Ajay Kumar

Type‐V composite pressure vessels (CPVs) for hydrogen storage face challenges in balancing high structural strength, lightweight construction, and permeation‐barrier performance. In this study, hybrid 4 carbon and 3 polyethylene (4C3PE) laminates alternating reinforced with graphene nanoplatelets (GNP) are prepared. A comparative multi‐scale analysis was conducted for Type‐V laminate architectures, integrating analytical hoop‐stress, finite element analysis (FEA) simulations, and ASTM D3039 tensile experiment analysis to develop a reliable design framework. Experimental characterization of the 4C3PE laminate revealed that a 2 wt.% GNP loading provides an allowable ultimate tensile strength of 648 MPa, with uniform dispersion of GNPs of an average agglomerate size (0.42 ± 0.11 μm), and a low void content below 1.5%. The carbon fiber‐polyethylene interlayers function as compliant barriers, reducing interlaminar shear stresses and preventing microcrack propagation. Structural scaling studies indicate that the 4C3PE architecture with unidirectional (0/0/0) _s stacking sequences is unsafe under 70 MPa pressure for configurations under 12C11PE. The 16C15PE laminate, as the optimal design, achieves a balanced Factor of Safety of 3.11 by maintaining circumferential stresses at 208.605 MPa within allowable limits, despite the weight penalties associated with thicker laminates. Microstructural observations suggest that GNP‐assisted crack deflection, PE‐mediated delamination suppression, and the formation of tortuous diffusion pathways may reduce potential hydrogen‐permeation routes. The study establishes a framework for screening materials in laminated architectures, with the 16C15PE laminate and 2 wt.% GNP as a promising candidate for linerless Type‐V vessels. This groundwork will facilitate future tests on pressure‐cycling and hydrogen permeability for full‐scale vessel production.

High entropy alloy (HEA) nitride films have attracted considerable research attention in recent years due to their superior mechanical properties compared to their corresponding base HEAs. In the present study, nitride films of AlCoCrCuFeNiTi HEA have been synthesized via reactive sputtering. The films have been deposited in Ar and in He to study the effect of different discharge gases on the properties of the film. The nitride film of AlCoCrCuFeNiTi had a NaCl-type (B2) solid-solution when deposited in Ar. The thermodynamic parameters are calculated for both the nitride films and the lattice distortion, mixing enthalpy and mixing entropy of the metal sublattice were higher for the film deposited in He. The deposition in He resulted in an amorphous-like nature. The deposition rate and film thickness were much smaller in the film deposited in He due to the lower atomic mass of He when compared to Ar. Film deposited in Ar had a higher roughness and subsequently a higher wetting contact angle among the two. Both films were hydrophobic. A maximum hardness of 6.69 ± 0.33 GPa was achieved for the film deposited in He. The discharge gas has a significant influence on the phase, surface and mechanical properties. Nitriding the AlCoCrCuFeNiTi improved the film properties over the base HEA. The study provides valuable insights into the nitride films of AlCoCrCuFeNiTi via reactive sputtering, and the outcomes of the study could be used to design the (AlCoCrCuFeNiTi)N.

High entropy alloys (HEAs) are an advanced class of multi-principal element materials, while semi-solid processing (SSP) is a well-established technique for conventional alloys but relatively unexplored in the context of HEAs. Although both HEAs and SSP have been extensively studied independently, only limited research has addressed SSP of HEAs. This paper reviews HEAs, their strengthening mechanisms, alloy design strategies, and manufacturing routes, followed by a discussion of SSP approaches applied to HEAs. Several HEAs demonstrate promising mechanical and radiation-resistant properties, suggesting potential applications in aerospace and nuclear sectors. SSP may promote globular microstructures and microstructural refinement, which can enhance mechanical performance depending on alloy composition and processing parameters. Cooling slope casting, a variant of SSP that has received limited attention for HEAs, represents a promising direction for future research.

This study investigates the mechanical performance of linerless Type‐V composite pressure vessels (CPVs) with a new laminate‐level scheme for high‐pressure hydrogen storage. A cross‐linked Hot‐pressed 4C3PE schema incorporates (4) carbon fiber (C) and (3) polyethylene films (PE) via compression molding, infused with (VARIM) with Bisphenol A diglycidyl ether and Diethylenetriamine as (DGEBA/DETA) epoxy system, and further modified by graphene nanoplatelets (GNPs). Thermomechanical analysis, by employing TGA, DMA, and DSC, evaluates the superiority of the 4C3PE cross‐linked scheme over the pristine epoxy system DGEBA/DETA and conventional 4 carbon 4C‐DGEBA/DETA stoichiometry. The optimal loading of GNPs at 2 wt.% enhances mechanical properties, increasing ultimate tensile strength (UTS) from 442 to 648 MPa as 46.6%, and with 35% increase in tensile modulus. Similarly, flexural strength increased from 120 to 234.5 MPa, with 95.8% and 60% increase in flexural modulus, demonstrating an effective balance between in‐plane stiffness and out‐of‐plane bending resistance for Type‐V geometry. However, at 3 wt.%, agglomeration of GNPs leads to a decrease in strengths, reducing UTS to 546 MPa and flexural strength to 123 MPa. Fractography analysis via FE‐SEM also indicates that a 2 wt.% dispersion of GNP enhances interfacial bonding, mechanical strength, and gas impermeability qualitatively (25%–38%) by reducing micro‐voids through a crack‐arresting network formed by continuous macro (PE) barriers and micro (GNP) inclusions.

