Honeycomb-cored sandwich panels increase part stiffness at a lower weight than monolithic composite materials. This article illustrates an area of a honeycomb-cored sandwich structure composite cross section that is viewed using transmitted polarized light. This area shows the differences in the constituents and resin intermingling. The article discusses the factors that govern the honeycomb core movement and honeycomb core crush, with illustrations. Some common tests performed on honeycomb composites to characterize the skin-to-core bond strength are the climbing drum peel and flatwise tensile tests. The article concludes with a description on the reasons for core failure, which are analyzed after these tests.

A sandwich structure is comprised of layered composite materials formed by bonding two or more thin facings or facesheets to a relatively thick core material. This article describes the sandwich panel failure modes. It tabulates the nomenclature and definitions for loads, geometry, and material properties. The article illustrates critical strength-check locations for a flat sandwich panel. It discusses the analysis methods formulated for flat rectangular honeycomb panels; curved sandwich panel; and for each of the various sandwich panel failure modes. The article concludes with a discussion on flat panel stability analysis methods.

Lightweight structural cores are used on aircrafts to reduce weight and increase payload and fight distance. This article discusses the classification of lightweight structural cores, namely, honeycomb, balsa, and foam. It reviews the four primary manufacturing methods used to produce honeycomb: adhesive bonding and expansion, corrugation and adhesive bonding, corrugation and braze welding, and extrusion. The article describes cell configuration and properties of honeycomb. It discusses the factors influencing specification of structural cores, including materials, size, density, mechanical properties, environmental compatibility, formability, durability, and thermal behavior. The article provides information on the benefits and concepts of a sandwich panel containing lightweight structural cores.

Adhesive-bonded joints are extensively used in aircraft components and assemblies where structural integrity is critical. This article addresses the problem of how to inspect bonded assemblies so that all discrepancies are identified. It describes several inspection techniques and presents drawbacks and limitations of these techniques. Generic flaw types and flaw-producing mechanisms are listed in a table. The article discusses metal-to-metal defects, adherend defects, honeycomb sandwich defects, repair defects, and in-service defects. It reviews the methods applicable to the inspection of bonded structures, including visual inspection, ultrasonic inspection, X-ray radiography, and neutron radiography. The evaluation and correlation of inspection results are also discussed. The article concludes with information on the effects of ultrasonic wave interference in the ultrasonic inspection of adhesive-bonded joints.

Honeycomb is a product consisting of very thin sheets attached to form connecting cells. This article briefly explains the construction, core characteristics, properties, and testing methods of the honeycomb structures. It discusses the special processes carried out in customizing the shape of core to fit customer's specific needs. The article provides information on the basic concept of creating sandwich structures and its corresponding aspects like material selection, design guidelines, and structural efficiency.

This article focuses on the sample preparation methods for titanium honeycomb composites, boron fiber composites, and titanium/polymeric composite hybrids. These include mounting, sectioning, grinding, and polishing. The article also provides information on the sample preparation of unstaged and staged prepreg materials for optical analysis.

Maintainability is a function of the durability, damage tolerance, and repairability of a structure. This article discusses the configurations of composite structures, such as sandwich, stiffened-skin, and monolithic structures, used in commercial aircraft composites. It describes the considerations for maintainability of the composite structures during the conceptual design phase. Sources of the defects and damage, such as manufacturing defects and in-service defects, are reviewed. The article describes the nondestructive inspection methods that are used in the repair of composite structures to locate damage, characterize the extent of damage, and ensure post-repair quality. It lists suggestions that can be used as design guidelines for adhesive bonding, general composite structure, sandwich structure, material selection, and lightning-strike protection. The article also provides the basic considerations for personnel, facilities, and equipment during maintenance.

This article describes the chemistry of phenolic resins and reviews their characteristics and properties for various composites fabrication processes. The fabrication processes include solution/hot-melt process, pultrusion, vacuum infusion, filament winding, sheet molding, and hand lay-up. The article illustrates the manufacturing process of phenolic honeycomb and provides information on the applications of phenolic composites.

This article discusses the historical background of composite construction in recreational equipment and sporting goods. It provides information on the applications of composites in baseball bats, tennis rackets, and golf clubs. The applications of composites in bicycling, winter sports, aquatic sports, track, field, and archery equipment are also discussed.

