Ultra high molecular weight polyethylene (UHMWPE) is widely used in biomedical applications, e.g. as a bearing surface in total joint arthroplasty. Recently, equal channel angular extrusion (ECAE) was proposed as a processing method to achieve higher molecular entanglement and superior mechanical properties of this material \[1\]. Numerical modeling can be utilized to evaluate the influence of such important manufacturing parameters as the extrusion rate, temperature, shape of the die, back pressure and friction effects in the ECEA of polyethylenes \[2\].

In this paper we focus on the development of efficient FE models of ECAE for UHMWPE. We study the applicability of the available constitutive models traditionally used in polymer mechanics for UHMWPE, evaluate the importance of the proper choice of the friction parameters between the billet and the die, and compare the accuracy of predictions between 2D (plane strain) and 3D models.

The numerical modeling results are compared with experimental data obtained by extrusion of GUR 1020 and GUR 1050 resins at various temperatures and deformation rates. The resin is compressed to a green state at a specific temperature and pressure before the extrusion. The extrusion is performed using a steel die with two 50mm x 50mm x 200mm channels connected at a sharp right angle. No lubrication between the material billet and the die is used to reveal the frictional effects. Front and back pressure are delivered by 50-ton hydraulic cylinders. The front-pressure punch is velocity controlled which allows a variable extrusion rate. The back-pressure punch is force controlled to deliver a constant hydrostatic pressure applied to the billet during extrusion. The process temperature is controlled using a set of heater cartridges embedded into the die. After the extrusion, the polyethylene billet is extracted from the channel using the extracting punch and cooled to room temperature. The extrusion and extraction of the billet is simulated in finite element analysis including rate, temperature and friction sensitivity of the process. As a result of finite element simulations we obtain spatial distribution of stresses and strains within the billet during and after the process which is crucial for understanding the material behavior and the resulting changes in its mechanical properties.

References:

\[1\]      Reinitz SD, Engler AJ, Carlson EM, Van Citters DW. Equal channel angular extrusion of ultra-high molecular weight polyethylene. Mater Sci Eng C 2016;67:623–8. doi:10.1016/j.msec.2016.05.085.

\[2\]      Mitsak A, Aour B. Numerical and experimental investigation of HDPE behavior during 2-ECAP process using 90° and 120° dies. J Brazilian Soc Mech Sci Eng 2017;39:2055–69. doi:10.1007/s40430-016-0563-1


On Numerical Modeling of Equal Channel Angular Extrusion of Ultra High Molecular Weight Polyethylene

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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