Department of Mechanical Engineering

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    Assessing latent initiator based multiple healing in epoxy matrix GFRP laminated composites
    (Department of Mechanical Engineering, NITS, 2020-07) Prasad, Tankeshwar
    The matrix of any structural materials typically consists of brittle polymer, which is susceptible to crack initiation and growth. To resist this flaw, the concept of self-healing is introduced. Present research work demonstrates a latent initiator based healing agent is used externally into the damage region to restore its original mechanical properties after healing followed by a strong covalent bond at the interface. Also, healing can be possible in the multi-step. In comparison to another healing approach, the healing efficiency of healed samples was found higher compared to the virgin sample. In order to achieve this objective, latent initiator based healing agent grafted silica nanoparticles were synthesized using the one-pot/sol-gel method (IFSs) and multi-step process/post-synthesis grafting method (IGSs). Further, the performance and healing ability IFSs and IGSs reinforced epoxy composites have been investigated. After detail investigations, the results concluded that IFSs/IGSs has no healing capability for the resistance of crack in the epoxy nanocomposites. Looking opportunity towards maximum healing efficiency with unaltered mechanical properties, imidazole as a suitable latent initiator based healing agent for extrinsic healing capabilities of IFSs/epoxy composites using have been investigated. After a successful demonstration towards enhancing the toughening and healing performance of nanocomposites, multiple healing capabilities of GFRPs laminated composites using the same healing agent have been investigated further. Initially, the effect of varying content of imidazole on tensile, flexural and hardness properties of epoxy nanocomposites was demonstrated. Composites (IENC-110) added with 10 wt. % of imidazole and 1 wt. % IFS showed maximum enhancement in tensile strength by 61 % (66 MPa) compare to NE (41 MPa) respectively. However, the tensile modulus is remained unchanged as compared to NE. For flexural properties, the significant enhancement in flexural strength and flexural modulus by ~96 % (102 MPa), and 15 % (2.83 GPa), respectively for IENC-15 composites was found. Similarly, the maximum enhancement in hardness for IENC-110 composites by 19 % (24.57 HV) was found as compared to that of NE (20.71 HV). Further, multiple fracture test of SENB was performed to evaluate fracture toughness and healing performance of epoxy nanocomposites. The results showed the maximum recovery in fracture toughness for IENC-110 composites by 67 % (1.17 MPa.m0.5) as compared to the virgin sample (0.70 MPa.m0.5) was achieved over 3rd number of healing cycles. However, the maximum healing efficiency for IENC-110 composites of 140 % due to critical peak loads while 167 % due to fracture toughness at the 3rd number of healing cycles was achieved. Finally, the appearances of hackel marks in the fracture surface under fractography analysis also justify the significant enhancement in surface roughness. Further, multiple healing capabilities of GFRPs laminated composites using the same healing agent have been investigated. The effect of varying content of imidazole on tensile, flexural and hardness properties of GFRPs composites was demonstrated. The maximum enhancement in tensile strength, tensile modulus, strain and modulus of the toughness of GFI-10 composites of ~34 % (~464 MPa), ~13 % (~6.80 GPa), ~13 % (~8.16 %) and ~64 % (~22 MJ.m-3) respectively were found. This is mainly ascribed to the formation of strong interface between the fiber and the matrix due to the addition of imidazole. Further, the optical micrograph of the tensile fracture surface of the virgin sample showed poor through-thickness delamination where the fibers are failed like a broom. In contrast, the addition of imidazole in epoxy/GFRPs composites restricts the through-thickness delamination and reduced the blooming effect with partial fiber breakages. For flexural properties, the maximum enhancement in flexural strength, flexural modulus, flexural strain and work of flexural of GFI-10 composites of ~34 % (~389 MPa), ~22 % (~19.70 GPa), ~100 % (~0.04 mm/mm) and ~72 % (~16.76 MJ.m-2) respectively were found. This attributed the formation of strong bonding between glass fiber and matrix due to sustaining the more flexural stress. Similarly, for hardness properties, the maximum enhancement in the hardness of composite (IEGF-110) added with 10 wt. % of imidazole and 1 wt. % of IFS of 21 % (74.44 HV) was found. This may be attributed to the high packing density of the final network. Further, multiple fracture test of DCB was performed to evaluate fracture energy and healing performance of GFRPs composites. The results demonstrate a maximum recovery in fracture energy for GFI-10 composites by 83 % (1.87 kJ/m2) as compare to the virgin (0.37 kJ/m2) over 12th healing cycles. It suggests that healing with excess (10 wt. %) imidazole with respect to epoxy within the delamination surface increases the number of bonds that bounds the delaminated surfaces strongly during the repetitive healing. However, the maximum healing efficiency for GFI-10 composites of 154 % due to critical peak loads while 182 % due to fracture toughness at 12th number of healing cycles was achieved. Finally, the optical micrograph of the mid fracture surface of DCB samples showed the relatively rough fractures surface because of fiber bridging and fiber pull-out for GFI-10. Thus, the capability of imidazole to restrict the damage in FRPs composites is evident from the fractography investigation. This work successfully demonstrates the capability of imidazole introduce healing capability in GFRPs.
