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This study investigates the vibration behavior of delaminated cylindrical shells composed of symmetric cross-ply composite material are partially or completely filled with fluid. An incompressible, non-viscous and irrotational internal fluid is considered. The classical shell theory and Helmholtz's equation with the velocity potential function are employed to derive the governing equation for the vibration of delaminated symmetric cross-ply laminated cylindrical shells. The primary focus is to understand the impact of varying fluid heights, densities and velocities on the natural frequencies of the shells, as well as the effects of shell length, thickness-to-radius ratio, and delamination's position in the thickness and circumferential directions. The study findings indicate that the natural frequencies decrease considerably as the height of the fluid increases and that the delamination position significantly influences the observed frequency variations. Moreover, the internal fluid density and shell length affected natural frequencies. This research contributes not only to our knowledge of the behavior of cylindrical shells with delamination and fluid filling but can also assist in designing structures that mitigate undesirable vibrations and promote the creation of more efficient and dependable structures. [ABSTRACT FROM AUTHOR]

Carbon fiber resin-based composite materials are widely employed in the manufacturing of composite shells. During the curing process, the temperature gradients and cure degree gradients make it easy to generate thermal strains in both carbon fibers and resin, with the resin experiencing cure shrinkage strain due to the curing reaction, ultimately leading to residual stresses and strains. In this paper, a three-dimensional thermo–chemo–mechanical coupled curing model of the composite shell was established based on a resin test, and the changes of temperature, curing degree, residual stress, and strain during the solidification of the composite shell were investigated. First, the curing property parameters and elastic modulus of HCM-2184 resin were obtained through a curing dynamic test and a tensile test. Then, considering the heat release and shrinkage reaction of solidification, a coupled thermo–chemo–mechanical curing model was developed with the CHILE ( α ) elastic model, and the curing process of the composite shell was simulated numerically. The results show that the resin used in the test belongs to the autocatalytic reaction. For thin composite shells, the heat accumulation inside the shell during curing is not obvious. During the curing process, the curing shrinkage behavior of the resin is an important factor for the generation of residual stress and residual strain. [ABSTRACT FROM AUTHOR]

Laminated composite structural components, quite often in the form of shell, manage to find wide applicability in industries where they are exposed to active loads leading to large-amplitude vibrations. The assumption based on linear strain-displacement relation lead to erroneous displacement/stress predictions, therefore the inclusion of geometric nonlinearity happens to be vital for efficient component design. The present analysis is intended to inspect the effects of aspect ratio, dynamic load amplitude and edge constraints on the nonlinear forced vibration characteristics of a laminated shell under harmonic excitations. The finite element analysis has been carried based on the kinematics of first-order shear deformation theory including geometric nonlinearity. A time domain analysis has been presented using modified shooting technique with unstable portion of the response being obtained using continuation schemes. The scheme employed is competent to get the complete stable and unstable branches post bifurcations. The nonlinear vibration response corresponding to variations in the forcing frequency for laminated open shells has been obtained. The assessment of outward and inward half cycle nonlinear frequency response exhibits that for both cylindrical and conical shells the response amplitude in the inward motion is greater than that in the outward motion during a cycle. This is due to destabilizing action of the membrane stress resultants during inward half cycle. Frequency response curves, temporal variation of response/stresses and FFT of the stresses have been acquired to analyse the nonlinear steady-state forced vibration behaviour of open shells. The uneven half cycle time and greater higher harmonic contributions depicted in the nonlinear response can be judiciously employed for the safe dynamic design of open shells. [ABSTRACT FROM AUTHOR]

