The analysis of composite materials using optical microscopy is a process that can be made easy and efficient with only a few contrast methods and preparation techniques. This article is intended to provide information that will help an investigator select the appropriate microscopy technique for the specific analysis objectives with a given composite material. The article opens with a discussion of macrophotography and microscope alignment, and then goes on to describe various illumination techniques that are useful for specific analysis requirements. These techniques include bright-field illumination, dark-field illumination, polarized-light microscopy, interference and contrast microscopy, and fluorescence microscopy. The article also provides a discussion of sample preparation materials such as dyes, etchants, and stains for the analysis of composite materials using optical microscopy.

Microscopy is a valuable tool in materials investigations related to problem solving, failure analysis, advanced materials development, and quality control. This article describes the sample preparation techniques of composite materials. These techniques include mounting, rough grinding, and polishing. The preparation techniques of ultrathin sections are also summarized. The article explains the illumination methods used by reflected light microscopy to view a specimen. These consist of epi-bright-field illumination, epi-dark-field illumination, epi-polarized light, and epi-fluorescence. The article also provides information on transmitted light microscopy.

This article describes testing and characterization methods of ceramics for chemical analysis, phase analysis, microstructural analysis, macroscopic property characterization, strength and proof testing, thermophysical property testing, and nondestructive evaluation techniques. Chemical analysis is carried out by X-ray fluorescence spectrometry, atomic absorption spectrophotometry, and plasma-emission spectrophotometry. Phase analysis is done by X-ray diffraction, spectroscopic methods, thermal analysis, and quantitative analysis. Techniques used for microstructural analysis include reflected light microscopy using polarized light, scanning electron microscopy, transmission electron microscopy, energy dispersive analysis of X-rays, and wavelength dispersive analysis of X-rays. Macroscopic property characterization involves measurement of porosity, density, and surface area. The article describes testing methods such as room and high-temperature strength test methods, proof testing, fracture toughness measurement, and hardness and wear testing. It also explains methods for determining thermal expansion, thermal conductivity, heat capacity, and emissivity of ceramics and glass and measurement of these properties as a function of temperature.

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.

The reflected light microscope is the most commonly used tool to study the microstructure of metals, composites, ceramics, minerals, and polymers. For the study of the microstructure of metals and alloys, light microscopy is employed in the reflected-light mode using either bright-field illumination, dark-field illumination, polarized light illumination, or differential interference contract, generally by the Nomarski technique. This article concentrates on how to reveal microstructure properly to enable the proper identification of the phases and constituents and, if needed, measuring the amount, size, and spacing of constituents, using the light optical microscope. The discussion covers the examination of microstructures using different illumination methods and includes a comparison between light optical images and scanning electron microscopy images of microstructure.

Analyzing the structure of composite materials is essential for understanding how the part will perform in service. Assessing fiber volume variations, void content, ply orientation variability, and foreign object inclusions helps in preventing degradation of composite performance. This article describes the optical microscopy and bright-field illumination techniques involved in analyzing ply terminations, prepreg plies, splices, and fiber orientation to provide the insight necessary for optimizing composite structure and performance.

Microstructural analysis of the composite matrix is necessary to understand the performance of the part and its long-term durability. This article focuses on the microstructural analysis of engineering thermoplastic-matrix composites and the influence of cooling rate and nucleation on the formation of spherulites in high-temperature thermoplastic-matrix carbon-fiber-reinforced composites. It also describes the microstructural analysis of a bio-based thermosetting-matrix natural fiber composite system.

This article introduces the concepts of electron and light microscopy with some general features of imaging systems and the ideas of magnification, resolution, depth of field, depth of focus, and lens aberrations as they apply to simple and familiar light-optical systems. In addition, it describes the differences between electron and light in the context of their respective microscopy techniques.

This article focuses on the modes of operation, physical basis, sample requirements, properties characterized, advantages, and limitations of the characterization methods used to evaluate the physical morphology and chemical properties of component surfaces for medical devices. These methods include light microscopy, scanning electron microscopy, atomic force microscopy, energy-dispersive X-ray spectroscopy, Auger electron spectroscopy, secondary ion mass spectrometry, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy.

This article describes the various aspects relating to the selection and preparation of ultrathin-section specimens of fiber-reinforced polymeric composites for examination by transmitted light microscopy. It provides information on the contrast-enhancement methods used by transmitted-light microscopy and optimization of microscope conditions. Examples of composite ultrathin sections analyzed using transmitted-light microscopy contrast methods are also presented.

This article provides information on the basic components of a light microscope, including the illumination system, collector lens, and optical and mechanical components. It describes optical performance in terms of image aberrations, resolution, and depth of field. The article discusses the examination of specimen surfaces using polarized light, phase contrast, oblique illumination, dark-field illumination, bright-field illumination, interference-contrast illumination, and phase contrast illumination. Special techniques and devices that may be used with the optical microscope, to obtain additional information, are also described. The article concludes with information on photomicroscopy and macrophotography.

This article provides an overview of the origin of metallography. It presents information on how to select a section from a specimen and prepare it for macroscopic analysis. The article describes the macroscopic analysis of steel fracture surfaces with emphasis on ductile, brittle, and fatigue fracture with illustrations. It discusses microanalysis with a focus on the method of light microscopy and includes information of scanning electron microscope in fractography. The article also explains the characteristics of solidification, transformation, deformation structures, and discontinuities that are present in a microstructure. It concludes with information on image analysis.

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 reviews photographic principles, namely, visual examination, field photographic documentation, and laboratory photographic documentation, as applied to failure analysis and the specific techniques employed in both the field and laboratory. It provides information on the photographic equipment used in failure analysis and on film and digital photography. The article describes the basics of photography and the uses of different types of lighting in photography of a fractured surface. The article also addresses the techniques involved in macrophotography and microscopic photography as well as other special techniques.

This article describes the microcrack analysis of composite materials using bright-field illumination, polarized light, dyes, dark-field illumination, and epi-fluorescence.

Failure analysis is an investigative process that uses visual observations of features present on a failed component fracture surface combined with component and environmental conditions to determine the root cause of a failure. The primary means of recording the conditions and features observed during a failure analysis investigation is photography. Failure analysis photographic imaging is a combination of both science and art; experience and proper imaging techniques are required to produce an accurate and meaningful fracture surface photograph. This article reviews photographic principles and techniques as applied to failure analysis, both in the field and in the laboratory. The discussion covers the processes involved in field and laboratory photographic documentations, provides a description of professional digital cameras, and gives information on photographic lighting and microscopic photography. Special techniques can be employed to deal with highly reflective conditions and are also described in this article.

Measuring the thickness of thin films can be accomplished in many ways. This article focuses on the optical method of single-wavelength ellipsometry, two multiple-wavelength methods of reflectometry and spectroscopic ellipsometry for measuring the thickness of thin films. The general capabilities, principles and applications of ellipsometry and reflectometry are discussed in terms of nondestructive methods.

This article discusses the preparation of photomacrographs of fracture surfaces. It provides useful information on the equipment used, such as view cameras, 35-mm single-lens-reflex cameras, and stereomicroscopes. The article describes the role of lenses, focusing, camera magnification, and selection of lens aperture in a microscopic system. It illustrates the lighting techniques employed in photography and highlights the use of different films. The article concludes with a list of auxiliary equipment used in fracture surface photography.