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    Investigation of Mechanical and Tribological Properties of Mg-alloy based Hybrid Reinforced Composite Fabricated through Powder Metallurgy
    (Department of Mechanical Engineering, NITS, 2025-11) Kumar, Sudhir
    Advancements in material science have driven the rapid development of magnesium-based metal matrix composites (Mg-MMCs) to meet the growing demands of modern engineering applications. These composites offer an excellent strength-to-weight ratio, improved corrosion and wear resistance, and the ability to withstand elevated temperatures, making them ideal for high-performance applications. While pure magnesium has poor mechanical and physical properties, its limitations can be mitigated by incorporating reinforcements, such as ceramic particles in the form of fibers, whiskers, or particulates. These reinforcements greatly improve the strength, ductility, toughness, and abrasion resistance of the composites. The synergistic interaction between the magnesium matrix and reinforcing particles results in microstructural refinement and optimization of the composite’s mechanical behaviour. However, challenges such as inhomogeneous distribution, poor wettability, and weak interfacial bonding between the matrix and reinforcements often arise during liquid metallurgy-based fabrication techniques. Researchers have increasingly adopted the powder metallurgy technique to address these limitations. Overall, magnesium metal matrix composites are recognized as promising candidates for advanced structural and functional applications, providing a well-balanced combination of lightweight characteristics and high mechanical integrity. In this research, hybrid composites of magnesium alloy (AZ91) reinforced with titanium carbide (TiC) and reduced graphene oxide (rGO) were studied. The powder metallurgy method was used to synthesize magnesium alloy-based hybrid composites. The tribological behaviour of fabricated composite samples were examined using a pin-on-disc tribotester per the ASTM G99 standard. Using the Taguchi method, the design of the experiment (DOE) was constructed. And, the L9 orthogonal array opted for tribo-performance evaluation. Also, an ANOVA and regression analysis were carried out to ascertain the relative impact of the tribological factors on the responses. In the present investigation, three variable factors were considered, i.e., reinforcement percentage of TiC (0-10%) keeping constant 0.5 wt.% rGO, disc sliding velocity (0.5 to 1.5 m/s), and applied load varies between 10 to 30 N. It was found that the load parameter had a considerable impact on both the wear rate (WR) and the coefficient of friction (COF). Sliding velocity, on the other hand, had a minimal effect on WR. The concentration of reinforcement exhibits a moderate impact. Taguchi’s predictive results were also compared with experimental results. The optical microscope (OM) v examination of the microstructure of the fabricated hybrid Mg-MMC revealed significant grain refinement and a uniform distribution of reinforcement, thereby enhancing the microstructure. The worn surfaces were analyzed using scanning electron microscopy (SEM), and surface characterizations were used for wear mechanics analysis. In further research, the tribological and mechanical behavior of Mg-hybrid nanocomposites has been studied. Magnesium alloy (AZ91) based composite were fabricated by reinforcing nano-sized titanium carbide (nano-TiC), with weight percentages (wt.%) varying from 0.5% to 2% while maintaining a constant 0.5 wt.% of nano-reduced graphene oxide (rGO) throughout the experiments. Hybrid magnesium metal matrix nanocomposites (HMMMNCs) were prepared using a powder metallurgy procedure. The microhardness and compressive strength of the composite samples showed a significant improvement, with increases of approximately 45.9% and 44.3%, respectively, compared to the matrix material. This improvement in strength is attributed to the synergistic reinforcement effect of both nano-TiC and rGO. Additionally, at the optimal nano-TiC concentration of 1.5 wt.%, the wear rate and coefficient of friction (COF) of the HMMMNCs were decreased by ~40.7% and ~49.33%, respectively. This reduction is primarily due to the formation of a hardened ceramic phase in the contact region, which mitigates heat-induced softening. Additionally, various analytical tools, including XRD, SEM, and a surface roughness profilometer, were utilized to characterize the developed composite materials and analyze the worn surfaces. The analysis of the worn surfaces revealed that abrasive wear was the dominant wear mechanism at lower loads, whereas higher loads and sliding speeds led to adhesive wear, plastic deformation, and transfer film formation. Mg-MMCs have garnered significant interest across various industries, including automotive, aerospace, electronics, sports, marine, and equipment manufacturing. Further research is recommended to explore alternative processing methods as well as to examine the wear behaviour of HMMMCs under diverse environmental conditions. Additionally, the scope of analytical modeling and simulation may be considered in future work to predict and validate the tribological and mechanical performance of HMMMCs under different loading and environmental conditions.