To further enhance the fatigue resistance of spiropyran‐based photochromic materials and to explore the functionality of organic–inorganic metal oxide microcapsule shell materials, cross‐linked (P(MMA‐PETA)) and homopolymer (PMMA) shells have been developed by cross‐linking TiO2 and hybridizing ZnO on a PMMA matrix. PMMA/TiO2 photochromic microcapsules and PMMA/ZnO photochromic microcapsules with ultraviolet (UV)‐absorbing function are prepared by successfully encapsulating spiropyran photochromic compounds using these two composite shells. The results show that both microcapsules exhibit a complete spherical core–shell structure with good UV resistance and thermal stability. The TG test underlines a 50% coating rate of PMMA/ZnO microcapsules on spiropyran photochromic material, with an optimal ZnO addition of 10% and particle size range from 2 to 8 µm, effectively blocking UV‐A and part UV‐B radiation. Further, a 75% maximal coating rate is observed for PMMA/TiO2 microcapsules on spiropyran with optimal TiO2 addition at 2–4%, a particle size of around 5 µm, diffusely reflecting 48% of UV rays. The photochromic fabrics prepared with PMMA/TiO2 microcapsules have better UV resistance, with a UV protection factor value of 59.48, and excellent fatigue resistance after at least 30 cycles of UV–visible light irradiation. [ABSTRACT FROM AUTHOR]

Carbon fiber resin-based composite materials are widely employed in the manufacturing of composite shells. During the curing process, the temperature gradients and cure degree gradients make it easy to generate thermal strains in both carbon fibers and resin, with the resin experiencing cure shrinkage strain due to the curing reaction, ultimately leading to residual stresses and strains. In this paper, a three-dimensional thermo–chemo–mechanical coupled curing model of the composite shell was established based on a resin test, and the changes of temperature, curing degree, residual stress, and strain during the solidification of the composite shell were investigated. First, the curing property parameters and elastic modulus of HCM-2184 resin were obtained through a curing dynamic test and a tensile test. Then, considering the heat release and shrinkage reaction of solidification, a coupled thermo–chemo–mechanical curing model was developed with the CHILE (α) elastic model, and the curing process of the composite shell was simulated numerically. The results show that the resin used in the test belongs to the autocatalytic reaction. For thin composite shells, the heat accumulation inside the shell during curing is not obvious. During the curing process, the curing shrinkage behavior of the resin is an important factor for the generation of residual stress and residual strain.

Airframe construction in conical form is the most desired shape of flight hardware due to their low drag profile and are located at the fore-end region of flight vehicles encountering high drag loads. Owing to their tailoring capability, materials with orthotropic mechanical properties are preferred choice. Delamination defects formed in them while manufacturing or when subjected to loads would unfavorably influence the mechanical performance of the orthotropic airframe. In the current work, FE simulation of delamination which is embedded in orthotropic cone shaped shells under external pressure load is performed as per the method cited in published literature. A layer wise element based on shell theory has been used and the effect of delamination size and its through the thickness position on the mechanical performance of the cone shaped shell is investigated. Circumferential and rectangular shapes of defects have been simulated. The investigation is performed for metal and composite materials with 3 types of stacking sequences generally used in practical designs. Verification of the procedure is carried out by equating with the procedure cited in published studies on shells of thin orthotropic cylinders. The eigen value of the first mode is taken as the critical buckling factor under external pressure. The buckling factor of the delaminated cone is normalized with the buckling factor of the ideal cone. The normalized buckling factor is showed graphically with the normalised defect size. Global, as well as local buckling and also symmetric as well as asymmetric buckling shapes, are observed in the results of the simulation. Shift from global mode to local mode of buckling is also observed in certain cases. Drastic reduction in buckling capability with the local mode is observed when the defect location is close to the surface and more prominent for an outer surface case. [ABSTRACT FROM AUTHOR]

The effect of the interface stiffness and interface strength on the low-velocity impact response of woven-fabric semicylindrical composite shells is studied using finite element (FE) models generated with continuum shell elements and cohesive surfaces. The intralaminar damage is accounted for using the constitutive model provided within the ABAQUS software, while the interlaminar is addressed utilising cohesive surfaces. The results show that the interface stiffness has a negligible effect on the force and energy histories for values between 10 1 N/mm 3 and 2.43 × 10 6 N/mm 3 . However, it has a significant impact on the delamination predictions. It is observed that only the normal interface strength affects the maximum impact force and the delamination predictions. Increasing its value from 15 MPa to 30 MPa resulted in an 8% growth in the maximum force, and a substantial reduction in the delaminated area. The obtained results serve as guidelines for the accurate and efficient computation of delamination. The successful validation of the FE models establishes a solid foundation for further numerical investigations and offers the potential to significantly reduce the time and expenses associated with experimental testing. [ABSTRACT FROM AUTHOR]

