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Fiber-reinforced polymer matrix composites are increasingly considered for lightweight cryogenic pressure vessels due to their excellent combination of tailorability, specific mechanical properties, and relatively low coefficients of thermal expansion. However, significant challenges must be overcome to fully utilize PMCs for cryogenic fuel tanks in terms of transverse microcracking and subsequent permeation of cryogenic fuel. Gas permeation and microcrack densities of cryogenically cycled composites are highly influenced by their layup, ply thickness, load case, and manufacturing defects like voids and resin rich zones. There has been a significant amount of research on measuring gas permeation of composites fatigued under pure thermal or uniaxial thermo-mechanical stresses. However, results demonstrate that the gas permeability should be measured under biaxial thermo-mechanical stresses to properly gauge the leakage characteristics of damaged composites. This paper summarizes the results from over a hundred papers on the key parameters that influence the gas permeability of composites, appropriate testing methods to cycle composites for permeability measurement, methods to limit the evolution of transverse microcracks, and materials traditionally used for the fabrication of all-composite cryogenic fuel tanks. Thin plies and nanofiller-toughening of the matrix have been shown to provide significant improvements in transverse microcrack suppression within cryogenically cycled composites. [ABSTRACT FROM AUTHOR]

The composite shell of composite high pressure hydrogen storage vessel (CHPHSV) is the main structure in bearing inner pressure. Its failure will lead to leakage or burst of CHPHSV, which will cause serious safety problem and economic losses. So the security of CHPHSV has always been a key and difficult problem in academia and industry, which restricts the large-scale application of hydrogen. In this paper, the failures of composite shell of type III, type IV, and type V vessels are reviewed in experiment study, simulation method, optimization design, and damage detection, focusing on the burst modes (safe or unsafe), the influence of hydrogen-thermo-stress field, and the epistemic uncertainty. Firstly, the burst modes, failure behavior, test method, and influencing factors are summarized in the experiment study, and experiment for type V composite pressure vessel is discussed. Secondly, the simulation method is reviewed in the aspect of first ply failure (FPF) analysis and last ply failure (LPF) analysis. The damage evolution of safe burst mode and unsafe burst mode is summarized. Besides, the influence of hydrogen-thermo-stress field and the uncertainty characteristic are also reviewed. Moreover, simulations of micro-crack and permeability for type V composite pressure vessels are summarized. Then, the optimization design methods based on deterministic parameters and uncertain parameters are reviewed. Finally, the damage detection methods of the composite shell of CHPHSV are summarized. The experiment, numerical simulation, and optimization are important for design of the composite vessel, and the damage detection can significantly reduce the degree of uncertainty and maintenance safety. In the future research, precise model considering multiple damage modes, hydrogen-thermo-stress field effect should be established for simulation of safe and unsafe burst mode. Uncertain quantization should be studied for burst pressure with combination of stochastic uncertainty and epistemic uncertainty. Besides, the robust design method based on the reliability of CHPHSV considering the epistemic uncertainty of design parameters should be established for a larger safety margin. [ABSTRACT FROM AUTHOR]

Resin matrix filament wound composite shells are widely applied in the fields of military, aerospace, energy transportation, pressure vessel, and civil engineering. The curing and winding are regarded as the necessary procedures during molding, and they are the key factors affecting the final performance of the composite shells. This paper discusses the application of a new molding process called the heated-mandrel winding process, to take the place of the traditional molding process, which has a two-step procedure. It is proved that the heated-mandrel winding process can not only improve the product quality and production efficiency, but can also reduce the labor cost, without moving the wound shell from the winding machine to the oven. In contrast to the traditional molding process, some properties of the composite formed with the heated-mandrel winding process, including the curing degree and elastic modulus, will be changed because of the heat conduction from the heated mandrel during winding. Therefore, the traditional winding tension system design method is no longer suitable for this new process. Taking the temperature changes into account, this paper uses a theoretical investigation and calculations to suggest a tension system model that describes the relationship between the changeable parameters and the winding tension and to calculate the appropriate tension values for winding, based on the heated-mandrel winding process. The accuracy of the model is verified using an experiment. This paper applies an analytical algorithm based on simple iterative steps to design the tension system. The calculation procedures are simplified, and fewer calculation cycles are required in the analytical algorithm proposed in this paper because it is easier to calculate a few simple linear equations rather than complex nonlinear differential equations under the condition that some initial parameters can be known. As seen during practical application, the model is suitable for a tension system design based on the heated-mandrel winding process and provides further quality improvement in the molding shells. [ABSTRACT FROM PUBLISHER]

