Fiber Angle Research Articles

On the role of local reinforcement in an adhesively bonded AL/CFRP energy absorber under axial loading: A theoretical investigation and optimization

AbstractThis paper aims to develop a novel theoretical model that incorporates the effects of local composite reinforcement using adhesive bonding on the energy absorption of aluminum structures under axial loading. The goal is to optimize energy absorption prior to any connection failures and to prevent uneven structural deformation. Moreover, it strives to reduce the structure's weight and material usage, achieving superior results compared to traditional global reinforcement techniques. The theoretical model was validated through experimental testing and finite element analysis, demonstrating good agreement with the predicted results. The results reveal that increasing the CFRP fiber angle, layer thickness, and number of layers generally leads to improved energy absorption capacity. An optimization analysis was performed to determine the optimal design parameters, yielding a fiber angle of 80°–90°, composite thickness of 1.5 mm, and aluminum thickness of 2.5 is the best configuration, offering the highest specific energy absorption and adequate peak load capacity for maximized energy absorption. The proposed model offers significant improvements over existing approaches, enhancing the predictive capabilities and practical applicability of energy absorption predictions in engineering design.Highlights A novel theoretical model for energy absorption in locally reinforced hybrid AL/CFRP structures. The influence of design parameters, such as CFRP layer count, fiber orientation, and thickness ratio. Optimization to maximize the average crushing force while meeting weight and geometric constraints. Findings can inform the design of safer and more efficient energy‐absorbing structures in various applications.

An investigation of clay percentage variation on composite materials sustainability identification by digital image correlation

ABSTRACT The study focuses on stress and strain evaluation of composite resin material with the reinforcement of clay in the glass-reinforced epoxy composite (GREC). The strain measurement used the DIC technique. The tensile test specimens were prepared from the laminate sheets as per ASTM D638 standard. The influence of nano clay weight percentage such as 2.5%, 3.5%, and 4.5% during preparation of GREC is studied in the article. The fibre orientation angles are 90°, and the fibre volume percentage is 45%. Hand lay-up methods are used to prepare the composite resin material. The samples were tested as per the standardised procedures. The specimen rupture at a localised strain reached a maximum value of 0.01293, 0.01571, and 0.0143 with 2.5%, 3.5% and 4.5% Nano clay, respectively. The material behaviour in terms of major strain (εyy), Poisson’s ratio (µ) and thickness strain (Δt) is evaluated at the gauge length of the specimen. DIC strain measurement clearly demonstrates the 3.5% percentage of clay addition as it yields better results as elastic modulus and tensile strength have improved. The composite resin with clay addition could be used in various applications, such as low-cost housing, structural works, medical devices, automotive panels, etc

Optimized design of energy absorption of aluminum foam filled CFRP thin-walled square tube based on agent model

PurposeAluminum foam-filled thin-walled unit structures have received much attention for their excellent energy absorption properties. To improve the energy absorption effect of car energy absorption box under axial compression, this paper optimizes the fiber lay-up sequence, fiber angle and aluminum foam density of aluminum foam filled carbon fiber reinforced plastic (CFRP) thin-walled square tubes.Design/methodology/approachDesign of sample points required to construct the proxy model using design of experiments (DOE) method, and the data sample points of different models are obtained through Abaqus simulation and test. A double high-precision proxy model with the maximum specific energy absorption (SEA) and the minimum initial peak crash force (PCF) as the evaluation index is constructed based on the response surface function method. The NSGA-II multi-objective genetic algorithm was used to optimize the design parameters and obtain the optimal solution for the Pareto front, and the results were verified by using the multi-objective optimization toolbox in design-expert.FindingsThe results show that the optimal solution to the multi-objective optimization problem with the inclusion of the lay-up sequence is ρ = 0.5g/cm3 for a fiber lay-up angle varying in the range ±15–90° and an aluminum foam density varying in the range 0.2g/cm3-0.5g/cm3, with a lay-up method of [±87°/±16°/±15°/±89°]. The two optimization methods correspond to SEA and PCF errors of 2.109% and 4.1828%, respectively. The optimized SEA value is 18.2 J/g and the PCF value is 18,230 N. The optimized design reduces the peak impact force and increases the specific energy absorption, which improves the energy absorption effect of thin-walled energy-absorbing boxes for automobiles.Originality/valueIn this paper, the impact resistance of CFRP thin-walled square tubes filled with aluminum foam is optimized. Based on numerical simulations and experiments to obtain the sample point data for constructing the dual-agent model, we investigate the effect of filling with different densities of aluminum foam under the simultaneous change of fiber lay-up angle and order on its mechanical properties in this process, and carry out the multi-objective optimization design with NSGA-II algorithm.

