Analysis Of Composite Structures Research Articles

An analytical method for vibration analysis of arbitrarily shaped non-homogeneous orthotropic plates of variable thickness resting on Winkler-Pasternak foundation

A highly applicable analytical approach is proposed for the dynamic analysis of composite plate structures with complex variation of geometric characteristics (shape/boundary and thickness) and material characteristics (Young's modulus, shear modulus and density) resting on Winkler-Pasternak foundation with general elastic boundary conditions. Boundary conditions of the plates are treated by the penalty method, so that the admissible functions can use any complete set of orthogonal polynomials, which is obtained by Gram-Schmidt orthogonalization process. The interval where the in-plane coordinate variables of the plate domain are located can be selected as the orthogonalization intervals, so as to avoid the normalization procedure of coordinates and simplify the operation process. In order to calculate the energy integral of the arbitrarily shaped plate, the plate domain segmentation strategy is introduced. To verify the effectiveness and accuracy of the proposed method, convergence study and numerical verifications for different orthogonalization intervals, weight functions, penalty spring stiffness and the truncation number of orthogonal polynomials are carried out. Taking regular hexagonal plates as examples, the effects of the parameters of thickness, nonhomogeneity and foundations on the vibration characteristics of the plates are studied. These results can be used as reference data for future research.

Isogeometric analysis of multilayer composite shell structures: Plasticity, damage, delamination and impact modeling

A comprehensive Isogeometric Analysis framework for damage modeling of laminated composite structures is presented. The formulation is based on a multilayer approach that employs Kirchhoff–Love shell theory coupled with anisotropic elastoplastic damage to model the mechanical behavior of the individual plies. The plies are connected at their interfaces through a mixed-mode cohesive damage model that is used to represent delamination. The ply no-interpenetration condition is enforced using a penalty formulation. The formulation ensures a smooth transition from the opening mode, which is governed by the cohesive damage law, to the closing mode, which is governed by the penalty approach, and results in a significantly more stable numerical methodology overall. The resulting framework is deployed on a series of simulation cases with increasing complexity of the geometry and mechanical phenomena modeled. In all cases, experimental data is used for model validation purposes and for demonstrating the superior robustness and predictive capabilities of the formulation presented.

Parametrically-upscaled continuum damage mechanics (PUCDM) model for plain weave woven composites: Part II model validation and parametric studies

In this second of the two-part paper, the two-level parametrically-upscaled continuum damage mechanics models (PUCDM-1 and PUCDM-2) developed in the first part Xiao et al. (2022) are applied for multiscale analysis of plain weave composite structures. The material damage response in the intra-yarn unidirectional microstructures and the woven yarn–matrix mesostructures are respectively represented by level-1 and level-2 PUCDM models. The models bridge material length scales through explicit functions of the lower-scale morphological descriptors (representative aggregated micro/mesostructural parameters or RAMPs) and material properties (Xmat) with high computational efficiency. The paper focuses on model validation with experiments and parametric studies. The model is validated with observations from tensile tests on an hourglass-shaped specimen with good agreement at multiple scales. The validated PUCDM model is then employed for the analysis of multiscale deformation and damage mechanisms in single-edge notched bending (SENB) tests on woven composite beams. Parametric studies are performed to investigate the effect of lower-scale morphology and material properties on the structural damage response of the woven composite beams.

A Reduced Order Model based on Artificial Neural Networks for nonlinear aeroelastic phenomena and application to composite material beams

Applications of composite materials in industry have increased due to their high stiffness-to-weight ratio. In the particular case of unidirectional fibers or perpendicular fabrics, the materials behavior is orthotropic, so that an extra degree of freedom, related to the orientation of the fibers, must be included in the structural optimization. Composite material thin walled beam models have been developed for reducing the computational cost of the simulations. Traditionally, these models have been coupled with potential aerodynamics to calculate the aeroelastic response, and thus, the viscous nonlinear effects have been omitted. In order to capture these effects, this manuscript focus on the development of a Reduced Order Model enhanced by an Artificial Neural Network for the analysis of composite structures under aerodynamic loads. The presented methodology shows the training process of the neural network, the comparison with high fidelity simulations and the design optimization of a carbon fiber laminated foam beam. It is demonstrated that the model reduces the computational cost by orders of magnitude, while still capturing structural couplings and being capable of increasing the flutter velocity by more than 10% with respect to the longitudinal orientation.