The torus is a promisingly potential alternative to traditionally cylindrical pressure vessels due to its capability to store more hydrogen energy within limited space. Constant angle winding is widely used in practical filament winding. Hence, it is necessary to study constant angle winding on the torus. This paper presents constant winding angle curve on torus, a new winding trajectory, and gives a sufficient and necessary condition that makes it nonslip and non-bridging, and a computational formula for determining the lower bound of the winding angle of stable constant winding angle curve. By combining with semi-geodesics, we propose an integration design method for winding pattern and develop a computer aided path design system for filament winding torus, which can design constant angle winding pattern or approximate equilibrium winding for toroidal composite pressure vessels. Since our approach uses constant winding angle curve and integration trajectories besides semi-geodesics, our method has more design space for optimizing fiber path, and outperforms the existing methods. [ABSTRACT FROM AUTHOR]

A numerical process simulation framework is introduced in this paper to describe and predict the process temperature evolution during the laser-assisted tape winding (LATW) process of a type-IV pressure vessel made of glass-reinforced high-density polyethylene (G/HDPE). A local optical-thermal model is fully coupled with a global thermal model for the simulation of continuous adjacent hoop winding cases. The predicted tape and substrate temperatures are compared with the experimental data to validate the process model's effectiveness. The inline temperature was measured by an infrared thermographic camera during the continuous winding. The continuous process temperature of the substrate is affected significantly due to the previously wound layers including the pressure vessel, and a gradual increase of the temperature of the roller and the air inside the liner. A considerable temperature increase calculated as 80-120°C takes place for the substrate during winding of two consecutive layers of (G/HDPE) prepreg tape at the liner ends. The influence of pressure vessel size on the tape and substrate temperatures is investigated for different liner radii using the validated process model. The peak substrate temperature is found to increase approximately 45°C by reducing the radius of the pressure vessel from 272 mm to 68 mm while maintaining all other process conditions constant. [ABSTRACT FROM AUTHOR]

In order to unravel the damage mechanisms occurring in composite-overwrapped pressure vessels (COPVs) subjected to crash conditions, a combined experimental-numerical study has been performed. For the purpose of generality and simplicity, quasi-static contacts on filament-wound cylinders are considered in this paper, as a precursor for geometrically complex impacts on COPVs. Rings with different wall thicknesses are tested to assess how failure mechanisms change when transitioning from thin-wall to thick-wall cylinders. The experimental results are used to identify, which mechanisms occur, and the numerical model is subsequently exploited to analyze the corresponding mechanisms. Based on the understanding of the mechanisms, a method to improve the damage tolerance of thick cylinders is presented. The rings are locally pre-delaminated during manufacturing to promote the growth of these pre-delaminations instead of the initiation of fiber failure. [ABSTRACT FROM AUTHOR]

Laser-assisted tape winding is an automated process to produce tubular or tube-like continuous fiber-reinforced polymer composites by winding a tape around a mandrel or liner. Placing additional layers on a previously heated substrate and variation in material and process parameters causes a variation in the bonding temperature of fiber-reinforced thermoplastic tapes which need to be understood and described well in order to have a reliable manufacturing process. In order to quantify the variation in this critical bonding temperature, a comprehensive temperature analysis of an adjacent hoop winding process of type-IV pressure vessels is performed. A total of five tanks are manufactured in which three glass/HDPE tapes are placed on an HDPE liner. The tape and substrate temperatures, roller force and tape feeding velocity are measured. The coefficient of variation for each round is characterized for the first time. According to the statistical analysis, the coefficient of variation in substrate temperature is found to be approximately 4.8–8.8% which is larger than the coefficient of variation of the tape temperature which is 2.1–7.8%. The coefficient of variations of the substrate temperatures in the third round decrease as compared with the coefficient of variations in the second round mainly due to the change in gap/overlap behavior of the deposited tapes. Fourier and thermographic analysis evince that the geometrical disturbances such as unroundness and eccentricity have a direct effect on the temperature variation. In addition to the temperature feedback control, a real-time object detection technique with deep learning algorithms can be used to mitigate the unwanted temperature variation and to have a more reliable thermal history. [ABSTRACT FROM AUTHOR]

