Faculty Publications
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Item Recycling potential of MWCNTs/HDPE nanocomposite filament: 3D printing and mechanical characterization(Springer, 2023) Kumar, S.; Ramesh, M.R.; Doddamani, M.Fused filament fabrication (FFF) based additive manufacturing (AM) process is a widely used and emerging manufacturing process for polymer-based products. The recycled filaments are realized through wastage generated while extruding the constant diameter feedstock filament, which is otherwise dumped in landfills or incinerated, releasing hazardous and toxic gases that influence the ecological environment. The wastage of these filaments can be eliminated by recycling and reusing them, addressing materials circular economy effectively, presented in this paper. The functionalized MWCNT reinforced HDPE (high-density polyethylene) nanocomposite (NC) is realized through a brabender, which is further used for filament extrusion. The waste/unrecycled (W/UR) and the recycled filaments are checked for quality. The density of the recycled filaments increases compared to the W/UR filament in each extrusion pass. The crystallinity and tensile properties of the recycled filaments increase compared to the W/UR filament with each additional extrusion cycle. Further, these filaments are used for 3D printing, and investigated for density, XRD and tensile tests. It is observed that the density, crystallinity and tensile properties of the recycled prints increase compared to the W/UR print. The tensile strength and modulus of 1 × , 2 × and 3 × prints are 63.82, 67.11 and 67.76%, and 45.63, 55.34 and 97.81% respectively, higher than those of the W/UR print. The highest tensile strength and modulus are observed for 3 × print which is 67.76 and 97.81% respectively, higher than those of the W/UR print. 3D prints exhibited enhanced performance as compared to their respective filaments. Finally, the present tensile results are mapped on a property chart, and compared with the available HDPE composites. © 2023, Springer Nature Japan KK, part of Springer Nature.Item Investigation on hardness, impact, and compression responses of additively manufactured functionally graded nanocomposites(Elsevier Ltd, 2023) Kumar, S.; Ramesh, M.R.; Doddamani, M.Functionally graded nanocomposites (FGNCs) are fabricated using 3D printing for hardness, impact and compression investigations with different wt. % (0.5⟶H0.5, 1⟶H1, 3⟶H3, 5⟶H5) of functionalized MWCNTs in high-density polyethylene (HDPE). Further, they are extruded as feedstock filament for 3D printing. The hardness, impact strength, and compressive properties increase while the energy absorption decreases with a % increase in the functionalized MWCNTs. The highest hardness, impact strength, compressive moduli, and strength observed for FGNC-2 (H1⟶H3⟶H5) are 76.80, 119.99, 61.14, and 11.56%, respectively, higher than HDPE. The betterment in the mechanical properties is attributed to the strengthening and stiffening effects due to the homogeneous distribution of the functionalized MWCNTs in HDPE. The FGNC-2 exhibited the highest mechanical properties, and can be used in various applications wherein variational stiffness is required. © 2023 Elsevier LtdItem Buckling and dynamic responses of 3D printed nanocomposites and their graded variants(Elsevier Ltd, 2023) Kumar, S.; Ramesh, M.R.; Jeyaraj, P.; Doddamani, M.The experimental and numerical investigations are carried out for buckling and vibration of 3D printed functionalized MWCNTs/HDPE based nanocomposite (NC) and their functionally graded nanocomposite (FGNC) variants. Pcr(critical buckling load) is computed through MBC (modified budiansky criteria) and DTM (double tangent method) techniques. It is observed that Pcr of the 3D printed NCs and FGNCs increases with the functionalized MWCNTs content. The Pcr values for the NCs (H0.5-H5) computed using DTM and MBC increased in the range of 16–79%, while for FGNC-1 (H0.5-H1-H3) and FGNC-2 (H1-H3-H5), the Pcr increased from 54 to 91% compared to HDPE. Further, it is observed that the natural frequency of the NCs and FGNCs increases with the functionalized MWCNTs loading while decreases with rise in compression. The natural frequency of the NCs (H0.5-H5) and FGNCs increased up to 41% than HDPE. The highest Pcr and the natural frequency is noted for H5 and FGNC-2 prints. The experimental and numerical results showed good agreement. © 2023 Elsevier LtdItem Buckling behavior of non-uniformly heated 3D printed plain and functionally graded nanocomposites(John Wiley and Sons Inc, 2023) Kumar, S.; Ramesh, M.R.; Jeyaraj, J.; Powar, S.; Doddamani, M.The functionalized multi-walled carbon nanotubes (MWCNTs) (0.5–5 wt.