The limited availability of analytical solutions and the high cost associated with experimental testing motivate the use of computational tools to assess the dynamic behavior of load-bearing components, especially when a wide design space must be explored, as is often the case with composite structures. In this context, a novel high-order accurate discontinuous Galerkin formulation for transient and free-vibration analysis of multilayered plates and shells is presented and numerical validated. The starting point of the formulation is a generalized structural theory for multilayered shells with arbitrary curvature based on the expansion of the displacement covariant components throughout the shell thickness. The variational statement of three-dimensional elastodynamics allows deriving the strong form of the governing differential equations, which form the basis to obtain the corresponding discontinuous Galerkin weak statements. As the order of the through-the-thickness expansion and the order of the discontinuous Galerkin basis functions are free parameters, the proposed approach allows tuning the order of accuracy of the computed solution throughout both the shell thickness and the shell modeling domain. Numerical results are reported and discussed for several validation test cases in terms of h - and p -convergence analyses, demonstrating the high-order accuracy, robustness, and computational savings of the formulation. • Transient and free-vibration analysis of laminated shells with general curvature. • An Equivalent-Single-Layer theory using the covariant components of displacement. • A high-order accurate discontinuous Galerkin formulation for shell dynamics. • Numerical solutions obtained using structured and implicitly-defined meshes. • h p -convergence analyses for various plate and shell geometries. [ABSTRACT FROM AUTHOR]

Thin-walled cylindrical shells under axial compression load are prone to buckling. The influencing factors leading to a reduction of the buckling load are a major design challenge. The sensitivity to imperfection increases with rising slenderness. In literature, cylinders with the same parameters and different slenderness are rarely tested in a larger number of samples. In this contribution, seven cylindrical shells, six of them nominally identical, are tested on two different test rigs and compared with twelve specimens with a smaller radius and same wall thickness from a previous series of tests. It is shown how the imperfection sensitivity is dependent on the R/t-ratio. Additionally, it is demonstrated how the quality of the test set ups corresponds with the achieved buckling load. Finally, the suitability of selected design approaches is determined based on the test results. Based on that, recommendations for the choice of a suitable approach are given. [ABSTRACT FROM AUTHOR]

The main objective of this study is to design composite shells i.e. long, short, thin and thick for the different underwater applications. These shells can be a part of pressure hulls, underwater vehicles, pressurized tanks, underwater cables and underwater pipelines etc. This paper presents comprehensive procedures for the mathematical modeling of elastic buckling for submersible composite shells under hydrostatic pressure. First order shear deformation theory (FOSDT) was used for modeling. FOSDT theory was mathematically derived under hydrostatic pressure for composite shells, and it can be used for all types of submersible shells. After the derivation of the theory, mathematical code was formed on MATLAB for this modeling. From the given formulation one can design the shell structure according to his needs on different environment conditions. Different types of composite shells, including moderately thick, thick, long, and short, are investigated for the FOSDT formulation to check the accuracy range. The results were compared with previous studies and finite element analysis FEA. Three types of materials, Carbon/Epoxy, Glass/Epoxy, and Boron/Epoxy, were used with different cross-ply symmetric and unsymmetrical angle configurations. The layups used for the analysis were [0/90/0]s [90/0/90/0]s [02/902]s [90/02/90]s [0/902/0]s [0/0/0/90]s [90/90/90/0]s and [0/90].

The effect of the interface stiffness and interface strength on the low-velocity impact response of woven-fabric semicylindrical composite shells is studied using finite element (FE) models generated with continuum shell elements and cohesive surfaces. The intralaminar damage is accounted for using the constitutive model provided within the ABAQUS software, while the interlaminar is addressed utilising cohesive surfaces. The results show that the interface stiffness has a negligible effect on the force and energy histories for values between 101 N/mm3 and 2.43 × 106 N/mm3. However, it has a significant impact on the delamination predictions. It is observed that only the normal interface strength affects the maximum impact force and the delamination predictions. Increasing its value from 15 MPa to 30 MPa resulted in an 8% growth in the maximum force, and a substantial reduction in the delaminated area. The obtained results serve as guidelines for the accurate and efficient computation of delamination. The successful validation of the FE models establishes a solid foundation for further numerical investigations and offers the potential to significantly reduce the time and expenses associated with experimental testing.

