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.

This article describes the most significant tests to characterize the properties of constituent materials. It discusses the chemical, physical, and mechanical tests for determining the properties of reinforcement fibers and fabrics. The article provides information on some of the basic materials used for thermoset and thermoplastic resin matrices. It reviews the identification of the individual characteristics of thermoset and thermoplastic resin along with the test methods normally used for their determination. The article contains a table that lists properties and tests for uncured and cured thermoset-matrix resins and prepregs.

This article describes methods for analyzing impact-damaged composites in the aircraft industry. These include C-scan and x-radiography methods and optical microscopy. The article reviews brittle-matrix composite and tough-matrix composite failures. It explains the different types of composite failure mechanisms such as thermoplastic-matrix composite failure mechanisms, untoughened thermoset-matrix composite failure mechanisms, toughened thermoset-matrix composite failure mechanisms, dispersed-phase and rubber-toughened thermoset-matrix composite failure mechanisms, and particle interlayer-toughened composite failure mechanisms.

This article discusses bismaleimide (BMI) chemistry and the use of BMI in composites. An analysis of the applications illustrates how the advantages of BMIs have been exploited and perhaps suggests how these advantages might be extended to other applications. The article describes the mechanical properties of BMI composites. BMIs suitable for resin transfer molding processing are provided. The article concludes with information on the elevated-temperature applications of 5250-4 BMI system.

This article discusses the three basic elements of an epoxy resin formulation that must be understood when selecting a thermoset system. These include base resins, epoxy resin curatives, and modifiers. The article provides examples of epoxy resin formulations that illustrate how raw materials are combined to tailor a formulation to a specific application. It concludes with a discussion on general guidelines for the safe handling of epoxy resins and their associated products.

This article illustrates the polymer matrices used for composite materials. It describes the use of prepeg materials in manufacturing high-performance composites. The article discusses the various infusion processes for the development of fiber-reinforced composites, namely, resin transfer molding, vacuum-assisted resin transfer molding, and resin film infusion. It explains the composite- and matrix-toughening methods for fiber-reinforced composites, such as dispersed-phase toughening and interlayer toughening. The article concludes with information on optical microscopy, which provides an insight into the micro- and macrostructure of fiber-reinforced composites.

This article discusses the properties and applications of two types of polyimide resins: condensation polyimides and addition-type polyimides. It describes the chemistry of condensation-type polyimides during synthesis, processing of polyamide acid precursor solution to polyimide, and preparation of polyimide films from thermoplastic polyamic acid precursors. The article reviews the chemistry of several addition-type polyimides, including phenylethynyl-containing imide oligomers, nadic end-capped polyimides, and LARC RP46. It explains the preparation processes of nadic end-capped amic acid oligomer resin solutions, including the preparation of resin powder and resin disks, adhesive film, adhesive bond specimens, and films.

This article discusses the family characteristics, commercial forms, applications, resin grades, and mechanical and physical properties of traditional engineering thermoplastics in their neat (unmodified) form and as compounds and composites, namely, acrylonitrile-butadiene-styrenes, acrylics, high-density polyethylenes, reinforced polypropylenes, high-impact polystyrenes, polyvinyl chloride, styrene-acrylonitriles, and styrene-maleic anhydrides.

This article discusses the coating systems categorized by the generic type of binder or resin and grouped according to the curing or hardening mechanism inherent within that generic type. It focuses on the properties, advantages, and limitations of various autooxidative cross-linked resins, thermoplastic resins, and cross-linked thermosetting resins. The autooxidative cross-linked resins include alkyd resins and epoxy esters. The article examines the two types of coatings based on thermoplastic resins: those deposited by evaporation of a solvent, commonly called lacquers, and those deposited by evaporation of water, a class of coatings called water-borne coatings. The coatings that chemically cross link by copolymerization, including epoxies, unsaturated polyesters, urethanes, high-temperature curing silicones, and phenolic linings, are also described.

This article describes the dispersed-phase toughening of thermoset matrices by the development of multiphase-structure thermosetting matrices using rubber and/or thermoplastic materials. It discusses two main methods for manufacturing prepregs, namely, single-pass impregnation and double-pass impregnation. The article illustrates reflected-light optical microscopy techniques to evaluate the morphology of thermoplastic materials for determining the material quality and correlating key microstructural features with material performance.

