Fiber Composite Shells Research Articles

Fabrication of pressure visual fiber based on liquid metal control thermochromic pigments

AbstractIn this study, pressure visual fibers (PVF) with a core‐shell structure were prepared using a coaxial wet spinning process. The fiber composite shell consists of a luminescent material (as a light source) and a thermochromic pigment (as a filter light source) mixed with a polyacrylonitrile (PAN) matrix. The fiber core layer, on the other hand, was made of gallium‐indium alloy liquid metal. In operation, the filter light source is activated by joule heat drive (resulting in the fading of the thermochromic pigment), and the PVF releases phosphorescence upon exposure to ultraviolet light. When a certain pressure is applied to the fiber shell, the liquid metal in the core layer is squeezed, resulting in a local cross‐sectional area reduction, an increase in local joule thermal power, and thus local discoloration. This localized compression, in combination with a small rated current and the presence of an ultraviolet light source, converts the mechanical force (strain and compression) into an optical response. The excellent electrical conductivity of the liquid metal, combined with its compatibility with the soft matrix, makes it a promising candidate for applications in smart textiles and flexible sensing.Highlights The technology of visual fiber controlled by current is presented. The bendability and controllability of visual composites are improved. The composite fiber can be visualized when stressed.

Buckling performance of stiffened polymer composite cylindrical shell

The buckling of carbon fiber composite cylindrical shells (CF-CCSs) with annular ribs under external pressure was investigated numerically and experimentally. The effects of rib cross-sections, rib geometry and distribution on buckling load and buckling mode were analyzed numerically. In addition, the ribbed polymer composite cylindrical shell was fabricated and tested. The geometry, thickness, buckling load and final collapse mode of the ribbed polymer composite cylindrical shell were measured. Finally, a nonlinear buckling analysis with geometrical imperfections was carried out based on the measured data; the numerical results were in agreement with the experimental results. The results show that different rib cross-sections have limited influence on the load carrying capacity of CF-CCSs, but the distribution of the ribs and the geometry of the ribs have a greater influence on CF-CCSs.

Simulation analysis of curing of filament wound carbon fiber composite shell

To represent the temperature and degree of cure (DOC) more intuitively during the curing process of fiber-wound composite shell, wrote SDVINI, DISP, FILM, and HETVAL subroutines to characterize the fiber-wound composite curing process in ABAQUS. Comparing the temperature and DOC. The results indicate that the heat released from the resin curing process affects the internal temperature of the material, but the effect is small and can be ignored. The DOC on the surface of the fiber-wound shell during the curing process is slightly larger than that inside, but the difference is small and can be approximated as equal. And when the curing time is the same, the faster the heating rate, the faster the curing rate.

Predicting buckling of carbon fiber composite cylindrical shells based on backpropagation neural network improved by sparrow search algorithm

Predicting buckling of carbon fiber composite cylindrical shells based on backpropagation neural network improved by sparrow search algorithm

Experimental and numerical buckling analysis of carbon fiber composite cylindrical shells under external pressure

The buckling behavior of carbon fiber/epoxy resin composite cylindrical shells under uniform external pressure was investigated experimentally and numerically. Eight composite cylindrical shells with different length–diameter ratios and ply angles were designed and fabricated. The geometry, wall thickness, inner diameter and length of each cylindrical shell were measured, as well as the material properties of the corresponding sheet. All the composite cylindrical shells were subjected to external pressure in a pressure chamber, and the load and final collapsed mode were recorded. Nonlinear buckling analyses with geometric imperfection were performed according to the measured data; the numerical and experimental results were found to be consistent. Moreover, the effects of the length–diameter ratio, ply angle, and geometric imperfection on the buckling behavior of composite cylindrical shell were investigated numerically.

Numerical simulations of sympathetic detonation of solid rocket motors

According to the numerical simulation, the sympathetic detonation of fiber composite shelled propellant was analyzed. Comparing the effects of fragments and reaction products shows that the impacting effect of fiber composite shell fragments is limited and can not lead the sympathetic detonation. The reason for sympathetic detonation in the closer distance is mainly reaction products.