Hydrogen storage in lightweight composite pressure vessels demands materials with excellent thermal stability, reliable dimensional properties, and consistent curing behavior. In this study, carbon fiber reinforced epoxy laminates based on 4 carbon fiber layers with epoxy bisphenol A diglycidyl ether and hardener Diethylenetriamine as (4C-DGEBA/DETA) and other with our novel schema of 4 carbon fibers and 3 polyethylene films hot pressed with identical epoxy system as (4C3PE–DGEBA/DETA) analyzed and compared by using thermogravimetric analysis (TGA), Dynamic-mechanical analysis (DMA), and differential scanning calorimetry (DSC). TGA identified the degradation onset and differences in thermal stability between the two systems, while DMA provided insights into temperature-dependent viscoelastic behavior, including stiffness retention and damping characteristics. DSC used to evaluate curing characteristics and glass transition temperatures, revealing links between resin chemistry and thermal performance. The comparison showed that the modified 4C3PE–DGEBA/DETA system exhibited superior thermal resistance and dimensional stability compared to the baseline 4C-DGEBA/DETA composite. These results also improve the understanding of composite behavior in liner-less (Type-V) hydrogen storage pressure vessels and guide material selection and design improvements, supported by SEM surface morphology analysis for a novel 4C3PE laminate geometry.

High entropy alloys (HEAs) have attracted significant interest in recent years due to their exceptional structural and mechanical properties, yet their film behaviour is underexplored. The AlCoCrCuFeNiTi HEA has been studied for bulk, but has not been studied for film synthesis via magnetron sputtering and the role of substrate temperature on the HEA. In this study, films of AlCoCrCuFeNiTi have been synthesized via magnetron co-sputtering at different substrate temperatures (room temperature, 250 °C and 500 °C) on Si substrates. The study investigates the effect of substrate temperature on phases, composition, microstructure, and mechanical properties of AlCoCrCuFeNiTi films. The film synthesized at room temperature was amorphous, and the film synthesized at high temperature showed crystallinity. The 250 °C film had a mix of face-centered cubic and body-centered cubic phases, and the 500 °C film had primary face-centered cubic and B2 phases. The films had columnar cross sections and the 500 °C film had equiaxed grains and prominent grain boundaries. The 500 °C film had the highest average surface roughness of 5.02 nm, driven by grain growth. A maximum contact angle of 117.67° was achieved for the 500 °C film. At higher substrate temperatures, the film had better mechanical properties than the film at room temperature. The 250 °C film had the highest hardness of 4.82 GPa, and the 500 °C film had the highest reduced Young’s modulus of 103.92 GPa. The higher mechanical properties at higher substrate temperatures were due to the improved mobility of atoms at higher substrate temperatures, which allowed for compact, dense films. The substrate temperature has been found to have a strong impact on the phase, microstructure and mechanical properties of AlCoCrCuFeNiTi films. The study outcomes offer valuable insights for designing AlCoCrCuFeNiTi HEA films. Further study can be done on the effect of substrate bias on the behaviour of AlCoCrCuFeNiTi films.

