Browsing by Author "Ojha, N."

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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.
A comprehensive characterization of 3D printable poly ether ketone ketone
(Elsevier Ltd, 2024) Ojha, N.; Kumar, S.; Ramesh, M.R.; Balan, A.A.S.; Doddamani, M.
The current work focuses on the comprehensive characterization of a 3D printable biomaterial, polyether ketone ketone (PEKK). The PEKK granules are first characterized and then utilized for extrusion of the PEKK filaments. The extruded PEKK filaments are characterized for crystallinity, quality, and printability, wherein they exhibit amorphous nature, good quality, and appropriate printability. Utilizing the filaments, the samples are printed with the appropriate printing parameters, which are further characterized for layer adhesion, voids, and crystallinity, wherein they showed seamless layer adhesion, improper beads consolidation, and the amorphous nature. The as printed samples are further annealed at different temperatures (200 and 250 °C). The scanning electron microscopy (SEM) of the annealed samples (A-200 and A-250) revealed better void consolidation, while the X-ray diffraction (XRD) revealed better crystallinity compared to the un-annealed sample. The printed samples are also investigated for dynamic mechanical analysis (DMA), shape memory, and tensile properties. The storage moduli of the annealed samples are observed to be better than the un-annealed sample. The annealed samples exhibited better shape memory properties: shape fixity and shape recovery ratio of A-200 and A-250 samples, 90.28 and 90.75%, and 99.16 and 94.73%, respectively, compared to the un-annealed samples. The highest shape fixity ratio and the shape recovery ratio are noted for A-250 (90.75%) and A-200 (∼ 100%). The A-200 and A-250 samples showed enhanced tensile modulus and strength, 4.16 and 49.67%, and 36.61 and 35.06%, respectively compared to the un-annealed sample. The highest modulus is noted for A-250, while the strength is comparable (36.61 and 35.06%) for A-200 and A-250. © 2023 Elsevier Ltd
Influence of subsequent thermomechanical cycles on shape memory behavior of 4D printed PEKK
(Elsevier B.V., 2023) Ojha, N.; Kumar, S.; Ramesh, M.R.; Balan, A.S.S.; Doddamani, M.
The current study identifies and investigates the shape memory response of poly ether ketone ketone (PEKK) for the first time. 4D printed PEKK are subjected to annealing, crystalline behavior, and shape memory studies under susquent thermomechanical cycles. Scanning electron microscopy (SEM) revealed seamless bonding between the printed layers, confirming the suitability of the chosen printing parameters. Differential scanning calorimetry (DSC) results showed higher Tg (161.20 °C) and Tm (339.03 °C). Shape fixity ratio (Rf) is observed to be lower in the higher cycles (∼10% lower in cycle 8 compared to cycle 1), while the shape recovery ratio (Rr) is noted to be decreasing in each cycle ( 20% decreased in cycle 8 compared to cycle 1) due to reduction in storage modulus. The 4D printed PEKK exhibited excellent shape memory properties as compared to PEEK, making them potential materials in automotive and aerospace applications. © 2023 Elsevier B.V.
Investigating the effect of thermomechanical cycles on shape memory effect of four-dimensional printed glass fiber/polyether ketone ketone composite
(John Wiley and Sons Inc, 2025) Ojha, N.; Kumar, S.; Ramesh, M.R.; Doddamani, M.
Assessing the shape memory effect (SME) under repetitive thermomechanical cycles is crucial for designing structures undergoing subsequent fold and deployment during functioning, such as morphing structures and soft grippers. Four dimensional (4D) printing is a revolutionizing manufacturing technology, offering dynamic feature into three dimensional (3D) printed part. This work presents the first study on 4D printing and SME assessment of glass fiber (GF)/polyether ketone ketone (PEKK) composite for morphing structures and grippers in aerospace applications. GF/PEKK composite is developed using blending, and then filament is extruded for 3D printing. Annealing is performed on the 3D printed parts and evaluated using scanning electron microscopy (SEM), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and SME under subsequent cycles. The SEM analysis demonstrated the uniform distribution of GFs into PEKK with good interfacial bonds, indicating the appropriate selection of the process parameters. The composite depicted remarkable shape fixity (Rf) and shape recovery (Rr) of 91.07% and 96.08%, respectively, in first cycle. However, in tenth cycle, Rr is found to be decreased to 86.30%, a reduction of 9.78% is observed. Key findings of this research are the excellent storage modulus of 3150 MPa, which is 82.93% higher than PEKK. Thermal studies revealed very high glass transition temperature (Tg) of 175°C and thermal degradation temperature (Td) of 561.36°C, which is higher than PEKK (Tg = 161°C and Td = 548°C), demonstrating excellent thermal performance and showing potential for high-temperature shape memory applications. Highlights: Composite showed excellent shape fixity (91.07%) and shape recovery (96.08%). Quick shape recovery in 20 s showed potential for a swift actuator. Storage modulus of 3150 MPa is observed for the composite. Composite has a glass transition temperature of 175°C. Composite exhibited a high thermal degradation temperature of 561.36°C. © 2025 Society of Plastics Engineers.
Shape memory behavior of 4D printed CF/PEKK high temperature composite under subsequent thermomechanical cycles
(Elsevier B.V., 2024) Kumar, S.; Ojha, N.; Ramesh, M.R.; Balan, A.A.S.; Doddamani, M.
Shape memory effect (SME) in high temperature polymers (HTPs) has great significance in space for making self-deployable structures, needing high strength and stiffness during operation, signifying the necessity of exploring HTP composite with SME. This work investigates the SME of 4D printed carbon fiber/polyether ketone ketone (CF/PEKK) HTP composite under subsequent thermomechanical cycles for the first time. Scanning electron microscopy (SEM) revealed a uniform distribution of CFs in the developed composite, the extruded composite filament, and the composite prints with seamless raster and layer deposition, confirming a suitable selection of processing parameters. The CF/PEKK composite prints exhibited an excellent shape fixity, Rf = 90 % and 91 %, and shape recovery, Rr = 96 % and 89 % in the first and the tenth cycle, respectively. A significant loss of 7 % in Rr is observed in the tenth cycle. Glass transition (Tg) and degradation temperature (Td) of the CF/PEKK composite prints are observed to be 162 °C and 568 °C, while storage modulus is found 157.69 % and 38.69 % higher than the existing PEKK and PEEK, respectively. This study revealed an excellent SME of 4D printed CF/PEKK composite with outstanding Tg and Td, showing great potential for space applications. © 2024 Elsevier B.V.