Influence of multi‐walled carbon nanotubes reinforced honeycomb core on vibration and damping responses of carbon fiber composite sandwich shell structures

AbstractIn the present study, vibration and damping characteristics of the multi‐walled carbon nanotubes (MWCNT) reinforced honeycomb embedded sandwich composite shell structures have been investigated numerically using finite element (FE) method. The efficacy of the FE method by deriving the governing equations using higher order theory is verified by comparing the natural frequencies assessed using ABAQUS 3D FE model. The influence of MWCNT reinforcement, support condition, and radius of curvature on the dynamic performance of honeycomb sandwich shell with carbon fiber reinforced polymer (CFRP) composite face sheets are explored. In addition, the optimal ply orientations of the various configurations of CFRP sandwich shells with MWCNT/GFRP honeycomb are identified using the developed FE model coupled with genetic algorithm (GA) to enrich the natural frequencies and loss factors. Further, it can be observed that the reinforcement of MWCNTs in honeycomb core, geometry of shell structure, and optimal ply orientations significantly influences the natural frequencies and loss factors of the sandwich composite shell structures.

Dynamic instability of fiber composite cylindrical shell with metal liner subjected to internal pulse loading

Thin-walled cylindrical shells are commonly used structures in explosion containment vessels. When subjected to internal blast loading, these cylindrical shells are prone to dynamic buckling failure.In this work the dynamic stability of cylindrical fiber composite shells with metal liner subjected to uniform internal pressure pulse was investigated through both finite element simulations and theoretical modelling. In particular, pulse buckling of the inner metal liner and vibrational buckling of the outer fiber composite shell were observed and studied. Dynamic, Implicit analysis in ABAQUS Standard considering the initial geometric imperfections were conducted to study the mechanisms for the dynamic buckling of the inner metal liner and outer fiber composite shell. The simulated buckled shape using a simplified two-dimensional model could successfully reproduce the previous experimental results. The dynamic pulse buckling of the metal liner was found to occur during the plastic compression process. The effect of the buckling amplitude of the inner metal liner on the dynamic stability of the outer fiber composite shell was also revealed using numerical simulations. Instead of preventing the outer fiber composite shell from buckling instability, severely buckled metal liner with large buckling amplitude may even accelerate the growth of unstable mode of the fiber composite shell. The theoretical solution for the radial deformation of the metal liner was established by modelling the growth of the buckling mode as the amplification of the initial geometric or velocity imperfection. The most amplified mode and corresponding amplification were determined by the derived amplification function. The solutions for the radial deformation of the outer fiber composite shell were represented by a set of Mathieu differential equations. The dynamic instability of the fiber composite shells was determined from the Mathieu stability charts. The dependence of the dynamic instability of the bilayer composite shells on various parameters such as composite layup, thickness-to-radius ratio and impulse of pressure pulse loading was theoretically predicted and compared with the finite element simulation results.

Material response and failure of highly deformable carbon fiber composite shells

Very thin carbon fiber composite shells can withstand large bending curvatures without failure. The resulting high tensile and compressive strains require accurate modeling of the fiber-dominated non-linear effects to predict the mechanical response. To date, no universal modeling technique can precisely capture the behavior of such structures. In this work, successful representation of composite’s response was achieved by utilizing single fiber tension and compression experimental data, implemented to extend a basal-plane-realignment based non-linear carbon fiber material model. Numerical techniques were adopted to model the bending behavior of unidirectional carbon fiber composites that was recorded in a comprehensive experimental campaign. Observations show that high material non-linearity leads to a non-negligible neutral-axis shift and drastic reduction of bending modulus due to compressive softening. Tensile fiber failure is the driving mechanism in thin shells flexure allowing for elastic compressive strains of up to 3% without micro-buckling. As a result, a remarkable flexibility in thin shells is realized. With increasing thickness, the elastic flexibility is reduced as the failure-driving mode switches to compressive micro-buckling.