Mechanism Study of Bi-Material COPV Structure Based on Composite Structure Design Theory

Composite over-wrapped pressure vessels (COPVs) are widely used in aerospace, aviation, army, Navy, nuclear industry and other military and civil fields because of their light weight, high strength, high reliability and safety, leak before burst (LBB) failure mode safety and many other characteristics. Because the aerospace field has very strict requirements on the weight of platform structure products including COPV, it is necessary to improve the mass efficient of COPV and achieve the characteristics of light weight and high strength. In this paper, through the optimization of composite material grid theory algorithm, the relationship between bidirectional stress and internal pressure of cylinder and dome of isotropic material is deduced. On this basis, the grid theory equations of bidirectional stress and internal pressure load of COPV cylinder and dome are deduced, and the wall thickness equations of ordinary rotating curve head, equal tension head and hemispherical head are proposed. According to the grid theory model of membrane stress of COPV cylinder, the author completed the grid theory algorithm derivation of elastic and plastic lined COPV. This paper is the exploration of composite dome structure analysis, which lays a foundation for the subsequent solution of composite dome grid theory.

Vibration Analysis of Composite Internal Door Panel of a Car

Abstract: The main objective behind this paper is to develop a suitable model of internal door panel for cars, to conduct a static structural analysis of internal door panel by finite element method and to compare the performance of glass fiber material with previously recommended materials of internal door panel. This paper deals with the mechanical behavior and vibration analysis of glass fiber-based polymer composite beam structures. Glass fiber has been widely used for many applications due to its high strength, flexibility, stiffness and resistance to chemical this extended work the inactive basic Limited Component Investigation of inside entryway board of a vehicle by considering glass fiber composite materials was conducted. The entryway board of the vehicle was utilized to create the geometric show of the inward entryway board by CATIA V5 R20 modeling program. This 3-D geometric demonstration was imported to utilize ANSYS Workbench 19.0. Model analysis of the internal door panel has been done using ANSYS software.

Holistic determination of physical fracture toughness values and numerical parameters for delamination analysis considering multidirectional-interfaces

Delaminations are a concern for the structural integrity of fibre composite structures. The decisive material parameter for delaminations is fracture toughness. Structures usually have a multidirectional ply stacking. However, interface orientation dependant fracture toughness values and R-curve effects are neglected in numerical delamination analysis. This work investigates interface orientation specific fracture toughness values and considers R-curve effects in mode I to improve simulation accuracy. Therefore, mode I, mode II and mixed mode fracture toughness values of different interface ply orientations are determined experimentally and verified using numerical analysis of the characterisation specimens with cohesive zone modelling. In this way, an engineering methodology is provided for the experimental characterisation and comprehensive numerical modelling of delaminations in mesoscale progressive damage analysis of multidirectional composite structures. In addition, a full parameter set for the simulation of four different interfaces of M21-T700GC prepreg material is given. It can be shown that the use of standard 0°//0°-values leads to very conservative results. The use of interface specific values increases the accuracy. Ultrasonic scans of the DCB specimens are used to compare the crack front shapes for validation. Not only the load displacement curves of the characterisation specimens are well captured, but also the crack front shapes. This demonstrates that by smearing the microscale effects, the material behaviour can be captured phenomenologically correct by mesoscale modelling suitable for industrial use.