• A Bloch wave based numerical vibration correlation technique (BW-NVCT) is proposed. • BW-NVCT predicts buckling loads without high experimental or computational costs. • A novel implementation of the Bloch wave method is used for twofold acceleration. • BW-NVCT is shown in high accuracy and efficiency for engineering composite shells. • Results indicate that BW-NVCT can capture both global and local buckling modes. The buckling load revealing structural capacity bears significant value for the design of engineering composite shells, especially in the aerospace industry. Non-destructive methods are prevailing for critical buckling load prediction. However, the experimental costs and computational time for the analysis are unaffordable, especially for large-scale and complex shells. Despite the numerical vibration correlation technique (NVCT) and its modifications proposed for faster critical buckling load prediction, the efficiency requires further improvement. For composite shells with rotational periodicity, analyzing one substructure based on the Bloch wave method can be an alternate for the analysis of the entire shell. Since the NVCT comprises the linear buckling analysis and repeated frequency analyses, twofold acceleration can be performed. Thus, the Bloch wave based numerical vibration correlation technique (BW-NVCT) is proposed. Firstly, the formulations for the Bloch wave method and the NVCT are derived. As the curve of Bloch wave numbers and buckling loads is monotonous or principally comprise a single peak, the computations in the Bloch wave method to determine the minimum buckling load are further reduced. Then, the implementation of BW-NVCT is presented wherein the Bloch wave calculations are simplified compared with the Bloch wave buckling analysis method. Secondly, three types of composite shells including the Z33 composite cylindrical shell, the pressure vessel and the nozzle are analyzed by the proposed method. By applying Bloch boundary conditions to the substructure, the linear buckling loads, natural frequencies are in high accuracy with respect to results by finite element analyses directly. In addition, predicted critical buckling loads by the BW-NVCT are in excellent precision and most importantly, remarkable efficiency is achieved compared with both the NVCT and the dynamic explicit analysis. Results show that the proposed method can capture both global and local buckling modes, even when bend-twist coupling exists. It is concluded that the BW-NVCT is widely applicable for composite shells and is substantiated as an effective method for fast buckling load prediction. [ABSTRACT FROM AUTHOR]

The existing literature extensively explores the influence of stacking sequences on symmetric flat laminates subjected to low-velocity impacts. However, this is not true in the case of curved laminates. Therefore, the main goal of this study is to analyse the effect of stacking sequences on the impact response of semicylindrical woven composite shells. For this purpose laminates with [0] 8 , [45] 8 , [＋15,−15] 2 S , [＋22.5,−22.5] 2 S , and [＋30,−30] 2 S , were considered in order to evaluate the impact response of layer orientations. Additionally, laminates with [0 2 , 45 2 ] S , [0,45] 2 S , [0,45 2 , 0] S , and [45 2 , 0 2 ] S were employed to analyse the effects of changing the positioning of the layers in relation to the laminate mid-plane. The FE model was validated with the experimental results obtained for [0] 8 laminates, where good numerical–experimental correlation was obtained. The findings suggest that an increase in impact bending stiffness (IBS) leads to a rise in maximum force, accompanied by a decrease in maximum displacement, contact time, and dissipated energy. The primary mechanism responsible for dissipating the majority of impact energy is intralaminar damage, followed by delaminations and friction. Importantly, changing the layer positions has a significant impact on how each layer within the semicylindrical quasi-isotropic composite shell distributes and dissipates energy during the impact event. [ABSTRACT FROM AUTHOR]