An Analytical Method to Predict Dynamic Response of Cylindrical Composite Shells Subjected to Internal Blast Loading

Abstract The dynamic response of composite explosion containment vessels has been widely reported by experimental observations. In this study, we propose an analytical method to predict the dynamic response of open-ended cylindrical composite shells subjected to internal blast loading. The cylindrical composite shell has an out fiber composite shell with an inner steel liner, in which the outer fiber composite shell is simplified as a single elastic layer by an effective modulus in the hoop direction. Considering the impact between two layers during the dynamic response, the analytical solution for response histories of two layers could be obtained. Finite element analysis on the double-layer model is also conducted by ls-dyna. The analytical solution and the simulation result agree well, which demonstrates that the current analytical method can be employed in the design of this composite structure under blast loading.

On the optimal design of manufacturing-induced residual stresses in filament wound carbon fiber composite cylindrical shells reinforced with carbon nanotubes

Process-induced residual stresses occur in composite structures composed of dissimilar materials. As these residual stresses could result in fracture, their consideration when designing composite parts is necessary. In this research, the residual stresses behavior is characterized in terms of three manufacturing features including ‘environmental’, ‘materialistic’ and ‘dimensional’ features. In experimental part, after the fabrication of carbon nanotubes (CNTs) reinforced composite shells, the slitting technique is employed to measure the released strains. Then, the elements of the stiffness matrix are obtained accomplishing an extensive computational modeling in ANSYS commercial software. The obtained results of experimental and computational parts are correlated using a MATLAB programming code, and residual stresses are calculated by calibration factors. Additionally, a statistical analysis is carried out to analyze the influence of mentioned parameters in overall scale. The experimental results had a good agreement with the analytical ones. Finally, this study highlights the complexity and the multifaceted characteristic of residual stresses development in terms of mentioned parameters in CNT-reinforced carbon fiber composite shells.

Proper-Orthogonal-Decomposition-Based Buckling Analysis and Optimization of Hybrid Fiber Composite Shells

Composite cylindrical shells have been widely used in the fuel tanks of launch vehicles. To reduce the material cost of carbon-fiber-reinforced polymer shells, hybrid fiber composite shells composed of carbon fibers, glass fibers, and an epoxy matrix would be a more promising choice. Along with the development of heavy lift launch vehicles, the diameter of a required shell structure could become large. The buckling analysis of composite shells based on detailed finite element models was too time consuming. From the point of view of model size reduction, accurate reduced-order models for buckling analysis along with optimization methods were needed to improve the efficiency of the design and analysis cycle of composite shells. A combined proper orthogonal decomposition and optimization method is proposed in this paper for an efficient buckling analysis of composite shells. In the offline steps of proper orthogonal decomposition, one single finite-element-model buckling analysis is performed based on a full-order model of the initial design with the certain volume fractions of hybrid fibers. Furthermore, snapshots generated from the eigenvector values of the finite-element-model buckling analysis result from the initial design, and a proper orthogonal decomposition basis is determined. By using the obtained proper orthogonal decomposition basis from the initial design, the online steps of proper orthogonal decomposition can be carried out for the buckling analysis of any composite shell with varying volume fractions of hybrid fibers. To further improve the prediction accuracy for a large design space, the mixed proper orthogonal decomposition snapshot method is proposed by adding additional proper orthogonal decomposition snapshots into the original ones. The proposed method contributes to improving the prediction accuracy among the entire design space significantly. Finally, a low-cost optimization framework is established for hybrid fiber composite shells, during which the proper orthogonal decomposition method is used for accelerating the buckling analysis. In particular, a convergence criterion and an updated proper orthogonal decomposition basis strategy are proposed for the optimization framework, aiming at guaranteeing the credibility of the optimal proper orthogonal decomposition buckling result. By means of an illustrative example, the effectiveness and efficiency of the developed framework are demonstrated.