%) are compounded with high density polyethylene (HDPE), and, subsequently, used for extruding nanocomposite filaments to fabricate nanocomposites (NCs) and functionally graded nanocomposites (FGNCs) through 3D printing. The 3D printed NCs are investigated for coefficient of thermal expansion (CTE), and buckling under different non-uniform temperature distributions (case-1: left edge heating, case-2: centre heating, and case-3: left and right edge heating). A significant reduction in CTE is observed with MWCNT addition and gradation. The highest reduction in CTE is observed for H5 (5 wt.% of MWCNT in HDPE) NC and H1 ⟶ H3 ⟶ H5 (FGNC-2) among the NCs and the FGNCs. It is noted that Tcr (critical buckling temperature) is highest for case-3 and lowest for case-2. The highest deflection is noticed in case-2, while no significant difference is observed in case-1 and case-3 heating conditions. It is also observed that Tcr increases with gradation and MWCNTs addition. The H5 NC and FGNC-2 exhibited the highest Tcr among the NCs and FGNCs, respectively. The maximum deflection is noticed for HDPE, whereas the minimum deflection is noticed for FGNC-2 and H-5 NC among the tested samples. The results also revealed that Tcr is very sensitive to type of heating. © 2023 Society of Plastics Engineers.Item 4D printing of heat-stimulated shape memory polymer composite for high-temperature smart structures/actuators applications(John Wiley and Sons Inc, 2024) Kumar, S.; Ojha, N.; Ramesh, M.R.; Doddamani, M.High temperature shape memory polymers (HT-SMPs) have great utilization in self-deployable hinges/morphing structures for space/aerospace, and high-temperature sensors/actuators for electronics. However, HT-SMPs have many drawbacks, such as low stiffness, strength, thermal stability, and dynamic mechanical properties. This work aims at improving these properties of highly utilized space grade HT-SMP, PEKK (polyether ketone ketone), by reinforcing it with low-cost carbon fibers (CFs), and developing its composite via additive manufacturing. The additively manufactured CF/PEKK composites are annealed at 200 °C (CF/PEKK-A200) and 250 °C (CF/PEKK-A250), and for the first time, investigated for shape memory effect (SME). The shape fixity and the shape recovery of the CF/PEKK-UNA (un-annealed), CF/PEKK-A200, and CF/PEKK-A250 are noted to be 95.97%, 88.95%, and 86.40%, and 88.70%, 92.70%, and 95.19%, respectively with a significant weight saving potential of ?21%. Dispersion of CFs in PEKK and suitability of processing parameters (blending, extrusion, and 3D printing) are confirmed through scanning electron microscopy (SEM). Thermal degradation temperature ((Formula presented.)) of the printed CF/PEKK composite (?568 °C) is found to be ?3.5% higher than PEKK (?549 °C). CF/PEKK-A250 exhibited the highest storage modulus (4438.23 MPa), ~158% higher than PEKK (1722.3 MPa), while CF/PEKK-A200 demonstrated the highest tensile modulus (10.9 GPa), which is 138.5% higher than PEKK (4.57 GPa) and 312.88% higher than CF/PEKK-UNA (2.64 GPa). Moreover, CF/PEKK-A200 exhibited 237.46%, 138.51%, 127.08%, 61.48%, 32.93%, and 50.35% higher tensile modulus than PEEK, PEKK, PEK, CF/PEK, CF/PEEK, and CF/PEKK composites, respectively, showing great potential to replace them. Highlights: Printed CF/PEKK composites are investigated for shape memory behavior. The printed composites exhibited outstanding shape memory properties. Printed-A200 exhibited 138.51% enhanced tensile modulus than pure PEKK. Also, the printed-A200 showed 313% enhanced modulus than printed-UNA. (Formula presented.) (568 °C) of the printed composites is found ?4% greater than pure PEKK. © 2024 Society of Plastics Engineers.