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In this work, carbon nanotube (CNT) reinforced polypropylene (PP) composites (0.5, 1.0, 3.0, and 5.0 wt%) were developed using the melt compounding process. The developed composites were injection-molded into tensile specimens and pins to evaluate the mechanical and tribological properties of the composites. As the CNT content increased, the tensile strength and Young's modulus of the PP composites increased. The addition of the CNTs to the PP matrix beyond 1 wt% demonstrated agglomeration, and fractured tensile specimens confirmed this behavior. Developed materials demonstrated enhanced crystallinity up to 1 wt% CNT and, subsequently, decreased crystallinity beyond 1 wt% CNT, and an X-ray diffraction investigation confirmed this behavior. The measured coefficient of friction, online wear, and weight loss from the sliding wear test confirmed the least frictional resistance and maximum wear resistance for the 1 wt% CNT-PP composite. As the CNT content increased, the hardness of the CNT-PP composite increased up to 1 wt% CNT and decreased beyond this threshold. The worn-out surfaces of the CNT-PP composite observed using a scanning electron microscope and noncontact three-dimensional profiler confirmed the superior wear resistance of the 1 wt% CNT-PP composite. The CNT-PP composites considered in this study exhibited increased surface temperatures in the sliding wear condition because of the addition of the CNTs. The addition of the CNTs to the PP material increased the thermal conductivity of the composite.

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Polymer gears can replace metallic gears in many engineering applications; however, thermal sensitive mechanical properties of the polymers limit its wide application. Gear tooth surface interaction as well as material hysteresis generates heat in the gear operation. There have been many attempts to improve the gear performance by design modifications as well as with new materials to withstand against thermal damages. In this work, compressed air cooling method is adopted to improve the wear resistance of injection molded polypropylene spur gears. For the chosen gear and test conditions, continuous measurement of gear surface temperature confirmed that compressed air cooling lowers the temperature up to 15 C. Periodical measurement of gear tooth thickness confirms that wear resistance increases up to 100%. Continuous measurements of torque available in driver and driven end confirmed that a 2% increase in transmission efficiency of the gear pair. Test gear tooth surface after a finite number of cycles also confirms the effect of compressed air cooling on wear resistance. Mao model is used to predict the gear surface temperature and found to be in close agreement with experimental results.

Energy absorption is a key performance criterion for several engineering structures. Lightweight lattice structures are better suited for this purpose. The convolute design patterns that exist in nature are proven effective for several engineering applications. In this paper, a George lily flower leaf is considered to build a novel 3D open lattice pattern for specific energy absorption (SEA) purposes. A multi-cellular specimen is designed and fabricated using Vat photopolymerization 3D printing process. Quasi-static compression tests have been conducted and the performance of proposed structure is compared with 2.5D closed thin-walled structures and found the proposed 3D open lattice structure has shown significant improvement in SEA over other thin-walled structures.

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