This paper describes how risk-based risk control allocation models work on pressure vessels and piping. We begin by discussing the economic rationale for allocating risk control in a diversified organization such as an enterprise. Considering a probability model for risk control decision making under uncertainty and risk, we propose a model involving stochastic total-loss amount constraints with respect to various tolerable default levels. Our main objective is to develop a method that would allow shaping the risk associated with risk control outcomes. The direct and indirect losses caused by the simulated disasters can be estimated using the engineering and financial analysis model. Based on this model, we can generate an exceeding probability (EP) curve and then calculate how much loss will be eliminated or transferred to other entities should funds be allocated to risk control. Optimal natural disaster risk control arrangement with probabilistic formulation is explained in this paper. Results from the proposed formulations are compared in case studies. The model attempts to apply risk based budget guidelines to risk reduction measurement within a portfolio-based risk framework. [ABSTRACT FROM PUBLISHER]

Filament-wound composite pressure vessels, owing to the advantages of their high specific strength, specific modulus and fatigue resistance, as well as excellent design performance, have been widely used in energy engineering, chemical industry and other fields. A filament-wound composite pressure vessel generally consists of two parts, a cylindrical drum part and the dome parts. In the cylindrical drum part, the filament winding angle and the winding layer thickness can be easily determined due to the regular shape. In the dome parts, however, both the winding angle and the thickness vary along the meridian line. Performance of the dome parts, which strongly depends on the effect of end-opening and the winding mode, dominates the performance of a pressure vessel. In this paper, optimum design of the dome parts is studied by considering both geodesic winding and non-geodesic winding patterns. A hyperelliptic function is adopted as the basis function for describing the meridian of the dome shape. The dome contour is optimized by taking the shape factor (S.F.) as the objective and parameters in the basis function as the design variables. A specific composite pressure vessel is taken as the numerical analysis example with varying dome shape which is to be optimized. The optimum design solution is obtained through the particle swarm optimization algorithm. It shows that an optimized dome with non-geodesic winding has better S.F. as compared with geodesic winding. Influences of the slippage coefficient and the polar opening on the S.F. are also discussed. [ABSTRACT FROM AUTHOR]

Vacuum-bag-only curing is an attractive out-of-autoclave method as an alternative to conventional autoclave curing. Previous extensive researches provided great insight into void formation during the vacuum-bag-only method and these findings are reflected in current vacuum-bag-only cure cycles to minimize void content. Cure process can be further improved by taking into consideration cure-induced residual stress/strain. The present paper proposed a residual stress/strain reduction method and evaluated its effectiveness using a commercially available vacuum-bag-only material by fiber-optic-based in-situ strain monitoring and tensile tests. First, cure process monitoring and tensile tests were conducted for the manufacturer’s recommended cure cycle. Cure process monitoring showed that the material vitrifies during post-cure temperature dwell. Furthermore, the tensile test revealed that the vacuum-bag-only material has lower strength than conventional autoclave materials, suggesting the importance of the effect of cure-induced residual stress/strain. Then, two cure cycles were proposed based on the findings from the manufacturer’s recommended cure cycle tests and a cure kinetics model. In the proposed cycles, resin vitrifies at a lower temperature than the manufacturer’s recommended cure cycle, leading to reduced residual stress/strain. Cure process monitoring and tensile test results for the new cycles showed that the residual strain was reduced by 12–18%, and the strength was increased by 26% in the best case. Moreover, void content was not significantly affected by changing the cure cycle. Although vacuum-bag-only material was used in this research, the proposed concept can be widely applied for autoclave cures and other types of vacuum-bag-only processes with slight modification. [ABSTRACT FROM AUTHOR]