Effects of specimen thickness and fiber length on tensile and cracking behavior of UHPFRC: Uniaxial tensile test and micromechanical modeling

This study aims to investigate the effects of specimen thickness and fiber length on the tensile and cracking behaviors of ultra-high-performance fiber-reinforced concrete (UHPFRC). To this end, a uniaxial tensile test was conducted with three specimen thicknesses (30, 50, and 100 mm) and two fiber lengths (13 and 20 mm), and the fiber orientation, dispersion and specimen void were quantitatively evaluated based on image recognition. The test results indicated that fiber orientation was improved with the decreased specimen thickness and increased fiber length. Meanwhile, the initial cracking and peak stress, capacity to limit cracking were enhanced with the decreased specimen thickness. A modified prediction model considering the wall effect, flattening and squeezing effect was developed to predict the probability density function p(θ) of fiber orientation angle. Additionally, the uniformity factor μ2 was introduced to predict crack number, and the relationship between the μ2 and parameter ψ = (Vf × lf/df)/t was determined. Furthermore, a model was developed to convert the main crack width into uniaxial tensile strain. All models and relationships were validated using test data. A micromechanical model that considered the predicted p(θ) and conversion model was established to predict the uniaxial tensile response of UHPFRC, which was also successfully validated using test data.

Optimizing energy absorption and peak force in metal/glass fiber sandwich panels with trapezoidal cores

Sandwich panels with trapezoidal metal/glass fiber cores are increasingly popular due to their lightweight and energy-absorption properties. This study employs response surface methodology (RSM) and Box-Behnken design to investigate the effects of core angle, fiber orientation, and MCM-48 nanoparticles on the panels’ energy absorption and peak force, developing regression models with high R2 values of 0.9027 and 0.9228, respectively. Experimental tests were conducted to validate these models, showing minimal deviation from predicted values. Results indicate that increasing the fiber orientation angle from 30° to 90° enhances energy absorption and peak force by 72.18 and 46.9%, respectively, and adding MCM-48 nanoparticles up to 0.25% weight improves energy absorption by 60.8%. A core angle of 52° balances energy absorption and peak force, while integrating a metal wire mesh within the panels significantly enhances energy absorption and reduces core brittleness. The optimal parameters for maximum energy absorption and minimum peak force include a core angle of 58°, fiber orientation of 73.5°, and no nanoparticles. These findings provide valuable insights into the design and optimization of sandwich panels for various applications.

The effect of stacking sequences on energy absorption in axial crushing of CFRP stanchions for the cargo floor structure of airplanes

One of the remaining challenges for advancing the wide application of composite materials is to further improve the mechanical properties of composites. The fiber/matrix damage phenomenon produced by the composite model under axial loading has been observed through the establishment of a numerical model of composite damage. Axial crush tests have been performed on C-type carbon fiber reinforced polymers (CFRP) stanchions for the cargo floor structure of transport category airplanes using a finite element approach. The failure morphology and crashworthiness parameters of the specimens with different fiber layups have been recorded, and the effects of fiber orientation and angle of entrapment on the crashworthiness of the composites have been investigated. The present study demonstrates that the crashworthiness of composites can be effectively improved by fiber orientation design. Appropriate addition of 45° layer and 90° layer can effectively improve the crashworthiness of C-type CFRP laminates, and the performance of the two-angle and spiral laminates design is improved by 26% and 19%, respectively.

