Mechanical Engineering Journal (Aug 2021)
Analysis of orientation behavior in extruded tricalcium phosphate/poly(lactic acid) composite billet using finite element method and chain network model
Abstract
The poly(lactic acid) (PLA)-tricalcium phosphate (TCP) composite attracts much attention as a material for a bone fixation device because both have bioabsorbability. However, the applications of the composite bone fixation device are limited to low-loaded regions because of lower strengths. In this study, PLA and TCP/PLA composite cylindrical billets were extruded to improve their strengths, with the aim of clarifying the molecular orientation behavior of the PLA and TCP/PLA billets in extrusion. First, the effect of the orientation behavior in the PLA billets on the extrusion ratio (ER) was calculated. Next, the TCP/PLA billets were analyzed. The molecular orientation obtained by extrusion was investigated by a combination of the finite element method and the chain network model. Consequently, the orientation function of the extruded billet was found to increase with the ER. Furthermore, the orientation function of the TCP/PLA billet was higher than that of the PLA billet, which may be due to the change in the yield stress and n value of the billet by TCP addition. The orientation distribution in the radius direction of the extruded PLA billet showed that the orientation function at the surface region was larger than that at the center region. This orientation distribution might be because the movement distance of the surface region during extrusion was longer than that in the center region. The surface region in the billet was drawn by the difference of those movement distances and might be orientated. The workability of the PLA and TCP/PLA billets was also investigated using pressure during extrusion. The results showed that the extrusion pressure increased with the TCP content and ER. Therefore, extrusion workability decreased with the TCP content and the ER.
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