This paper presents a large deformation Kirchhoff–Love shell model hierarchically enhanced with through-the-thickness warping functions, arbitrarily chosen by the user. Two unknowns are introduced for each of them, representing its amplitudes in two directions tangent to the shell surface. NURBS are used to approximate reference surface displacement and warping amplitudes in the weak form. The transverse shear strains are linear functions of the warping parameters only and naturally free from locking. A patch-wise reduced integration avoids membrane locking and improves efficiency. Particular attention is paid to the modeling of composites made up of multiple stiff layers coupled with soft interlayers. The alternating layup with high stiffness ratios induces a significant sectional warping with transverse shear strains concentrated in the soft layers. Two warping models are investigated: (WI) all stiff layers maintain the same director orthogonal to the deformed surface with independent transverse shear deformations of the soft layers; (WZ) a single zigzag function linking these deformations. The numerical tests confirm the great accuracy of the hierarchic shell model in reproducing the solid solution with a small number of discrete parameters, provided that the correct warping model is chosen. WI is reliable for all alternating layups. WZ reduces the unknowns to five per surface point, regardless of the number of layers, and is accurate for uniform soft layers. • The Kirchhoff–Love composite shell is enhanced with warping. • The hierarchic approach is used for large deformations. • Transverse shear strains and zigzag effects are included. • An accurate and efficient isogeometric formulation is proposed. • Two warping models are studied for stiff/soft layups. [ABSTRACT FROM AUTHOR]

This paper investigates the impact dynamics of thin semicylindrical woven composite laminate shells, with a particular focus on understanding the influence of thickness. Utilizing the finite element (FE) method, the study evaluates both intralaminar and interlaminar damage associated with the impact response. The findings show that the implementation of the explicit FE method, along with a continuum damage mechanics model, for the intralaminar damage, and a surface-based cohesive model, for the interlaminar damage, may be used to correctly predict the load histories, as well as the maximum impact force, maximum displacement, contact time and impact bending stiffness (IBS). The numerical predictions reproduce well the linear response of the maximum impact force and maximum displacement to the thickness variation, as well as the 2nd order polynomial curve of the IBS, with errors ranging from 2.7% to 15.9%. Moreover, the damage areas and the effect of thickness on the damage severity were accurately replicated. These results' validation enables the prediction of the energy histories and the ensuing energy dissipation forms. According to the findings, the intralaminar damage is around 5 times more significant than the other energy dissipation forms. The accuracy of the simulation creates the possibility for more impact investigations using a similar numerical approach, reducing the expenditures of experimental testing. • Investigation of the impact dynamics on composite shells using the explicit finite element method. • Numerical predictions of intralaminar damage using a continuum damage mechanics model. • Numerical predictions of interlaminar damage using a surface-based cohesive model. • Prediction of energy dissipation forms for different thicknesses. [ABSTRACT FROM AUTHOR]

Abstract In this article the effect of a rectangular cutout on the buckling behavior of a thin composite cylinder was investigated using numerical and experimental methods. To verify the finite element results, a limited number of tests was carried out on perforated and non-perforated glass/epoxy cylinders with [90/−23/23/90] layups. In the numerical analysis, linear and nonlinear approaches were employed to study the effect of initial imperfections on the buckling of the cylinders. Several key findings including the effects of cutout size and orientation, and the mutual effects of the cutout and initial imperfections on the buckling behavior were investigated in detail. In the presence of cutouts, the effect of initial imperfections on the buckling load is a function of the cutout size. In cylinders with rectangular cutouts, buckling analysis revealed that a rectangular cutout in the circumferential direction causes around 8% more reduction in the buckling load than the same cutout in the axial direction. Also, numerical findings illustrated that elastic stress concentration factors for the circumferential cutouts are much greater than those for the axial cutouts; thus premature failure around the cutout will trigger earlier buckling in the cylinder with circumferential cutouts. [ABSTRACT FROM AUTHOR]

The numerical and experimental validation of multistable behavior of cantilever shells is addressed. The design of the laminated composite shells is driven by a recently proposed semi-analytical shell model, whose predictions are verified and critically examined by means of finite element simulations and stability tests on two manufactured demonstrators. In addition, the influence of the main design parameters on the shells stability scenario is discussed. Despite its simplicity, the reduced model allows to depict a fairly faithful picture of the stability scenario; therefore, it proves to be a useful tool in the early design stages of morphing shell structures. [ABSTRACT FROM AUTHOR]

In this work, a Boundary Element Method formulation for stress analysis of symmetrically laminated composite thick shallow shells is presented. The proposed formulation was obtained by coupling the boundary element formulation of shear deformable symmetrically laminated composite plates and the boundary element formulation for two-dimensional anisotropic plane stress analysis. Formulation uses the elastostatic anisotropic fundamental solutions proposed for these formulations. Domain integrals are transformed to the boundary by using the Radial Integration Method. Numerical examples are presented to demonstrate the efficiency and accuracy of the formulation. Obtained results concur with results available in the literature as well as with finite element results. [ABSTRACT FROM AUTHOR]