Structure Design on Thermoplastic Composites Considering Forming Effects.

Carbon fiber reinforced polypropylene (CF/PP) thermoplastics integrate the superior formability of fabrics with the recoverable characteristics of polypropylene, making them a pivotal solution for achieving lightweight designs in new energy vehicles. However, the prevailing methodologies for designing the structural performance of CF/PP vehicular components often omit the constraints imposed by the manufacturing process, thereby compromising product quality and reliability. This research presents a novel approach for developing a stamping-bending coupled finite element model (FEM) utilizing ABAQUS/Explicit. Initially, the hot stamping simulation is implemented, followed by the transmission of stamping information, including fiber yarn orientation and fiber yarn angle, to the follow-up step for updating the material properties of the cured specimen. Then, the structural performance analysis is conducted, accounting for the stamping effects. Furthermore, the parametric study reveals that the shape and length of the blank holding ring exerted minimal influence on the maximum fiber angle characteristic. However, it is noted that the energy absorption and crushing force efficiency metrics of the CF/PP specimens can be enhanced by increasing the length of the blank holding ring. Finally, a discrete optimization design is implemented to enhance the bending performance of the CF/PP specimen, accounting for the constraint of the maximum shear angle resulting from the stamping process. The optimized design resulted in a mass reduction of 14.3% and an improvement in specific energy absorption (SEA) by 17.5% compared to the baseline sample.

Analytical investigation of green composite lamina utilizing natural fiber to strengthen PLA

This work’s main goal is to investigate the effects of the natural fiber orientation angle on the lamina’s engineering constants, such as the shear modulus, major Poisson’s ratio, longitudinal and transverse Young’s moduli, and lamina level shear coupling coefficients. The PLA matrix of the three green composite laminas under study is reinforced with natural fiber. The three natural fibers under study are flax, jute, and bamboo fibers. The study assesses the performance of three PLA laminas reinforced with natural fibers for each of the previously listed engineering constants. The behavior of the green composite lamina for various fiber volume fractions is also presented in this study. This analytical investigation employs the macromechanics of lamina to do the examination. The investigation’s findings demonstrated that the volume % and fiber orientation have a considerable impact on the lamina’s engineering constants. The study offers a comprehensive variation of the lamina’s engineering constants for each fiber orientation angle between 0 and 90° and for each fiber volume fraction between 0 % (entirely matrix) and 100 % (completely fibers) in steps of 5 %. The outcomes of the presented study will help in the design of the facesheets for the composite sandwich structures. The results presented can be used to check the viability of using natural fibers to strengthen different polymer matrices. Bamboo-PLA lamina outperforms flax-PLA and jut-PLA laminae.

Effects of nozzle geometry and fiber orientation on the tensile strength of 3D printed continuous fiber reinforced composites

In material extrusion (MEX) based 3D printing, inter-filament voids are intrinsic to printing process. The void orientation, volume and shape are affected by multiple factors including the nozzle shape, stacking sequence and printing direction. In this study, the adverse effects of the inter-filament voids on tensile properties and damage modes were investigated numerically on 3D printed acrylonitrile butadiene styrene-carbon fiber (ABS/CF) continuous fiber-reinforced composites (CFRCs). Uniaxial tensile simulations were performed considering various nozzle geometries (circular, square), fiber orientations (θ=0o,30o,45o,60o,90o) relative to loading direction, and a regular stacking sequence of extrudates. The extrudate cross-section was modeled either using elliptical or superelliptical extrudates deposited from a circular or square nozzle, respectively. Excellent agreement was seen when the simulated results were benchmarked against several published experimental and numerical work. Simulated results showed that changing the nozzle shape from circular to square improved the mechanical properties across all fiber angles by lowering the void content by 7−8% and increasing the ultimate tensile strength (σT) by 11−18%, tensile stiffness (ET) by 6−8%, and the tensile failure strains (ϵT,fail) by 1−11%. For superelliptical extrudates the number of observed damage modes also reduced, and this is due to a 37.2% and 58.2% improvement in the inter-filament and inter-layer bond lengths, respectively. Also, when fiber angle became increasingly off-axis to tensile load direction, the strengths, moduli, and failure strains reduced for both circular and square nozzles. The significance of using microstructure geometries and explicitly modeling inter-filament voids for simulating MEX printed CFRCs was highlighted by comparing these results with both analytical calculations and simulated results of homogeneous solid CFRC blocks without voids.