Advances in cylindrical high‐end hydrogen storage systems for aerospace, undersea vacuum enclosures, and automobiles use Type V composite pressure vessels (CPV) as the next generation of sustainable energy storage. The latest liner‐less CPV (Type V) is most challenging. The basic need of this manufacturing aspect review on CPV is the transition toward a more sustainable hydrogen energy storage system. As analyzed through our review that Type IV pressure vessels optimized with this transition to Type V, where weight reduction is up to > 25%, higher load‐bearing efficiency is reported in past studies for Type V in comparison to Type IV vessels, with increase in volumetric density up to > 15% and more, and most importantly, hydrogen barrier performance as permeability is reduced from 10⁻¹² to < 10⁻¹⁶ mol m⁻¹ s⁻¹ Pa⁻¹ addressed. Type V pressure vessels eliminate the polymer liner, causing nonuniform stresses, which hinders in Type III/IV COPVs. This results in more uniform stress distribution and high burst performance at reduced mass. Studies show higher burst pressure and improved structural efficiency. At cryogenic CcH₂ hydrogen storage of up to 35 MPa pressure with improved epoxies is also explored. Mechanical characteristics of cross‐linked composite laminates, including thin films of clay, sand, polyethylene, and polyurethane, were also analyzed in the CcH₂ storage system. Strengthening (Type IV) composite pressure vessels with proper fiber/matrix alignment and polyethylene films instead of a polyethylene liner causes embrittlement and failure due to composite and plastic ties. Various stacking sequences related to flaws have been explored, Type IV (plastic liner) composite pressure vessels for improvement in Type V CPV. Filament winding techniques and automated fiber placements (AFP) used for winding sequence and stacking geometries of helical, hoop, and polar composite winding layers reveal that at 55° helical, followed by hoop winding, provides the highest strength. Based on our comprehensive review, we found that the fabrication and permeability challenges of liner‐less (Type V) vessels need further study. While recent advances in materials (e.g., high‐performance resins, nanoparticle reinforcement) and manufacturing techniques (e.g., AFP, out‐of‐autoclave curing) show promise, consistent and scalable solutions to address hydrogen permeation and structural integrity in liner‐less designs are still under active investigation.

Hemispherical end caps cover cylindrical pressure vessels mid‐surfaces for oil and gas, subsea vacuum enclosures, and automobile, and aerospace hydrogen carriers globally. This review discusses the importance of composite overwrapped cylindrical pressure vessel design characteristics like external pressures. The analysis of composite material properties and their resistive behavior on the cylindrical section is used to ensure accurate, safe, and effective pressure vessel operation at high pressures. Composite materials are popular for lightweight and end‐use performance in pressure vessel carriers for diverse applications. Current fibers include carbon, glass, and carbon/glass hybrid composite pressure vessels that employ less heavy material. Composite overwrapped pressure vessels (COPV) need accurate lamina sequence, laminate thickness, and fiber winding angles. Mandrel (liner) material, is also examined and suggested for metallic composite high‐pressure vessels (MC‐HPVs) including metal liners or circular rings circumferentially to decrease buckling and reinforce (Type‐III) COPV shells. The focus is on designing cylindrical components to prevent buckling in space rockets and automobiles under high‐pressure conditions, using stiffeners and holes for various stress scenarios. Genetic algorithm (GA) optimizes worst defects in composite cylinder shape on buckling, circular cutting holes on the shell for optimum stacking sequence lamination of fiber over the liner, and snap‐through reactions to support against buckling factors under pressure. The importance of autofrettage pressure and vibration on composite cylinder buckling was also analyzed. Liner‐less (Type‐V) composite pressure vessels represent the future of lightweight high‐performance pressure vessels, yet (Type IV) composite cylinders with plastic liners are light and strong and have numerous uses.Highlights: Buckling of cylindrical shells with mandrel material (liner) transition.

Low‐thickness/diameter cylindrical storage pressure vessels with composite overwrapping fail at diverse internal and external pressure circumstances, causing several faults that must be included and minimized to retain effectiveness and working capability. The bursting effect is caused by hoop (internal) stresses and can be reduced by composite lamination alignment and internal pressure resistance. Pressure vessel bursting faults vary with internal tensions and can induce fiber reinforced polymer fracture and composite cylinder failure under many failure criteria. Micro‐mechanical nondestructive testing uses independent failure criteria associated to modes like Tsai‐Wu, Tsai‐Hill, Azzi‐Tsai, Hoffman, and Chamis. Micro‐cracking of composite layers generates delamination in composite pressure vessels, causing porosity. Pressure vessel micro‐cracking was assessed using classical laminate theory. Composite material strain‐rate failures in mobile applications like hydrogen storage cars with composite pressure vessels are examined due to their widespread use. Finally, Polar, Helical, and Hoop winding sequences are consistently focused to optimize the design and analyze the parameters for the overall impact of different failure aspects as bursting behavior in cylindrical composite pressure vessels. Type‐IV composite pressure vessels have the best results due to their lightest weight but complexity of winding over the polar head geodesic and non‐geodesic curvatures overwrapped carbon include all these internal composite and liner geometry faults and optimize them to reduce failure issues to fix composite overwrapped pressure vessels (COPV's) design. Liner‐less composite pressure vessels (Type‐V) need more design and production study for high‐pressure and temperature applications.Highlights: Failure deals with the internal and external pressures exerted on composite pressure vessels. Failures like bursting of the pressure vessel, due to like micro‐cracking, delamination's and strain‐rate failures of composites. Failures detection through NDT inspection for polymer composite materials for composite pressure vessels. (COPV) perfect lamina sequence, liner materials and fiber winding angles must be considered for designing state of the art liner‐less Type‐V pressure vessels. Independent Failure criteria like (Tsai‐Wu & Hashin).