Corrosion, fatigue, and their synergistic interactions are among the principal causes of damage to aircraft structures. This article describes aircraft corrosion fatigue assessment in the context of different approaches used to manage aircraft structural integrity, schedule aircraft inspection intervals, and perform repair and maintenance of aircraft in service. It illustrates the types of corrosive attack observed in aircraft structures, including uniform, galvanic, pitting, filiform, fretting, intergranular, exfoliation corrosion, and stress-corrosion cracking. The article discusses geometric parameters such as pit dimensions, surface roughness, loss of metal thickness, and volume increase due to pillowing to quantitatively characterize the types of corrosion. It also explains the two most common fatigue life assessment methods used in the military aerospace industry: fatigue crack initiation and crack growth analysis.

This article addresses the issue of the implementation of composite damage tolerance requirements as it relates to military aircraft. It presents a brief introduction on the durability impact threat, damage tolerance impact threat, and other damage tolerance damage threats. The article summarizes damage tolerance criteria and durability criteria for military aircraft. It discusses the damage tolerance design philosophy for metallic structures and composite structures of the aircraft. The article describes the implementation of a damage tolerance analysis methodology in terms of the mechanics based model, the regression algorithm, and the semi-empirical analysis.

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 provides information on the applications of fiber-reinforced composites in commercial and military aircrafts. It tabulates the composite components in various types of aircraft. The applications of the composites in the components of Boeing 727, 737, 757, 767, 777, and 777-200 are schematically illustrated.

Composite bonded repair technology is based on the use of advanced composite repairs or reinforcements that are adhesively bonded to a damaged structure. This article discusses the key steps that are normally encountered in the design, certification, and application of an adhesively bonded repair. Some examples of successful repairs to military aircraft are also discussed.

Automated tape laying is a mature process used in both commercial and military aircraft applications. This article provides a brief history of the process and describes the use of commercially available flat and contour tape-laying equipment. It discusses the advantages and disadvantages of the tape laying. The article describes the various components of a ten-axis gantry-type tape laying machine and the tape laying process. It provides a discussion on typical material types and forms for tape laying and provides information on design guidelines for tape laying.

This article describes the various environments affecting corrosion performance, corrosion protection, and corrosion control. These include freshwater environments, marine environments, and underground environments. The article provides information on corrosion in military environments and specialized environments, representing less-well-known environments with more limited applications.

Advanced thermoplastic composites possess impact resistance, fracture toughness, and elevated temperature endurance properties due to their melt-fusible nature. This article presents the material options available for thermoplastic composites such as pseudothermoplastics, post-impregnated thermoplastics, and true thermoplastics. It describes the processing methods of thermoplastic composites, including weaving, seaming, autoclaving, preconsolidation, roll consolidation, roll forming/pultruding, thermoforming, press forming, hydroforming, and diaphragm forming. The article provides information on different types of joints, namely, fastened, adhesive bonded, dual polymer bonded, co-consolidated, and welded joints. It explains the joining methods of thermoplastic composites, such as press forming, diaphragm forming, autoclaving, ultrasonic welding, resistance welding, and induction welding.

Aging is a process where the structural and/or functional integrity of components will be continuously degraded by exposure to the environmental conditions under which they are operated. This article discusses aging mechanisms in various components of military systems such as structural parts, engines, and subsystems. It describes the aging management processes such as full-scale structural testing and practical life-enhancement methods. The article reviews control and prevention systems such as usage and health monitoring systems necessary to provide effective corrosion maintenance on military systems. Failure prediction techniques, namely, the equivalent pre-crack size approach, life-cycle cost modeling and simulation, and holistic life-prediction methodology are also discussed.

This article reviews corrosion problems in the U.S. Department of Defense (DoD) and discusses management and maintenance aspects of the practices that address the cost and readiness. It describes the plans to institute corrosion prevention and control strategies under DoD directives in engineering design, material selection, and fabrication processes for new acquisitions. The article also suggests a long-term strategy to reduce the cost of corrosion control.

This article discusses coating products available for use in the aerospace industry that are compliant with regulations requiring reductions in emissions from organic solvents. The coating products addressed include primers, topcoats, and chemical milling maskants. It describes their characteristics and limitations compared to conventional noncompliant materials. The article addresses the methods and products commonly used achieve regulatory compliance: waterborne coatings, exempt-solvent-based coatings, high-solids coatings, powder coating, and electro-deposition.

This article presents the damage tolerance criteria for military composite aircraft structures to safely operate the structures with initial defects or in-service damage. It describes the effects of defects, such as wrinkles in aircraft structures, and the reduction in compressive strength and tensile strength. The article reviews low velocity impacts in aircraft structures in terms of resin toughness, laminate thickness, specimen size and impactor mass, and post-impact fatigue. It explains the tension strength analysis, such as linear elastic fracture mechanics and R-curve methods, to predict the residual strength of the structures.

Carbon-carbon composites (CCCs) are introduced in fields that require their high specific strength and stiffness, in combination with their thermoshock resistance, chemical resistance, and fracture toughness, especially at high temperatures. The use of CCCs has expanded as the price of carbon fibers has dropped and their mechanical properties have increased. This article begins with an overview of the carbon conversion processes, fiber properties and microstructures, and interfacial bonding and environmental interaction of carbon fibers, followed by a detailed discussion on the various techniques available for processing CCCs for specific applications, including preform fabrication (fiber weaving), densification, application of protective coatings, and joining. The article closes with a description of the mechanical and physical properties and applications of CCCs. The main applications of CCCs, in terms of money and mass, are in the military, space, and aircraft industries.

This article provides information on the thermoplastic resins used as matrix materials for continuous fiber reinforced composites. It focuses on the materials that are suitable for fabrication of structural laminates and used for aerospace applications. The article provides a discussion on the background, categories, characteristics, product forms, properties, cost benefits, and processing techniques of thermoplastic resins. Strategies that have been advanced to deal with impregnation difficulties are also discussed.

This article describes the protective coatings technology used in naval aircrafts. It reviews the future needs and trends of the protective coatings technology based on advancing technology, environmental concerns, and operational requirements. The article discusses the standard finishing systems for aircrafts: the surface pretreatment system, primer, topcoat, advanced-performance topcoat, self-priming topcoat, and specialty coatings. It presents safe compliant solutions to environmental problems associated with the protective coatings technology. These solutions include the use of environmental regulations and hazardous materials, nonchromated pretreatments, waterborne technology, high-solids technology, and touch-up paints. The article also deals with the use of electrodeposition coatings, powder coatings, adhesive films, paint application equipment, and non-chromated sealants in the protective coatings technology.