Multiscale Fiber Remodeling in the Infarcted Left Ventricle using a Stress-Based Reorientation Law

The organization of myofibers and extra cellular matrix within the myocardium plays a significant role in defining cardiac function. When pathological events occur, such as myocardial infarction (MI), this organization can become disrupted, leading to degraded pumping performance. The current study proposes a multiscale finite element (FE) framework to determine realistic fiber distributions in the left ventricle (LV). This is achieved by implementing a stress-based fiber reorientation law, which seeks to align the fibers with local traction vectors, such that contractile force and load bearing capabilities are maximized. By utilizing the total stress (passive and active), both myofibers and collagen fibers are reoriented. Simulations are conducted to predict the baseline fiber configuration in a normal LV as well as the adverse fiber reorientation that occurs due to different size MIs. The baseline model successfully captures the transmural variation of helical fiber angles within the LV wall, as well as the transverse fiber angle variation from base to apex. In the models of MI, the patterns of fiber reorientation in the infarct, border zone, and remote regions closely align with previous experimental findings, with a significant increase in fibers oriented in a left-handed helical configuration and increased dispersion in the infarct region. Furthermore, the severity of fiber reorientation and impairment of pumping performance both showed a correlation with the size of the infarct. The proposed multiscale modeling framework allows for the effective prediction of adverse remodeling and offers the potential for assessing the effectiveness of therapeutic interventions in the future. Statement of SignificanceThe organization of muscle and collagen fibers within the heart plays a significant role in defining cardiac function. This organization can become disrupted after a heart attack, leading to degraded pumping performance. In the current study, we implemented a stress-based fiber reorientation law into a computer model of the heart, which seeks to realign the fibers such that contractile force and load bearing capabilities are maximized. The primary goal was to evaluate the effects of different sized heart attacks. We observed substantial fiber remodeling in the heart, which matched experimental observations. The proposed computational framework allows for the effective prediction of adverse remodeling and offers the potential for assessing the effectiveness of therapeutic interventions in the future.

A study on interactive fiber rubber composite structures subjected to bend-twist coupling

Abstract This paper investigates the deformation behavior of shape memory alloy (SMA)-integrated fiber-reinforced composites, with an emphasis on how different fiber orientations influence bend-twist coupling. The study combines experimental analysis, finite element simulations using Ansys, and analytical modeling via Classical Laminate Theory (CLT) to assess the mechanical response of these composites. The experiments revealed that composites with higher fiber angles (60°) exhibited dominant twisting behavior, while those with lower angles (30° and 45°) showed more pronounced bending deformation. The simulations corroborated these trends, offering detailed insights into the displacement behavior. The CLT model further predicted a decrease in deflection with increasing fiber angles, which was consistent with experimental results, although some deviations in Z-deformation were attributed to material and manufacturing factors. This research highlights the critical role of fiber orientation in achieving desired deformations in SMA-integrated composites, offering valuable insights for the design of adaptive structures. The findings demonstrate the potential for optimizing fiber configurations to tailor bend-twist coupling in advanced composite applications.

