theoretical value. A 2D axisymmetric, semi-infinite FEM model has been developed to predict the amount of elastic recovery after burnishing. The dynamic mechanical behavior of the material is modeled using a user material subroutine of the internal state variable plasticity model. The simulated dent geometry agrees with the measured data in terms of dent profile and depth. Acoustic emission (AE) process monitoring signals are recorded and the likely correlation with predicted residual stress, plastic strain, and temperature distributions are studied to obtain an in-process monitoring tool.