Honeycomb Fiber-reinforced Polymer Research Articles

Development of facesheet for honeycomb FRP sandwich panels

Honeycomb fiber-reinforced polymer sandwich panels with sinusoidal core geometry have shown to be successful both for new construction and rehabilitation of existing bridge decks. This investigation is aimed to study the strength properties of the facesheet and to develop an optimized facesheet configuration. A progressive failure model is developed using finite element method to predict the behavior of laminated composite plates up to failure, where the failure criteria are introduced through prescribed user-defined subroutines. The accuracy of the model is verified through correlations between finite element results and existing experimental data. This model is then applied to carry out a parametric study on facesheet. Three variables are included: material properties, including bidirectional stitched fabrics, unidirectional layer of fiber roving, and chopped strand mat; layer thickness; and layer sequences. The quality of each alternative is evaluated based on stiffness and strength performance. In order to further investigate the behavior of facesheet experimentally, coupon samples on selected configurations to evaluate compressive, bending, and shear strengths were tested. The test results are also used to validate the progress failure model developed in this study. Through this combined experimental and numerical study, the strength properties of facesheet are obtained, which permit the optimization of facesheet design.

Behavior of FRP Sandwich Panels under Synergistic Effects of Low Temperature and Cyclic Loading I: Experiment and Numerical Simulation Method

The paper is concerned with using experiments and numerical simulations to study the mechanical performance of a Honeycomb Fiber-Reinforced Polymer (HFRP) sandwich panel at different temperatures, especially at low temperatures coupled with cyclic loadings. All physical tests were performed in a temperature controlled room and used a three-point bending setup where the applied load gradually increased from zero to 36kN. Experimental results show that the stiffness of the panel becomes softer at some lower temperatures. In order to eliminate the influence of the initial conditions, an incremental method was introduced to process the experimental results. This method treated all displacements and strains as zero when applying a load of 4.5kN. Furthermore, the change in stiffness of the panel was obtained through the use of a special equivalent stiffness which involved measuring the change of the stiffness of the panel. After comparing different methods, the composite shell method was used to build finite element models for numerical simulations in ABAQUS. Reduction of moduli and Random Mesh Size Method (RMSM) were employed to simulate microcracking between fibers and matrix and debonding between the core and face sheets, respectively.

Behavior of Honeycomb FRP Sandwich Structure under Combined Effects of Service Load and Low Temperatures

This paper presents the experimental study about the behavior of honeycomb fiber-reinforced polymer (HFRP) sandwich structure with corrugated cores under the combined effects of service load and low-temperature cycling (ranging from 24°C to -35°C). The potential debonding at the interfaces between the corrugated cores and face sheets because of the service-load condition specific to bridge engineering at low temperatures and its impact on stiffness are studied in this paper. The finite-element analysis (FEA) was utilized to determine the load in the experiment. The experiment consisted of tests conducted at four different temperatures. The load-strain responses were monitored to study the behaviors of HFRP sandwich panels. On the basis of the observation and results from the experiment, this paper concludes that the deflection limit span over 400 can potentially be adopted in practice without incurring stiffness degradation because of interface debonding. The paper also shows that it is essential to study the tolerable size of cracks or defects at the interfaces before applying this deflection limit as a design criterion. The experimental results in this study serve as a necessary supplement to the material tests and confirm that the stiffness of the HFRP sandwich panels at the structural level will also increase when the temperatures are decreased at least up to the service-limit state. Finally, this paper verifies the important role that tensile stress plays in interface debonding and suggests that previous tests may underestimate the actual shear strength of the interfaces.

Modeling Technique for Honeycomb FRP Deck Bridges via Finite Elements

Honeycomb structures have been used in different engineering fields. In civil engineering, honeycomb fiber-reinforced polymer (FRP) structures have been used as bridge decks to rehabilitate highway bridges in the United States. In this work, a simplified finite-element modeling technique for honeycomb FRP bridge decks is presented. The motivation is the combination of the complex geometry of honeycomb FRP decks and computational limits, which may prevent modeling of these decks in detail. The results from static and modal analyses indicate that the proposed modeling technique provides a viable tool for modeling the complex geometry of honeycomb FRP bridge decks. The modeling of other bridge components (e.g., steel girders, steel guardrails, deck-to-girder connections, and pier supports) is also presented in this work.