Adhesive bonding is used to assemble composite components into larger structures. Finished components that are damaged during assembly or service are often repaired with adhesive-bonding techniques. This article summarizes criteria for adhesive selection and illustrates typical secondary adhesively bonded joint configurations. It discusses the highly loaded joint considerations of adhesives. The article describes the epoxy adhesives commonly used for the bonding or repair of composite structures. It discusses the surface preparation of composites and metals, and honeycomb processing, including perimeter trimming, mechanical forming, heat forming, core splicing, contouring, and cleaning. The article presents basic steps involved in the adhesive-bonding process and concludes with a discussion on adhesive applications and tooling.

This article discusses the requirements for designing repairable composite structures such as a honeycomb sandwich panel construction and integrally stiffened co-cured composite structures. It reviews the general and specific design guidelines for bolted or riveted repairs and adhesively bonded repairs of the composite structures. The article presents several examples to illustrate how these repairs can be achieved.

This article explores why structural element and subcomponent testing are conducted. It discusses the different types of failure modes in composites, and provides information on the testing methodology, fixturing, instrumentation, and data reporting. The article reviews various standard elements used to characterize composite materials for the various failure modes. Simple structural-element testing under in-plane unidirectional, multidirectional, and combined loading, as well as out-of-plane loading are discussed. Simple bolted and bonded joints, as well as data correlation are reviewed with analytical predictions. The article also provides a list of the ASTM testing standards applicable at the element level of testing for both polymer-matrix composites and metal-matrix composites. It concludes with a discussion on durability and damage tolerance testing.

This article describes the types of repair and presents reasons for avoiding damage to a structure or component during repair. It discusses the major standardization issues with emphasis on design, repair materials, repair techniques, and inspection.

This article discusses composites for unmanned space vehicles and provides an overview of key design drivers, challenges, and environment for use of composites in spacecraft, launch vehicles, and missiles. It describes the design allowable properties of composite materials. The article provides information on the specific state-of-the-art applications of composite materials for spacecraft missiles and launch vehicles. A discussion on the key applications, including solid rocket motor casings, payload fairings, and payload support structures, is presented.

This article introduces the principal methodologies and some technologies that are being applied for nondestructive evaluation of composite materials. These include ultrasonic testing (UT), air-coupled UT, laser UT, ultrasonic spectroscopy, leaky lamb wave method, acousto-ultrasonics, radiography, X-ray computed tomography, thermography, low-frequency vibration methods, acoustic emission, eddy current testing, optical holography, and shearography. The article presents some examples are for fiber-reinforced polymer-matrix composites. Many of the techniques have general applicability to other types of composites such as metal-matrix composites and ceramic-matrix composites.

This article reviews the history of prepreg and ply cutting technologies and outlines the options available for creating the necessary data and for nesting, cutting, and kitting the plies. It discusses the ways in which these steps influence the workflow for various applications. The characteristics of prepreg and ply cutting methods are presented in a table.

Successful adhesive bonding of organic-matrix composites is dependent on the nature of the adherend surfaces. This article emphasizes the critical importance of proper surface preparation in both thermoset and thermoplastic composites. It provides information on surface preparation for thermoset composite adherends along with a standard technique (water-break test) for verifying the adequacy of surface preparation for metal bonding. In addition, the article provides examples of good and bad adhesive bonds and describes some important process variables that are considered and controlled in bonding process for thermoset adhesives. The article concludes with a discussion on three different approaches for bonding thermoplastic composite composite panels together.

This article describes the failure analysis procedures for composites and the techniques to be used in these analyses. These procedures include a review of the available in-service records, materials and processing methods, print requirements, and manufacturing records; visual analysis and nondestructive part evaluation; and verification of materials and processing methods. The article discusses the determination of fiber, matrix, and void volume fractions and verification of ply lay-up and orientation. A review of composites processing parameters; fractography and surface analysis; and mechanical testing and stress analysis is also presented.

This article describes the sectioning process, some general practices, common tools, and guidelines on how to select a cutting tool for a given metallographic sectioning operation. It provides a discussion on the consumable-abrasive cutting and nonconsumable-abrasive cutting methods for metallographic sectioning. Other methods, including the use of hacksaws, shears, burning torches, wire saws, and electrical discharge machining, are also reviewed. The article reviews the issues related to the specimen test location for certification work as well as process troubleshooting and component failure analysis.