Numerical formulations of the Koiter theory allow the efficient prediction, through a reduced model, of the behavior of shell structures when failure is dominated by buckling. In this work, we propose an isogeometric version of the method based on a solid-shell model. A NURBS interpolation is employed on the middle surface of the shell to accurately describe the geometry and the high continuity typical of the displacement field in buckling problems and to directly link the CAD model to the structural one. A linear interpolation is then adopted through the thickness together with a modified generalized constitutive matrix, which allows us to easily eliminate thickness locking and model multi-layered composites. Reduced integration schemes, which take into account the continuity of the shape functions, are used to avoid interpolation locking and make the integration faster. A Mixed Integration Point strategy makes it possible to transform the displacement model into a mixed (stress–displacement) one, required by the Koiter method to obtain accurate predictions, without introducing stress interpolation functions. The result is an efficient numerical tool for buckling and initial post-buckling analysis of composite shells, characterized by a low number of DOFs and integration points and by a simple and quick construction of the reduced model. [ABSTRACT FROM AUTHOR]

A numerical stochastic strategy for optimising composite elastic shells undergoing buckling is presented. Its scope is to search for the best stacking sequence that maximises the collapse load considering the post-buckling behaviour. Its feasibility is due to a reduced order model built for each material setup starting from a hybrid solid-shell finite element model exploiting a multimodal Koiter method. The approach has no limitations concerning geometry, boundary conditions and material properties distribution. The collapse load is evaluated using a Monte Carlo simulation able to detect the worst imperfection shape, including a posteriori the imperfections in the reduced order model. For a limited number of parameters the proposal allows to analyse all the possible layups. In the general case, it uses a Monte Carlo scanning of the design parameters with different levels of adaptability. The optimisation of curved panels, also with stiffeners, confirms the feasibility and reliability of the proposed strategy. [ABSTRACT FROM AUTHOR]

In this work an isogeometric solid-shell model for geometrically nonlinear analyses is proposed. It is based on a linear interpolation through the thickness and a NURBS interpolation on the middle surface of the shell for both the geometry and the displacement field. The Green–Lagrange strains are linearized along the thickness direction and a modified generalized constitutive matrix is adopted to easily eliminate thickness locking without introducing any additional unknowns and to model multi-layered composite shells. Reduced integration schemes, which take into account the high continuity of the shape functions, are investigated to avoid interpolation locking and to increase the computational efficiency. The relaxation of the constitutive equations at each integration point is adopted in the iterative scheme in order to reconstruct the equilibrium path using large steps and a low number of iterations, even for very slender structures. This strategy makes it possible to minimize the number of stiffness matrix evaluations and decompositions and it turns out to be particularly convenient in isogeometric analyses. [ABSTRACT FROM AUTHOR]

The stability failure of the axially loaded cylindrical shell is considered as the last unresolved classical stability problem, although it has been investigated for over 100 years. Therefore designers rely on the application of empirical knockdown factors from the 1960s like the NASA SP-8007 for cylindrical shells and the NASA SP-8019 for truncated conical shells which are very conservative for modern shell structures. Perturbation approaches for the design of axially loaded cylindrical and conical shells are presented in this paper. These approaches deliver knockdown factors for a physical based estimation of the lower-bound buckling load and are suitable for research and industrial applications as they are independent from imperfection measurements and easy to implement. The corresponding numerical models are validated by means of high-fidelity buckling experiments and it shows that experimental buckling loads can be calculated very precisely in contrast to the previous methodology. Additionally, new robust knockdown factors are proposed for preliminary shell design which are based on curve fitting of numerical knockdown factors of the perturbation approaches. Thus, it is possible to utilize the load bearing capability of launch-vehicle primary structures up to 40% more effectively, resulting in considerable weight saving potentials for composite shell structures. [ABSTRACT FROM AUTHOR]

