Search Results for fiber break

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.

This article is an atlas of fractographs that helps in understanding the causes and mechanisms of fracture of a type of resin-matrix composites, carbon-epoxy composites. The fractographs illustrate the fracture modes found in composite prepregs, composite panels, solid rocket motor nozzles, and tension, flexural, compressive, and shear loadings.

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.

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 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.

It is recommended that repairs be made whenever damage consists of delamination cracks or broken fibers. This article provides an overview of the repair classification, characterization, and cycle of the composite ship structure. The methods outlined in this article, which covers gel coat repairs, patching, scarfing, and step repairs, have undergone extensive development and rigorous testing for use on composite ship structures. Resin infusion repair, which is a relatively new method for repairing marine composites, is also described.

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 reviews the planning of fatigue experiments, including the structure of a test plan, randomization, and nuisance variables. The statistical characterization of the S/N (stress/life) or e/N (strain/life) response of a single material tested under a single condition is discussed. The techniques for defining a mean fatigue curve and evaluating scatter or variability about that mean are explained. The article presents the standard techniques for statistical characterization of the fatigue strength or fatigue limit of a single material by use of the Probit method, the up-and-down (staircase) method, and two-point procedures. Stress-level selection methods are also presented. The article discusses the comparison of the fatigue behavior of two or more materials for data generated at a single stress or strain level. Treatments to compare data generated over a range of stress or strain levels are included. The article also summarizes the consolidation of fatigue data generated at different conditions.

Reinforcing fibers are a key component of polymer-matrix composites (PMCs), ceramic-matrix composites (CMCs), and metal-matrix composites (MMCs). This article discusses the mechanical and nonmechanical properties of these composites. It presents an overview of PMC, CMC, and MMC reinforcing fibers. The article describes cost-considered value-in-use of the ultimate-use temperature of selected fibers in three fiber categories: metal fibers or wires, oxide ceramic fibers, and non-oxide ceramic fibers.

This article discusses the fundamentals and operating principles of the following acoustic microscopy methods: scanning laser acoustic microscopy, C-mode scanning acoustic microscopy, and scanning acoustic microscopy. It describes the applications of acoustic microscopy for detecting defects in metals, ceramics, glasses, polymers, and composites with examples.

This article presents the basic guidelines considered in designing a composite structure, and the basic definitions of terms that apply to composites. It describes the analysis of a composite laminate based on stress-strain relationships, stress-strain load relationships, general load displacement case, and general load case solution. Factors affecting the composite materials properties and allowables of fiber-reinforced polymers are reviewed. The article discusses the process considerations for mold design, such as master model, metal tooling, composite tooling, and tool care. It explains the resin selection in designing the composite for use in a particular application. The article illustrates the various methods that are used to process a composite component, namely, wet lay-up, autoclave, resin transfer molding, and vacuum-assisted resin transfer molding. It provides a discussion on electromagnetic interference shielding, electrostatic discharge protection, metal plating, fire resistance, and corrosion resistance on composite materials.

Failure of structural polymeric materials under cyclic application of stress or strain is a subject of industrial importance. The understanding of fatigue mechanisms (damage) and the development of constitutive equations for damage evolution, leading to crack initiation and propagation as a function of loading or displacement history, represent a fundamental problem for scientists and engineers. This article describes the approaches to predict fatigue life and discusses the difference between thermal and mechanical fatigue failure of polymers.