Intelligent design of multi-layered variable stiffness composite structure based on transfer learning

Variable stiffness composite structures offer more flexible design space than thin-walled metal structures and have greater potential for vibration-resistant design. When faced with multiple new types of design problems, the complex modelling and analysis procedures frequently prove to be both time-consuming and costly in terms of optimization. In this study, an innovative multi-layered variable stiffness (MVS) composite structure with high design flexibility is proposed, with images representation for curvilinearly stiffened paths, non-uniform layouts, and fiber and layup angles. Moreover, an intelligent optimization method based on transfer learning is proposed for addressing a variety of factors affecting dynamic design, including boundary types, structural features, and dynamic responses. The objective of the transfer learning model is to facilitate the inheritance and sharing of variable stiffness features, thereby enabling the efficient design of new problems with limited datasets. The validation of different examples shows that the transfer learning can effectively acquire the structural features from the existing source domain datasets, thereby significantly reducing the data for some new target domains by approximately 50%. In comparison to the initial constant stiffness (CS) structures, the different optimized configurations indicate that the MVS composite structures are capable of effectively enhancing the dynamic responses by 10%∼146% for natural frequency and dynamic compliance. Furthermore, the MVS optimized configuration displays superior dynamic responses in some problems, when compared to the CS optimized configuration.

Aspect ratio-dependent volume resistivity in unidirectional composites: Insights from electrical conduction behavior

The electrical properties of carbon fibers serve as the foundation for the multifunctional applications of carbon fiber-reinforced composite structures. In scenarios that exploit the electrical characteristics of materials, accurate estimation of electrical resistivity stands as a critical factor. This study endeavors to elucidate the electrical conduction behaviors in unidirectional composites with different fiber orientation angles (0°, 15°, 30°, 45°, 60°, 75°, and 90°) and aspect ratios, thereby deriving the volume resistivity within an arbitrary Cartesian coordinate system. Employing thermal infrared imaging technology and finite element analysis, we identified distinctive electrical conduction behaviors associated with aspect ratios in carbon fiber composite plates. Notably, a critical aspect ratio exists wherein the diagonal yarn is the only conductive path between two electrodes. Below this critical threshold, no direct conductive path exists, and current flows through the shortest distance between parallel yarns. Conversely, beyond the critical aspect ratio value, multiple yarns form conductive paths between the two electrodes. Based on the electrical conduction behavior of unidirectional composites under different angles and aspect ratios, the volume resistivity with finite boundaries was derived and examined under an arbitrary Cartesian coordinate basis.

Modeling Electrical Conductivity of Injection-Molded Polymer Composite Bipolar Plates

Bipolar plates can be responsible for up to 40% of the total stack cost and 80% of the weight of a polymer electrolyte membrane fuel cell. To reduce these cost and weight limitations, this work explores modeling and injection molding of polymer composites. A fiber contact model was developed to predict electrical conductivity based upon direction in the material, fiber length and diameter, fiber resistivity, fiber volume fraction, and fiber angle of alignment. Fiber alignment was measured experimentally by imaging cross sections of injection-molded nylon/nickel-coated carbon fiber (NiCF) composites. Composites were molded with NiCF loadings ranging from 5 to 40 wt%. Up to 15 wt%, modeling predictions show good correlation with experimental conductivity measurements. Samples with at least 15 wt% NiCF exceeded the United States Department of Energy technical target for bipolar plate conductivity (>100 S/cm), reaching 250 S/cm.

Modeling Electrical Conductivity of Injection-Molded Polymer Composite Bipolar Plates

Bipolar plates can be responsible for up to 40% of the total stack cost and 80% of the weight of a polymer electrolyte membrane fuel cell. To reduce these cost and weight limitations, this work explores modeling and injection molding of polymer composites. A fiber contact model was developed to predict electrical conductivity based upon direction in the material, fiber length and diameter, fiber resistivity, fiber volume fraction, and fiber angle of alignment. Fiber alignment was measured experimentally by imaging cross sections of injection-molded nylon/nickel-coated carbon fiber (NiCF) composites. Composites were molded with NiCF loadings ranging from 5 to 40 wt%. Up to 15 wt%, modeling predictions show good correlation with experimental conductivity measurements. Samples with at least 15 wt% NiCF exceeded the United States Department of Energy technical target for bipolar plate conductivity (>100 S/cm), reaching 250 S/cm.

