Design and Analysis of Composite Panels

Design and analysis of stiffened composite panels including post-buckling and collapse

The non-linear stability analysis of composite cylindrical panel subjected to concentrated in-plane mechanical and localized thermal loadings are reported here. The buckling of composite panel subjected to concentrated in-plane mechanical loading/ localized thermal loading is solved in two steps as the prebuckling stress distribution within the panel is not known a priori. In the first step, the semi-analytical expressions for the pre-buckling stresses within the composite cylindrical panel under in-plane mechanical/ thermal loadings are developed by solving in-plane elasticity/thermoelasticity problem. Subsequently, using these in-plane stresses within the cylindrical panel, the governing equations for nonlinear stability of layered composite panel are formulated using variational principle. The cylindrical panel is modeled based on Donnell’s shallow shell theory considering higher order shear deformation theory and incorporating von-Karman geometric nonlinearity. The Galerkin’s method is used to solve the non-linear governing partial differential equations. The influence of different types of mechanical and thermal loadings, initial geometric imperfections, and radius of curvature on the postbuckling equilibrium paths is investigated.

The vibroacoustics behavior of aircraft-type stiffened panels is classically analyzed using deterministic methods such as the finite element and boundary element method at low frequencies or energy based methods at higher frequencies. In the present work, a general semi-analytical method based on modal expansion technique is developed to predict the vibration and acoustics radiation of both metallic and composite flat stiffened panels. Both unidirectional and bidirectional stiffened panels with eccentric stiffeners and various shapes are analyzed using the same matrix formulation. The presented model is also able to predict the response of both regular and irregular stiffened panels. The contributions of the force and moment modal coupling at each beam location are accounted for together with the effect of interaction between ribs in the case of orthogonal stiffened plate. The response to various types of excitations (point force, diffuse acoustic field, and turbulent boundary layer) are presented in terms of their joint acceptance. The model is numerically validated by comparison with the FEM/BEM and hybrid FEM/SEA methods for various configurations and excitations. Excellent agreement is found.

This paper focuses on Deterministic and Reliability Based Design Optimization (DO and RBDO) of composite stiffened panels considering post-buckling regime and progressive failure analysis. The ultimate load that a post-buckled panel can hold is to be maximised by changing the stacking sequence of both skin and stringers composite layups. The RBDO problem looks for a design that collapses beyond the shortening of failure obtained in the DO phase with a target reliability while considering uncertainty in the elastic properties of the composite material. The RBDO algorithm proposed is decoupled and hence separates the Reliability Analysis (RA) from the deterministic optimization. The main code to drive both the DO and RBDO approaches is written in MATLAB and employs Genetic Algorithms (GA) to solve the DO loops because discrete design variables and highly nonlinear response functions are expected. The code is linked with Abaqus to perform parallel explicit nonlinear finite element analyses in order to obtain the structural responses at each generation. The RA is solved through an inverse Most Probable failure Point (MPP) search algorithm that benefits from a Polynomial Chaos Expansion with Latin Hypercube Sampling (PCE-LHS) metamodel when the structural responses are required. The results led to small reductions in the maximum load that the panels can bear but otherwise assure that they will collapse beyond the shortening of failure imposed with a high reliability.

Aims of research. Polymer unidirectional composite laminate panel behavior with interlaminate defects under action of different dynamic loads is consider. Methods. Normal modes and eigenvalues of rectangular composite panels in the presence multiple delamination different sizes ellipsoidal form are calculated. The dependences of the maximum deflections from the frequency of the stationary pressure field action are constructed. Distribution field of panels plies failure index under action of nonstationary pressure field by using different failure criteria for composites is determined. Results. Modeling methodology composite panels behavior in the presence multiple interlaminar defects under action of different dynamic loads is developed. Analysis of failure panel with the use of different failure criteria for composites is carried out.

The modeling method of fiber-reinforced composites by state-based peridynamics was studied. The one-parameter nonlinear constitutive model was used to get the nonlinear relationship between force vector state and deformation vector state. Then the governing equation for laminate with nonlinear inplane behavior was built. A compensation modification method was also proposed to reduce the surface effects. A scalar function was introduced in the equation of force vector state in order to describe the damage. After the proposed compensation modification method was verified to reduce strain energy error of particles in the boundary region effectively, both unidirectional and orthotropic composite panels under uniaxial tension load were modeled. The resulting stress-strain curves fit well with the test data. Also, progressive damage analysis of composite panels with a center-hole was carried out, and the corresponding damage results agreed well with the experimental and simulating results of a relevant published research.

Buckling analysis of piezoelectric cylindrical composite panels reinforced with carbon nanotubes

The effect of in-plane stresses on the stability behaviors of constant stiffness and variable stiffness composite panels, exposed to aerodynamic pressure, is studied using the finite element method. The dynamic pressure from the high velocity airflow is evaluated from the first-order piston theory, and the eigenvalue analysis is performed to investigate the flutter or divergence type of instabilities in such composite panels under combined mechanical and aerodynamic loads. Attempt is made to understand the effect of the lamination parameter on the stability characteristics of edge-supported and cantilever composite trapezoidal panels. Finally, the limit cycle oscillation of variable stiffness plates subjected to aerodynamic pressure is investigated.