The feasibility of probabilistic design methods to overcome conservatism associated with deterministic design methods for unstiffened cylindrical composite shells has been shown, but studies are frequently based on assumptions regarding relevant uncertainties due to the lack of available data. The reliability based calibration method suggested here relies on extensive measurements regarding the statistical characteristics of thickness, fibre volume fraction, fibre orientation, material stiffness and geometric imperfections of 11 previously tested cylinders. Furthermore, the stiffness of the potting of tested cylinders is estimated using Finite Element Analysis and the introduction of a pre-stress state through the potting process investigated. Following a sensitivity study, Bayesian inference is used to update the information of relevant uncertain variables. Monte Carlo simulation is employed to compute the distribution functions of the buckling load, and these are used to calibrate structural safety factors at a chosen reliability level. A multiplicative error model is established to compute safety factors covering the model uncertainty inherent to the approach. In combining these two safety factors in a Bayesian sense, a transparent, updatable safety-factor concept is developed, leading to less conservative design loads than currently considered. [ABSTRACT FROM AUTHOR]

A semianalytical method hybridizing hierarchical theory and finite-strip method (FSM) is developed to analyze buckling behavior of composite laminate shells in this paper. The Legendre orthogonal polynomial series are chosen as the hierarchical shape functions for the shell strips. The critical buckling loads and modes of cylinder shells with various radiuses subjected to axial loads are calculated by the proposed hierarchical finite-strip method (HFSM). The efficiency of HFSM is noted as the method combines the advantages of both hierarchical theory and FSM. The convergence and precision of HFSM are also demonstrated by several numerical examples. [ABSTRACT FROM AUTHOR]

The paper presents the calculation of the stress-strain state of the composite shell of the mixing device in the production of concrete used in underground construction. A mathematical model obtained earlier by the authors, which develops due to the influence accounting of the temperature field, was used. The problem was solved in the linear formulation with varying rigidity characteristics of separate layers as a result of an aggressive environment. The calculations results are shown. [ABSTRACT FROM AUTHOR]

Space launcher vehicle structures are designed as thin walled cylindrical and conical structures which are prone to buckling and are sensitive towards geometrical imperfections. Small deviations in dimensions, which still are within manufacturing tolerances, may lead to a tremendous decrease in load carrying capacity. Thus, imperfections have to be considered during the design phase and this is commonly done using empirical knock down factors. Besides this approach, imperfections can be considered by applying numerical or analytical structural models. Composite materials are used to exploit the light weight potential of unstiffened thin walled structures. For this type of shell structure, the buckling load of the geometrically perfect shell and the imperfection sensitivity are significantly influenced by the laminate stacking sequence. In this paper, the influence of the laminate stacking sequence of composite shells with rotational symmetric imperfections on the buckling behavior is studied and laminate stacking sequences leading to the highest buckling loads of an imperfect shell structure are identified. These stacking sequences are evaluated further by applying non-rotational symmetric imperfections and localized imperfections and the stacking sequences leading to optimum designs of the geometrical perfect shell structure are considered as reference structures. [ABSTRACT FROM AUTHOR]

Due to a lack of statistical data, unstiffened cylindrical lightweight structures are designed following a knockdown factor (KDF) approach described in the NASA SP-8007 (Weingarten and Seide, 1965). This approach aims at a lower-bound, conservative design. The basis for the proposed KDFs are a number of tests with different, partially unknown boundary conditions and imperfection patterns for metallic cylinders that do not resemble the imperfection patterns achieved by state-of-the-art manufacturing methods for cylinders made of carbon fibre reinforced plastics (CFRP). Within this work, two CFRP tubes are manufactured using the filament winding method and are cut into a total of 12 cylinders from which optical measurements are taken to analyse characteristics of the corresponding imperfection patterns. 11 cylinders are tested in axial compression until buckling occurs and tests are accompanied by high speed displacement measurements, thermography and measurements of occurring load imperfections. Four different FE-models, which differ in the parameters considered, are set up for prediction of the buckling load of each cylinder. Model response showed the highest sensitivity to load imperfections. Negligence of this parameter lead to a 15% increase of the corresponding model bias while geometric imperfections made up for only 3%. [ABSTRACT FROM AUTHOR]