Generally, in functionally graded material structures, a ceramic material as reinforcing part is distributed in a metallic matrix. These structures benefit the merits of both their metallic and ceramic parts such as the mechanical strength and thermal resistance. An important aspect in the function and study of functionally graded material structures is the effect of temperature. Usually, the resulted thermal stresses are so high that partial failure of structure is inevitable. In this paper, by using of different exact and approximate mathematical models and solution techniques, the yielding of a functionally graded material cylindrical pressure vessel is studied. Different solution techniques such as closed form solution, FE solution of ABAQUS and semi-analytical solution of variable material properties are used. Based on the von Mises and Tresca’s yield criteria, the shape of plastic zone are obtained and compared. The influences of different structural parameters as well as the effect of failure criterion upon the results are studied. Accordingly, some justifications are made regarding the selection of different material parameters or failure models. [ABSTRACT FROM AUTHOR]

The main purpose of this study is to evaluate the effects of certain processing parameters on the mechanical performance of carbon/epoxy towpreg wound composite structures. For this purpose, composite sample productions and their evaluations were conducted in two steps. In the first step, dry winding of carbon/epoxy towpregs was used to produce flat composite plates. Their evaluation was performed by rheological analysis, interlaminar shear tests, and unidirectional tensile tests. In the second step, towpreg dry winding was used to produce composite pressure vessel samples. Their performance was evaluated by observing the effects of various winding process parameters on the safety of the vessels via hydrostatic burst pressure tests. Compared to the traditional wet filament winding, the main difficulty observed was maintaining the "straight towpreg path" necessary for efficient winding operations. This problem was prevented by applying higher tension forces during dry winding. Evaluation of the hydrostatic burst tests in terms of burst pressure, hoop strain and safe failure mode revealed that the optimum pressure vessel performance could be obtained in the vessel samples with "helical-hoop-helical winding layer sequence." On the other hand, use of "complex helical pattern" resulted in no advantages at all, due to basically higher number of undulation zones acting as stress concentration zones. [ABSTRACT FROM AUTHOR]

Influence of local loads on the stress state of the shell appears as the consequence of pressure, external forces, and moment influence. Loads which act directly upon the shell surface or the parts (nozzles) connected to the shell appear in their proximity, especially in the welded joint influence zones.The influence of the torque moment affecting the free end of a slanted branch on the pressure vessel cylindrical shell is considered in this article. The stress on the cylindrical shell was analysed on 245 models of different geometrical characteristics. Stress calculated by applying the finite element method was classified by maximum stress criteria. For every considered model, maximum stress envelope has been prepared. The regressive analysis enabled the determination of correlation functions, which allow calculation of stress maximum values on the cylindrical shell according to which the shell dimensions may be determined. Result analysis shows that the percentual error is within limits as follows: from −13.4 per cent to +12.7 per cent. [ABSTRACT FROM AUTHOR]

In this study, the fatigue behavior of 0.25 wt.% graphene nanoplatelets (GnPs) reinforced and unreinforced impact damaged basalt/epoxy composite pressure vessels (CPVs) was investigated. The CPVs were subjected to low-velocity impact (LVI) of 2.5 J, 5 J, 7.5 J, 10 J, 15 J, 20 J, and 25 J under internal pressure of 50 bar (hoop/axial prestresses: 98/49 MPa). Then, to detect fatigue life changes, fatigue tests were performed at load rates of 30% of ultimate hoop stress (σHS), where sweat damage occurred in the basalt/epoxy CPVs under alternating internal pressure. Considering the remaining fatigue life and formation of the damages in the CPVs for all impact energies, to investigate the fatigue behavior and GnPs effects of CPVs subjected to low-velocity impact, an impact value of 5 J was preferred. The 5 J impact damaged CPVs were subjected to fatigue cyclic following ASTM D 2992 at load rates of 20%, 25%, 30%, 35%, and 40% of the σHS. The fatigue life of damaged CPVs was compared by that of undamaged over S-N curves. As the impact energy increased, the impact damage area increased. The increased size of damage reduced the fatigue life of basalt/epoxy CPVs. At the fatigue load rates mentioned above, the GnPs improved the fatigue life of damaged basalt/epoxy CPVs by about 3.5, 3.2, 11.3, 2.4, and 5 times, respectively. [ABSTRACT FROM AUTHOR]