Preparation and sound transmission loss analysis of carbon fiber composite sandwich panel

Automotive industries are struggling hard to optimize vehicle body through different ways; like shape for its aerodynamics and aesthetics, weight of materials to be used for fuel efficiency, material conservation, recyclability, and others. The century’s competitive material in the industry is composite material especially natural composites are preferably based on different perspectives. As B-pillar is one of the critical structural support members of sedan cars, different considerations are taken to analyze and replace its outer panel with natural Nettle fiber composite. Mainly it should overcome two things; B-pillar must overcome the stress developed due to the system as it is a structural member and safeguard the occupant in the case of side crash. Considering these properties of the B-pillar, a natural fiber called Abirbara/Aleblabit/Ethiopian origin stinging nettle with S-glass hybrid composite was used to replace its outer panel with Ansys analysis. It is observed that Abirbara fiber, which can be extracted from the Abirbara plant is abundantly available in Ethiopia and is not yet used widely as composite materials. This work started with plant harvesting (collecting) and fiber extraction, which was performed through mechanical methods. The composites were prepared using chemically treated fiber with different orientations based on predetermined performance. Different mechanical properties were measured by using UTM machines and its tensile strength, compression strength, bending strength values are 153.166 MPa, 212.7 MPa, and 370 N peak load, respectively, whereas water absorption is 1.6% in 48 h. The model of the sedan car B-pillar panel was prepared by SpaceClaim software and analyzed for impact using Ansys software. Crush simulation of B-pillar panel with conventional material and composite material was computed. So the Ansys analysis shows that the energy absorption of EOSN fiber composite B-pillar panel is 2.61 and 0.15925 kJ for conventional materials. It is concluded that Abirbara composite can be used for B-pillar outer panel, which results in reduction of weight of the vehicle, fuel consumption, and an increase in energy absorption.

This paper presents the analysis and optimization of sandwich plates simply supported on all four edges with a foam-reinforced web core subjected to inplane compressive loads. Due to many failure modes of this kind of sandwich structure such as overall instability of the sandwich as a whole, face plate instability, face wrinkling and instability of the webs, the analysis of each mode is investigated and discussed in order to understand the physical behaviors of the whole structure and its components. Then, the sandwich plate subjected to a uniaxial compressive load is optimized for the minimum weight by taking into account the above four failure criteria. The “weakest link in the chain” concept is used, by which each of these assumed independent failure modes occurs at the same buckling stress in order to attain the minimum weight. Additionally, for any given set of materials, the optimum face thickness, web component thickness, web core component spacing, core depth, and foam core modulus for any values of in-plane compressive loads is evaluated analytically. A factor of merit is derived for the special cases of the same orthotropic and isotropic face and web materials. Thus, the best material can be selected, or a rational compromise can be made between weight savings and cost.

Vibration-based detection of skin-stiffener debonding on composite stiffened panels using surrogate-assisted algorithms

Vibration and damping characteristics of hybrid carbon fiber composite pyramidal truss sandwich panels with viscoelastic layers

The effect of progressive damages in composite materials is incorporated into a geometrically nonlinear solid shell element formulation to investigate the dynamic response of composite structures under the blast wave pressure loading. The effect of material damages such as fiber failures, matrix cracking, and fiber-matrix shearing failures on the behavior of composite structures is addressed via reducing their stiffness corresponding to detected failures. Two separate failure criteria are used for unidirectional and woven composites. In addition, the strain-rate effect on the material strength is taken into account. For the dynamic formulation, the trapezoidal rule is chosen for the time integration. Various numerical analyses of composite panels are conducted under the static and dynamic loading conditions to validate the effectiveness of the present formulation. The analysis results clearly exhibit the significant effect of material damages on the structural behavior of the composite panels. Also, the analysis results are in good agreement with the available experimental data.

On the basis of well-known literature, an analytical tool named LEAF (Linear Elastic Analysis of Fracture) was developed to predict the Damage Tolerance (DT) proprieties of aeronautical stiffened panels. The tool is based on the linear elastic fracture mechanics and the displacement compatibility method. By means of LEAF, an extensive parametric analysis of stiffened panels, representative of typical aeronautical constructions, was performed to provide meaningful design guidelines. The effects of riveted, integral and adhesively bonded stringers on the fatigue crack propagation performances of stiffened panels were investigated, as well as the crack retarder contribution using metallic straps (named doublers) bonded in the middle of the stringers bays. The effect of both perfectly bonded and partially debonded doublers was investigated as well. Adhesively bonded stiffeners showed the best DT properties in comparison with riveted and integral ones. A great reduction of the skin crack growth propagation rate can be achieved with the adoption of additional doublers bonded between the stringers.