This article begins with a discussion on fiber-reinforced composite materials and describes the generic behavior and structure/property relationships of composites. The article summarizes lamina properties and presents equations that help in the calculation of lamina properties. Composite laminates are constructed from lamina with uniaxial fiber orientation and frequently from textile fabrics as well. The article explains the characteristics of symmetric in-plane and through-thickness laminates; asymmetric in-plane and symmetric through-thickness laminates; asymmetric laminates; and curved laminates. It provides information on controlled thermal expansion composites, metal-matrix composites, and ceramic-matrix composites. The article illustrates the types of bonded joints and concludes with a discussion on design for manufacturing.

This article discusses the methods of analyzing the directional dependence of the mechanical properties of composites, especially those perpendicular to the major plane of the laminate. It provides a description of the common indirect load cases and direct out-of-plane load cases. The article concludes with a discussion on composite materials that are reinforced in the z-direction (also known as three-dimensional, or 3-D composites).

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.

In the design of composite structures for durability and damage tolerance, the primary concerns are out-of-plane failures, such as delamination, material degradation associated with environment, stability under compression loading, large degree of scatter in fatigue life, and bearing failure of joints. This article presents an introductory discussion on the fatigue damage process, methodologies assessing fatigue behavior, and life prediction models. It describes the damage mechanisms introduced for a quasi-isotropic laminate under tension-compression fatigue loading. Delamination is a critical issue in fatigue and generally results from high interlaminar normal and shear stresses. The article schematically illustrates the structural elements in which high interlaminar stresses are common. It concludes with a discussion on the classification of fatigue models such as mechanistic or phenomenological, for composite materials under cyclic loading.

This article focuses on various thermal analysis techniques used to verify the cure of a polymer composite. The techniques include differential scanning calorimetry (DSC), modulated DSC, thermomechanical analysis, dynamic mechanical analysis, and dielectric analysis. The article also provides an overview of the composite failure modes affected by matrix resin and testing approach.

The properties of unidirectional composite (UDC) materials are quite different from those of conventional, metallic materials. This article provides information on the treatment of UDC stress-strain relations in the forms appropriate for analysis of thin plies of material. It explains the development of the relations between mid-surface strains and curvatures and membrane stress and moment resultants. The article discusses the properties, such as thermal expansion, moisture expansion, and conductivity, of symmetric laminates and unsymmetric laminates. It describes the distribution of temperature and moisture through the thickness of a laminate. Stresses caused due to mechanical loads, temperature, and moisture on the laminate are analyzed. The article concludes with information on interlaminar cracking, free-edge delamination, and transverse cracks of laminates.

This article reviews various rapid prototyping (RP) processes such as stereolithography, powder sintering, hot melt extrusion, sheet lamination, solid ground curing, and three-dimensional printing. It discusses the various material prototypes produced by RP technology. The list of materials includes particulate and fiber-reinforced polymers, ceramic-matrix composites, and metal-matrix composites. The article also provides information on freeform-fabrication techniques for composite part lay-up.

Continuous fiber composite materials offer dramatic opportunities for producing lightweight laminates with tremendous performance capabilities. This article describes the kinematics of fabric deformation and explains the algorithms used in draping simulation. It discusses the basic components, such as laminate and ply, of continuous fiber composite. The article provides information on the core sample and ply analysis. It details producibility, flat-pattern evaluations, and laminate surface offset. The article discusses various interfaces, such as the structural analysis interface, the resin transfer molding interface, the fiber placement and tape-laying interface, and the laser projection interface.

Testing of fiber-reinforced composite materials is performed to determine uniaxial tensile strength, Young's modulus, and Poisson's ratio relative to principal material directions, that helps in the prediction of the properties of laminates. Beginning with an overview of the fundamentals of tensile testing of fiber-reinforced composites, this article describes environmental exposures that often occur during specimen preparation and testing. These include exposures during specimen preparation, and planned exposure such as moisture, damage (impact), and thermal cycling techniques. The article also discusses the test procedures, recommended configurations, test specimen considerations, and safety requirements considered in the four major types of mechanical testing of polymer-matrix composites: tensile test, compression test, flexural test, and shear test.

Knowledge of fatigue behavior at the laminate level is essential for understanding the fatigue life of a laminated composite structure. This article describes fatigue failure of composite laminates in terms of layer cracking, delamination, and fiber break and interface debonding. It discusses the fatigue behavior of composite laminates in the form of a relation between applied maximum fatigue stress and fatigue life. The article explains Weibull distribution and parameters estimation for fatigue data analysis and life prediction of composite laminates. It analyzes the fatigue properties and damage tolerance of fiber-metal laminates such as ARALL and GLARE laminates. The article concludes with a discussion on the effects of fatigue on notched and unnotched specimens.

Detailed analyses and test correlations are typically required to support design development, structural sizing, and certification. This article addresses issues concerning building block levels ranging from design-allowables coupons up through subcomponents, as these levels exhibit a wide variety of test-analysis correlation objectives. At these levels, enhanced analysis capability can be used most effectively in minimizing test complexity and cost while also reducing design weight and risk. The article discusses the examples of tests for which good correlative capability has shown significant benefit. These include notched (open and/or filled hole) tension and compression, inter/intralaminar shear and tension, and pin bearing.

This article provides a discussion on adhesively bonded joints and elastic-plastic mathematical model for an adhesive in shear. It discusses the design rules for thin bonded structures and reviews computer programs for the highly loaded stepped-lap joints. The article describes the two-dimensional effects associated with load redistribution around flaws and with damage tolerance. The elastic-isotropic geometric stress-concentration factors and empirically established correlation factors of mechanically fastened joints are discussed. The article provides information on the identification of optimal joint proportions for single-row joints, and the design and analysis of the stronger multirow joints, with particular regard to the bearing-bypass interaction.