Multiscale analysis of composite structures with goal-oriented mesh adaptivity and reduced order homogenization

We present a multiscale finite element approach for composite structure analysis, applying reduced order homogenization to obtain an accurate surrogate model for microscale RVE computations and establishing macroscale mesh adaptivity towards an error control of a user-defined quantity of interest. By means of the so-called nonuniform transformation field analysis, reduced variables are deduced from a space–time decomposition of inelastic strain fields. Considering the macroscopic dissipation power as a volume-averaged microscopic dissipation power, closed-form macroscale constitutive relations are established, thus resulting into a reduced order homogenization problem. For ease of error estimate, we propose a multifield formulation for the reduced order problem. Based on duality techniques, a backward-in-time dual problem is derived from a Lagrange method, leading to error representations aiming at the quantity of interest. Accordingly, an efficient error estimator combined with a patch recovery technique avoiding nonlinear computations is proposed. The effectiveness of the resulting adaptive algorithm is illustrated by several numerical examples w.r.t. a prototype model.

Multiscale reliability analysis of composite structures based on computer vision

The geometric uncertainties of composite structures are considered in the multiscale reliability problem. A convolutional neural network (CNN) is developed and trained using deep learning to link geometric uncertainties and the randomness of structural responses or performances. The CNN training set includes graphical samples and corresponding stress components and strength characteristics of the lamina. A method for generating a graphical sample is developed, which integrates the stochasticity of the fibre shape, misalignment, arrangement, volume fraction, matrix voids, and stacking sequences of the laminates. The corresponding stress components are simulated using the Kernal–Hashin model and laminate plate theory. A reliability analysis procedure is developed using a Monte Carlo simulation. Numerical cases are presented to demonstrate the validity of the proposed method.

Stochastic, probabilistic and reliability analyses of internally-pressurised filament wound composite tubes using artificial neural network metamodels

Progressive damage analysis of composite structures in the presence of uncertainties is a computationally-expensive and highly-complex process. This work tackles these issues by developing efficient finite element (FE)-based surrogate models that are constructed with artificial neural network (ANN) models and design of experiment (DOE) methods. The proposed framework for building surrogate models (metamodels) can capture various multi-scale uncertainties. In addition, to alleviate the computational burden in non-deterministic analyses, a novel strategy is proposed using the Plackett-Burman method to determine sources of uncertainties that have significant impacts in scattering the response. The response surface methodology (RSM), along with FE analysis, is used to create datasets. The RSM and ANN metamodels are constructed by using these datasets. Key results show that for complex models, ANN metamodels have more accuracy than RSM ones. The surrogate models are used for stochastic, probabilistic and reliability analysis of filament wound composite tubes. As a result, this multi-scale surrogate-based framework significantly decreases the computational time and cost of the analyses. Reliability analysis demonstrates that the statistical correlation between ply properties is significant, and it must be considered for an accurate evaluation.

Developing Equations for Free Vibration Parameters of Bistable Composite Plates Using Multi-Objective Genetic Programming.

For the last three decades, bistable composite laminates have gained publicity because of their outstanding features, including having two stable shapes and the ability to change these states. A common challenge regarding the analysis of these structures is the high computational cost of existing analytical methods to estimate their natural frequencies. In the current paper, a new methodology combining the Finite Element Method (FEM) and Multi-Objective Genetic Programming (MOGP) is proposed for the analysis of bistable composite structures, leading to some analytical relations derived to obtain the modal parameters of the shells. To achieve this aim, the data extracted from FEM, consisting of the ratio of the length to width (a/b) and the thickness (t) of the laminate, is split into Train and Validation, and Test, subsets. The former is used in MOGP, and four formulas are proposed for the prediction of the free vibration parameters of bistable laminates. The formulas are checked against the Test subset, and the statistical indices are calculated. An excellent performance is observed for all GP formulas, which indicates the reliability and accuracy of the predictions of these models. Parametric studies and sensitivity analyses are conducted to interpret the trend of input parameters in the GP models and the level of sensitivity of each natural frequency formula to the input parameters. These explicit mathematical expressions can be extended to the other bistable laminates to obtain their natural frequencies on the basis of their geometrical dimensions. The results are validated against the experimental data and verified against FEM outcomes.

