Design Of Composite Sandwich Structures Research Articles

External mean flow effect on sound transmission through composite sandwich structures filled with porous materials

A theoretical model is developed to investigate the influence of external mean flow on sound transmission loss (STL) through composite sandwich panels filled with porous materials. The equations of the motions for the composite laminate plates are established by adopting the first-order shear deformation theory. The porous materials in between the sandwich structures are characterized by an equivalent fluid model. Employing the fluid-structure coupling condition, the displacement continuity at fluid-structure interfaces is guaranteed. To validate the proposed theoretical model, a comparison among the present theoretical predictions, the existing theoretical and experimental results are executed, with overall agreements achieved. A systematical investigation is carried out to explore the influences of the external mean flow, incidence angle and laminate scheme on the coincidence frequency and sound transmission loss of the sandwich structures. This work provides a helpful guideline for the vibroacoustic design of composite sandwich structures.

Low velocity failure and integrity assessment of foam core sandwich panels

Impact resistance and energy absorbing capability are of great interest in the design of composite sandwich structures. This paper experimentally studies damage, failure and energy absorption properties of foam core sandwich panels with aluminum and glass fiber reinforced plastic (GFRP) facesheets subjected to low velocity impact. Tests are performed using a drop weight impact tower at different impact velocities. The energy absorbing capabilities of aluminum and composite facesheet sandwich panels with PUR and PS foam core are evaluated by means of absorbed energy-time histories and by specific parameters as normalized absorbed energy, specific energy absorption, and crush force efficiency. Stiffer panels behave better at lower impact velocities, while more ductile ones do better if impact energy is increased.

An analytical approach for global buckling of composite sandwich cylindrical shells with lattice cores

In this paper, a new analytical approach is developed for global buckling of composite sandwich cylindrical shells with lattice cores under uniaxial compression by using the smeared stiffener method. The stiffness contribution of stiffeners is evaluated through the new force and moment effect analysis of the stiffener network on a general unit cell. In these analyses, outer skin-stiffener and inner skin-stiffener interactions are considered, appropriately. The equivalent stiffness of the composite sandwich cylindrical shells with lattice cores is then computed by superimposing the stiffness contribution of stiffeners, outer and inner skins. The critical buckling load is calculated by Rayleigh–Ritz method. Finally, various test examples with different scales of the structure, outer and inner skins ply stacking sequence, outer and inner skins thicknesses were analyzed and the results were compared with results obtained by finite element methods and other works. The results show that the proposed approach has high prediction accuracy and low computational cost for the global buckling analysis of composite sandwich shells with lattice cores. Also, another advantage of the developed approach is able to prediction of the global buckling load of stiffened composite cylindrical shells with better accuracy. Therefore, the proposed approach is highly attractive for the preliminary design of composite sandwich structures in the aerospace industry.

Optimal design of composite sandwich structures by considering multiple structure cases

Acting as primary and secondary structures, sandwich components made of laminated composite face sheets are widely applied in aerospace structures. For simultaneous optimization designs of both stacking sequences of the face sheets and the core thickness, the design problem for composite sandwich structures becomes a combinatorial one by involving both discrete and continuous design variables, for orientation angles of the face-sheet laminate plies are constrained to discrete permissible designs while the core thickness is continuous. Additionally, practical structures like solar arrays are required to satisfy given constraints under multiple structure cases, which involve multiple finite element models and make the problem more complicated. In this study, for optimal designs of composite sandwich structures under multiple structure cases, an optimization model is firstly established by involving both discrete and continuous variables meanwhile integrating all structural cases into a single problem formulation. A stacking sequence optimization method proposed previously by the authors which utilizes two-level approximations and a genetic algorithm is extended to solve the above problem, and an optimization framework is developed by interfacing the improved method with the finite element software MSC.Patran/Nastran. Numerical applications are conducted to demonstrate the feasibility of this optimization system.

Damage and failure mode maps of composite sandwich panel subjected to quasi-static indentation and low velocity impact

In this contribution, modes of damage and modes of failure of composite sandwich panel subject to quasi-static indentation and low velocity impact were investigated. This study was conducted through the use of the finite element analysis, existing formulae and experiments. The damage and failure modes of composite sandwich panels were analyzed with some deliberation. With these results, damage and failure mode maps were compiled to facilitate the design of composite sandwich structures. Existing formulae that predict limit loads for damage modes which includes matrix shear/tension damage and core buckling, were reviewed and compiled to plot the damage mode map. The failure modes of facesheet cracking, overall core crushing and core shear fracture, were investigated to configure the failure mode map. Preferred damage and failure modes for impact resistance were also discussed in term of energy absorption. Extensive quasi-static indentation and low-velocity impact tests were carried out to verify these modes. The results of the finite element analysis are also included to complement the work reported in this contribution.

Optimum Design of Composite Sandwich Structures Subjected to Combined Torsion and Bending Loads

This research is motivated by the increase use of composite sandwich structures in a wide range of industries such as automotive, aerospace and civil infrastructure. To maximise stiffness at minimum weight, the paper develops a minimum weight optimization method for sandwich structure under combined torsion and bending loads. We first extend the minimum-weight design of sandwich structures under bending load to the case of torsional deformation and then present optimum solutions for the combined requirements of both bending and torsional stiffness. Three design cases are identified for a sandwich structure required to meet multiple design constraints of torsion and bending stiffness. The optimum solutions for all three cases are derived. To illustrate the newly developed optimum design solutions, numerical examples are presented for sandwich structures made of either isotropic face skins or orthotropic composite face skins.

Multiscale approach for the design of composite sandwich structures for train application

In the present work a multiscale approach is considered for the design of composite sandwich structures for a roof of railway vehicle. The procedure consists in different steps that start from cost/benefit analysis on materials and their manufacturing process and cycle up to analysis of sub-components and entire structures. Each step is characterized by experimental, theoretical and numerical studies. The design activities herein presented count experimental campaigns able to characterize both the properties of novel sandwich material, manufactured expressly for transportation industry, the sandwich and joint behaviors. Analytical and numerical approaches have been used to validate and optimize the structural layout. Finite element analysis has been also performed on a test article to verify the “new” sandwich roof in regard to structural requirements suggested by European Code.

A Feasible Methodology for Engineering Applications in Damage Tolerance of Composite Sandwich Structures

In this paper, a feasible methodology is proposed for the damagetolerant design of composite sandwich structures and the residual safety evaluation of low-velocity impacted composite sandwich structures. This methodology is based upon the implementation of an event-driven failure criterion called Damage Propagation Criterion. In this criterion, the impact-damaged composite sandwich structure is considered to be unsafe if the damage will propagate to a specified characteristic location near the damage zone under the desired compressive load. The critical far field stress corresponding to the initiation of damage propagation at the specified characteristic location is used as the only characteristic value in this criterion. For a sandwich structure with low-velocity impact damage, this critical far field stress can be determined through either Sandwich Compression After Impact (SCAI) test or numerical analysis by using a modified analytical model or a nonlinear finite element model. Both the experimental and numerical approaches are briefly introduced with examples in this paper. At the end of this paper, the feasible methodology is introduced for the engineering applications in damage-tolerant design of composite sandwich structures and the residual safety evaluation of impact-damaged composite sandwich panels.