Radial compression performance of glass fiber reinforced polyurethane composite tube with open-hole

Glass fiber reinforced polyurethane matrix composite (GFRP) is a novel composite material. GFRP circular tubes are widely used in engineering because of its excellent mechanical properties. It is inevitable to open holes on GFRP circular tubes when connecting with other components due to the use requirements and structural needs. The radial compression test, theoretical analysis, and finite element calculation of GFRP circular tubes produced by the braiding-winding-pultrusion process are carried out, to study the influence of holes on the compression performance of tubes. The GFRP circular tube has four layers with different fiber angles. From the inner to the outer structure layer, they are the inner woven layer, winding layer, longitudinal fiber layer, and outer woven layer. The mechanical properties of a 0° unidirectional plate are better than those of a 90° unidirectional plate according to the mechanical properties test. The radial compression tests are carried out on GFRP circular tubes with a length of 300 mm, an outer diameter of 140 mm, and a wall thickness of 6 mm. The theoretical calculation of the bearing capacity of the GFRP circular tube under the radial compression load in the elastic stage and the failure stage is well matched with the bearing capacity obtained from the test. The theoretical calculation can effectively predict the bearing capacity of the GFRP circular tube. The radial compression test of GFRP tubes is simulated by ABAQUS, which is a finite element software. The good agreement between the finite element calculation results and the test results verifies the feasibility of the finite element. Based on the above research, finite element models are established for different types of GFRP circular tubes to study the influence of opening ratio on the load borne by GFRP circular tubes. The results show that the hole with the opening rate less than or equal to 1/10 has little effect on the load of the GFRP circular tube. This paper studies the influence of opening on the radial compression properties of GFRP tubes, which has certain reference value for the opening of composite tubes in engineering.

Understanding the effects of mineralization and structure on the mechanical properties of tendon-bone insertion using mesoscale computational modeling

Tendon-bone fibrocartilaginous insertion, or enthesis, is a specialized interfacial region that connects tendon and bone, effectively transferring forces while minimizing stress concentrations. Previous studies have shown that insertion features gradient mineralization and branching fiber structure, which are believed to play critical roles in its excellent function. However, the specific structure-function relationship, particularly the effects of mineralization and structure at the mesoscale fiber level on the properties and function of insertion, remains poorly understood. In this study, we develop mesoscale computational models of the distinct fiber organization at tendon-bone insertions, capturing the branching network from tendon to interface fibers and the different mineralization scales. We specifically analyze three key descriptors: the mineralization scale of interface fibers, the mean, and relative standard deviation of the local branching angles of interface fibers. Tensile test simulations on insertion models with varying mineralization scales of interface fibers and structures are performed to mimic the primary loading condition applied to the insertion. We measure and analyze five representative mechanical properties: Young's modulus, strength, toughness, resilience, and failure strain. Our results reveal that mechanical properties are significantly influenced by the three key descriptors, with tradeoffs observed between mutually exclusive properties. For instance, strength and resilience plateau beyond a certain mineralization scale, while failure strain and Young's modulus exhibit monotonic decreasing and increasing trends, respectively. Consequently, there exists an optimal mineralization scale for toughness due to these tradeoffs. By analyzing the mesoscale deformation and failure mechanisms from simulation trajectories, we identify three fracture regimes closely related to the trends in mechanical properties, supporting the observed tradeoffs. Additionally, we examine in detail the effects of the mean and relative standard deviation of local branching angles on mechanical properties and deformation mechanisms. Overall, our study enhances the fundamental understanding of the composition-structure-function relationships at the tendon-bone insertion, complementing recent experimental studies. The mechanical insights from our work have the potential to guide the future biomimetic design of fibrillar adhesives and interfaces for joining soft and hard materials.