Implementation of multiscale mechanisms in finite element analysis of active composite structures

Interrogation of composite structures for inherent damage is investigated implementing three-tier analysis scheme. The analysis starts at the structure level where a general-purpose Finite Element code ABAQUS is employed to obtain the stress field in the second level of analysis that is the composite laminate. A special material routine is prepared to propagate the local fields to the individual plies and hence to the third level of analysis which is the microstructure modelling of the composite. Through the third level of analysis, interface damage between fiber and matrix is checked implementing a certain failure criteria. The interaction between the different length scales; that are, structure, macro, and micro scales, is implemented using the non-mechanical strains caused by damage. Embedment of electrically active fibers in the laminate serves as a tool to interrogate the structure for inherent damage through the electric displacement generated due to the electro-mechanical coupling. To verify the developed multi-scale model, a comparison with the experimental results of a tube problem under combined internal pressure and axial load is presented. The results show good agreement in both the undamaged and damaged state. As an application, a plate with a hole under biaxial load is solved. The output includes not only the structure global behavior during damage but also detailed information about the location of damage within the structure, the plies that exhibit damage, type of damage and the fiber/matrix debonded length. Comparison between the electric displacement of the active fibers in the undamaged and damaged states is presented as well.

An efficient trans-scale and multi-stage approach for the deformation analysis of large-sized thin-walled composite structure in aircraft assembly

An efficient trans-scale and multi-stage approach for the deformation analysis of large-sized thin-walled composite structure in aircraft assembly

Reliability analysis of composite sandwich structure for fuselage skin based on surrogate model

Composite structures are characterized by multiple source uncertainties in mechanical properties, geometric dimension, etc., and multiple failure modes, which bring challenges to their design and application. In order to explore the reliability analysis method of composite sandwich structures with multi-source uncertainties and multi-failure modes, a parametric finite element model and an acoustic boundary element model were established for deterministic analysis of a fuselage skin sandwich structure. Considering the randomness of the mechanical properties of composite materials and the laminate thickness, the structural reliability models were established for three typical failure modes of sandwich structures: static strength failure, global buckling and vibration noise. In order to reduce the computational effort, the Kriging surrogate models of failure modes were constructed, and the subset simulation method was used to predict the system failure probability of the sandwich structure of fuselage skin. The proposed computational framework provides support and tool for the fine design of composite sandwich structure.

Stress analysis of composites with interfacial bridged cracks and damaged zones

Stress analysis of composite structures with bridged cracks and damaged zones is performed with the direct boundary integral equations method in axisymmetric formulation. It is assumed that: a) the crack faces interact in some zones behind of the cracks edges (bridged zones); b) these zones width can be comparable to the whole crack size; c) adjacent parts of the structure can be connected by mechanical ligaments (including interfaces ahead of cracks fronts) and the relative displacements of these parts can occur under the loading (these zones consider as damaged zones). The boundary element software to solve axisymmetric problems of elasticity with interfacial bridged cracks and damaged zones was developed. The results for different properties of composite materials and bonds are presented. Applications the bridged crack approach to modeling of cracks self-healing is remarked.

Composite sandwich panel closeout analysis and test

This paper presents an analysis methodology for composite sandwich panel 90° closeout with multi-layered non-uniform facesheets and core. A detailed 2D finite element model was constructed to model honeycomb core through the thickness as well as simulate top and bottom facesheets and the transition region. 2D equivalent material properties of the facesheets are calculated based on classical lamination theory. Elemental stresses of core are used to calculate failure index and margin of safety for various loading conditions based on tension/compression and shear interaction theory. Facesheet strength is checked by interlaminar shear and tension interaction equation with the utilization of failure index. Theoretical failure modes and critical locations obtained from this approach are compared with structural testing of specimens. The predicted failure loads, deflection, facesheet load ratio, and strains are in good agreement with test data. The methodology is verified to be a simple, efficient, and reliable method for the analysis of composite sandwich closeout structures.