Experimental research on blast power of fiber reinforced anti-hard target warhead

Abstract Fiber reinforced anti-hard-target warhead is a new-type sample munition, which is only designed based on theoretical analysis and numerical simulation in laboratory. This warhead consists of carbon composite casings and high explosive, which can greatly reduce the damage to objects outside the damage range. In order to evaluate its blasting damage effect on concrete target, the three types of charges were researched by means of experiment, which are bare charge, charge with carbon composite material shell and charge with steel shell. Experimental results show that the peak overpressure of charge with carbon fiber composite shell is higher than that of charge with steel shell, but is lower than that of bare charge in the case of the same TNT equivalence. No fragments and fragment effect exist for distant target under the condition of charge with carbon fiber composite shell. However, the experimental result of the charge with steel shell is completely contrary. According to the blast effect in the concrete target, the charge with carbon composite material shell is optimal in matched impedance and detonation propagation. Also, the effective energy produced by the detonation of explosive with carbon composite material shell is the largest.

Dynamic Failure Behavior of Cylindrical Glass Fiber Composite Shells Subjected to Internal Blast Loading

The dynamic response of open-ended cylindrical glass fiber composite shells subjected to internal blast loading is studied in the current paper. The experimental observation on response characteristics of cylindrical glass fiber shells is presented, in which failure modes of composite structures are especially concerned. It is found that dynamic buckling may occur in the inner steel liner, which may consequently cause delamination and fiber fracture of the outer glass fiber shell and thus limits the blast loading resistant capability of glass fiber explosion containment vessels. The other failure mode is obvious circular plastic expansion of the inner steel liner and fiber fracture of the outer fiber shell. There exists an interesting case that hoop winding fibers fail but fibers with a winding angle do not fail, based on which the hybrid filament wound method for cylindrical composite containment vessels is proposed. The current study may contribute to further understanding on the design and application of glass fiber composite explosion containment vessels (CECVs).

Geometric imperfections and lower-bound methods used to calculate knock-down factors for axially compressed composite cylindrical shells

The important role of geometric imperfections on the decrease of the buckling load for thin-walled cylinders had been recognized already by the first authors investigating the theoretical approaches on this topic. However, there are currently no closed-form solutions to take imperfections into account already during the early design phases, forcing the analysts to use lower-bound methods to calculate the required knock-down factors (KDF). Lower-bound methods such as the empirical NASA SP-8007 guideline are commonly used in the aerospace and space industries, while the approaches based on the Reduced Stiffness Method (RSM) have been used mostly in the civil engineering field. Since 1970s a considerable number of experimental and numerical investigations have been conducted to develop new stochastic and deterministic methods for calculating less conservative KDFs. Among the deterministic approaches, the single perturbation load approach (SPLA), proposed by Hühne, will be further investigated for axially compressed fiber composite cylindrical shells and compared with four other methods commonly used to create geometric imperfections: linear buckling mode-shaped, geometric dimples, axisymmetric imperfections and measured geometric imperfections from test articles. The finite element method using static analysis with artificial damping is used to simulate the displacement controlled compression tests up to the post-buckled range of loading. The implementation of each method is explained in details and the different KDFs obtained are compared. The study is part of the European Union (EU) project DESICOS, whose aim is to combine stochastic and deterministic approaches to develop less conservative guidelines for the design of imperfection sensitive structures.

Buckling response of advanced grid stiffened carbon–fiber composite cylindrical shells with reinforced cutouts

In this paper, we present the initial buckling and post-buckling responses of axial loaded advanced grid stiffened (AGS) composite cylindrical shells with reinforced rectangular or circular cutouts. The AGS cylindrical shells were reinforced by various local grid configurations near the cutout areas. The effects of different reinforcing grid configurations on critical loads were then examined and compared to those of different skin-reinforcing designs using Finite Element Analysis (FEA) simulations. A high-fidelity non-linear analysis procedure was proposed to predict the non-linear buckling response of the shell structures. The simulation results indicated that the grid reinforcements can reduce or eliminate the risk of local buckling response near the cutout areas and increase the critical load of the shell more effectively than the skin reinforcements. Furthermore, those results showed that an optimum grid reinforcement configuration exists, which significantly improved the initial buckling and post-buckling resistance of the cylindrical shells under axial loading. The above findings can potentially be useful to the analysis and optimum design of AGS composite cylindrical shells with cutouts.