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    Environmental Friendly Milling of Inconel 718: Dry, Air cooled and Bio-Based Minimum Quantity Lubrication Machining
    (Department of Mechanical Engineering, NITS, 2026-01-07) Sharma, Deepak Kumar
    Sustainable manufacturing has become increasingly important due to the environmental and health risks associated with mineral-based cutting fluids. As a safer alternative, bio-based lubricants especially those from vegetable oils are gaining attention because they are biodegradable, renewable, and naturally lubricating. This research focuses on the development, analysis, and use of nanoemulsions based on Putranjiva roxburghii oil for the eco-friendly and efficient milling of Inconel 718, a hard-to-machine nickel-based superalloy widely used in aerospace, marine, and high-temperature applications. The Putranjiva roxburghii seeds, available in certain regions, were processed using a traditional oil extraction method to obtain the base oil. Known for its good tribological performance, this non-edible oil was selected as a sustainable base fluid. To improve its heat, transfer and lubrication characteristics, two nanoparticles silicon dioxide (SiO2) and graphene were added in different weight percentages (0.25%, 0.5%, 0.75%, and 1%). Additionally, hybrid nanoemulsions were created using equal parts of SiO2 and graphene. Emulsions with varying water-to-oil ratios (from 100:5 to 100:30) were also prepared to find the best composition for Minimum Quantity Lubrication (MQL) use. A range of characterization techniques was applied to analyze the nanoparticles’ size, shape, and distribution, along with the thermal, rheological, and surface properties of the nanoemulsions. Results showed that adding nanoparticles significantly improved thermal conductivity, specific heat, and wettability compared to the base oil. The 0.75 wt.% graphene nanofluid showed the highest thermal conductivity, while the hybrid nanofluid (0.5 wt.% each of SiO2 and graphene) demonstrated the best wettability on Inconel 718. These findings suggest that no single nanofluid composition is perfect for every application, highlighting the need for multi-objective optimization based on machining requirements. The performance of these nanoemulsions was tested through face milling experiments on Inconel 718 under dry, air-cooled, and MQL conditions using cemented carbide cutting tools. Machining parameters like spindle speed, feed rate, and depth of cut were varied, and Box’s evolutionary optimization method was used to find the best settings. The nanoemulsions, delivered through an MQL system, were evaluated against performance indicators such as surface roughness, tool and workpiece temperatures, tool wear, cutting force, torque, and power consumption. The findings clearly showed that Putranjiva roxburghii oil-based nanoemulsions performed better under MQL conditions. The hybrid nanofluid in particular provided excellent cooling and lubrication of the combined benefits of wear resistance of SiO2 and high thermal conductivity and lubricity of graphene nanoparticles. This formulation achieved a minimum surface roughness of 0.29 µm 54.7% better than dry machining and 46.3% better than air cooling. The lowest recorded tool and workpiece temperatures were 41.1 °C and 31.46 °C, respectively, at 180 rpm spindle speed, 16 mm/min feed rate, and a 100:20 emulsion ratio. Microscopic inspection showed that tool wear was much lower under MQL, especially with the hybrid nanoemulsion, which showed minimal abrasive and crater wear. In contrast, dry machining resulted in noticeable abrasive wear and built up edge formation. MQL also led to more consistent cutting forces, reduced torque and power consumption, and longer tool life. However, improper dispersion or agglomeration of nanoparticles especially in hybrid mixtures could reduce surface quality and thermal stability. This emphasizes the need for stable and uniform nanoparticle dispersion for effective application. This study showed that nanoemulsions made from Putranjiva roxburghii oil, especially the hybrid type, are a promising and eco friendly alternative to traditional cutting fluids. Their better heat transfers and lubrication improved machining results. Future research can work on improving nanoparticle stability and studying the environmental impact and biodegradability of these fluids.