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-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.

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 provides non-proprietary and non-competition-sensitive information related to aircraft applications. It presents an overview of reliability and commonly used measurements. Failure modes that cause the negative performance are reviewed based on many types of sources. These include manufacturer service bulletins, reliability and customer service departments, literature reviews, demonstration programs, in-service evaluations, design guides, and surveys of commercial and military aircraft maintenance organizations. The article also describes lessons learned while attempting to avoid overlapping maintainability, reparability, and materials choice.

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.

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 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 begins with an overview of the various types of damage that take place in advanced composite components. These include holes and punctures, delaminations, disbonds, core and resin damage, and water intrusion. The article describes various damage detection techniques, such as visual inspection, tap testing, and ultrasonic inspection, in field conditions. Designing for repair involves various considerations including structure types and repair types. The types of repairs together with other issues surrounding advanced composite repair technology are discussed. The article also provides a discussion on the design considerations, instructions, and materials for repair. It explains various paint-removal methods for composites. The article concludes with a discussion on curing equipment such as portable repair systems, vacuum bags, and ovens and autoclaves.

Designing composites for structural performance initially involves meeting a set of desired performance specifications at a minimum cost. This article discusses the factors that are considered in designing the manufacturing of polymeric composites. It describes the various aspects of manufacturing, forming process, and post-processing and fabrication for designing the composites.

In-process inspection during composite material lay-up is essential if the structural, dimensional, and environmental performance designed into a part is to be consistently achieved. This article discusses the requirements to be met by the facilities and equipment to produce high-quality composites. It reviews the procedures that are allowed and prohibited in controlled-contamination areas of lay-up. The article emphasizes significant areas, such as material control and lay-up process, in which quality-control personnel can be effective in preventing production problems. It concludes with a discussion on automated tape laying and fiber placement, as well as the numerically aided lay-up process.

The goal of design is to improve the overall performance of the metal or ceramic matrix rather than to create a material with different response than the base matrix. This article focuses on the design for manufacturing polymeric composites. Specially developed methods including contact molding, compression-type molding, resin-injection molding, and pultrusion are described. The article also discusses the various factors to be considered in designing for composite manufacturing.

This article describes common design criteria and identifies the design considerations that have a significant effect on the end product. The design criteria include cost, size, mechanical properties, repeatability and precision of parts, damage tolerance and durability, and environmental constraints.

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.

Nuclear energy harnesses the power of atomic interactions, whether through the fission of large nuclei or the fusion of light elements. Additive manufacturing (AM) can play several roles in this sector and is actively being researched and applied, although challenges remain. This article provides a discussion of the opportunities, challenges, and example use cases of AM in the nuclear and wind energy sectors.

For most nondestructive evaluation (NDE) applications, the term thermography actually refers to surface-excited thermography (SET) that involves thermal mapping of surface temperature as heat flows from, to, or through a test object in response to excitation applied to the sample surface. This article discusses the strategies for implementing thermography for NDE, including the steady-state/whole-body approach and transient heat conduction. It describes the most common signal-processing methods, such as thermographic signal reconstruction, lock-in thermography, and pulsed-phase thermography. The article concludes with a discussion on the use of thermal methods for thermal diffusivity measurement and characterization of multilayer structures.

This article introduces the principal methodologies and some advanced technologies that are being applied for nondestructive evaluation (NDE) of fiber-reinforced polymer-matrix composites. These include acoustic emission, ultrasonic, eddy-current, computed tomography, electromagnetic acoustic transducer, radiography, thermography, and low-frequency vibration methods. The article also provides information on NDE methods commonly used for metal-matrix composites.

This article provides information on the potential applications of fiber-reinforced polymer (FRP) composites for maritime craft and offshore drilling platforms. The key benefits gained from using FRP materials together with an examination of the drawbacks and major issues impeding the more widespread use of composites in marine structures are presented.

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.

Microwave and guided wave (GW) nondestructive evaluation (NDE) techniques are capable of detecting corrosion damage, cracks, and other defect types in inaccessible areas. This article describes the operation principles of the techniques and provides information on hidden corrosion detection and the applications of microwave NDE devices and GW ultrasonic NDE devices.