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 provides the general mechanical testing guidelines for the characterization of lamina and laminate properties. Guidelines are provided for tensile property, compressive property, shear property, flexure property, fracture toughness, and fatigue property test methods. The article also tabulates selected standards for lamina and laminate mechanical testing.

This article presents a comprehendable and comprehensive physics-based approach for characterizing the strength of fiber-reinforced polymer composites. It begins with background information on the goals and attributes of this method. The article then addresses the characterization of fiber failures in laminates, because these are at the highest strengths that can be attained and, therefore, are usually the design objective. An exception would be if the design goal is to maximize energy absorption, rather than static strength. The discussion proceeds to situations in which the matrix fails first, either by intent, by design error, or because of impact damage. The state of the modeling propagation and arrest of matrix damage follows. Comparisons of this physics-based approach are then made to empirically based failure theories.

This article begins with a review of the purposes of mechanical characterization tests and the general considerations related to the mechanical properties of anisotropic systems, specimen fabrication, equipment and fixturing, environmental conditioning, and analysis of test results. It provides information on the specimen preparation, instrumentation, and procedures for various mechanical test methods of fiber-reinforced composites. These include the compression test, flexure test, shear test, open hole tension test, and compression after impact test. The article describes three distinct fracture modes, namely, crack opening mode, shearing mode, and tearing mode. It presents an overview of fatigue testing and fatigue damage mechanisms of composite materials and reviews the types of mechanical measurements that can be made during the course of testing to assess fatigue damage. The article concludes with a discussion on the split-Hopkinson pressure bar test.

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.

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 presents the failure of polymer-matrix composites and the methodology for fractography. It provides a detailed discussion on the types of translaminar, interlaminar, and intralaminar failures. The article also presents a discussion on the types of fatigue failures, and the influence of composite architecture. It provides details of the fractography associated with defects and damage.

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.

Damping is the energy dissipation properties of a material or system under cyclic stress. The vibrational and damping characteristics of composites are important in many applications, including ground-based and airborne vehicles, space structures, and sporting goods. This article describes the damping characteristics of unidirectional composites, when they are subjected to longitudinal shear, longitudinal tension/compression, and transverse tension/compression. It presents equations that govern the overall damping capacity of beams that are cut from laminated plates. The article discusses the effect of temperature on damping and provides information on the relationship between damping and strength.

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.

Delamination is one of the most commonly observed failure modes in composite materials. This article describes the three fundamental fracture failure modes of composite delamination, namely, opening, in-plane shearing, and tearing or scissoring shearing modes. It discusses the characterization and analysis of delamination. The article also reviews the prediction of delamination factors, such as flexbeam fatigue life, and skin/stiffener pull-off strength and life.

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 describes three design-life methods or philosophies of fatigue, namely, infinite-life, finite-life, and damage tolerant. It outlines the three stages in the process of fatigue fracture: the initial fatigue damage leading to crack initiation, progressive cyclic growth of crack, and the sudden fracture of the remaining cross section. The article discusses the effects of loading and stress distribution on fatigue cracks, and reviews the fatigue behavior of materials when subjected to different loading conditions such as bending and loading. The article examines the effects of load frequency and temperature, material condition, and manufacturing practices on fatigue strength. It provides information on subsurface discontinuities, including gas porosity, inclusions, and internal bursts as well as on corrosion fatigue testing to measure rates of fatigue-crack propagation in different environments. The article concludes with a discussion on rolling-contact fatigue, macropitting, micropitting, and subcase fatigue.

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).

The prepreg hand lay-up process is a versatile, reliable, cost-effective, and high quality process for fabricating large or small components. This article discusses the technique characteristics and applications of the process. It describes the stages involved in the process of lay-up, namely, lay-up definition, ply-kit cutting, layup, debulking, and preparation for curing. The article concludes with a discussion on the component properties and design guidelines of the prepreg hand lay-up process.

A unidirectional fiber composite (UDC) consists of aligned continuous fibers that are embedded in a matrix. This article describes a variety of analytical methods that are used to determine the various physical properties of the UDC. These properties include elasticity, thermal expansion coefficients, moisture swelling coefficients, static and dynamic viscoelastic properties, conductivity, and moisture diffusivity.

The goal of micromechanics and analysis is to use the predictive methodology to develop tailored composites and also to make accurate predictions of their performance in service. This article reviews results derived from micromechanics analyses, based on finite-element method of unidirectional fiber reinforced metal matrix composites (MMCs). It discusses the elastic deformation and elastic-plastic deformation analysis of discontinuously reinforced MMCs. The article provides an overview of analysis of strength, fatigue, and fracture toughness for macromechanics fiber-reinforced and discontinuous reinforced composites.

This article provides an overview of the finite-element-based analyses (FEA) of advanced composite structures and highlights key aspects such as the homogenization of materials properties and post-processing of numerical results. It discusses the analysis of composite structures based on micromechanics and macromechanics. The article describes the FEA of 3-D solid elements, 2-D cylindrical shell elements, and 1-D beam elements. It contains a table that lists the commercially available finite element codes related to the analysis of fibrous composite materials. The article presents classical examples of the mechanics of composite materials to illustrate the aspects of multilayered composite structures.