Two‐stage annealing method for short carbon fiber‐reinforced nylon 6 in fused filament fabrication

AbstractThe mechanical properties of short carbon fiber‐reinforced nylon 6 (CF‐PA6) components formed by fused filament fabrication (FFF) are significantly affected by the process parameters of additive manufacturing and heat treatment. In this study, the effects of printing speed, carbon fiber aspect ratio, and annealing temperature on fiber orientation were investigated by observation of single‐layer‐single‐fiber samples. Furthermore, a two‐stage annealing process was proposed to increase the tensile modulus of CF‐PA6 based on the correlation analysis results between the degree of fiber alignment and the variation of tensile modulus. According to the calculation of the Pearson correlation coefficient, the tensile modulus was highly correlated with the degree of fiber alignment under different printing speeds and fiber aspect ratios. The variation in tensile modulus and fiber orientation was also consistent when the annealing temperature was lower than the crystallization temperature. Conversely, the variation of tensile modulus and fiber orientation were opposite, as the annealing temperature was higher than the crystallization temperature because of the influence of crystallinity. Through increasing the degree of fiber alignment and crystallinity of the parts, the proposed two‐stage annealing method could increase the tensile modulus of the parts to 9.0 GPa, which was 16.81% higher than that of single‐temperature annealing.Highlights The effects of annealing temperature, carbon fiber aspect ratio and printing speed on fiber orientation were illustrated. The relationship between the degree of fiber alignment and the variation of tensile modulus was established. The proposed two‐stage annealing method, considering fiber orientation and crystallinity, significantly increased the tensile modulus of CF270‐PA6 parts from 7.7 to 9.0 GPa. The quantitative analysis of the fiber orientation is realized by the statistical analysis of the plane fiber orientation angle of the single‐layer‐single‐fiber sample.

Buckling Analysis of Variable Stiffness Composite Cylindrical Shells Under Axial Compression Considering Imperfection Sensitivity

Thin-walled composite cylindrical shells are nowadays widely used as primary structures in the aerospace industry. The so-called variable stiffness (VS) composite cylindrical shells with flexible stiffness tailoring characteristics have been made possible by existing AFP techniques. Considering the inherent imperfection sensitivity property of axially compressed thin-walled cylindrical shells, the buckling behaviors of the axially compressed VS composite cylindrical shells with initial geometric imperfections and delamination imperfections are investigated respectively in this paper. The design buckling loads of the axially compressed VS composite cylindrical shells are first determined by the probing method, which is verified by comparing with the existing test data and numerical simulation results. Additionally, a parametric study is conducted to investigate the effects of delamination imperfections on the buckling loads. The constraint delamination sizes of the VS composite cylindrical shells based on the design buckling load in this paper are given. Furthermore, the effects of continuously variable fiber angles on the buckling loads are investigated considering the imperfection sensitivity. The specific VS composite cylindrical shells with both high- buckling loads and low-imperfection sensitivity are obtained. Results indicate that the effects of imperfection sensitivity need to be carefully considered in buckling design of the axially compressed VS composite cylindrical shells.

Impact of stacking sequence on burst pressure in glass/epoxy Type IV composite overwrapped pressure vessels for CNG storage

The shift from metallic to composite pressure vessels for storing compressed natural gas (CNG) is driven by the goal of reducing environmental impact by using lighter higher-performing structures. This work focuses on enhancing the internal pressure strength of a type IV composite overwrapped pressure vessel (COPV) by optimising the stacking sequence of the overwrapping composite layers. Parametric finite element (FE) models are developed to reveal symmetry effects. In these models, both the thickness build-up and fibre angle variation at the turnaround zones are accurately modelled. Subsequently, the stacking sequence is optimised with the objective function of maximising burst strength. The parametric modelling demonstrates that representing the COPV as an axisymmetric continuum reduces computational costs in 5400× while yielding results comparable to full 3D continuum models. Experimental burst tests are carried out to validate the numerical predictions, and the difference in pressure between them is 12.6 %.