Sinusoidal Core Research Articles

Advanced Materials and Structures: Analysis Methods and Results

Advanced and innovative materials are used increasingly in civil and aerospace engineering. To meet the demands of advanced materials in structural applications, novel analytical and experimental techniques have been developed to simulate and characterize the material responses and structural behaviors. To this end, this special issue of the Journal of Aerospace Engineering aims to present a collection of invited papers concerning the analytical and experimental techniques for advanced and emerging materials and structures in civil and aerospace engineering. The papers selected for this issue are primarily based on the presentations delivered in the three “Advanced Materials in Structures” sessions organized by the ASCE Aerospace Division’s Committee on Advanced Materials and Structures at the 44th AIAA/ASME/ASCE/AHS/ACS Structures, Structural Dynamics, and Materials (SDM) Conference, Norfolk, Va., April 7–10, 2003. Seven papers based on the presentations have been peer reviewed and are included in this special issue. Among them, a wide range of analytical and experimental techniques are covered, ranging from constitutive modeling, to advanced numerical simulation, and to novel experimental characterization of composite materials and novel structural systems. The papers address critical issues in the rapidly growing fields of civil/aerospace materials and structures, including application of advanced materials (e.g., braided composites and coating materials), novel structures (e.g., sinusoidal core configuration and z-pin reinforcement), advanced experimental methods (e.g., ballistic impact tests), as well as analytical/numerical techniques (e.g., the nonlinear, strain ratedependent constitutive models and linear time-dependent acoustic wave propagation) in support of test methods and applications. In most papers, a balanced approach of analytical, numerical, and experimental correlations is adopted, and their advancement to the state of the art in advanced materials and structures is illustrated. In “Ballistic Impact of Braided Composites with a Soft Projectile,” Roberts et al. experimentally investigate the impact behaviors of aluminum plates, braided composite plates, and braided composite half-rings subjected to a soft gelatin projectile. The failure modes are identified, and an estimate of the penetration threshold is provided, which is useful for damage-tolerance evaluation of aerospace components (i.e., fan cases in commercial jet engines) under impact of high-strain energy density. Ivancic and Palazotto’s “Experimental Considerations for Determining the Damping Coefficients of Hard Coatings” characterizes the dynamic behavior of a titanium plate coated with magnesium aluminate spinel, representing a turbine compressor blade. Various experimental tests using dynamic ping and laser vibrom-

Performance Evaluation of Repair Technique for Damaged Fiber-Reinforced Polymer Honeycomb Bridge Deck Panels

All-composite, fiber-reinforced polymer honeycomb (FRPH) sandwich panels are an innovative application of modern composite materials in civil engineering. These panels have become increasingly popular for use as full-depth bridge decks and have been used to span both transversely between steel or concrete girders and longitudinally between abutments. Although several bridges using FRPH panels have been installed in recent years, a method to repair the panels if they are damaged has not been thoroughly investigated. This paper presents the analysis and full-scale evaluation of a 9.75 m (32 ft) long FRPH member that was subjected to severe core-face delamination damage and subsequently repaired. As such, the work presented herein is the first of its kind to be conducted for FRPH bridge members. The damaged member when repaired was shown to have approximately 65% more capacity than a similar undamaged member. The additional capacity was achieved using a single wrapping layer over the face plates and sinusoidal core. This wrapping layer is believed to have prevented a failure (at the resin bond line) between the face plates and core by engaging a shear-friction type clamping force. The contribution of the wrap layer is considered using simple calculations, rigorous finite-element models, and experimental data. Acoustic emission monitoring was used to compare the performance of the damaged and repaired specimens under sustained load.

Modeling and characterization of fiber-reinforced plastic honeycomb sandwich panels for highway bridge applications

Fiber-reinforced plastic (FRP) composite decks have been increasingly used in highway bridge applications, both in new construction and rehabilitation and replacement of existing bridge decks. Recent applications have demonstrated that FRP honeycomb panels can be effectively and economically used for highway bridge deck systems. This paper is concerned with design modeling and experimental characterization of a FRP honeycomb panel with sinusoidal core geometry in the plane and extending vertically between face laminates. The analyses of the honeycomb structure and components include: (1) constituent materials and ply properties, (2) face laminates and core wall engineering properties, (3) equivalent core material properties, and (4) apparent stiffness properties for the honeycomb panel and its equivalent orthotropic material properties. A homogenization process is used to obtain the equivalent core material properties for the honeycomb geometry with sinusoidal waves. To verify the accuracy of the analytical solution, several honeycomb sandwich beams with sinusoidal core waves either in the longitudinal or transverse directions are tested in bending. Also, a deck panel is tested under both symmetric and asymmetric patch loading. Finite element (FE) models of the test samples using layered shell elements are further used to correlate results with analytical predictions and experimental values. A brief summary is given of the present and future use of the FRP honeycomb panel for bridge decks. The present simplified analysis procedure can be used in design applications and optimization of efficient honeycomb structures.

Mechanical Properties of Composite Panels Reinforced with Integrally Woven 3-D Fabrics

An investigation is reported in which six three-dimensional cellular fabrics were designed and woven. They consisted of two facings connected by an integrally woven sinusoidal core. In lateral compression, the ratio of the cell-repeat distance to the fabric thickness determines the resistance of the fabrics to buckling. Composite panels were fabricated by impregnating the fabrics with resin. Formulae developed allow the cross-sectional area and second moments of area of the panels to be calculated. Tensile tests were performed on the panel facings and whole structures to measure the Young's moduli and strengths in the longitudinal (weft) and transverse (warp) directions. Flexural tests were made to measure the beam flexural rigidities. The structural analysis of the beam sections together with the tensile properties of the beams enables flexural properties to be accurately predicted. The properties of the 3-D beams in flexure are comparable to those of other engineering materials, but the fabric-based, ce...