The nonlinear dynamics of cantilever bistable shells with asymmetric stable configurations is investigated. The possibility of maximizing the kinetic energy associated with snap-through motion offered by the considered cantilevered shells is pursued to enhance the sought-after energy harvesting capabilities. Through an experimental campaign under harmonic forcing the resonance scenarios around the stable configurations are analysed. The resulting nonlinear behaviour observed for high amplitude excitation is adopted to guide a reduced order model derivation. By combining the experimental response with two double-well oscillators derived from FE simulations, a double-well quintic oscillator capturing the observed softening behaviour is proposed. It involves a parameter identification phase in which a nonlinear damping model is introduced. A numerical continuation approach is adopted to discuss the local periodic solutions around each stable configuration in terms of resonance curves, bifurcation diagrams and basins of attraction. The global dynamics involving regular and chaotic dynamic regimes as well as snap-through motion is eventually described. • A novel cantilever composite shell with asymmetric double potential wells. • Experimental evidence of the exploitation of the bistable shell nonlinear dynamics. • Extracted kinetic energy maximization from the triggering of snap-through phenomena. • A nonlinear quintic Duffing–Holmes model for describing in- and cross-well dynamics. [ABSTRACT FROM AUTHOR]

Abstract: Thermally loaded unsymmetric laminates can display separate bending and twisting responses combined with alternating regions of bistability when fabricated with initial curvature in the unstressed state. The twist response is bistable, and represents the minimum potential energy paths that join two orthogonally-oriented bending modes. These two bending modes are each monostable for moderate changes in temperature, but become bistable for large changes. A Rayleigh–Ritz model using von Kármán plate kinematics extended to account for initial curvature is presented. Results are compared against both experimental data and a finite element model. The present model captures the shell-like behavior of initially curved laminates without the need for more complex shell kinematics, and thus represents a useful tool for the initial design of thermally actuated morphing structures. [Copyright &y& Elsevier]

Abstract: Nonlinear forced vibrations of water-filled, laminated circular cylindrical shells are studied by using the Amabili–Reddy nonlinear higher-order shear deformation theory and energy approach in the Lagrangian description. The fluid is modeled by potential flow. It is assumed that the shell is subjected to a steady harmonic concentrated force acting in the radial direction. Pseudo arc-length continuation and collocation technique is used to carry out bifurcation analysis and to obtain nonlinear frequency–amplitude responses. Direct time integration of the equations of motion has also been performed by using Gear’s backward differentiation formula (BDF) to obtain time histories, phase space diagrams and Poincaré maps. The effect of internal fluid and lamination angle on the frequency–amplitude response in the neighborhood of the resonance frequency, traveling wave solution and internal resonances of simply supported shells are investigated. It is shown that water-filled composite shells may exhibit complex nonlinear dynamics including a rare and intricate 1:1:1:1 internal resonance. [Copyright &y& Elsevier]

Abstract: The dynamic response of an aerospace layered structure composed of a combination of conical and cylindrical shells is hereby modeled. In the low and the mid-frequency ranges a WFEM derived ESL approach implemented within a FEM is used in order to predict the response of the shell. Furthermore, in the high frequency range the CLF of the connected subsystems are calculated using a WFEM/FEM approach. These CLF are implemented within a SEA approach in order to predict the structural response. The accuracy and robustness of the developped approaches are exhibited by comparisons to experimental measurements on a layered conical-shell-conical configuration. [Copyright &y& Elsevier]

This paper addresses the active control of mechanical vibrations induced in laminated composite doubly curved shells. A three dimensional energy based finite element model has been developed for this analysis. The laminated shell is integrated with a patch of active constrained layer damping (ACLD) treatment in which vertically reinforced 1-3 piezoelectric composite is used as the material of the constraining layer. Both in-plane and out-of-plane actuations of the constraining layer of the ACLD treatment have been utilized for deriving the finite element model. Investigation has been carried out to see the performance of the patch when the orientation angle of the piezoelectric fibers of the constraining layer is varied in the two mutually orthogonal vertical planes. The analysis revealed that the vertically reinforced 1-3 piezoelectric composites which are in general being used for the distributed sensors can be potentially used for the distributed actuators of high performance light-weight smart composite shells. [ABSTRACT FROM AUTHOR]