Investigation of Impact Strength and Hardness of UHMW Polyethylene Composites Reinforced with Nano-Hydroxyapatite Particles Fabricated by Friction Stir Processing

The impact strength and surface properties of polymeric materials are of critical importance in various engineering applications. Friction stir processing (FSP) is a novel method for the fabrication of composite materials with superior mechanical properties. The main objective of this study is to investigate the impact strength and Rockwell hardness of UHMW polyethylene composites reinforced with nano-hydroxyapatite particles fabricated through FSP. The spindle speed (ω), tool traverse speed (f), volume fraction (v) of strengthening material and shoulder temperature (T) were key processing parameters. The analysis of variance (ANOVA) indicated that the selected processing parameters were significant. Microscopic investigations unveiled that high levels of (v, f) and low levels of (T, ω) caused agglomeration of the reinforcing particles and induced voids and channels, which consequently reduced the impact strength and hardness of the manufactured composite. However, medium conditions of processing parameters exhibited better distribution of particles with minimum defects, and hence resulted in better mechanical properties. Finally, the models to predict the impact strength and hardness are proposed and verified. Sets of process parameters favorable to maximize the impact strength and Rockwell hardness were worked out, which were believed to increase the impact strength, Rockwell hardness number, and ultimate tensile strength by 27.3%, 5.7%, and 11.2%, respectively.