Torsion of honeycomb FRP sandwich beams with a sinusoidal core configuration

A combined analytical, numerical and experimental investigation of honeycomb fiber-reinforced polymer (HFRP) sandwich beam samples subjected to torsion loads is conducted. The sandwich panel considered in this study has unique sinusoidal core geometry in the plane extending vertically between face laminates, and it has been used primarily as decking systems in highway bridges. Using a homogenization process and mechanics of materials approach, the equivalent core material properties for the honeycomb core geometry are found, and the material properties of face sheets are obtained by micro/macromechanics. Equivalent material properties of the core and face sheets are then used to evaluate effective torsional stiffness properties of HFRP panels. The torsional analysis includes the evaluation of core equivalent in-plane and out-of plane shear properties and panel apparent torsional stiffness properties. Finite element models using layered shell elements are used to correlate with the analytical and experimental results for HFRP beams samples in torsion. Two types of models are presented in the finite element simulation: an actual geometry model, where the core and face sheet geometry are defined by layer shell elements, and an equivalent plate model, for which the equivalent material properties of the core and face sheets are utilized. In order to verify the accuracy of the analytical and numerical predictions, several honeycomb sandwich beam samples with sinusoidal core waves oriented along the longitudinal or transverse or vertical directions and with different face sheet configurations are experimentally tested in torsion. The present analysis and characterization procedures can be used in design applications and optimization of honeycomb structures, and they can also be employed to verify or refine in-plane and out-of-plane shear equivalent material properties for the present and other honeycomb FRP panels.

Transverse Shear Including Skin Effect for Composite Sandwich with Honeycomb Sinusoidal Core

Honeycomb fiber-reinforced polymer (HFRP) sandwich panels with sinusoidal core geometry have been used extensively for new construction and replacement of bridge decks. The core geometry used consists of large cavities and represents a new type of core configuration. This study is concerned with the behavior of HFRP panels under transverse shear considering skin effect, and addresses the two contributing factors due to shear warping and bending warping. Shear warping corresponds to the assumption of having a hinge connection between facesheet and core, and bending warping is induced for the assumption of a rigid connection. All previous studies have been focused mainly on shear warping, neglecting for the most part bending warping. A closed-form solution based on proper description of displacement field at the interface is derived considering shear warping. The accuracy of this solution is verified by finite-element (FE) results. The FE model is then applied to study bending warping effect, and also the core-facesheet constraint or interface bonding effect. The equivalent shear stiffness and the stress distributions subject to skin effect are defined, and suggestions for future design considerations are given.

Buckling Behavior of Honeycomb FRP Core with Partially Restrained Loaded Edges under Out-of-plane Compression

Fiber-reinforced polymer (FRP) sandwich deck panels with sinusoidal honeycomb core geometry have shown to be efficient in both new construction and rehabilitation of highway bridge decks. The sandwich panel consists of top and bottom laminated face sheets bonded to the honeycomb core, which extends vertically between face sheets. This paper is focused on the study of the buckling capacities of the core components under out-of-plane compression. The facesheet and core are attached by contact molding and are, therefore, not rigidly connected. Thus, this problem can be described as the instability of an FRP core panel with two rotationally restrained loaded edges. An elastic restraint coefficient is introduced to quantify the bonding layer effect between the facesheet and core, and a simple and relatively accurate test method is proposed to obtain the restraint coefficient experimentally. A combined analytical and experimental study of compression is presented. By solving a transcendental equation, the critical compression buckling stresses are obtained, and a simplified expression to predict buckling strength is formulated in terms of the elastic restraint coefficient. The analytical solution is verified by finite element (FE) analysis. Compression tests are carried out to evaluate the effect of the bonding layer thickness, and the experimental results correlate closely with analytical and FE predictions. A parametric study is conducted to study the core aspect ratio effect on the buckling load. The method described in this paper can be further extended to determine local buckling capacities of other structural shapes with elastic restraints along the loaded edges.