This introductory article describes the various aspects of chemical structure that are important to an understanding of polymer properties and thus their eventual effect on the end-use performance of engineering plastics. The polymers covered include hydrocarbon polymers, carbon-chain polymers, heterochain polymers, and polymers containing aromatic rings. The article also includes some general information on the classification and naming of polymers and plastics. The most important properties of polymers, namely, thermal, mechanical, chemical, electrical, and optical properties, and the most significant influences of structure on those properties are then discussed. A variety of engineering thermoplastics, including some that are regarded as high-performance thermoplastics, are covered in this article. In addition, a few examples of commodity thermoplastics and biodegradable thermoplastics are presented for comparison. Finally, the properties and applications of six common thermosets are briefly considered.

An alkyd is an ester-based polymer derived from the polycondensation reaction of polyhydric alcohol and polybasic acid. This article provides useful information on the chemistry, production, coating formulations, modification, commercial products, and application methods of alkyd resins. It also provides a section on drying oil, which is used in the manufacture of resins. The article describes the three categories of metals that have been used in drier compounds: primary driers (active or oxidation driers), secondary driers (through-driers), and auxiliary driers. It also provides information on the oil length of an alkyd resin and on solvents, which play a critical role in the formulation and use of the coating. The article concludes with a description of the concerns that a user, specifier, or applicator should be aware of when using alkyd coatings.

Vat polymerization (VP) is an additive manufacturing (AM), or three-dimensional (3-D) printing process in which 3-D objects are produced by hardening a liquid polymer into the desired shape. With the introduction of new materials and improvements in material properties, VP offers a good alternative for AM for low-volume production. This overview of the VP process begins with an introduction to two main processes of VP, namely stereolithography apparatus and digital light processing, and then moves on to discuss the characteristics of the feedstocks used as well as their selection criteria. The article then covers safety issues associated with feedstock handling and the manufacturing constraints related to part orientation and design, providing some key tips for VP support structures. This is followed by a discussion on postprocessing/finishing of VP parts. A brief concluding section considers some special topics related to AM process.

Pultrusion is an automated process for manufacturing composite materials into continuous, constant cross-sectional profiles. The article provides an overview of the pultrusion process and the wide range of materials that can be used to provide a broad spectrum of composite properties. It discusses the mechanical, physical and material properties of pultruded products, and the orientation options available to utilize the properties advantageously. The article also provides guidelines for designing pultruded products.

Pultrusion is a cost-effective automated process for manufacturing continuous, constant cross-section composite profiles. This article describes the process characteristics and advantages of pultrusion. It provides information on the applications of pultrusion and discusses the processing equipment and tooling, the material composition, and the process control essential for a basic understanding of the pultrusion process.

Filament winding is a process that allows the precise lay-down of continuous reinforcement in predescribed patterns at a high rate of speed. This article discusses the filament winding process and includes a comparison to other compacting and curing processes. The article describes design factors, and techniques to produce aerodynamic surfaces, improve surface smoothness, and avoid slipping and bridging of filament. The article discusses tooling and the equipment used in the filament winding process, namely, mandrel design, winding machines, tensioners, and ovens.

Cyanate ester resins are a family of high-temperature thermosetting resins that bridge the gap in thermal performance between engineering epoxy and high-temperature polyimides. This article discusses the chemistry, properties and characteristics of the cyanate ester resins. It describes the processing procedures for the cyanate ester resins and provides information on properties for selected applications, such as space applications, radomes, and printed circuit boards.

This article provides a discussion on polyester coating applications such as powder coatings, can coatings, and automotive paints. It includes an overview, structure, properties, and benefits of vinyl ester resins. The article discusses the additives for both unsaturated polyester and vinyl ester coatings, namely, curing systems, thixotropic agents and fillers. It exemplifies polyester and vinyl ester coating, lining and flooring systems that are used for top-to-bottom protection of industrial plants and equipment. The article also highlights the concerns to be addressed when using polyesters and vinyl esters.