Stability analysis of the pile-prestressed anchor composite structure based on failure mode

Pile-prestressed anchor composite structure is widely used in retain engineering, whose stability analysis is mainly based on the slip line passing through the bottom of pile. However, the existing stability analysis is unable to comprehensively consider the actual slip line passing through pile body, pile bottom and the soil under pile. Based on multiple failure modes, a stability analysis model of composite structure considering both the effects of prestress and pile body is established, and the dynamic search algorithm for the model is proposed. We compare the proposed model with the software of LIZHENG deep foundation pit and the existing calculation model and find the effectiveness of our model. It is found that the safety coefficient of the composite structure is directly proportional to the prestress, pile length and pile diameter, but inversely proportional to the pile spacing. Meanwhile, the safety coefficient increases firstly and then decreases with the increase of slip line depth. Increasing the prestress of anchor in the middle and lower part of the slope has a more obvious effect on improving the safety coefficient. The proposed stability model and search algorithm can consider multiple failure modes and obtain the safety coefficient. In addition, it can comprehensively evaluate the stability of the pile-prestressed anchor composite structure retaining slope, which has superior application value.

Study on the gas sensor at room temperature based on polypyrrole materials

This paper presents the results of synthesising polypyrrole (PPy) modified Dodecylbenzene sulfonic acid (DBSA) with nanostructures oriented to applications for NH3 gas sensors operating at room temperature. The outcomes of surface morphology and chemical composition structure analysis of PPy film were studied by field-emission scanning electron microscopy (FE-SEM), fourier-transform infrared spectroscopy (FT-IR), and ultraviolet-visible spectroscopy (UV-Vis). The products were obtained by electrochemical method with the nanostructured PPy film, the conductivity of the PPy film depends on the concentration of DBSA denaturant. The experimental results showed that these PPy films have a great potential application as a new sensitive layer for gas sensors.

Failure analysis of composite F-joint structures under tensile loading: Experimental and numerical study

This paper presents an investigation on the failure process of two different types of composite frame joints (F-joints), one is connected by high-lock bolts (FH) and the other reinforced by high-lock bolts and adhesive (FHA). The mechanical behavior of F-joints subjected to out-of-plane tension load is analyzed by experiment and numerical simulation. Test results show significant differences in the damage process, failure modes and strain distribution between FH and FHA. The strength of FHA increases nearly 13% compared to FH. Three-dimensional finite element models considering failure criterion and damage evolution are developed and implemented in the commercial code Abaqus/Standard through a user-defined subroutine UMAT. Cohesive zone model is used to simulate the adhesive layer damage of FHA. Simulating failure load and the damage process match the experimental data. The information on the failure mechanism and final failure load of composite F-joints is useful for the optimal design of such joints.

Large deflection of composite beams by finite elements with node-dependent kinematics

In this paper, the use of the node-dependent kinematics concept for the geometrical nonlinear analysis of composite one-dimensional structures is proposed With the present approach, the kinematics can be independent in each element node. Therefore the theory of structures changes continuously over the structural domain, describing remarkable cross-section deformation with higher-order kinematics and giving a lower-order kinematic to those portion of the structure which does not require a refinement. In this way, the reliability of the simulation is ensured, keeping a reasonable computational cost. This is possible by Carrera unified formulation, which allows writing finite element nonlinear equilibrium and incremental equations in compact and recursive form. Compact and thin-walled composite structures are analyzed, with symmetric and unsymmetric loading conditions, to test the present approach when dealing with warping and torsion phenomena. Results show how finite element models with node-dependent behave as well as ones with uniform highly refined kinematic. In particular, zones which undergo remarkable deformations demand high-order theories of structures, whereas a lower-order theory can be employed if no local phenomena occur: this is easily accomplished by node-dependent kinematics analysis.