Axial temperature distribution optimization of mandrel for heated mandrel winding method

The heated mandrel winding method is a new process based on the internal heat-curing method. With the advantages of high production efficiency, good pressure resistance, and so on, the thermosetting fiber composite shell produced using the heated mandrel winding method has been used as a high-pressure shell. Because of the differences between the heated mandrel winding method and the internal heat-curing method, it is especially important to ensure that the axial temperature is distributed as expected. To this end, the structure of the mandrel is improved, wherein the distribution of the holes is rearranged. An experiment shows that the improved mandrel improves the heat transfer. Furthermore, the steam heating process for mandrels with core pipes of different diameters is numerically simulated using FLUENT. The distributions of the flow field and temperature field are compared, and the influence of the mandrel-to-core-pipe diameter ratio on the temperature distribution on the external surface is analyzed based on the flow field characteristics of steam in a cavity. The conclusions provide the theoretical basis for the optimization of the mandrel structure.

The Numerical Simulation Research of Steam Heating Process of Heated Mandrel Winding

The external curing method is usually adopted as the traditional molding process of thermoset fiber composite shell, which places the wound shell into the thermal compression reactor or the oven to cure. This kind of process greatly limits the molding efficiency because winding and curing proceed respectively and separately. The internal curing can be adopted because of the hollow structure of the cylinder-shaped shell, which heats the mandrel with high pressure steam to realize the in-situ curing of the wound shell. This paper researches the new fiber composite molding process named heated mandrel winding. Not only does the heated mandrel winding inherit the advantages of internal curing process, it also greatly improves molding efficiency and quality. This paper introduces the process principle of heated mandrel winding and uses the finite element analysis software FLUENT to carry out the numerical simulation of steam flow and heat transfer during the mandrel heating process, and the simulation results are verified by experiment. According to the simulation results, the distribution and changing course of the flow field and temperature field of the system are obtained, and the relationships between the physical quantities including pressure, temperature and velocity and the parameters of the steam control and channel structure are analyzed.

New Connection System for Confined Concrete Columns and Beams. II: Theoretical Modeling

The concept of confined concrete has been widely accepted throughout the structural engineering field, such as the spiral, steel tube, or carbon fiber composite shell confined concrete, etc. In the present study, this concept has not only been used in the structural columns, but also in joints. In this connection system, the steel tube is interrupted at the floor, the concrete in the connection zone is confined by a stiffening ring with multiple lateral hoops, and the reinforced concrete beams are continuously arranged through the joint. The structural behavior of this new connection system in axial compression tests and reversed cyclic loading tests is presented in a companion paper. In the present study, the bearing strength of composite columns and the joint in axial compression is obtained based on the stress and strain analyses. The critical volume fraction of transverse stirrups of the composite column and the effective confining radius in the stiffening ring are proposed based on the thick cylinder model with the assumption of plane stress state. By using these solutions, it is favorable to obtain the stress distribution in confining concrete and the bearing strength of the confined concrete. For the reversed cyclic loading tests, the Clough hysteresis model is used to simulate the hysteresis loops of the specimens without considering the stiffness degradation in the unloading process. The results of the theoretical modeling are generally in good agreement with the experimental observations.

Experimental research on behavior of composite material projectile penetrating concrete target

Projectile made of carbon fiber composite material shell and metal warhead penetrates concrete target at speeds of 336 m/s, 447 m/s and 517 m/s. The angles between the perpendicular of target surface and projectile axis are 0° and 30°. The thickness of concrete target is 200 mm and the compression strength is 30 MPa. The experimental results indicate that the strength of composite material structure is high. Composite projectile can go through concrete target without fiber segregation and breakage. The percent fill is 18.5% in the composite material projectile. It is about twice as that of metal projectile, if the density of metal is taken as 7.8 g/cm3. Comparing with metal projectile, low-density, high-strength composite material can lessen projectile weight, improve charge-weight ratio of detonator and enhance destructive powder.