Type IV COPVs (Composite Overwrapped Pressure Vessels) are among the most suited structures for hydrogen storage. However, its complex modes of failure and requirement for periodic maintenance has led the industry to apply high safety factors on designs. This is one of the challenges inhibiting the widespread usage of the H2 in commercial vehicles. Structural health monitoring based on optical fibers is an emerging technology that can overcome these problems, as a neural network of sensors can be integrated to the structure during manufacturing and is readily accessible over the vessel lifetime. This gives information about the real structure condition, reducing overall maintenance costs. Here, core optical fibers were embedded in type IV COPVs during the manufacturing process and monitored with OBR (Optical Backscatter Reflectometer). Sensors were interrogated during an impact detection test and a pressurization test until burst failure. Fibers were capable of detecting the position and intensity of the damage in the first test and provided strain profiles over the entire length of the vessel for longitudinal and circumferential directions on the second. Optical microscopy of vessel sections showed matrix accumulation around the optical fiber as the main cause of sensor's failure. During pressurization, steep peaks of strain in the dome regions from the early measurements indicated the burst failure site. [ABSTRACT FROM AUTHOR]

This work provides an exploratory investigation into the applicability of a two-parameter fracture mechanics approach based on the J-Q methodology to characterize fracture behavior in cracks located at geometrical discontinuities of pressure vessels submitted to pressurization and depressurization cycles. Numerical models in plane-strain condition were employed to characterize crack driving forces and constraint changes in a flawed structure subjected to shakedown. The material exhibits elastic–plastic behavior and nonlinear kinematic hardening following the Chaboche model. The results indicate that the application of cycles of loading exceeding elastic limits, but still below the allowable stress for design of pressure vessels, increases the crack driving force and decreases the constraint level. It is possible to conclude that the methodology based on J-Q is highly effective to characterize the fracture conditions in geometrical discontinuities of pressure vessels. A lower probability of unstable fracture may be assumed for ductile and high-toughness materials after few cycles of pressurization and depressurization are applied. However, due to the increase in the driving force, the crack may be more susceptible to a subcritical tearing. Assuming that the material toughness is high enough to avoid any ductile tearing during pressurization and depressurization cycles, the observed phenomena close to the crack tip may be compared to instability of strains when shakedown is not guaranteed. [ABSTRACT FROM PUBLISHER]

A general design and analysis methodology is presented for the development of thick-wall thermoplastic composite pressure vessels for deep-water marine applications. A parametric study was performed to determine the optimum tapered radius, initial radial clearance, and plug length of the plug-supported end-caps employed here as end-closures since it was found that these optimum parameters could improve the performance of the composite pressure vessels by minimizing bending and shear stresses near the ends. Stress and buckling nonlinear finite element analyses (FEA) were performed taking hygrothermal effects into account. An equivalent coefficient of thermal expansion to model coefficient of moisture expansion for FEA software, where moisture absorption is not an input, is introduced to fully model hygrothermal effects. Based on the FEA results and taking the pressure vessel weight, ease of fabrication, mechanical and environmental performance, and cost into account APC-2/AS4 thermoplastic composite was found to be a suitable material system for the pressure vessel. An in situ thermoplastic composite filament winding/tape laying system employing infrared local and global heaters was developed in the Advanced Materials Manufacturing Laboratory of the University of Hawaii at Manoa, and was employed to manufacture the thick-wall composite pressure vessels. The manufactured pressure vessels had excellent quality, were instrumented by strain gages, and then successfully tested in the Hawaii Institute of Geophysics of the University of Hawaii at Manoa high-pressure water-filled pressure chamber. The strain gage results from the experiments were compared with those obtained from the FEA and excellent agreements were achieved. [ABSTRACT FROM AUTHOR]

Structural durability and damage tolerance characteristics of pressurized graphite/epoxy laminated thin composite cylinders are investigated via computational simulation. Both unstiffened and integral hoop stiffened cylinders are considered. A computer code is utilized for the simulation of composite structural degradation under loading. Damage initiation, growth, accumulation, and propagation to structural fracture are included in the simulation. The increase of burst pressure due to hoop stiffening is quantified. Results demonstrate the significance of the type and size of local defects on the structural durability of pressurized composite cylindrical shells. [ABSTRACT FROM PUBLISHER]